Duckworks - The Least Boat: Part Three

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By Paul Austin - Dallas, Texas - USA

The Least Boat: Part Three

To Part One

To Part Two

The Least Boat I Can Build

After the last two articles, I’ve decided to look at deadrise boats and flat bottomed boats. William Atkin made a statement concerning deadrise small craft. He said that when a v-bottom boat heels the underwater shape is so different on one side of the keel than the oth-er, the irregular shape shakes the boat just enough to ruffle some of the wind out of the sail.

This has convinced me that a sailboat cannot have very much deadrise on a short length.

To take advantage of the reduced wetted surface, a v-bottom boat can have a deadrise bow with flat bottom after it, or a flat bottomed bow with the deadrise after the midsection. This is why I believe the Eric Sponberg Halfling, which has a v-bow yet a flat bottom amidships, is the perfect shape for any craft under 8 feet.

Longer than 8 feet, a sailboat has some choices. In the case of rhe Olin Stephens Blue Jay the bow lifts so that the water hits the deadrise first, as you see below. This is accomplished by having the deepest deadrise aft of the boat’s midpoint, where the skipper would sit. The compromise Olin made was for the waterline to just touch the stern, with the chine well out of the water. It’s a great formula for a 10-15 footer - bow above the waterline, the deadrise handling the waves, the stern just touching the waterline with the chine above the water for the last 3 1/2 feet. Olin has created a lifted after run on a deadrise boat with enough deadrise for the center-board and its’ trunk to provide some ballast on the keel.

I’ve put in the waterline in blue. The Gifford Jackson Marisol is very close to this, although I have no idea if he knew of Blue Jay. You can see the deadrise is gradual at the bow. The sides come in gradually, too, toward the bow as if in agreement with the Bolger statement that the curve of the sides should match the curve of the bottom. This is just enough length at 13 feet to have the sides and bottom meet at a traditional looking bow. If the waves kick up, the bow is there to smack them off of the forward section.

Here is the view of the planks, with their gradual turn from Blue Jay’s width to its bow and stern. The bow sections are narrow, the flare is greatest at the bow, and the stern is narrow, about 3 feet 2 inches. This is close to a canoe with a square stern, cut short.

An observant designer will see that the next to the last frame at the stern is 1 foot 7 inches, while the third frame from the bow is 1 foot 6 inches. This means the sections aft of the widest part do not curve inward any more severly than the sections forward of the midpoint curve toward the bow Everything is so gradual, no wonder the water flows under and around Blue Jay so well.

If you had grown up with canoes, you'd recognize this shape.

But this is a keel boat, nonetheless, with parts to make.

The Atkin Willy Winship is close in LOA and shape to Blue Jay. Usually flat-bottomed boats usually have rockerat the bow to keep the boat above the water. However, rocker drawn up to the bow creates friction at that bow where the waves hit a flat surface. The Atkin solution is to have a slight rocker by putting the bow in the water. Taking some of the rocker out eases the water along the bottom, as the water moves somewhat close to parallel to the waterline, provided the bow meets the waves first. The Atkins then made the bow sec-tions narrow to reduce wetted surface while placing the bow in the water for some stability and performance against waves. It’s another great formula---fairly slight rocker with flared sides, narrow at the chines, bow in the water with a lifting stern.

This is just a boat shape, in its’ simplest form. Beautiful sheer, simple shape, perfect balance, quiet turns of the lines. The crew’s seat can be moved around somewhat without ruining the trim of the boat. When we compare Stephens with Atkin, we see the Blue Jay chine is under water less than with Winship. Possibly the flare of the Winship topsides was meant to help this out by softening the angle.

However, we are back to building parts. Willy Winship requires all 5 of its’ frames on a ladder with supports for the stern and the bow and four braces to create this beautiful shape. Maybe we can learn from Olin and the Atkins, to build a boat with the least trouble.

We can use the WAAM method here (wrap around a midframe). The simplest and strongest bow is the up-right bow of cutters. Then our after run lift will be created by the flare of the sides. This flare is created simp-ly by the tilted stern. The chines are taken directly from Atkin’s Cabin Boy. Since their curve is gradual, the chine might not break when you bend them.

Now for the profile. The increasing flare will lift the bottom as it bends. How much simply depends on the builder. In my case, I’ll go with what the plywood does. I’ll cut a slight curve to the upright bow, just for looks. I’ll try to make up for the upright bow with some sheer dip near that bow.

As with the usual WAAM style, this boat needs chines on the outside and solid pine transom and bow piece. I’ll use spacer sticks to keep the shape where it is until I’ve clamped and glued the bottom on. I put the spacer sticks 6 inches from the bottom so that I can use them to hold the boat as I move it around. If this is to be a 10 -15 foot sailboat, I’d make it a sprit rig cutter, with a small jib for getting away from the dock and approaching the dock at the end of the day.

If there is one complaint about sprit rigs, it is that the sail twists. In strong gusts, this is good, but in a small boat it will make trimming the sail difficult. In light air, this is frustrating. However, the closer you peak the sail to the mast, the less twist you’ll get. A boom will also reduce the twisting somewhat.

Now for some sprit designs. First comes the Michalak Slam Dink. It is the handsomest sprit rig I’ve ever seen on a small boat. While it is not peaked very high above the mast top, the angle from the throat to the peak has a nice similarity to the sheer toward the stern. This means it won’t beat to windward with the best of them, but it will get you home safely in bad weather. It’s probably the best all around sail shape for an 8 foot-er. What I like best is the two sprits are tied off close together, so you can get to both of them at the same time.

I think I would have preferred the peak over the leeboard for response and balance. But tht is a small matter only for Slam Dink. This is a great little project. The main idea is that if there is a wrinkle, it should be from the peak to the tack; if it’s from the throat to the clew will get you thrown out of the yacht club.

Now we’ll move up to a 10 footer, the Atkin Vintage, which has the sprit rig sail the Atkins favored on all their small boats. As you can see, it is peaked a bit higher than Slam Dink, with two 8 foot spars and an 8 foot mast. The boom is snotted a little closer to the clew, giving you a few more feet of sail area. There will be less twist in this sail than for Slam Dink, with slightly better windward movement. The tradeoff is the sail will need more attention to keep smoothly curved, as they said in the 19 century, for the sail to be full and by.

Below is a 17th century sprit rig design. This was drawn by Melbourne Smith for the Revolutionary Priva-teer Lynx, 75 feet, which is a sail training ship in Newport Beach, CA. This is the lifeboat for Lynx, about 18 feet (I’m guessing here) with heavy spars for the main and mizzen sail boom and sprit.

I have to thank Melbourne for his generous help on some technical matters with articles in the past. It’s the only way I can drop his name without sounding like a name-dropper. Someday I’ll have to visit him, to see what’s in his fridge.

One advantage of the mizzen mast is the main peak can be sheeted off to the top of the mizzen mast, to trim it, as long as it is not trimmed too tight. This sail design is worth looking at for camp cruising and the Texas 200. The aspect is low, the main sprit can be dropped, reducing the sail area considerably, and the downwind leg could be sailed with jib and mizzen alone, wing and wing. Not only that, but the sails cover most of the boat, providing the crew with shade. Finally, a very high peaked sprit rig is on Gavin Atkin’s Bluestone. This lapstrake boat was inspired by the river craft which sailed the rivers of England and the Thames. It’s an ingenious design in many ways, only one of which is the sail.