Bulkhead Scarf

[minaret]

Originally Posted by Cheechako

I like the idea of using two 3/8 thick pieces glued together with the joint in different places.
or...I might make a rabbet joint the full depth of the table saw blade I have, overlapping the two pieces. Then glue and clamp flat out side of the boat (can you get that into the boat?) No reason a 4" overlap joint with proper glue shouldnt be as strong as any other part of the plywood is there?

Scarf joints are recommended over lap joints for a reason. With bulkheads you usually need to do the joint in the boat, or you'll never get it in. I would not do either a lap or staggered butts, but to each their own...

[Blue Stocking]

Originally Posted by minaret

Scarf joints are recommended over lap joints for a reason. With bulkheads you usually need to do the joint in the boat, or you'll never get it in. I would not do either a lap or staggered butts, but to each their own...

The sheets of plywood are made with butted veneers.
Scarfs were originally developed to join solid lengths of material where a difference in grain conditions could exist with in the contacting surfaces, and to allow bending ability to take place.
But--like you said, to each his own.

[zeehag]

i need to do this in my after portion , at the bulkhead for galley and battery containment and mast supporting blocks--have supported my mizzen, next it dig outthe fridge remnants and re beam and bulkhead repair.. did bow--wasnt too bad---used regular marine ply with lots of penetrating epoxy--will do same in after portion. the mahogany problem is why i have to do this--phillipine mahogany rots like pine. ouch....now to find a locale in which to destroy and remake my boat...lol

[minaret]

Originally Posted by zeehag

i need to do this in my after portion , at the bulkhead for galley and battery containment and mast supporting blocks--have supported my mizzen, next it dig outthe fridge remnants and re beam and bulkhead repair.. did bow--wasnt too bad---used regular marine ply with lots of penetrating epoxy--will do same in after portion. the mahogany problem is why i have to do this--phillipine mahogany rots like pine. ouch....now to find a locale in which to destroy and remake my boat...lol

Good luck, Zee, were rootin for ya!

[zeehag]

got her so it is workable for a coupla yrs max--so i have bought some time on her--we shored up some parts, and i am seeking wood.. fun this boating thing..LOL..i love it!

[Hi Ho]

One other option is to use bisquets. From the picture it looks like you could aslo add a backer on the forward side of the bulkhead fro the hull out past the joint and stop just inside of the face of the cabinet. If you are working with something more than 1/2" stock such as 3/4" you could use the full lenghth rabbet joint as suggested. with expoy doesn't take a much clamping so doing inside the boat is not that bad.

[minaret]

Originally Posted by Hi Ho

One other option is to use bisquets. From the picture it looks like you could aslo add a backer on the forward side of the bulkhead fro the hull out past the joint and stop just inside of the face of the cabinet. If you are working with something more than 1/2" stock such as 3/4" you could use the full lenghth rabbet joint as suggested. with expoy doesn't take a much clamping so doing inside the boat is not that bad.

Seriously? Biscuit joining a bulkhead? And I mocked the lap joint...

[Hi Ho]

I only suggested this because it is not a structural bulkhead and if he can back the joint up as discriped he will have a very solid joint. His boat manufacturer used a butt joint, my C&C Landfall was built the same way with the main bulkhead with nothing more than a glued butt joint. On my C&C the bulkhead joint did not fail but it did rot out. I replaced mine 6 years ago with bisquets in the joint and there has been no movement in the joint on my 1/2" thick bulkhead

[Blue Stocking]

Originally Posted by Hi Ho

I only suggested this because it is not a structural bulkhead and if he can back the joint up as discriped he will have a very solid joint. His boat manufacturer used a butt joint, my C&C Landfall was built the same way with the main bulkhead with nothing more than a glued butt joint. On my C&C the bulkhead joint did not fail but it did rot out. I replaced mine 6 years ago with bisquets in the joint and there has been no movement in the joint on my 1/2" thick bulkhead

Dont worry Hi Ho, its easy to become a legend in your own mind around here.
One of the problems with the internet is that one never knows whom one is criticizing.

[zeehag]

i would do what minaret sed in a heartbeat--he is smart. fixes lots of big bux boats....

[minaret]

Originally Posted by Blue Stocking

Dont worry Hi Ho, its easy to become a legend in your own mind around here.
One of the problems with the internet is that one never knows whom one is criticizing.

Hey, I'm not criticizing anyone, just criticizing biscuit joining a bulkhead, as I'm sure many other's would. As I already said, to each their own. I was brought up to scarf a bulkhead, and it's such an easy joint to make I can't imagine why you wouldn't. But I'm sure there are as many other opinions on that as there are people who make a bulkhead. Seem's like you are the one criticizing people, what's your problem?

[minaret]

Originally Posted by Blue Stocking

Dont worry Hi Ho, its easy to become a legend in your own mind around here.
One of the problems with the internet is that one never knows whom one is criticizing.

Oh, now you've got nothing to say? Don't feel like explaining yourself? Wutta pansy...

[foolishsailor]

Have to agree with minaret. A scarf joint is not just about joining different grains it is also about increasing the gluing surface, and more importantly preventing the issues associated with the point of contact between materials with vastly different properties glue and wood. One is brittle and one is not, even if one uses better wood glues versus epoxy.

A butt joint even one that is glued like a resawn frame is a point of failure as there is a "sudden" change in the material properties along with minimal gluing surface. A scarf allows a gradual change in properties along with a large glued surface. A vastly superior solution.

There is no reason to fear a scarf joint. One can build a scarf jig and use a hand or power planer to make the scarf, even a relative wood novice can do it. Google scarf jig and see how easy.

Just cause many in the industry use butt joints and epoxy doesnt make it right, in fact it is the opposite of right. Epoxy catastrpohically fails when placed in a situaion where there is high frequency flexing

[foolishsailor]

Originally Posted by Blue Stocking

The sheets of plywood are made with butted veneers.

This is not comparable as the but joints exist in what 5 to 15ayers depending on thickness? This is effectively a single layer.

I would disagree with minaret somewhat on the biscuit joint. Biscuits are crap but FesTool makes a great joiner that produces a structural superior joint not using biscuits but there own almost dowel like plug. You will still have potential issues on the asthetics of the join but it will be structurally sound.

Scarf is still better

[zeehag]

i thinki would not want to trust the repairs ineed to do in my formosa to biscuit joints-- thre is way too much weight supported by this combination of bulkhead and support blocks to warrant anyhting besides a scarfing....i may add a nice i beam to the mix for peace of mined.....