A Photo & Discussion Forum for Wharram Design Enthusiasts
OK all right here's my 10 bucks" builders and Friends" has proved invaluable to me. I'm putting together the rudders for my tiki 30'. I'm using full 1" x 7" red Cedar I'm engineering quarter-inch splines for joining the planks together, I'm adding about 2 inches to the forward edge of the rudder I feel that a somewhat larger rudder will be a good thing. Now my question is should I laminate quarter-inch plywood on either side of my 1 inch cedar plank to obtain a 30 mm thickness as the plans call for.OR I was planning to glass them heavily -even considering woven roving and polyester resin to bulk them up to 30 mm which would pretty much make up the thickness called for..... Simplest solution is to Glass with 10oz. cloth and eproxy and use them as they are what are you all think do I need 30 mm thickness??? Is the whole thing just a bad idea??
Here's my thoughts from the peanut gallery.
I would laminate 1/4" ply on both sides and sheath them with 6oz glass cloth.
My reason for this is that it will bring the rudders 30 mm and will add a lot of strength and stiffness to them, give you some material thickness to put a taper on aft of rudders and the 6oz cloth will protect and seal them from moisture, be a good surface for painting and would be minimum weight.
Would be concerned that Red Cedar would be somewhat weaker along the grain without some added reinforcement if the rudders took a hit, the 1/4" ply would add a lot of stiffness and ruggedness.
Using enough epoxy & glass cloth to build up them up to 30 mm would weigh more than the 1/4" plywood & 6oz cloth.
The Red Cedar is a bit soft, as is Okoume plywood. I would use 1/4" Hydrotek as it's harder an it would still be lighter than building it up with glass.
First, why not build them per plans? Quick and easy.
Second, the rudders are plenty large by design. Any poor sail trimming on your part will be amplified in the rudders. I had some serious difficulties on my T30 when there was too much lee or weather helm do to lack of proper sail trim, to the point that the autopilot could not steer the boat. That extra rudder area will only make this worse.
Fiberglass on the rudders (and almost everywhere else, for that matter) is for abrasion resistance, not strength (hence the lightweight materials called for.) Below the waterline, it is not uncommon nor unwise, to add an extra layer of e-glass to the bottom where grounding will occur, again for abrasion resistance.
Thanks for your comments if I had a sheet of three-quarter inch plywood that would certainly be quick and easy but I don't I've got a bunch of 1 inch red cedar planks. Unless I use three-quarter A C from the local lumberyard- marine grade plywood is pretty hard to come by . I drew out the rudder on a piece of Masonite and they really don't look undersized-- and of course there's two of them I'm used to having only one rudder. The design has very efficiently used every scrap of the4by8 plywood , I just thought since I was not restricted to a 4 x 8 sheet of plywood and I would make the rudders larger... I'm used to PIVER trimarans- they all have undersized rudders --much improved by going larger.
Not to mention that wood moves- expands and contracts with moisture. Encapsulation in epoxy may work- until moisture gets in. A 7" board will grow an eighth of an inch and will behave as one board. Cut the 7" boards in half and swap ends and glue to minimize cupping. Look at the end grain so it goes in opposite directions, board to board. I am no expert on boats.
The Piver trimarans have undersized rudders, and the rudder in the Pahi 26 and 31 seems small to me, but I have a Tiki 26 and it's rudder is very powerful. The Tiki 30 is a newer design than the Tiki 26, so I suppose it's rudder is at least as efficient. I' m not sure it is a good idea to make bigger rudders, you will have greater wetted surface --so your boat will be slower-- and perhaps you will need more force to change course.
Thanks to all of you for your input. My edge glued rudder blank is unacceptable, I will finish shaping it--- shine it up and it will be a lovely souvenir. May be a name plate for the side of my house.