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.
SPLIT MOULDS
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.
