: Michael, Thanks for the response. Your Rangely boat is one of the boats that
: eventually lead me to the wherry. The wherry (as I enlarged the drawing)
: ended up at 51". The length will be 13' thouhg I may yet stretch that
: some. That you used no ribs is definitely what I wanted to hear. Tom

With a beam of 51 inches your displacement will be pretty good. At a rough estimate the area of the boat will be about 32 square feet, so if you have a water line at 4 inches you'll displace about 10 2/3 cubic feet of water, or about 640 pounds.

There are a couple of questions then: "How much of a load do you mean to carry? and "How high is the sidewall or freeboard?"

If the sidewalls are high, or you are planning to carry heavy loads, or you plan on the draft of the boat exceeding 4 inches, then you have to consider the effect of water pressure on the sides of the boat. The deeper the boat sinks the more the water wants to cave in those sides. You need adequate reinforcing -- and this could be ribs, thwarts, or a seat mount -- which increases in strength as the boat goes deeper into the water.

Even the shortest canoe has at least one thwart, usually somewhere near the middle of the boat, to keep the sides of the boat from coming together, like the shell of a man-eating clam, and gobbling up the paddler.

Be careful about "apple and orange" comparisons. A round bottom, narrow, stripbuilt canoe or kayak hull can get away with the monocoque, ribless design thanks to the strength of glass fiber cloth and the bracing of a deck (the boat is stressed like an eggshell) or thwarts. You won't get exactly the same benefits with a flat-bottomed and wider boat.

Simply replacing the outside of the boat with a seamless fiberglass skin over a wood core is not going to address the issue of stiffness in the boat, or hull strength. In some boat designs (pre fiberglass era) the closely spaced ribs served mainly as nailing points for ataching the planks. If the ribs were too far apart the planks could swell or warp and the caulking material in their seams could loosen, letting in water. In other boats the ribs were for strength to prevent crushing of the sides when the boat was heavily laden. While you may not need all those ribs, you will probably need something.

As a general thought, if you are going to use fewer ribs, and put them further apart, they are going to need to be stronger. So, if you were to change a design to replace 1 inch thick ribs every foot you might end up with 1.5 inch thick ribs every 18 inches. If you pulled out all, or almost all of the ribs you might get the needed cross bracing from a bulkhead spanning the width of the boat. Or, you might use two bulkheads that span the beam of the boat, and come up somewhere near half the heigh of the sidewalls -- and put a seat on top of them.

In canoes, some of the strength comes from the gunwaleI. Same goes for row boats. If you are planning on rowing this boat and you plan to install your oarlocks on the gunwale, you need to have adequate strength here or the sides will flex and deform as you apply rowing effort. Again, suitably placed ribs help transfer the forces generated. While I'm on rowlocks : buy them early in the design/building process and you can see how thick your gunwales have to be to support them.

Unless you are building for super light weight you are usually better to build for strength and durability. I'd look at boats of similar size, see what the dimensions of the ribs used on them are, and then try to draw some conclusions from the comparisons.

If you do go with ribs, try to adjust the spacing between them for convenience and economy. (That may mean you have to make them thicker and stronger.) For example, if they are 30 inches apart you can slice your 60 inch glass cloth in half, and lay a strip neatly between the ribs. You put in your fillet at the junction of rib and side, neatly covering the rough edges of that glass sheet -- eliminating sanding into the corner. Then, when you cover the ribs with bias-cut strips of glass cloth you just overlap the first piece by 2 to 3 inches, and feather the edge when you go to finish it. An increased overlap gives you more room to work when you sand, and slightly greater physical properites, too.

You can build over the ribs just as you would build over forms, with the hull upside down. If you don't want to use nails or screws to hold the strips on the ribs, then use a drop or two of epoxy to glue the strips to the ribs. Clamps or duct tape should hold them in place until the epoxy sets up. For tough spots use a screw, and remove it after the epoxy sets up. Drill out a shallow, neat hole where the screw was, and you can fill it with a short dowel or wood plug. A contrasting color wood would make a dramatic accent and give the impression that the boat was held together with dowels !

Sounds like a fun building promect with some design concerns to address. Have fun.

PGJ