BUILDING THE DECK
There are a number of methods that you can look at to build your decks. You can use an in-place hardboard mould, a purpose built female deck mould on which the deck is laid up in one piece or sections, fibreglass sandwich panel moulded decks or straight plywood sheathed in fibreglass.
HARDBOARD IN-PLACE DECK MOULD
This method involves building a timber and hardboard mould on the hull and after the decks and cabin are completed, the hardboard mould is removed in pieces from underneath. This method is well proven and thousands of decks have been built this way. Using the hardboard, you will finish with a smooth interior but the outside will have to be finished. You must sand the exterior of the decks, cabin and cabin top to achieve an acceptable finish. If you choose, it would be a simple matter to attach any suitable fabric lining material to the smooth interior. Think of this option as a male moulded deck and superstructure.
The camber boards or temporary deck beams are cut and installed at say 24” [610mm] centres by nailing to the deck shelf. Next install sufficient longitudinal battens or deck stringers to support the hardboard lining. Generally stringers should be about 9” [230mm] apart and these are checked into the temporary camber boards. You can expect to use ¼” [6mm] hardboard or a similar material. While we refer to hardboard in this text, you may be using a similar material such as melamine coated plywood however, to avoid confusion, we will refer to the lining as hardboard. The whole structure of camber boards and stringers should be set ¼” [6mm] or at a thickness equal to your lining material below the upper surface of the deck shelf. This is so that the fibreglass laminate will run smoothly from the hardboard lining material across the top of the deck shelf and go on either up the bulwark or on to the exterior of the hull to form a “Coffee can” hull to deck join.
Nails should be kept to a minimum when fastening the hardboard to the framing for the in-place deck mould. Any nail heads will show (unless covered with a lining material) on the finished laminate from inside. Fasten the hardboard to the framing using contact glue.
The upper smooth face of the hardboard will provide the surface on to which you will laminate the deck. Study the sketches shown here and your plans which should give you sufficient guidance for the deck join and other features of fabricating your particular deck and cabin. You will note that there are certain areas that the hardboard will not cover for a particular reason. It will only extend out to the inboard edge of the deck shelf because as you laminate will go from the hardboard and bond on to the top of the deck shelf.
After all of the hardboard sheeting is completely installed, remove any unevenness by placing bracing under the formwork. Radius all edges and corners a minimum of 3/8” [10mm] – these radii will need to be fine sanded and coated, with two or three layers of polyurethane to make them non-stick for the fibreglass laminate. This radius can usually be achieved through the careful application of resin putty (bog) using a putty knife with a rounded end. Cabin top edges will have to be formed from an easy-to-sand timber.
PREPARING FOR THE DECK LAMINATE – HARDBOARD DECK MOULD
Once you are satisfied with the finish of the form work for your deck and superstructure, you should then cover all the hardboard surfaces with four coats of non-silicone wax polish – consult your fibreglass supplier for the correct material. Allow at least one hour drying time between each coat of wax. Pay particular attention to the corners and joins. The areas to be waxed are those where you will later want to remove the formwork such as the hardboard and any special shaping you have arranged for the corners. When the final coat of wax has been applied and polished, you should then coat the entire area to be laminated with a PVA release agent.
Talk to your resin supplier about the supply and use of this material.
Do not wax or cover with release agent those areas where you want the fibreglass resin to stick to the surface. Areas such as the top of the deck shelf, tops of bulkheads, the toe rail, the hull sides where the laminate will be bonded to the hull, either outside or inside the bulwark, or any other area where you want the fibreglass of the deck to be bonded to an area of the hull or elsewhere as noted.
PLYWOOD PADS
Now is the time to consider where you are going to place any plywood inserts to allow for later through bolting of the various fittings. The ply inserts should be the same thickness as the core material and the fittings will include such items as chain plates, stanchion bases, windlass, bow fittings, cleats, sail track, winches and mast step or where the mast will go through the deck in the case of a keel stepped mast. The plywood pads may be only slightly larger in area than the base of the fitting concerned. The idea is that the plywood will not crush, as might happen with foam or balsa, when the fitting is through bolted and the bolts tightened. Although balsa core has excellent compressive strength, it is not equal to the type of strains imposed by through bolting the fittings. At this stage, you can make up all of the plywood inserts, mark their location, and identify each piece before they are put aside ready for installation at the same time as the core material.
APPLYING THE DECK LAMINATE
The first job in fabricating the deck will be to install the inner laminate. The inner laminate will consist of a varying number of layers of mat and roving. The number of layers will depend on the type and size of your boat however the laminate should be clearly shown in your plans.
INSTALLING THE DECK CORE
Before installing the last of the mat, check over the laminate and carefully sand off any humps or bumps. When you are satisfied with the evenness of the laminate installed so far, simultaneously install the last one or two layers of the mat and the core material. The core material will usually be ½” or ¾” [12mm or 20mm]. The core material, usually end grain balsa or PVC foam comes in sheets that are usually made up of small squares of material attached to a scrim cloth and in most areas you can install complete sheets however, in some areas such as the cabin sides and cockpit you will need to cut the sheets to fit. It is a good idea to prepare one area at a time, say one third of the deck and cabin area can be pre-fitted with the core sheets. These sheets should be numbered and laid out in an area adjacent to where they will be placed and in a manner similar to which they will be applied to the deck and cabin. It is necessary to work quickly when installing the core so everything should be well prepared.
When installing the last layers of the Mat before the core is to be fitted make it a resin rich layer as some resin will be absorbed by the core material. Next, lay the core sheet on the wet mat and apply enough pressure to feel that the balsa is well bedded. The resin should squeeze up between the joins in the blocks and where the sheets join. It may be necessary to use a system of weights to hold the core in position. This should only really be necessary in difficult areas, such as where there is excessive camber or where you are installing the core where it will not lay smoothly in position. It is a good idea to use plastic sheeting under any weights, so that the weights do not get glued to the core surface. You may want to look at using “Vacuum Bagging” to install the deck core – see later chapter.
Once the core is installed and the resin has cured so that the core stays in place, then fill any gaps with resin putty and seal the top of the core with two coats of resin. You can then lightly sand the surface to remove any rough edges and other irregularities before proceeding. If necessary, you may also use a resin putty screed to smooth out the surface however do not overdo this as you may impede the bond between the core and the outer layers of the laminate – your materials supplier should be able to advise you at this stage. The more attention you pay to achieving a smooth surface to the core the easier it will be to end with a smooth outer and final surface finish to your deck and cabin. Some designs may suggest solid glass cabin sides, cockpit sides and coamings but stick with the core material, if possible. On some occasions you may be required to apply the core to near vertical surfaces. Depending upon what material you are using the answer to this problem and any others should be in the manufacturer’s brochure or available from your supplier.
Once the core is in place and dressed off to your satisfaction, it is time to install the final outer deck and cabin laminate. Use the same techniques here as suggested for laminating a male moulded hull. There is no point in installing more laminate than your plans specify. You will do more harm than good if you put in extra layers causing excessive weight in the wrong place. This will be your last opportunity to even out your laminate and make life easy when you come to the final finishing of your decks and superstructure. Once you have installed the outer laminates then it is time to consider finishing the surface using similar techniques to those explained in the chapter on building male moulded hulls.
When considering the deck to hull join there are three possibilities that we have available - chemical, secondary and mechanical bonding. It is common to use at least two, chemical and mechanical or secondary and mechanical however, secondary bonding on its own is the most common and is usually sufficient.
The chemical bond is where the deck is bonded to the fibreglass of the hull structure whilst they are both in a “green” state but this is difficult to achieve as one would have cured before a chemical bond is possible. If too much time has elapsed between the lamination of the hull and the installation of the deck, you will not achieve a true chemical bond. Secondary bonding is more common where the two surfaces have been sanded and cleaned in preparation for the join – if necessary, read again the earlier text on “Secondary Bonding” before you go further. We have made test panels to simulate a secondary bonding and in destruction tests, the laminate has usually failed elsewhere before it failed at the join.
Add to this a mechanical join, which is achieved when the toe rail is bolted through the hull and deck laminates where they meet at the sheer or where the rubbing strip is bolted through the deck laminate which has been brought over the edge of the hull. Another join can be made when bolting the rubbing strip through the deck shelf and any inner bonding that joins the underside of the deck to hull. So now we have the possibility of bolting both vertically and horizontally!
LAID TEAK DECKS
It is possible to install a teak deck on top of the fibreglass deck but this means screwing into the fibreglass laminate and possible leaks, at a later date. Keep the thickness of the teak down to say 3/8” [10mm] and install the teak planks using a marine polysulphide or epoxy. The grooves or spaces between the planks should be filled with polysulphide.
There are specialists who do this type of work and so it may be worth while employing the expert for his experience and specialised knowledge.
NON-SKID DECK FINISHES
All horizontal surfaces and anywhere where a person might place a foot should be finished with non-skid. This can be achieved using either a prepared deck paint which incorporates pumice or other non-skid material, or by applying fine clean sand in the last two coats of the outer surface paint. Washed, coarse beach sand is probably the most effective and can be sprinkled on to the deck through a stocking or a tin with holes punched in the top. The sand is applied to the penultimate coat and areas around the cabin, hatches, winches and coamings should be masked so that you have a clear area when applying the final coat. Another method is to apply one of the synthetic or cork based non-skid materials which are sold in sheet form and are cut, fitted and glued to your decks.
No matter what method you use to create a non-skid surface, make sure you arrange the non-skid material in such a way as to provide small sections, strips or panels of smoothly finished deck around the edges of the sheer, around the inner surface of the decks where they meet the bottom edges of the cabin sides. There should be a small smooth strip around all hatch coamings and areas where fittings are to be installed. Check out other boats, you can obtain many ideas from the boats you see in the local marinas.
Before you finish your decks, you should consider your hatches. If you are going to fit commercially made hatches, do not cut the hatchways in your deck until you have the items on hand and can make accurate templates or take proper measurements off the hatches themselves and leave a clear strip around the hatch.
