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SWA
04-25-2005, 09:39 PM
The boat is a Snipe day sailor. The thickness of the hull at the point is 2", can I use 2.5" screws or should I go with 3"? Am planning on using square drive silicon bronze screws. As always the expertise of this forum is always appreciated.

Steve

Bob Smalser
04-25-2005, 10:31 PM
Actually, they don't sound near big enough from here. Especially if the bottom is plywood where countersinking isn't generally advised.

You want a screw where the unthreaded shaft penetrates the bottom completely so only the threaded portion bites the daggerboard trunk. That's how you size them for maximum joint strength and no danger of "bridging", where the threads bite in both pieces to be joined and seperate them rather than pull them together.

http://pic3.picturetrail.com/VOL12/1104763/6791366/94403513.jpg

I.E., for a 7/8" plywood bottom I'm currently using #14 bronze 2 1/2" on 3" centers into 7/8" by 3" bed logs glued to the bottom. The designer called for #16's but the difference between #14 and #16 is small and using the smaller diameter allows room for a refastening repair some day.

2" is a pretty thick bottom for a small boat. You sure?

[ 04-26-2005, 12:40 AM: Message edited by: Bob Smalser ]

Bob Smalser
04-26-2005, 08:16 AM
PS...this is one installation where you don't want the screws to do any straining at all to pull the two members together.

http://pic3.picturetrail.com/VOL12/1104763/6791366/94420615.jpg

I clamped the trunk down tight into poly sealant and let the goo set up over night before driving any screws.

LazyJack
04-28-2005, 09:11 PM
This shows the dagger board trunk installation in my gunning dory. I drilled down through the bedlogs, through 7/8 pine bottom plank, the xynol/epoxy sheathing and the 1/2 inch oak false bottom. I then removed the trunk, chased the holes with an oversize bit, filled them up with epoxy, then after cure, set the trunk in place and drilled again with the original bit. I then bedded the trunk in xynole set in thick paint and fastened it down with 1/4 inch bronze carriage bolts run up from the bottom. It is stronger than hell and has never seeped.
http://www.imagestation.com/picture/sraid166/pb084e944cd23b41a8eef6b8ead06055d/f44e6eaf.jpg