September 15, 1998 Issue

Dreamboats

by Richard Carsen

Vesica seems to me the latin for what we call a fish (form). And that is exactly what it represents. Most of us have seen the sign of the early Christians, xristians, as it again is used today, you can see it on bumper-stickers. It derives from the Greek ixtos (the x is the mexican x which sounds like ch), which means fish, and which was close to xristos, the anointed one. It also had meaning in another way; the ancients loved to do puns, riddles and meanings in meanings and again in other meanings.

The oldest pictures, where some god gives a king permission to build a temple, show the deity handing the king a pin, a ring and a roll of rope; eventually, in later pictures, first the rope is dropped and then the pin. The king is just handed the ring. However....

With a pin, a ring and a rope you can build a complete edifice, or a boat. You could set out a line, sighting in on the rising of a star or other heavenly body at a specific time of the year, and by creating a vesica perpendicular to that line, create a line perpendicular to the first line, etc. etc. etc. Even primitive cultures in the depths of Indonesian jungles, know how to do this. Of course, you can also set out the longitudinal axis and the sides of a double-ended boat, albeit a very primitive one. Some native American tribes set out the basic outline of their boat (canoe) in this manner.

Now, if you take any boat and look at the main waterline at rest, even boats with transoms, you will find that that waterline has the shape of a vesica, the aft point is where the transom touches the water. This vesica however will be somewhat mis-formed; instead of the pure arc, part of a circle, it will have bulges in places, in the buttocks, or hollows, near the stem. However, the two sides are still equal, though they are mirror images of each other.

Now, when I tilt the boat towards port or starboard, the lines, and the area they enclose, become unequal. I have found that something can be deduced from the shape, the now distorted shape, of these two areas.

It was the scow which first put me wise to that. The scow crabs, that is, she has a sideward component to her movement. The scow is vesica shaped with the ends cut off. But when you tilt her, you again form a vesica, with one of the chines as the longitudinal axis, but greatly un-equal areas at each side. Look at the draw-ing. Now, by the law that governs the action of toils (air or hydro), there now exists a force, when the craft moves thru the water, that will pull it in the direction of the largest area and the greatest bend; more about the latter later.

I had a double ended cruising-sailing kayak. When the ends are not resting on or in the water, you have a very elongated scow form. For five years my brother and I used to tack this craft in a small lake formed by the cutoff arm of the river. It was a long curving lake, probably less than a mile across, so the movement of the craft could be accurately observed. It obviously didn't go where it looked but higher into the wind than it looked. It crabbed, upwind.

Lewis, in We The Navigators, says that all the builders of native outriggers he asked denied that the overbuilding of their craft towards the outrigger had anything to do with making them more weatherly. It was, they said, to offset the pull of the outrigger. I am sure they are sincere; it is probably pretty hard to gauge this effect in a large expanse of water, with few solid points to go by. However, Lewis gives a trip he made with time and distances traveled, having a favorable wind in the first half of the journey, and having to tack in the second half. He observes that basically they move the craft in a series of undulations, letting the craft run upwind till the movement is exhausted, then falling off to let the sails fill again. As dinghy sailors we are all familiar with that. However, the total resulting move in the direction of the wind takes place in a sort of narrow reach, doing 10, maybe 15 degrees to windward.

Taking this information and setting it out on graph paper, assuming the speed of the tacking craft to be the same as when it ran with a favorable wind (I think that was 8 mph), which, seen the way it is done, is really bending over backwards, there was no way I could achieve the upwind target at the distance stated without some outside help. Was there a current setting in that direction? Lewis does not mention this. I think that it was the crabbing to windward as a result of the canoe being overbuilt at that side (the outrigger side).

I have seen an actual hull, and it is not the first time I have thought to notice this, that was twisted. By mistake? If this had been a rough affair, I could have accepted that. But this canoe was beautifully carved and finished. Those who did this could not possibly have missed the almost spiral general twist.

Think of an area where there are certain prevailing winds. Let's say, going out you are usually tacking; going home the wind is full. The twist would, in this case turn the craft clockwise round its center. With the ama attached in the clockwise direction, it could tack with the ama to the right, but go home with the ama to the left of the course-line with the wind blowing in over the aft quarter. The twist was such that whichever way you looked along the center of the canoe, the forward bulge would always be to the right, the aft bulge always to the left. Whichever was forward, the forward one would always pull toward the ama, towards the contrary wind, the aft one always away.

This may well be the reason that in certain areas there were or are double canoes with dissimilar ends, who are paired back to front to one another. The purpose, frequent traffic between two islands, and action in the prevailing wind, may well have been the same as that of the twisted hull. In the Ceylon outriggers I described, although I did not notice it in the main hull (then, I was unaware of this), I certainly noticed it in the amas. I was sure the twist was for a reason, although I then couldn't fathom what this reason was.

Figure A shows profile of simple scow. B shows the plan with flaring sides, seen from below the bottom. C is a sectional view. D shows this section when heeled. The broken line in B shows the shape of the waterline in this heeled situation.

The hip, buttock, diminishes the up-wind movement of the bows. E shows one way to deal with that by making the craft narrower toward the aft. It would still be the break between bottom and the sloping aft part.

E 11 flattens the hip out even more, by shortening the horizontal bottom part and making that slope up somewhat. The heeled waterline now shows a stronger foil shape, favoring the windward pull of the head.

G shows the bottom of a wide flattie, heeled. They were hard to move thru the wind; the heavy hip is pulling the transom to windward, but forcing the stem down-wind. To correct this they introduced a V-bottom aft.

H shows the change in the shape of the vesica favoring the head to move to windward.

It shows what happened to a sharpie when heeled. The ends were supposed to be raised above the water. The waterline then shows the pattern of the scow. It is my thought that this vessel sports a sharp bow instead of the flat transom, but was otherwise conceived as a scow in the way the Chesapeake watermen named their craft, a sharpie scow!

J shows the bottom of a traditional Dutch flatbottom craft, all rounded out of an original rectangular concept.

Turn to Chapelle's American Small Sailing Craft, page 157, "the extreme de-velopment of the Casco Bay Hampton Boat of the square sterned model". If you think of the stem as some kind of forward skeg, you can see how in profile the bot-tom is like drawing F. However, forward there is a "real difference. You feel how the deep forefoot would press against the wa-ter, creating resistance there, while the wide but high hips, when heeled, turn the craft around its center into the wind, by creating a downwind force there. This boat is indeed extreme, but if you look at other designs in the book you sec again and again, not as exaggerated, the same idea, all nicely rounded and flowing into stems and skegs.

As you know by now, I am a fan of the dhow, that age-old trading vessel you find in the Indian and Arabian seas. Here the sharply sloping stem ends on the forward part of the keel; this is the deepest part of the vessel. In the aft quarters, the hips, like the Hampton boat, arc high and full. Again, while the deep forepart provides the necessary resistance, the high hip, the ship's widest part, is alt of the middle, at the break of the quarter deck, when heeled, provides the pull at the quarter that makes the craft face thc wind. The one I sailed tacked beautifully and without hesitation.

All this does not mean that center-boards or leeboards do not greatly improve performance; but the boat is a unit, with every facet co-operating. I hope that this will help you plan the shape of your dreamboat more efficiently.

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September 1, 1998 Issue

Strip Plank Construction

By Ted Warren

Why Strip Plank?

Strip plank is a light weight, strong method of constructing hulls because the wood serves as a core material and as a structural material for longitudinal bending stresses caused by the rig loads and the sea. Wood bonded with epoxy is a modern structural material with a higher strength or stiffness per pound than steel, aluminum or fiberglass. Dick Newick says that if wood were an invented material it would be called Miracle Fiber W.

Which Wood?

Cedar is an excellent core material. I use western red cedar, but the main requirement is that it is light and that it epoxies well. Secondary requirements are that it is rot resistant and pleasant to work with. Meade Gougeon made the comment that dense woods have more fiber and therefore more strength and stiffness. He constructed the amas for Adrenalin using Douglas fir as a core. It's denser, but twice as stiff as cedar, so it you "run the num-bers" you find that the core stiffness is the same at identical overall weight.

The wood should be available in rea-sonably clear, straight grain lumber. I weigh the lumber that I use and have found that WRC varies from 181bs to 261bs per cubic foot, and averages 22 1bs per cubic foot, as the book says. If you have an understanding lumber yard (tell them that you are building a boat) take a scale and a friend and pick through their stack.

Ripping the Strips

Step one is to setup your bench saw. I use a Freud thin-kerf ripping blade. The blade must be adjusted to be parallel to the fence. I attach a hardwood ripping fence to the aluminum fence on the saw and I lightly wax the wood. I use a "teatherboard" to hold the piece against the fence and avoid kickback. Be careful, though, when completing the cut, the strip can kick back. Now move the saw outdoors. This reduces the sound level, the dust level, and keeps the motor cooler. I like to rip all of the wood that I will need for the project at once. I put the strips in stacks of 10, held together with electrical tape. I don't use a bead and cove on the strip edges as the epoxy is gap filling and I want to go sailing as early as possible.

Scarfing to Length

I build a bracket onto the side of the mold forms to hold the strips at full length and scarf them. I use a bench disk sander to cut the 8:1 scarfs in the strips. I have a jig which holds the pieces at the correct angle to the sandpaper. With 36 to 40 grit paper on cedar the bevels are cut very fast. The strips are placed in the brackets, thickened epoxy is applied to the joints, they are wrapped with plastic and clamps are applied when in a bundle.

Mold Form

I use a female mold form with stations spaced 24" or 12" on center depending on the hull length and local curvature. Most builders report that they wished that they had used more stations at the areas of high curvature. I prefer female mold forms be-cause I have found that the hulls are more fair and I like to be able to construct the insides as the hull sits in the mold form. I can then delay finishing the outer skin as long as I want to. The hull will be closer to the design shape as compared to removing a hull shell off of a male mold and then building the insides on a loosely supported structure.

Cutting a Taper

In order to avoid cutting "cheater strips" or allowing runout at the sheer, I taper the entire stack. This also reduces the tension that accumulates on each successive piece as it goes through a compound bend. Measure the distance along the mold at each station. Take the longest measure-ment and use that as the divisor at each station. The quotients should vary from 1.0 to O.x. Take one full length strip and mark at each station the width of the strip times the quotient. Take a long fairing batten and draw the taper line. Stack all of the strips together and clamp them. Using a hand held power plane, cut them all to the correct taper. If you do this right then the strips will fit from the keel to the sheer with almost no runout.

Making a Hull

Almost any hull can be strip planked in one day. If it's longer then 30', or you prefer the security of an additional pair of hands, you will need more than one person. The strips should be clamped in their brackets and the edges buttered with a mixture of epoxy, silica, and your favorite filler (I use microspheres). Each one in turn is pulled from the holding bracket into the mold form. Starting at the center-line (I hope that you marked it) fasten the strip to the moldform. For pieces that are 1/4" or thinner you should use 9/16" staples. For thicker hulls you can use sheet rock screws and a screwgun. Don't be cheap with the staples. One trick that I use is to cut floating male mold stations in areas of high curvature. The strips can be stapled from the outside into the floating ply station. When all of the strips are rayed up, take a squeegee and. smooth out the inside of the hull. This will save you effort in the next step.

Clean Up the New Hull

After the epoxy sets you need to pull out the staples. I use a 1/4" chisel with the edge ground to a concave curve. I put the corner of the chisel under the crown and pop the staple out. Most staples come out at once, some will just raise one leg into the air. Ignore them for a while. Come back after all of the well-trained staples are out and pull the reluctant staples with a large pair of pliers. When you get good at this, you will be able to do 1000 staples per hour. Now you need to knock off the bumps inside the hull. You can use a paint scraper, a Surform, or a disk sander with a soft foam rubber pad under the disk. Don't sand too much, you just want it good enough for the glass to lie down flat.

Applying the Reinforcing Fabric

The inside surface is now smooth but has holes, gaps, and bare wood in places. There are two techniques to applying the fabric. The first one is to fill the holes and gaps with thickened epoxy and coat the inside surface with epoxy and allow it to setup. The second method, which I prefer, is to squeegee in a thin layer of epoxy with silica and microspheres added. Do only the width of the fabric at a time. The fabric will then be laid into the hull and gently pressed into the epoxy mixture. The goal here is to have continuous contact between the fabric and the epoxy and the epoxy to the hull.

Mix up a generous amount of epoxy and pour in onto the fabric in an "S" pat-tern. Take a plastic or rubber squeegee and work the epoxy into the cloth and the cloth into the underlying thickened epoxy. When the cloth is fully wetted out, use the squeegee hard to pull out any excess epoxy that you can. It is better to use more epoxy than needed to wet out the cloth and then squeegee the excess off.

There are two possible problems that you will face now. Dry areas in the cloth will form due to not wetting out thoroughly enough and from the wood absorbing epoxy. The second problem is that the wood may outgas forming bubbles between the hull and the fabric. In both cases the solution is to check the work at regular intervals as the epoxy sets up and squeegee more epoxy into the fabric, driving out entrapped air. Heat will compound the problem of outgassing.

I have used peelply at times, but I don't like to use it on the insides of the hull. You will have to add much more epoxy to get the peelply to wet out to the fabric. When you pull the peelply you have a very even epoxy surface, but that's due to filling the weave fully with epoxy. A well squegeed surface will look some-what dry with the fibers in the fabric stand-ing out, and I believe that this is lighter construction for hand layup.

Interior Structures

Add the interior structures now, bulk-heads, stringers, ringframes, beams, etc. This should make the structure stiff enough to remove the hull from the moldform and invert it.

Finishing the Outside Surface

The outside surface should be sanded with a disc sander with a soft foam rubber pad and 40-60 grit sandpaper, I use the 8" Makita sander with electronic speed con-trol. I feel that I get the best results by changing the paper very often and using the slowest speed, 1200 rpm. I then finish with the Milwaukee 1/2 sheet orbital sander. This is by far the best orbital sander that I have ever used. It packs a lot of power and cuts fast.

Now comes the fun part, fairing the hull. I mix up large quantities of Microlite, from Gougeon, in System Three Epoxy. I then glop it all over the hull, about 1/8" thick. After it has set up I sand again, starting with the disk sander and finishing with the orbital sander. You will be remov-ing huge amounts of fairing compound, but I've found this faster then a local area approach. Now clean the hull, and find all of the low spots and fill them with the same mixture. Sand again, and repeat until you are satisfied with the fairness of the hull.

Now you are ready to apply the outer fabric. Drape the fabric over the hull and pour epoxy onto the fabric in an "S" pat-tern. Squeegee it into the cloth until its thoroughly wetted out. Use lots of epoxy. Now squeegee out the excess. If you are not going to use peelply then squeegee out very hard. If you use peelply you will need to leave enough epoxy to wet out the peelply. Place the peelply over the hull and squeegee it into the epoxy thoroughly.

After the epoxy has set, mark the hull for all low spots. Mix up some fairing compound and spread it into the low spots and sand (well, not while it's wet). You then need to fill the weave in the cloth especially if you have not used peelply. I make a thin mix of epoxy and some Microlite and roller this on. If you make it too thick it won't roller on smoothly. The purpose of the small amount of Microlite is to allow you to easily sand the epoxy, it breaks up the monolithic surface of epoxy and allows the sandpaper to cut. Use the orbital sander now to finish the job.

You must use an interface primer between the epoxy and the finish paint if you want to avoid peeling. I use Interlux 404 two part epoxy primer and have had no problems with peeling. The two part linear polyurethane paints are great, but I have been using the one part paint, Interlux Brightsides lately with very good results. Brightsides will NOT work without the primer. It stays on the hull as a soft gooey mess when applied directly over West or System Three.

One other thing, unless you are using aircraft epoxies you should paint the hull a light color. Most boat formulated epoxies are designed for strength and fracture resistance and not for high temperatures. If you paint your hull black and it is in direct summer sun the epoxy that you used will soften.

About Reinforcing Fabrics

The common fabrics are fiberglass, kevlar and carbon fiber. I've never used kevlar, but friends who have swear that they would never use it again. It's very hard to wet out and it's a very abrasive material. Carbon fiber is my favorite material for strip plank, when I can afford it for a project. I use a 4.7 oz. unidirectional cloth 48" in width. It has a light fill of dacron to hold it together. I buy it from Techniweave in New Hampshire. It makes a very rugged strip plank hull. The wood core is safely encased in a very strong skin. The hull feels more like aluminum then wood. 4.7 oz. carbon fiber has a breaking strength of 1404 1bs per inch per layer compared to 6 oz. fiberglass cloth which breaks at 250 1bs per inch per layer. The carbon fiber will wet out easily if it has been sized.

Fiberglass is not just fiberglass but is available in an assortment of weaves, in-cluding unidirectional. S-500 is an 8 oz. unidirectional material which is very strong but almost as costly as carbon fiber and a pain to apply, it benefits from a layer of light woven cloth applied over it as you go. The most common weave for boat construction is basket weave, which is usually symmetrical in warp and fill (warp are the yarns that run the long way on your roll). The other class of weaves are the satin weaves, including crowfoot, twill, and others referred to by the number of harnesses used.

In addition, the weight of the yarns will vary from style to style. These weaves are usually asymmetrical, that is, stronger in the warp than the fill. This is ideal for strip planking, since we need the strength and stiffness perpendicular to the wood grain. One style that I have used is a 6 oz. crowfoot that is about 80% warp. It's available from Defender Industries and is referred to as a racing finish cloth. It is somewhat harder to wet out, but takes less epoxy to fill the weave. It's best to talk to your supplier and ask about the fiberglass cloth available. Make sure that the heavier direction of the material runs perpendicular to the woodgrain.

Epoxies

I use both Gougeon West and System Three epoxies. They are both excellent epoxies that have accumulated a huge number of nautical miles and years on boats. My opinion is that West is oriented more towards the controlled environment shop and System Three is oriented to the backyard builder. West seems to set to a harder surface and System Three seems to be more forgiving as to temperature, humidity, and other uncontrolled vectors. West sells mostly through distribution and their price is higher. System Three sells by mail order, but I believe that they pay the shipping for orders over $100.

Both epoxies have been formulated with concerns for things like recoatability, toxicity, resistance to moisture, and many other factors important to boat builders, not the least of which they have no volatile organics in them. Both of them have a mild odor which makes working in the shop that more pleasant.

Always wear gloves when applying epoxy. I use the yellow rubber dish wash-ing gloves because they are much stronger then the thin vinyl gloves. If a mixed batch of epoxy starts to fire off and bubble, remove it from the area. The fumes are not healthy. Wear a mask and skin covering when sanding "new" epoxy. Wear a mask when measuring and mixing additives to the epoxy.

Philosophy

Enjoy building your boat, it's a quality experience. Build your boat to sail, not as monument to your craftsmanship. I'm going out to the boatshop now to mix up some epoxy and apply some carbon fiber to a jib boom that I am building. Bye.

Ted Warren, Tiny [Dancer 21' proa, Zachary D 29' trimaran, Openly Defiant 40' tri boat abuilding. http://www.warrenmultihulls.com

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