I didn't mean to infer a block on the board itself. Our two blocks are on the CB trunk wall. In the 37 I cruised on, the line went through the trunk ends, into the for & aft cabins. I don't know how the 31 is laid out?
Our fit is snug enough that we did actually have a few coats of bottom pant too many once, and let's hope that that's your problem as well. It is the easy fix!
I would definitely use a 1/8" fuse line on the pennant. When our board is fully down, rather than tie a rolling hitch on the pennant every time, we hook the "fuse" line onto a 1" loop of webbing, that I sewed onto the pennant, 15 years ago. It still works great!
My personal take, is that the wood board, as drawn, is the way to go. The folks who have had centerboard
, and skeg problems, didn't have anywhere NEAR the amount of glass that I have. The 1/8" min. that I suggested on the sides, may be 6 or 8 layers of 10 oz. fabric
, I don't really remember... I even glassed the inside of the axle pin hole 1/8" thick before doing the sides, and later glued in a hole liner of rubber hose in the axle hole, as a cushion! You do have to make the board about 3/8" thinner as a wood board, then, since the wood densities vary, making it difficult to longboard sand into a perfect foil, I get it close, fill the low spots with microballoons, sand fair again, then put on 4 coats of resin. Next, sand most of that resin back off! Now that you have a surface that is all plastic, it will sand uniformly.
The process of 4 coats on, 3 coats sanded off, may have to be repeated more than once, until the shape is a really fair foil, with NO hollows or flat spots, and a very sharp aft edge. The idea is to shape it before the glass, not after!
When glassing the sides, you can let the glass run past the aft edge, about 1/2", every layer. Trim it with a razor blade, while firm but green. Then wrap the forward, top, and bottom edges each time. Putty that piece hanging off the back, so that the top surface of the face that's up, blends into it. Now lay a sheet of glass on the top the same way.
Each time, fair in the glass wraps a get it so the next side layer will have no voids from non faired glass edges.
Do this until the glass sides are over 1/8" thick! Now you have the sides, but big bulbs at the wraps, and not enough glass at the top, bottom, and front.
Make yourself some glass tapes by cutting 10 oz. cloth on the BIAS. (Dressmaker's roller blade fabric
cutters, like a pizza cutter
... and a straight edge, on a pressboard table top, make this REALLY easy.) This homemade bias cut tape will have ALL of it's fibers going across the joint, making it twice as strong, and it wraps a radius MUCH better. I can LITERALLY fiberglass
a tennisball, with bias cut glass! I have put three staggered width tapes like this, on every ply seam, and every radius, on the entire boat as well.
You want 1", 1.5", 2", wide tapes for the front, and like 7", 8", 9" wide tapes for the top & bottom. Lay up three or fore in one day, then the next day sand off the overlaps on the sides completely, so the board is fair again.
Do this process until it is about 3/16" thick on the edges, at the top (still full width) 1/3rd of the board. Do The front until the forward radiused edge, and the bottom, are 3/8" thick, gently tapering into the 1/8" thick sides.
At the bottom 10" long "contact zone", where the front foil edge goes around the radius, to the bottom of the board... I let the glass tapes overlap, so it is even thicker here!
I wanted it where taking out a 1/4" chunk on impact, will not let the wood get wet.
Now do a final shaping sand to flatten those tape wraps on the sides, then coat & sand several coats of epoxy
until it is fair, and NO exposed glass fiber shows anywhere. The wrap from the bottom of the mini keel
into the trunk, needs to be as thickly glassed as well, BUT LEAVE CLEARANCE!
We did our rudder
and skeg in a similar fashion, and it all requires that the piece start out too thin, or with too much clearance... to make room for the glass.
Yes, this is many weeks of hard work, but if you make it out of a more rot
resistant but lower density core
, it needs to be glassed just as thick to keep it from crushing on impact, and the extra buoyancy works against you in the effort required to crank the board down.
Other than a couple of soft groundings, we had one case where our board "while down", was strafed by a barnacle encrusted crab pot line... at great speed and impact! It only made a 1/16" deep scratch across the board, which we filled a year later. (NO water
got to the wood)
On launching day, I hit a log SO hard with the skeg, that it lifted the main hull
almost out of the water
. Although I discovered transom frame damage 10 years later, the skeg took the blow without the wood getting wet.
I have heard many complaints about Searunner's Centerboard
/ trunk, minikeel, rudder, and skeg problems. I don't think that a non swelling more rot
resistant material, is the answer. Epoxied & glassed wood is an incredibly strong, hard, stable, long lived material. (Mine is 31 years old!) I think the impact zones & really high stress points, need a LOT more glass than has normally been the case. IMO. Since these areas represent less than 1% of the boat's surface, the extra weight is minimal.
Hope this helps, and you don't have to make your board over... Mark