I am building a weekender and I'm ready to build the rudder and rudder box. I cut out the rudderbox about 2 yrs. ago for no particular reason out of straight lumber and it is now curved. I'm thinking now about making the entire assembly from 3/4 plywood. It seems like a better material because of the strength needed for this application. What do ya'll think?
I just finished building mine and used 1/2" plywood for the sides of the box and 3/4" lumber for the stem and rudder. I pretty much had to go with that width as I am using the Racelite rudder Gudgeons from Duckworks.Â
http://www.duckworksbbs.com/hardware/p-g.../index.htm They are going to look nice and they are very heavy duty.
O and I should say that I am using a tiller rather than a steering wheel setup so my box is designed a little different.
I'm also going with a tiller and the duckworks hardware. I guess I'll head to the lumber yard today for the plywood. Thanks
I used 1/2 ply for the box and 1/2 ply doubled for the rudder and upper part (tiller instead of wheel)  plenty strong and that's what I had laying around as scrap........  glassed the rudder then cut it down to fit neatly in the box halves..........glassed the box as well....had read about breaking rudders and it's shallow here so I went for the heavy duty approach.  time will tell   bruce
I used 3/8" hydrotech ply for the sides of my rudder box. I am buiding the Triad not a Weekender. The rudders and box are comparable. I think as long as you do a good job sealing the plywood, edges and sides, that it will hold up. I don't think you need 3/4" but it's your choice.
Merenti hydrotech plywood is remarkably strong. I supported the edges of a 4'x4' piece and then stood in the middle. I weigh about 320. It flexed very slightly but not like 1/2" construction grade fir plywood. The reason I did the test was concern over the nose of my boat being 3/8" ply and my figuring I might have to kneel on it. The nose is cut from a 4'x4' piece of ply but is roughly a triangle with 4' sides. It is supported along each edge and by the mast box assembly. I have stood in the center of the nose and the ply does not flex at all. Sorry to be so verbose but I hope it helps.
After breaking 3 rudder boxes, the latest, greatest, is 3/4 " plywood with 2x4 2x2 structure. I kept the same rudder and used plastic cutting boards to build up between the rudder and rudder box, it also provides for less friction raising and lowering it.
Greg
I can think of a dozen things wrong with the rudder box and blade arrangement used here. Over the years it has been a continuous source of "discomfort" for builders.
It's important to use materials that are well suited to their tasks. Plywood makes for a poor rudder blade. The veneers fail in "rolling shear", it can warp, delaminate, etc. Strip planking with solid lumber, is the preferred (hands down) wooden method, though naturally this isn't called for in the plans. This would be especially true in the highly loaded blade used in this arrangement.
Inert materials are the best, like 'glass, sandwich composites, high density plastics, some metals, etc. These don't have the issues associated with wooden blades.
Sealing a blade in 'glass isn't always the best choice either. If you do, you have to keep after all nicks, dings, divots, scratches, etc., or your trap moisture inside the blade, causing other issues.
Protect the leading edge. Metal is a common method, but a long standing well proven method is to saturate a length of rope and glue this to the leading edge of the blade. I've done this for years without a single failure, so have many others.
The rudder box really needs to be a composite of solid wood and plywood. It can be sheathed, but the only place that really needs special attention is the contact patch between the blade and box. The easy way around abrasion here is Teflon, HDPE or other self lubricating plastic. You can also toughen up the area, with graphite or metal, but this doesn't address the issue, just postpone it.
The real problem with these rudder boxes is the blade wracks the box until it fails. To prevent this the box should be through bolted together, not screwed or glued. When in doubt about strength, just through bolt the damn thing and be done with it is the usual rule.
Use really good solid wood for the forward spacer that holds the pintal fasteners (also through bolt). The plywood used in the sides of the box needs to be good stuff too, with as many veneers as available. The veneer count is what gives plywood it's strength, so if you have just three veneers per piece of plywood, don't expect it to hold much. If you can't find 5 ply 1/4" plywood (as an example) then use two layers of 3 ply, glued together. Yep, it'll be thicker and heavier, but it'll be strong enough.
The Stevenson design sailboats all lack lateral area in the main appendage. This places unusually high loads on the rudder and rudder box, so this assembly has to be stout or your be fixing it fairly quickly.
I glassed the inside of my rudder box and then coated it with 2 layers of epoxy with graphite mixed in. I can add a rope to the leading edge of my rudder blade. I will need to sand off the oiled wood in that area but will need a small groove or flat spot anyways. I am wondering if there would be any gain in coating the portion of the rudder blade, that slides inside the rudder box, in epoxy with graphite? Currently only the inside box sides have graphite in their coatings. My rudder blade is mahogany but not strip planked.
With the inside of the box being "hardened" up with graphite and epoxy, it will easily abate the solid wood blade. Use a Teflon or other plastic disk as a big thrust washer to protect the blade or epoxy coat and use a sheathing in this area.
Solid wood blades can work if the grain is nearly vertical and it's never allowed to get good an saturated. They have a tendency to cup, warp, etc. if they wet/dry cycle much.
A small groove is a good idea and the way I do it. I tack the rope at the top, glue it into the groove and tack it at the bottom to keep it taunt until it dries. I pull the tacks when fairing it.