Born in Victoria Australia Bruce was educated at Eltham High School & then studied yacht design through the US based Westlawn Institute of Marine Technology. Bruce entered the marine industry and for several years operated a boat yard in Brisbane where he completed an informal boatbuilding apprenticeship.
Site: http://www.bruceroberts.com/ Detailed text, photos and illustrations showing the various methods of sail and powerboat boatbuilding in Fiberglass Sandwich, Single skin fiberglass, Male & Female moulding. Building the shell; hull, deck and cabin construction. Specialist tools required.
On sandwich hulls where there is a bulwark or toe rail, we recommend that this be solid glass which means that any core material be removed. You will later add stiffness to the bulwark by carrying the deck laminate and bonding up to the top of the sheer. You may also add bulwark posts or webs to complete the strength of the bulwark.
Solid glass hulls naturally have solid bulwarks.
Internal tanks in fibreglass boats are easy to build and make most use of the available space giving maximum capacity for fuel and water in the area selected. Purpose resins have been developed for coating the inside of these tanks and, properly built, they should provide an economic, maintained free alternative to fabricated tanks. Post-curing of the tank resin is necessary in water tanks to rid them of chemical taste and this can be done with the heat from a light bulb. Once they are fully cured they can be filled with water and lemon juice and left until the boat is ready for launching – pump them out before launching to save weight. All tanks should have inspection access.
Webs can be made from solid fibreglass which has been laid up flat on a laminating table. An alternate method is to fit plywood or hardboard webs and then install the laminate on either side including the bonding on to the hull. The webs are generally set on ribs or stringers so as not to create a “hard spot” where they meet the hull. The tops of the webs should be fitted with a 1” x 2” [25mm x 50mm] timber or foam rib. Cover this rib with the web laminate, excluding the very top, and it will add strength to the arrangement and provide a landing for the plywood sole. Before proceeding, study the section of your plans covering the installation of the ribs, stringers, web floors and bulkheads. Often the bulkhead positions will govern all the spacing of the transverse webs, so marking out the bulkhead locations is an important step in your building programme. We generally recommend spacing the webs and ribs, if required, equally between the bulkheads, but there may be exceptions to this rule so the best idea is to follow the designer’s recommendations.
As the bottom stringers are generally installed first it is a good idea to include the engine stringers and beds at this time. The location of the engine stringers, if called for, especially if there is a twin engine installation, will govern the spacing of the other bottom stringers. Engine bed stringers can be all foam and glass construction or they can have timber or steel inserts. You plans should specify the recommended method(s) for building the engine beds for your particular boat. Size of the engines, both physical and by horsepower ratings will be important factors in deciding just how you build the beds. There are special high density cores available for this purpose - check with your supplier for details. Overkill in this area is recommended.
Usually engine beds have a laminate that consists of alternate layers of mat and roving with extra layers on the top of the beds. A required system of athwartships webs is installed to support the engine beds. These webs will be cut away below the engine to allow room for the sump. If you are using a foam and glass, or a foam glass with timber or steel inserts, it is best to build the basic core structure and then laminate the complete structure as one unit. This avoids as much secondary bonding as possible. The area under and around the engine will need to be particularly well covered with interior gelcoat. On smaller boats, engine beds can be made from plywood on edge, heavily glassed and with angle iron bolted to the tops to support the engine. This is a well proven system.
If you are interested in using C-Flex and cannot get the material locally, then you should contact any Bruce Roberts Design office for supply details or contact: Seeman Fiberglass Inc. 6117 River Road Harahan LA 70122.
C-Flex is a unidirectional fiberglass reinforcement that is manufactured in long (up to 250’ – 77m) x 12” (300 mm) wide planks in two grades. The heavier grade, CF65 is used for most applications including boats of a variety of sizes.
C-Flex contains rigid rods of solid GRP (much like fishing rods) on ½” (12 mm) centres which give it a self-supporting nature when spanning an open framework. The rods have a very high glass/resin ratio which means that they impart high strength qualities to the structure in the direction which they run. The spaces between the rigid rods are filled with unsaturated strands of continuous roving, and when saturated, these also become excellent unidirectional reinforcements. A light fiberglass cloth holds the material together and gives C-Flex the ability to follow the exact contours of most surfaces and to conform to compound curves such as boat hulls.
C-Flex calls for a similar male mould to that used to build a PVC cored hull except he frames have to be closer or intermediates used. Maximum recommended frame spacing is 18” (450 mm). The frames are made in the same manner as for a cored hull and as the fore and aft battens are spaced at 4” to 6” [100mm to 150mm] apart, less are required than for a conventional mould. Light battens (or strips of C-Flex) of 1” x 3/8” [25mm x 10mm] are placed vertically on each frame. If you read the chapter on building a male batten type mould and consider the fact that you will use less fore and aft battens but will add some vertical battens, you will have an understanding of how to build a mould to support the C-Flex. If you want more information, we recommend the book C-Flex by Barry Kennedy.
On most round bottom hulls, the easiest place to start planking C-Flex is with the first piece running along the centre line or keel. Because of the flexible nature of the rods, they will bend sideways, allowing the planks to be butted alongside each other all the way to the sheerline. It is also possible to start at the sheer and work upwards to the keel in the same manner and, as stated earlier, this may not be quite so easy. C-Flex will follow a compound curve without deforming so you should be able to complete the planking without having to shape any planks. The C-Flex will only need ice picks or staples to hold it in place.
If you try to make it sideways bend beyond a certain point you may, occasionally, have to help the material by taking two small 2” [50mm] C or G clamps and fasten them tightly to the ends of the single hard rod on the inside of the bend - then pull from both ends. As long as the pull is in line with the strand and kept on the proper part of the clamp, the material can readily be pulled into place. Alternatively, if you can foresee that there is going to be a problem, you may start to install the planking in the middle of the hull rather that at the sheerline. Along the waterline may be a good starting point. Now you can let the planking run out at the ends when it reaches the sheer and keel lines.
If you have already started with the C-Flex parallel to the sheer, and you find that the curve is becoming too tight, you can stop, wet out the C-Flex that is already installed and allow the resin to cure. Next take a plank of unsaturated C-Flex and place it over the frames letting it fall naturally in place. Butt the unsaturated plank alongside the cured plank in the middle of the hull and let it fall across the ends or across the area where you are having the problem. Mark along the edge of the unsaturated plank. Now cut along your scribed line using a hand power saw equipped with an abrasive cutting blade. Be sure to set the blade so it just cuts through the C-Flex and not into the battens or frames. Remove the off-cut wedge shaped pieces and now you can go on to install the C-Flex with a fresh straight fore and aft line to work from.
On most V bottom boats, particularly power boats we have found the easiest place to start is with the first plank run fore and aft along the chine with half the plank on the bottom and half on the side of the hull. Try to keep the same two small rods each side of the chine batten and this will assure you of a good start to the clean edge you will be looking to obtain in this area. Examine some production fibreglass power boats and you will see what I mean.
CUTTING C-FLEX
Tin snips will cut unsaturated C-Flex or bunch it together and cut it with a hacksaw.
To cut saturated fully cured C-Flex you need to use a hand power saw or angle grinder fitted with an abrasive cutting blade. This method can be used to cut both the saturated and unsaturated material. If you need to make a long diagonal cut on unsaturated C-Flex, place a piece of scrap timber under the material and cut through into the wood.
INSTALLLING C-FLEX TO THE MOULD
Ice picks, staples or large nails can be used to hold the material in place. Generally, it is only necessary to staple the two outside rods in each plank. After the resin has cured, the staples can be removed or, if you have used stainless steel, have their ends ground from the inside. The planks should be butted side to side and not overlapped.
Check over the job carefully before saturating; sight along the hard strands of the C-Flex to view the fairness of the hull. You will find that by putting in a few extra staples and pulling a few hard strands, you will be able to save a lot of work later
SATURATING THE C-FLEX
Once the C-Flex is in place, the material is wet out from the outside with a coat of slow cure resin. This resin does not always wet through the C-Flex completely but this is not a problem and can be rectified once the hull is turned. It is important to use a slow cure resin to avoid shrinkage.
You can use spray guns or hand rollers and brushes to apply the resin. Roll a coat over an area, let it soak for a few minutes then squeegee off the excess. Do not over saturate – any dry areas can be fixed later.
LAYING UP OVER THE C-FLEX
After the C-Flex has been saturated and the resin has cured, the hull should be lightly sanded to remove any high spots and resin build-up.
The amount and type of laminate you will be installing over the C-Flex will depend on the design and size of boat you are building. Your plans will show the amounts and type of reinforcing fibreglass required.
The best practice is to start with a layer of chopped-strand mat next to the C-Flex, laid up wet, in combination with a layer of woven roving. Usually the roving are run at right angle to the C-Flex. We recommend that half the layers of roving, in the laminate, are across the grain of the C-Flex and the other half run fore and aft in the same direction as the C-Flex or diagonally.
The first layer of your laminate should be a light chopped strand mat, either 1 or ½ oz per square foot [300 or 450 g/sq.m]. These are easy weights to work with and will provide a good key between the core material and the bulk of the laminate that follows. This first layer is very important as the bond between it and the core material must be as perfect as possible. If in doubt, make up some sample pieces using scrap core material as a base. For the bulk of your hull laminate, you should use only unwaxed general purpose laminating resin. The final layer of the outer laminate should also be a chopped strand mat and the resin should be waxed to facilitate the sanding that will come next.
WHICH DIRECTION?
There are at least five directions you may use to apply the various layers of the glass laminate. The first layer of mat should be laid in the most convenient direction. You need only butt the joins in the mat. Most fibreglass mats have a slightly braided edge that will blend and make a clean join, if carefully rolled, and this join will not be visible after the resin has cured.
You should apply a layer of the resin to the core before laying the mat. The first layer of CSM must be carefully wet out and rolled to remove any bubbles. Do not over saturate the mat, but roll out the excess resin, with a steel roller. If you work from the top then the resin will flow down through the laminate.
TWO LAYERS AT ONCE
It is good practice when laminating a hull to apply a layer of the mat and a layer of roving simultaneously – mat always first. The method is to lay up the mat and use the roving to help soak up the excess resin, which the mat often holds. The roving and mat are rolled out at the same time. If you become proficient, you will find this method of installing your laminate offers the smoothest finish and the best resin/glass ratio. The object of the exercise, when laminating, is to have the correct resin to glass ratio. The strength is in the glass so you do not want a resin rich laminate nor do you want your laminate to become resin starved - you will soon recognise a good laminate.
LAMINATING WITH A TEAM
Another method of applying your laminate is to have a team of helpers, so the laminating can be completed without any interruptions, over a few days. You should have enough help to apply at least one full layer (mat and roving) over the hull per day. Do not apply more than two layers per day as the curing process will generate too much exothermic heat and may distort and damage your laminate. Using this method, you will apply one layer all over the hull before starting the second layer. Some of your team may be installing the second layer a few hours behind you, while the others are still completing the first layer. Four people are the maximum who can be gainfully employed on one hull, one mixing the resin and pre-cutting the lengths of fibreglass fabric and three applying the laminate. Within reason, the faster you build up the laminate, the better the bond will be between each succeeding layer. Technical data can be obtained from your materials supplier and, in most cases, they will be happy to visit during lamination to see that everything is being done in a proper manner.
NOTES ON LAMINATING – ALL METHODS
For ease of handling, try to obtain mat and other fibreglass materials that are about 30” [760mm] wide. When laminating, always overlap the joints of the preceding layer and if you are using a unidirectional roving, change the direction for each layer. Never allow the edges of one layer to lay over the edges of the previous layer. Not only will this weaken the laminate, it will also cause a high spot.
Wherever possible, always tear edges of the mat to blend in to the surrounding laminate and always start and finish with a mat layer - never laminate roving to roving without a mat between. It is a good idea to trim the sheer as each layer of laminate cures. It is easy to trim around the sheer and anywhere else where trimming is required, when the laminate has just cured and before it reaches its final hardened state. A sharp trimming knife will do the job nicely. If you let the laminate set really hard before trimming the sheer, you will need to use a jig saw or diamond saw to cut off the excess laminate.
When you have completed the design laminate for hull or deck, do not be tempted to add extra layers to “make it stronger”. If you have any queries about the laminate, please consult your designer. Do not, under any circumstances, just add a little more because you believe you will improve the strength of you hull, you are adding unnecessary weight and wasting money.
The extra laminations needed for the keel and other areas below the waterline can be added once the full hull laminate is complete. If you have used an isothalic resin, for increased resistance to water permeation, it is advisable to coat all areas below the waterline with several layers of vinyl ester resin and fiberglass tissue.
The easiest way to check if your hull has any unfair areas, it to have sunlight or strong artificial light shining from one end as you look along the hull either with or against the light. If you really want to check the fairness, then the best time is at night. Shine your torch along the hull and you will soon see all the imperfections in the surface. Use this technique frequently during the final fairing process.
At this stage, you can expect your hull to show some imperfections and these can be removed during the final fairing operation. You have to decide the standard of finish you are prepared to accept. Set your standards as high as possible. Work towards this goal and you will end with a hull you can be proud of. The resale value of your boat is important and the better the finish the higher the value.
FINISHING THE
If your hull has been carefully laminated and will not require too much finishing, you will be a lot closer to achieving a good looking boat than a sloppy builder and you will avoid a lot of back breaking hand sanding.
The first process in finishing a hull, is to sand the surface with a disc sander running at not more that 4000 RPM. Use a soft pad (Ferro type) equipped with 30 to 40 grit open coat floor sanding type discs. The soft pad will prevent you from digging holes or causing other imperfections as you sand the hull. After you have sanded the outer layer of the mat, you must decide whether you need a professional plasterer to apply your screeding material. If your hull is unfair and has many humps and hollows, you would be best advised to have a local tradesman screed your hull with resin putty “bog”.
The type of resin putty to be used here is made from waxed resin with enough industrial talcum powder or micro balloons or other suitable filler mixed to a suitable thickness similar to soft butter, not too thick and not to thin. You will need a steel screed that is about 2’0” [610mm] long. The best screeding tools are made out of the type of steel that is used for making handsaws so an old saw with the teeth ground off would serve the purpose.
The resin putty “bog” will have extra added accelerator, about a half to one percent – talk to your supplier for the correct amounts. Make sure you experiment with your resin putty mix, before you start hull. Colours can be added to different bog layers to show what progress you are making. If you hull is reasonably fair or even if it is not, you may elect to do your own screeding using the materials as outlined in this chapter. You will soon get the hang of it.
The method is to start at the keel line and work down towards the sheerline, screeding down the hull, until you have covered the entire surface. Now sand off to a smooth finish and repeat the process working along the hull or diagonally so that the hips and hollows are covered from at least two directions. If your “bog” starts to cure prematurely or if it contains lumps and foreign matter; throw it away because it will only cause tracks and grooves in the area you are trying to screed. You will have very little success if you use “bog” that is not smooth and of the correct consistency. You will need some practice to decide the right amount of the catalyst to use with each mix. It is not wise to use a mix with a setting time of longer than fifteen minutes, as your “bog” will probably suffer from under cure and clog up your sanding discs when you get to that stage. If your mix is too fast, because too much catalyst is used, it will set before you have a chance to screed it out. It is best not to leave your “bog” unsanded overnight as you will have a difficult job to sand it the next day. At least sand the worst before leaving it overnight.
The final hull laminations are so important that they are repeated here. The final layer in your lay-up should be a chopped-strand mat … The extra laminations needed for the keel and other areas below the waterline can be added once the full hull laminate is complete. If you have used an isothalic resin, for increased resistance to water permeation, it is advisable to coat all areas below the waterline with several layers of vinyl ester resin and fiberglass tissue.
Experienced laminators, and this includes builders who have laid up their own hull, can apply a layer of the mat and a layer of woven roving in one operation. The advantages are that the laminate can be rolled out and any previously formed irregularities can be eliminated by using firmer pressure on the high spots and a lighter pressure on the low areas, thus ironing out the laminate and resulting in an even surface. Keep this in mind when installing your main laminate.
Once your hull has been screeded and spot filled, sanded off and any surface tissue or finishing cloth that is required has been applied, you are ready for final hand sanding and painting.
PAINTING YOUR
Now a final sanding of the refilled areas, one last check over your hull and you are ready for the final finishing. Usually you will be applying one of the polyurethane or epoxy finishes. One last word on finishing - no matter how smooth and fair you think your hull is you may find it is not as perfect as you thought. When you apply the final gloss, the truth will become apparent. If you consider your finish absolutely perfect, then you will most likely be satisfied with the result. If you accept less than a perfect finish now, you may be disappointed later.
There is a wide selection of paints that are suitable for protecting the outside of a fibreglass hull - some for above the waterline, some for below. The method of application of your finish coating, will depend upon which material you select. If you believe your hull surface is sufficiently good to accept a high gloss finish, then you may be spraying your final coats. If you are of the opinion that your hull surface will not look it’s best with a shiny smooth surface, then you may prefer to roll and brush on the finish coating.
When you roll on your finishes using a short nap mohair roller, you will achieve a slightly orange peel effect. This can be used to advantage by rolling the second last coat, lightly sanding the finish and then spraying the final coat. This will take away the high gloss finish that may not be appropriate for your hull. No matter what material you select as a finish coat, make sure you try samples before committing yourself to applying the material to the complete hull surface. In some cases rolling followed immediately by brushing can give a passable finish to an imperfect hull.
One last job before you turn you hull is to trim the sheerline after carefully marking it from the sheer batten. You should have been doing this right through the laminating process, but if not, you will need to do it now. You will need a tungsten tipped saw or a jigsaw fitted with a tungsten or diamond blade, to cut the fibreglass. It is much easier to trim the sheer while the hull is upside down and close to the ground.
PREPARING FOR TURNING
After you trim the sheerline, install a 3” x ¾” [75mm x 20mm] timber batten around the sheer. Scarf the batten to a length that will go right around one side of your hull. The batten is first clamped in place and then secured to the hull using self tapping screws that are located every twelve inches [305mm] around the batten. The screw should be long enough to go through the batten, the outer laminate and some way into the core, not so long as to go into the mould. After the mould is removed, install a similar batten inside the sheerline. The reason for fitting the outer batten before the hull is turned over is to protect the edges of laminate and add some stiffness to the hull shell after the mould is removed. Once the hull is turned and the mould is removed, you will find the hull is quite flexible, so the outer batten is part of the system that will keep your hull in shape until you can install the inner laminate, bulkheads and other hull stiffening.
TURNING THE
There are several methods that have been used to successfully turn the hull and remove the mould former from the hull shell. In some respects, the method you will choose will depend on the size of your boat. Boats up to, say 25 feet [8 metres], can be handled without mechanical assistance. A few bottles of cheer and a number of your friends will take care of the turning over operation. For larger hulls a more serious approach is required.
If you are building in a shed, it is a simple matter to turn you hull and mould over in one operation. Use two chain blocks and endless slings that are placed around the hull about 25% in from the bow and stern. The chain blocks are then used to raise the hull and mould off the floor and rotate the entire structure in the endless slings. The hull can then lowered into a prepared cradle. Next attach the chain blocks to the mould structure and lift the mould out of the hull. The hull is now moved out of the way and mould lowered and inverted ready for re-use, sale or demolishing. Another method of turning hulls of any size is to use a crane fitted with a spreader bar and two endless slings. Assuming the hull is in shed, it then has to be removed either by using pipe rollers placed under the strongback or dragged out on skids.
MOVING HULLS
You can move large, bulky and heavy hulls and decks by the use of the simplest of devices. A few 2” diameter [50mm] pipe rollers 9’ [230mm] long can be used to roll your hull, if you set down planks for the rollers to run on and keep taking the rollers from the back and placing them at the front as the hull moves along the desired path – angle the rollers if you want to move the hull in that direction. You should use 4” x 2” [100mm x 50mm] timber levers say 5’0” [1.5 M] long when you want to lift the hull and mould structure to slip pipe rollers under the strongback or bedlogs.
Another method we have used to turn large hulls is to build a framework around the hull. A strong cradle built over the hull while it is upside down and braced through and under the sheer will make a good turning over cradle. Use three sets of frames, one forward of the keel, one in the middle of the keel and one aft of the keel. Diagonally bracing will be required. See illustrations shown here for extra guidance. Use coach bolts throughout the assembly of your turning over cradle. When upright, the cradle should be capable of supporting the hull until you complete the project. Once your hull is in the upright position, the crane can lift the mould from the hull and turn it upright ready for disposal. If you reuse a mould you may be liable to pay the designer of your boat a royalty payment. It is wise to check the legality of such a move.
If you are considering building a chine hull such as a power boat, single or double chine sail boat or similar craft, you should consider using the “Ezi-Build” fibreglass technique. There are two main Ezi-Build methods - one where you build an inexpensive female mould and lay up the hull in that mould and another where you pre-make the hull panels and assemble them inside a simple frame mould.
First we will look at the female mould method. Back in the early 1960’s, we were designing fishing trawlers that could be built of fibreglass using inexpensive one-off or limited production moulds. With the current rise in the number of people interested in power boats and the acceptance of chine hulls in general, we decided to simplify and streamline our original methods to make them suitable for one-off production by amateur and professional builders.
When looking at these techniques, we were developing a new range of power boat designs using the latest CAD software so that these designs did not involve difficult curves but instead were easily assembled in simple one-off moulds. These new designs all reflected the ability of the computer to produce absolutely fair, developable hull surfaces suitable for turning flat sheets of fiberglass into attractive hulls. Most of the original designs were directed towards steel or aluminium but the demand for similar fiberglass methods led us to develop computer lofted hulls with full developable surfaces and the result is the Ezi-Build technique.
ALWAYS STUDY YOUR PLANS
Once you have selected a design to build, and armed with a suitable set of plans and full size patterns, your first step should be to carefully study these plans. This advice applies no matter which building method you are using. Every hour of study can save many hours of construction time. Make sure you have allowed adequate study time before you start to build your boat.
LAYING OUT THE PATTERNS
If you are working with printed full size frame patterns, you should not open them until you are ready to use them and you will need an area at least as wide and tall as the boat you are building. This area should be as wide as the beam of the boat plus a minimum of one foot [305mm]. The depth should be the depth of the hull, plus a minimum of 3 feet [1 metre]. This space will be the minimum required to construct the frames over the patterns. This procedure will be explained in your plans and should be easy to follow.
“EZI-BUILD” MAKING THE FRAMES
When marking the frame shapes on to the timber, you should use a dressmakers wheel or nails, as shown in your plans, for transferring the shape of the patterns to the timber framing material. Remember, that you are making frames for a female mould. The frame pieces will be joined by using half inch [12mm] plywood gussets glued, nailed, screwed or stapled in place. Screws are strongest but staples are quickest and most convenient. Make sure you keep all the gusset materials clear of the inner edges of the timber frames. Later, you may need to trim these inner edges with a plane and nails or gussets will interfere with this process.
Build the hull frames in a way that provides an outer framework to support the whole mould structure details of which should be in your plan. In designs under 32 feet 10 metres, the bottom of the support structure can be canted 45 degrees which will enable the whole structure to be tilted, side to side, for easy lamination. On larger hulls, it is advisable to hang scaffolding inside the hull structure to support planks for working from.
You may want to consider a split mould. Here you build the mould in one piece, but with the intention of separating the mould down the centre line so that laminating can take place from a corridor up the centre of the hull. This is a bit more complicated and should only be used on larger hulls, if at all.
To achieve a split mould, the centre line board and the stem and the transom centre line boards are all doubled up and bolted together so they can be separated when the mould is completed and you are ready to commence the laying up process. The transom can be a one piece affair that is designed to be installed after the hull is assembled.
When you are laying up in a split mould, you install the basic laminate in the normal manner except that each layer is stepped back at the centre line where it will later be joined. After the laminating is completed, the mould is reassembled by moving the two halves together bolting along the centre line. Now you install the remainder of the laminate plus the extras usually installed in the areas of the keel etc.
For one-off boats, the relatively cheap Ezi-build mould, which is easy to disassemble, has eliminated much of the need for the more complicated split mould and, for those of you who think that these methods present more work than is justified, compared to building a one-off hull over a male mould, let me assure you after having sanded many fibreglass hulls, I feel these methods are by far the best and fastest way to build a one off fibreglass power boat or multi chine sailboat hull.
SETTING UP THE FRAMES
After assembling all the frames, they are set up on a system of bedlogs so that the whole structure is true and level in all directions. If the bedlogs are level the hull structure will also be level. It will be necessary to run a centre line wire or string line up the centre of the bedlogs. The frames will all have a centre line marked on the top headstock and the bottom cross bar. It is a simple matter to set up the frames spaced as shown on our plans. A plumb-bob hung from the headstock centre line of each frame assures that the frame is vertical and on the centre line. A large builders square can be used to make sure the frame is square off the centre line.
SETTING UP THE STEM
Install the stem and centre line board, which is an extension of the stem and runs the full length of the bottom of the hull, simultaneously with the frames and using adequate props and bracing. A tip on setting up the frames – if the frames forward of frame 5 are set up with their forward face on the station line and the frames aft of frame 5 are set up with their aft face on the station line, then most of the bevelling and fairing will be avoided. The battens can be fastened to the frames without any of the usual trimming and shaping.
The best sequence for installing the frames is to set up the centre frame first, usually station 5. Make sure this frame is truly vertical, using a plumb-bob hung from the centre line marked on the headstock. Use a large carpenter’s square to ensure the frame is at right angles to the centre line. Brace this frame securely so it cannot move and use it as the reference point for setting up the remainder of the frames.
When all the frames, stem, centre line board and transom centre line board are in position and securely braced, then you can start to install the battens. Battens are best if made from 5/8” [15mm] thickness timber. Scarf the battens into full length pieces, the length of the hull plus a few inches for trimming. The batten width may vary. For the bottom you may use wider battens up to 4” [100mm] and for the sides a width of 2” [50mm] best. You should have a stock of wider boards of the correct thickness and then rip the battens to selected width depending on the requirements of your particular hull shape.
INSTALLING THE BATTENS
First install the chine battens, one close to each side of the chine. Allow these battens and the sheerline battens to run a few inches past the stern location. Now you may install the transom section of the mould. Camber boards are half checked at right angles to and on to the transom centre line board. Once the camber boards are in place, batten up the transom vertically. It is usually not necessary or advisable to nail the side and transom battens together, use plywood strips outside the battens placed near the intersection of the side and transom battens to hold the battens fair.
You should have a fully developed and expanded transom pattern in your plans. Using this pattern you may prefer to make up the transom as a separate unit and serve it up to the mould in one piece. If you make the transom as a separate unit, it can be at least partially laid up away from the main mould. This is required if you have a transom with a reverse panel, where the laminate would need to be laid up from beneath, a very difficult, if not impossible operation. If you build the transom in place, then the transom pattern can be used to cut the lining material.
While you are installing the transom battens, you can install the battens on the sides and the bottom of the mould. Always install battens on alternate sides of the centre line, working progressively on both sides.
After all battens are in place, install fairing gussets or strips of one half inch [12mm] thick by four inches [100mm] wide plywood, clench nailed on the outside of the battens, one or two strips between each frame. The strips run from sheer to the chine and from the chine to the centre line. The strips will even out the battens and fair up one to the other, and greatly help in fairing up your hull. You will need two people to install these plywood strips. As you will be attaching the mould lining with contact cement rather than nails, you should make sure the battens are fair before you start to install the lining material.
CHOOSING THE MOULD LINING
When all the battens are installed and you are satisfied with the fairness of the mould, the next job is to install the lining. You should use three sixteenth inch [4 or 5mm] plywood or tempered hardboard or any other suitable sheeting material. If you use plywood it will need to be coated but be sure that the coating is compatible with the fiberglass – do a test. From this stage onward work closely with your fibreglass materials supplier and take his advice on the correct wax and release agent to use on the mould.
INSTALLLING THE MOULD LINING
No matter which mould lining material you choose, it will need to be attached to the battens with a contact type cement. Nail only where absolutely necessary as the nail heads will show up in the finished laminate and can be difficult to fill. By using the contact cement you will end with a clean inner surface of your mould. Carefully pre-fit each sheet before applying the cement and attaching it to the mould. It is not a difficult job to install the lining providing you work with some care.
FINISHING THE MOULD
Once you have installed the mould lining, you should fill any small gaps with mould wax. Also, radius any areas where you need to have rounded corners. For this job, you can use body filler or any other polyester based material that is compatible with the fibreglass laminate you will be installing.
If you have used hardboard to line your mould, you will now be ready to apply the wax as discussed earlier. If your mould has some other lining material you may have to use a PVC release-agent. You should talk to your material suppliers about the most suitable system.
INSTALLING THE LAMINATE IN THE EZI-BUILD MOULD
Even if you later intend to paint the hull the most important part of the laminate is the gelcoat and first layer. We would recommend you use some form of gelcoat, either pigmented or clear.
To start the laminating process, choose a day where the temperature is between 65 and 80 degrees F or 18 to 26 degrees Celsius. Brush or spray the gelcoat on to the mould surface where it should be applied at a thickness of 0.5mm. You can measure the thickness of the gelcoat by using a special gauge obtainable from your fibreglass supplier.
Ideally, you should use a clear isothalic NPG gelcoat and back it up with a layer of surface tissue and vinyl ester resin. This is important so see your resin supplier about getting the right materials if you want to be sure of increased resistance to water permeation and avoid any possibility of osmosis, at a later date.
You will need two or three helpers as you start to lay up the hull and it is advisable, for temperature control, to be at the same stage of lamination each day with each successive layer. If the laminate overheats from applying too much material at one time, it may cause distortion and pre-release from the mould.
FIRST LAMINATES
The day after you have applied the gelcoat, you should apply the first layer of light chopped-strand mat, usually ½ ounce per square foot [150 g/m 2]. This layer is very important and should be carefully rolled out to avoid any chance of air bubbles. Air bubbles in any layer are a nuisance but in the first layer, they could lead to problems. Vacuum bagging is one solution to avoiding these voids – see chapter.
Once the gelcoat and first layer of mat are in place you will have passed the most critical stage of your laminating process. Providing you follow some form of temperature control, you should go on to complete the laminate without any problems. As mentioned earlier, always finish your laminating at the same part of your hull each day. Three willing workers can lay up a fifty foot [15 metres] hull in a few days. Two layers of fibreglass per day, one mat and one roving, is a reasonable amount to install at one go without causing the laminate to overheat. New resins are being formulated all the time so you must have the latest technical data and support from your materials supplier.
The number of layers of mat and roving required will be shown in your plans. After the layers that cover the whole hull surfaces are completed, you will most likely be required to install extra layers in the areas of the keel and below the hull waterline. Most laminate schedules call for overlapping and or interleaving the various layers in the areas such as the chine and keel, thus building up extra strength where it is required.
Again, we remind you to trim the sheerline of your hull each day. This will usually be done as work progresses and about an hour after the final layer for the day has been installed. Once you have installed the basic laminate and any extra layers called for in your plan laminate schedule, you should add any stringers, sole shelf, deck shelf etc and any other reinforcing members called for in your plans.
You should then install all the ribs, stringers, bulkheads and web floors before you remove the hull from the mould. After you have completed the installing of the stringers and ribs etc and if you do not plan to use the mould again, you may prefer to remove only the mould above the chine or water line, leaving the bottom section to act as a cradle.
EZI-BUILD
If you are building an Ezi-build sandwich hull, then you will lay up the outer laminate plus any extra layers in the critical areas, before you install the core material which may be PVC foam or end grain balsa. In either case, the best method to install the core is to use Vacuum bagging techniques that are described elsewhere in this book although the core can be installed manually. If you intend building a sandwich hull, please read the chapters on one off building, where you may pick up a few ideas on the handling of core materials.
PANEL CONSTRUCTION
The panel method of building a one off fiberglass boat is a variation on the Ezi-build technique. The method is ideally suited to building chine hulls including catamarans and any power boat or single or multi-chine sailboat hull. The main advantage of using this technique is that a full mould is not required. You will retain the advantage that a minimum of finishing is required for the outer surface of your hull. Very little filling and sanding will be needed to achieve an excellent professional standard of finish.
For panel construction, the system of building the female frames and setting them up on a set of bedlogs, is similar to the methods used when building an Ezi-build mould. Only a few battens are required to hold the frames square and vertical. The technique of setting up the basic framework to hold the fibreglass panels is similar to the first stages of building the Ezi-build mould. The fewer battens required and the absence of a mould lining material, are the main differences between the Ezi-build and the Panel methods.
Additional bracing is used on the outside of the frame assembly and once the frames and the few battens are installed, the mould is ready for the fibreglass panels. The success of the Panel method depends upon the builder obtaining accurate information such as computer generated full size patterns for the frames and either patterns or computer lofted offsets for the panels. We have successfully used this method when designing power catamarans and out builders report excellent results using the technique.
LAMINATING PANELS
Once you have the basic framework in place, you can think about laminating the panels. Before you proceed, check over your framework to make sure it is true and level. It is very important that the framework is sufficiently braced to insure that the shape will be maintained during the installation of the panels.
LAMINATING TABLE
First you will have to build a laminating table. The surface of the table is very important as any blemishes in the surface of the table will be faithfully reproduced in the outer surface of your laminate, so it should as smooth as you can make it. The top surface of the laminating table can be made from any one of several materials, however ¼” [6mm] tempered hardboard backed up with adequate framing would be my choice. There are many others to choose from as long as they have a smooth shiny surface and are compatible with polyester resins, should serve nicely. As the sandwich panels can be large, the table top material is best if available in one piece. Check this out as the fewer joins the better. In most cases, you will need to prepare the surface with a wax and release agent. See preparing the Ezi-build mould.
Once the panels are laminated they are laid inside the framework and joined together. The method of making each panel is quite simple, providing you have accurate patterns or offsets for each panel.
Using masking tape, mark out the shape of each panel on the laminating table and lay up the required laminate to form one panel. If you are using a core material, it should be installed while the laminate is on the table. Consider which way the panel will need to bend, if any, when it is laid in the mould, before installing the core on your laminate. Depending which brand you are using, cores often take a bend better in one direction than another. Usually only outer laminate and the core are installed while the panel is on the table.
STEPPING BACK THE LAMINATE
The edges of the panels do not receive the full laminate or core. These are stepped back from the edges so that after installation, the full laminate can be completed where two panels join. When a panel has been laminated, it is removed from the table as soon as possible. The panel is installed in the framework while it is still “green” as it is easier to fit into place while it still has some flexibility. When you have all the panels in place and they have been joined, the remainder of the inner laminate is then installed.
Some deck parts, cabin sides, cabin tops and other areas of your boat can have both sides the sandwich laminated while the panel is still on the table. This is only recommended in areas where there is a minimum bend required to place the panel in its final location. Installing the interior laminate, stiffeners, if required, and bulkheads etc., follow similar methods to those used in other fibreglass hulls.
Before we consider any internal reinforcement, we must consider how we are going to bond this to the hull. The term secondary bonding refers to any laminating where you are adding to the cured laminate. For instance, where you are installing a bulkhead, a web floor, a stringer or a rib, you would be making a secondary bond.
If you find it necessary to stop work on your basic laminate for over 48 hours, you will have to make a secondary bond when you recommence the laminating process, although I doubt if most builders would class it as such. Usually, a secondary bond can be as good as a primary bond as long as proper preparation has been made.
In practical terms, it is impossible to build a fibreglass boat without incurring many situations where secondary bonding is required. Providing you understand the process and take due care, there is no reason to expect any problems during construction, or when the boat is finished.
There are several things you can do to prepare a fibreglass hull for secondary bonding. In all cases you should sand the primary part so that no shiny surface, dirt or any other foreign material remains where the new part is to be bonded in place. In addition, the hull interior surface can be wiped with styrene or acetone to remove any impurities and help key the surface for further laminating but, you should talk to your materials supplier about this to obtain the best recommended methods for any particular brand of resin or climatic condition. Always prime coat plywood before you bond it into place.
Single skin fibreglass hulls will almost certainly require stringers, ribs and web floors.
There is no reason why you should not lay out the system of ribs and stringers with foam and then apply the laminate simultaneously. A problem that may occur is that the foam cores of the stringers and ribs are easily damaged and you would need to be very careful until you have installed some fibreglass covering. A foot in the wrong place and you can do damage. Electrical wiring and plumbing can be placed in these stringers but if there is ever a problem you will never know where it is coming from, as we once found out to our cost, so it may be best to keep the wiring and plumbing external. Wiring can be set into cored deckheads but you have to know where the lights are going to be and some certification authorities are not keen on this.
Stringers and ribs are usually foam cored. Rigid urethane foam of about 2 ½ pounds density can be purchased in sheets of a thickness equal to the depth of your stringers and ribs. Cut this material into strips on a band saw or other fine bladed saw and, if you are careful, you can even use a handsaw. Angle the saw to make stringer cores that are wider at the base than the top. Alternating the cutting angle will ensure there is no wastage. Stringers and ribs can be various shapes to play special roles in the hull. For instance, a stringer that will form a deck shelf will be flat on the top to accept the deck panel, but angled underneath. A sole stringer will be flat on the top and shaped to fit the contours of the hull. The engine bed stringers may be vertical on the inside and flared outwards on the outer sides.
All the shapes can be arranged when you cut the foam into strips, so make sure you have the right materials on hand. The various lengths of foam stringer material are butt joined and placed in the hull where they are quickly fastened into position with a hot mix of resin putty. A few spoon size lumps of putty set about 6 inches [150mm] apart will hold any foam stringer in place until you are ready to apply the stringer laminate.
Once any stringers and ribs are in place, the next big job is to install the bulkheads. In some cases, the bulkheads may be fitted before the webs, where the bulkhead itself serves as a web. Bulkheads are generally made of one or more sheet of plywood. As most boats are wider than the available plywood sheets, you can order pre-scarfed plywood or rebate and glue the sheets although this is not as strong but, with furniture attached, there is little difference by the time the boat is finished. Another method is to make the bulkheads out of more than one layer of plywood. In the case of ½” [12mm] bulkheads you can laminate two layers of ¼” [6mm] and for ¾” [20mm] you can laminate two layers of 3/8” [10mm] and so forth. Stagger the joins of the sheets and glue and temporally staple together. Before you bond the bulkhead to the hull, be sure to give it a prime coat of resin, where it is to be bonded. This prime coat should extend all around the edge of the bulkhead and about 6” [150mm] on to the bulkhead surface. As you will probably want to paint the bulkhead, at a later time, limit the resin to areas where you will be bonding only. Generally speaking, epoxy resins and glues can be used over polyester but not the other way and it is best to have bare plywood for any bonding and gluing.
In many cases, bulkheads will be installed on a rib where an angle joint of fibreglass should be extended for 4” to 6” [100mm to 150mm] on to the hull and the bulkhead reducing a small amount each layer to avoid a hump. A number of holes of about 2” [50mm] diameter may be cut around the perimeter of the bulkhead then chamfered from both sides to accept the fibreglass.