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Seabrook Skiff & Launch
Laid out below is a brief description of the building process for our dinghies. This is an on-going project to help our customers understand what operations are carried out in the construction of a dink, and to provide a guide for those who would undertake the work themselves. It is not complete, but will be expanded upon from time to time when I have nothing else to do. Eventually, it will be a complete manual to accompany the sale of bare hulls for the convenience of home craftsmen. Generally, the information provided is common to each of the four hull styles we have available; the subject boat in the photos is a Sparrow. Please feel free to comment on this project or ask questions by E-Mail.
The first stage of construction for a fiberglass boat is the "casting," in the parlance of the trade, of a hull. This begins with a female mold, which ultimately produces the exterior surface of the finished boat. The inside of the female mold is polished to a slick, smooth surface. However slick, smooth, and shiny the mold is, is exactly the shininess the boat will have. Into the mold is sprayed pigmented gel coat, of whatever color the boat is to be. It's a polyester-based resin that bonds with successive layers of polyester resin and glass fiber. Epoxy-based resins may be utilized, but they are as much as four times as expensive.
The next operation in the building of a hull is to apply glass and resin to the exposed surface of the gel coat on the interior of the mold. The lay-up of these successive layers provides the strength of the hull. First a mat of chopped-strand glass is applied in sheet form and saturated with resin, followed by variously woven cloth layers to the desired thickness, also saturated with resin. The last coat of resin remains tacky, ready to chemically bond with resin that is used to attach the other fiberglass components that make up the interior of the boat. The rest of the process is described below with the aid of some illustrative photos. This is the way we do it in our shop and this is the way we recommend that you do it, if you buy a bare hull and finish it yourself.
The first photo shows the bow of a bare hull with a glob of resin-based putty mixed with glass fibers in the lower stem area. This is to provide extra strength where a towing eye will be installed.
If the bow eye is a bolt-through type, install it now. Next to be installed is a fiberglass fabrication which forms the foredeck. We have a mold for this, but it can be made up from flat sheets of glass and resin if desired. The piece in the photo includes a Schedule 40 PVC 2" diameter pipe bonded to the vertical face of the foredeck structure and heavily glassed over for strength and to prevent water from entering the void formed when the piece is in place.
The tube forms the mast step for boats that are to carry a sailing rig and may be omitted if desired. The bottom of the tube must be capped and a drain hole drilled so that any water entering the tube will drain into the bilge. The photo below, left, shows the foredeck piece ready for installation. The photo at right shows the piece in place, ready for final installation, which is accomplished by applying three layers of fiberglass tape and resin, bridging the lines of intersection between the foredeck and the hull. The lines of intersection are worked into a nice cove shape for a smooth joint to the hull. A hole is then formed in the deck to accept the heel of the mast.
The next operation is the installation of a plywood stiffener for the transom. The stiffener is not absolutely necessary, but it makes the boat a lot stronger in the sternsheets and is installed as a matter of course in all our dinks. If an outboard engine is ever hung on the transom, the stiffener is required, and one never knows how many times the boat will be sold to a new owner with different ideas as to the purpose of the vessel. This installation is shown in place in the photo below, left, bonded into the hull with two layers of glass mat between the hull and the plywood and two layers of mat on the interior side.
Holes are pre-drilled in the plywood, then glass fiber is worked into them to allow a positive bond between the hull and the interior glass, rather than a simple bond to each side of the plywood. Care must be exercised in the future attachment of fittings to the transom so as not to let water penetrate into the plywood, which might cause rot. If the boat is to have a drain hole through the transom, now is the time to drill it, work in a drain tube fitting, and seal the plywood against moisture infiltration around the fitting.
The photo at right, above, shows the after seat in place, ready for bonding to the hull. We have a mold for this piece also, though it could be fabricated to any configuration to suit the whims of an owner. Sometimes we work in a small stowage compartment here, either with a lid, or open on the forward face conecting with the interior of the boat.
The void formed by the full-length keel and skeg is visible in the photos and now is the time to either bridge over it with glass, forming a sealed void, or fill it up with something, either of which operations will form a smooth bottom on the inside of the boat. Our standard is glass-over-foam which provides additional positive flotation. When the forward and after seats are in place, access holes are cut for the installation of foam. At this time, the drainhole through the transom is connected to a tube along the bottom of the boat and through the forward face of the seat. Water in the boat may then drained through the transom. A rubber plug is used while in the water to prevent a leak. Now the seats are filled with foam, then the divots from the access holes are replaced and glassed in.
At this point, whatever structure is planned to form the rowing seat(s) is installed, whether it be supports for thwarts or a fabrication to form a longitudinal seat. Below is a partially completed standard Sparrow for rowing, including the longitudinal, hollow, fiberglass rowing seat. If the dink is to be a sailing model, a daggerboard trunk must be worked into the seat at the appropriate location. There are no photos of the daggerboard trunk available right now.
The interior surfaces have been finished and gelcoated. She's ready for wood trim and other finishing details. A Sparrow at this stage of completion will cost $1240, not including the mast step. The hull to the left in the photo is just the same except that it has no longitudinal seat, but is to be fitted with a mahogany rowing thwart. At this stage it costs $1150.
Below is another shot of the boat above, set up for placing the wood trim at the gunwales. The boat is braced athwartship to maintain the proper shape of the boat while the wood is being installed. At this stage, the inwales have been attached from the outside with screws through the hull into the wood. The screws are countersunk to present a smooth surface for the outer rubrail to seat on. The wooden parts are epoxy saturated to prevent damage from moisture that may become trapped between the wood and glass surfaces. On the portside of the dink in the photo, the outer rail is clamped in place prior to attachment. It takes quite an effort to get the wood to bend into its desired shape. Once things are set up correctly, more screws are driven through the rail, through the glass, and into the inner wale. The screwholes are then plugged and the gap between the two wales is filled with a sandable bedding compound, such as 3M 101. When that is cured, the woodwork is sanded and finished with varnish if mahogany, or oiled if teak.
This boat is nearing completion! There is not much special knowledge required from this point on to complete a spiffy little boat; just expert craftsmanship, which is one of the things we sell. Later, more info will be presented here on how to fashion the spars, daggerboard, oars, rudder and tiller. The rigging details will be examined, and the fabrication of the various fittings and the proper method of installation will be explained. I hope this document has answered some of the questions you may have about the construction of the Sparrow Dinghy.
see the photo pages listed on the New Dinghies Page
This page last updated 7 Feb 99
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