Glue vs. screws

[mustangermatt]

I have cs 17 #97's hull assembled and faired with the stringers in. I am reviewing the seat framing on the plans now and I noticed that there are alot of parts screwed rather than glued.

My very limited experience with the epoxy has been that the wood will split or break before the joint itself fails. With the screwed joint the fastener usually pulls out of the wood first (but not always).

So is there an overwhelming reason not to continue with the epoxy joints for the interior construction and framing?

Thanks

Matt

[Melissa Goudeseune]

Matt,

this is the exact thinking I've been using with my mini-paw. I've omitted (or removed) screws wherever possible, in favour of an epoxy joint.

For example: I used #10-24 through-bolts to hold the keel in place while the epoxy cured. Once it was cured, I heated the bolts to remove them, and filled the holes with epoxy and thin scraps of wood.

Michel

[Designer]

You are mostly right but there exceptions. Where there is lots of glue surface area such as stringers and inwales etc. the load on each fiber is very light. You are better off without fasteners in the above case as they will eventually show through. There are areas of high stress with small glueing areas like the center thwart to the side seats on the CS's that carry the side load from the mizzen mast and would surely fail with glue only. The knees on the catspaws and Spindrifts will fail without mechanical fasteners as they are high stress concentration areas with endgrain glue joints, which are always suspect.

On the minipaw keel I would like to see the forward fastener left in. As there is a lot of bend forward, the forward most fibers are doing most of the work and if they fail the stress will move to the next few fibers and so on until it opens up. They often will not fail till months or years down the line.

I have seen the glue joint fail on decks forward because the span is very short and the ply has to be bent too much. It is a good idea to flatten out the deck camber forward to cut down on the stress at the glue joint.

You just have use your judgement as to whether to fasten or not. If the plans say to use fasteners and they not being used as temporary clamps then it is a good idea to use them.

When I build a Spindrift, I fasten the knees, the ends of the gunwales, the ends of the keel, the mast step and one screw through the beam into the centerboard trunk rail, the rest of the boat is held together with just epoxy.

[mustangermatt]

Thanks , that was exactly what I needed

[Steve Day]

This one is for Graham and anyone else who would like to weigh in on this subject.

I was contemplating my centerboard trunk the other night and was wondering if there was enough support for the side loads that will be encountered there. On the Spindrift 10N the after part of the CB trunk lays along the forward nesting bulkhead, but that is the only direct support the trunk gets for side loads other than the fiberglass at the base of the trunk where it mates to the hull.

From your comments on screws, Graham, I take it that there are a couple needed through the forward nesting bulkhead into the after end of the trunk. This didn't really dawn on me until I read this thread just now, and I don't have the plans to consult here to corroborate this. Am I on the right track?

Thanks,

Steve

[Garry]

Details, details. Got to watch those details, don't we Steve.

I Just realized the same thing, Steve. My drawing shows screws into the daggerboard trunk. I remembered the screws into the corner blocks but not the ones in the daggerboard trunk.

At least it will float (I think). :wink:

[Designer]

Yes Steve, there are three screws through the forward bulkhead/ doubler and into the trunk.

[John Yow]

On a similar note, the drawings show 1" ring nails at the center thwart. I am interpreting that to mean that the inner edge of the seat top is to be nailed in addition to gluing, is that correct?

Thanks,

John

[Steve Day]

Graham,

Thanks for the quick answer. I didn't get the chance to look at the plans last night, so I'm glad you answered my question. I will plan to put those screws in after I cut the boat in half.

Looks like I'll be able to limber up the saw this weekend. I've put it off enough! :wink: I want to make sure the mast step is complete before I cut, but that will be done on Saturday morning.

I should have pictures this weekend.

Steve

[John Yow]

ps: I meant to say: nailed along the entire length of the seat top.

John

CS 17 #102