The Specifications allow the use of fiberglass-reinforced plastic in the construction of a Thunderbird yacht provided that components are made from molds that have been approved by the International Thunderbird Class Association. Contact the Association for further information.

Alignment

Proper alignment of the bulkheads can be ensured by drilling a small hole in each at the intersection of the centerline and WL 2A and stretching a wire from stem to stem. Allow for sag by sighting down the wire.

Laminated Stem

Many boats have been constructed with a laminated stem and forefoot. Some local fleets have a jig for this. It can be built without too much trouble. Half inch laminations provide a good compromise between ease or bending and number of glue joints. Since the laminated stem must conform to the dimensions shown on the plans for the solid stem, spring-back of up to an inch on the forward end would be allowed for. In all known cases, laminations have had glue joints in the horizontal plane. Use short sections of 2 x 4 wood under clamps to avoid crushing the wood. Crushed wood is more likely to rot.

Chine Blocks

It is desirable to fasten a small block of wood 10 each bulkhead at the chine slot to provide an adequate means of drawing the chine stringer into the slot.

Transom Layout

Enough extra material should be left at the top of the transom to allow for the sheer line bevel.

Keelson

It is advisable to refrain from beveling the outer keel strip to the bearding lines until fairing the entire hull in preparation for planking.

Fairing

The forward parts of the boat are the most critical. Use the bending lines on the keelson, stem and forefoot to achieve planes in which the plywood can lay absolutely fiat against the stringers stem; forefoot and keelson. Cut notches about 1/8" inch deep and 3/4 inch wide in bottom stringers at lowest part of hull before planking to serve as limber holes to drain bilge water down to center of boat where it may be more easily removed.

Motor Well

Many builders have expanded the motor well both athwartships and by running the side panels aft to the transom. The well should be matched to the builder's choice of motors. In particular, most flat pitch propellers have 3 blades which means that the hole should be larger than shown in the plans. Be sure that you ventilate the fuel storage compartment. See outboard well layout in wood boat plans.

Floor Timbers

Do not rely completely on the floor timber patterns because for a particular boat they may be too short. Make sure floor surface of all timbers are the same height.

Planking

Experience has shown that one of the most critical areas is along the stem and forefoot between bulkhead Nos. 1 and 2 where the planking is attached. It is absolutely vital to fair this area carefully so that the best possible glue joint between the planking and the stem and forefoot is obtained. The joint should also be reinforced by screws on approximately 3-inch centers staggered on the glueing surface. Probably due to the load of the mast on the forefoot, some boats have developed leaks resulting from cracks in this area. This should be avoided if careful workmanship is employed and the above recommendations are heeded. It is also wise to avoid keeping the shrouds too tight, especially when cold weather contraction is anticipated. Class rules do not allow stepping mast on deck which subjects mast to greater stress. Some builders have devised saddles at the step to spread some of the mast compression load to bulkhead No.2 and adjoining hull stringers. Screws are recommended for fastening plywood to the keel.

Fiber-glassing the Hull

It is strongly recommended that the hull be fiberglassed to avoid checking of the plywood. In filling nail and screw holes, be sure to use a putty (non-oily) which is compatible with fiberglass. In fiberglassing your boat the best approach is to consult an expert. Each side of the boat can be covered with one piece of cloth since the cloth can be made to take the compound curve without any trouble. Using laminating resin for all but the last coat eliminates the need for sanding between coats. The same resin may be used for the last coat when the mylar technique is employed. This technique requires expert advice and prior experience or practice.

Waterline

Many builders mark the waterline on the hull (using a transit) while it is still upside down and in a perfectly level position. The bottom paint should come up about 3~inches above the actual waterline which will itself probably be above LWL since most boats are turning out heavier than Seaborn anticipated. Also, a more pleasing effect is obtained if the waterline is higher at the bow than at the stern. If possible, it is a good idea to look at a boat in the water.

Paint

The hull paint used must be compatible with fiberglass.

Turning Over

After the boat is turned over, further construction will be greatly simplified if the hull is leveled both longitudinally and athwartships. An alternate method is to square everything off the bulkheads.

Deck Beams

The patterns given in the plan should be used with caution as they may be too short for a particular boat some boat builders have substituted yellow cedar for oak. Deck beams may be installed fore and aft instead of athwartships.

Cockpit Stringers

If a one piece cabin side and cockpit coaming is installed per the plans, it is advisable to use Douglas fir or Honduras mahogany cockpit stringers to provide a good screw base for fastening the sides to. Some builders have made the coaming a separate piece from the cabin side so that it might be tilted out to provide a more comfortable backrest. in this case. cedar stringers are adequate. Athwartship cockpit coaming should be slanted aft at the top.

Cabin Roof

Many builders have found that it is simpler to construct the cabin roof away from the boat. Some fleets have a jog for this. Even lacking such a jig, it is worthwhile to build one rather than installing formers in place of the cabin. some builders have found that with time, a slight crack develops in the fiberglass over the joint between the roof and the cabin sides. Be sure to use 3/4 inch x 2 inch wood glued and fastened the cabin side and windshield to accept cabin roof fasteners, use extra care in fitting these joints. Extra glass or a molding may be used over this joint. The cabin hatch can be laminated on the same jig as the cabin roof. Hatch configurations range all the way from per plans to tilting and sliding designs to pure sliding designs.

Windows

Plexiglass has a very high coefficient of expansion (details may be obtained from the distributor) so ample room should be allowed during installation. Auto rubber extrusions for 3/4 inch mounting have made successful installations. Buy the rubber extrusion before cutting out window openings. some persons have installed the glass or plexiglass from the inside. With this method, unless a perfect seal is obtained, the water is more readily able to leak into the boat than it is with the conventional method of installation.

Cabin Arrangement

Cabin arrangement is completely optional so long as the required equipment is included. Consequently, the builder can exercise his ingenuity here to his heart's content.

Keel

Some builders have bedded the keel in Thiokol. This has proven to be an effective barrier but has created serious problems in the few instances where keel removal has been required. Keel bolts should be sealed at the top and bottom ends.

Rudder

The rudder shaft should be either monel or stainless steel. Efforts to substitute bronze have been unsuccessful. The bronze, not being sufficiently strong, has allowed the shalt to bend under stress. Some builders have effectively utilized teflon shrink fit tubing on the rudder shalt to act as bearings. Some provision should be considered to prevent damage to the rudder by the propeller. A line tied to a cleat on the bottom of the tiller and to a cleat on the centerline of bulkhead 6 can be adjusted so the rudder will not contact the propeller (many skippers leave this line connected while racing). Many builders have found it helpful to drive a taper pin through the tiller cap and top of the rudder shaft to secure the installation. In using the type of rudder cap specified in the plans, some difficulty has been experienced with the straps weakening and failing. They may be strengthened by welding on a stiffener or the builder can choose a sturdier fitting. Some people have designed and built their own fittings. Some builders have lengthened the tiller so that the boat can be steered from the quarter- berth seat.

Cabin Hatch

If a tilting hatch is used, the gasket behind the hinge should extend beyond the edges of the hatch so that any water caught in the groove will run outboard and not down into the cabin. Also, the telescoping sash hardware is necessary only on the front portion of the hatch and simple fixed links will suffice on the back portion.

Many racing skippers and manufacturers use a sliding rather than a tilting main hatch.

Interior Construction

It is a good practice to fit all pieces to the boat and use the plans only as a guide.

Cockpit layout Attention is called to the fact that cockpit layout is optional. Some builders have eliminated the athwartship seat in favor of extending the side seats the full length of the cockpit. With this configuration there is a tendency for water to gather at the forward end of the cockpit. To prevent this, the floor should be sloped alt with about 1 - 1/2 inch fall from bulkhead No.4 to No.6 or slope floor toward cockpit drain. To reduce cockpit volume, raise floor and extend coamings to the top of the seats.

Cockpit Drainage

One arrangement which has proven satisfactory consists of scuppers with ball check valves located on the crease between the level and sloped parts of the cockpit floor. Hoses can be lead about one foot forward with a slight fall through hull fittings just above the waterline on each side. The lines should not be crossed under the floor to the opposite side.

Backing Blocks

Installation of the chainplate backing blocks can be facilitated by making them in two separate pieces, one to be fitted between the stringers and the other to complete the assembly. Before decking over, backing blocks should be installed as required for mounting mooring cleats, genoa winch supports, etc.

Lightning Protection

When properly grounded, the standing rigging serves as a lightning rod. A lightning rod which can conduct off the current generated by a lightning strike provides complete protection within a conic "umbrella" extending downward from its highest point at an angle of 60 degrees to the vertical. For a Thunderbird, this means that a minimum of two shroud chainplates should be connected to the keel bolts by the equivalent of a No.6 AWO wire (or heavier) each.

Electrical Wiring

Wire routing should be planned early in the construction so that wires can be easily installed in concealed areas which are protected from the weather. Navigation lights should be installed in accordance with the International Rules except where other Systems are mandatory. Side lights should be located where they will not be blanketed by the jib (forepeak, hull sides, alt cabin sides, etc.). some builders have concealed the wires running to the cabin lights in the cleats where the cabin roof is nailed to the sides. The wires are inserted before the cabin roof is installed. it is convenient and economical to use pre-tinned wire to avoid corrosion. A 12-volt system uses less current for a given lamp brightness than a 6 volt system does. Consequently, line losses are less and battery life is longer. Use switches which include circuit breakers to avoid discharging battery.

Cockpit

It is advisable to make the cockpit floor and seat tops sturdier than called for in the plans.

Mast and Boom - Aluminium

Almost all racing Thunderbirds are using aluminum masts and booms. Aluminium masts and booms are much stiffer than wooden spars. Thunderbird sailmakers cut sails for aluminum spars. Almost all North American racing Thunderbirds sail with Spartech masts and booms. Spartech designed the mast extrusion die for the Thunderbird. Spartech is located at 15230 N.E. Redmond, Washington 98052, with phone number (206) 883-2126. If wooden spars are cheaper and cost is a concern, get an aluminum boom first.

Mast - Wood

Wooden spars slightly larger than the plans will provide better performance on today's sails. Less rounding on the mast will help. Increase boom dimensions to 2 1/4 inch x 3 1/2 inch in the center and 2 inch x 23/4 inch at the ends.

Boom - Wood

It is a good idea to through-bolt the aft one or two feet of sail track. Experience has shown that the tremendous pull exerted by the leach of the mainsail tends to pull up the track if it is fastened only by screws. A slotted boom (rather than track) performs satisfactorily.

Mast Fittings - Wood Masts

It is a good idea to extend the forestay tang upwards so that the spinnaker eye bolt passes through it. Rigging toggles should be used in combination with the turnbuckles on the shrouds and stays to allow more flexibility in the rig. There are several methods of installing ends on the wire shrouds which can be done by the home builder. These include patented self-swaging fittings available in most marine supply houses and also aircraft type ends which may be swaged with hand tools obtainable from aircraft parts and repair establishments. If the masthead sheave is built in accordance with the plans, the builder should line the sheave recess with metal or put metal straps on either side of the sheave on the fore and aft side of the mast to prevent the halyard from jumping off the sheave.

Another possible installation is a half round block of nylon installed in place of the sheave. The nylon will last about 3 seasons. Some people extend the spinnaker track all the way down to the deck to allow the pole to be set horizontally at a very low position. Attention is directed to the fact that the Specifications allow a shorter spreader than is called for in the plans. Tangs for the jumpers and the lowers can be fabricated out of one strap, leading it under the spreader.

Genoa Track

It should be noted that the Specifications allow reasonable substitution of hardware. One place savings have be effected is in the amount of genoa track installed. Only the aft half of the track shown in the plans is really necessary. If a working jib is to be carried, some additional installation further forward is required. However, it is customary to sheet the working jib inside of the shrouds to a separate track or fixed fairlead. If you wish to race, see local racing Thunderbird marine catalogs.

Genoa Sheet Winches

It is suggested that for racing, the winches be located farther forward than shown on the plans. Considerable side loads on the coaming are generated by the sheets and in some instances, cracks have developed. The brackets shown in the plans provide adequate bracing. If a substitute is utilized, it should provide support to the coaming by being solidly anchored to the deck. Satisfactory mounting blocks have be constructed both from wood and from stainless steel. Whatever the design, care should be exercised to get a fair lead. Table of Contents