Installing the Thwart and Finishing Up

[Maria CS20 104]

Hey all, CS@) 104 here..............finnally preparing to install the Thwart seat after three years I wiil be done with all hull and interior stuff. Just built two platforms that fit each side of the centerboard trunk. Will sand and stain this week and get 7 or 8 coats of varnish on them over the weekend. I am making birrds mouth masts, found some great clear fir. Made a couple of practice pieces and I was supprized how easy it was. Tried using the router table, miserable failure as the tip of the router bit does NOT clean the inside peak of the cut at all and the pieces do not fit together properly. Table saw set up a breeze, but it appears that once set you must cut and complete ALL birdsmouth cuts on all pieces to be used to ensure all pieces have an exactness to the shapes, at least as much as possible.

I bought the #10 (3'') machine bolts for thwart install, they seem to be a bit in the thin side for the load they will carry ( about 3/16th wide including threads). I know I need 8 through the seat at the centerboard trunk (4 per side) and 4 through the cleats port and stbd., Am I missing something, do I need a bit larger machine bolt or is the engineer in me getting a bit carried away?

All input begged for...........

Thnx, Jim Atkinson

[hokeyhydro]

Sure you have the correct router bit? And the correct setup on bit height and cut depth? I ask because I've done several birdsmouth projects from 22' mast to skinny paddle shafts and my router & bit cut clean. I do use lots of featherboards including a hand made little one that sits over the bit to keep the strip from jumping and buggering the last inch or so.

[Designer]

Jim,

You are right about the thwart being highly loaded from the mizzen mast. Fortunately the side seating acts like a load bearing shelf relieving the fasteners of most of the shear loads.

I once inspected a lightly used CS17 whose builder eliminated the side seating/flotation compartments and carried the thwart from side to side. Close inspection showed that the three wood screws could not carry the shear loads and that the outer veneer on the outside of the sides had fractured.

One last tip an that joint. There will always be different expansion rates between the endgrain and solid wood of the thwart and the plywood side seats that will show a crack at the joint in time. I prefer to make a small V joint at the top where they meet and eliminate an unsightly crack.

[Maria CS20 104]

Thanks for both replies we move forward, but with one little question,,,,,,,,,,,,,,,,,,,,,what the heck is a v notch joint?

[John Burritt]

Cut a small chamfer on each side of each end - either w/ a plane or a router bit. This will give the inevitable open space at the ends of the thwart a finished look.