bertram31.com

I just added a new article to the Tips Page, entitled Hull Repair - B31

I've been putting off this project on Patrick Hancock's boat & the right time finally arrived. Still have a day & a half before this particular project will be complete, but here's the first 3/4 of it...

Could also be titled: How I spend my Holidays

So after all that does the hull get finished and faired smooth for all those laying in the V-Berth to behold. Or is it gonna get covered in monkey fur?

Its always the same you spend most of your time working on things nobody will ever see.
Pretty work Capt.

Thanks, JP...

This is the delam we discussed several months ago. Inside will only get smoothed off. The overhead, hull sides, and bulkheads get upholstered with off white, foam backed vinyl, like I did on "Buddy Boy".

Its always the same you spend most of your time working on things nobody will ever see.

I was thinkin' of laminating on a business card to the patch panel. Kinda' like a "Kilroy Wuz Here" thing...

Br,

Patrick

Pat
Your one of a kind.......thanks for sharing your work with us.......and you are one hellofa CRAFTSMAN.

Harry

Patrick,

Funny story, I went to school with the Kilroy family who's grandfather is the guy who did that in the Navy.

Dug

I vote for monkey fur.

If it was a 28 you could use spotted Hyena fur!!

Hey Kilroy, I think you already left your mark far and wide with this website and that tips page.

Besides the sentiment... I have a comment on the last bit on that repair description: the possibility of any stressing between the new patch and the original surrounding hull - that might cause the “stronger” patch to flex and crack the hull around it - could only happen through differential deflections.

Deflections of structures under stress are controlled by structural stiffness, i.e. moment of inertia, which relates only to the shape of the structure.

Without getting into too much math.... in a folded plate or shell structure, which is what a boat hull is... the structural stiffness is controlled only by the thickness of the material. In a shell, stresses will route themselves along the stiffest path (the thickest places).

By making the patch the same thickness of the original hull, it is guaranteed to behave (deflect) in the same manner as the original hull when placed under stress. Thus no differential stresses.

The other variable in deflection is the modulus of elasticity... but the patch and the hull are all glass composites, so the modulus of elasticity of the old and new remains the same.

Same family of materials (modulus of elasticity) and same stiffness/thickness = no stiffer path for the stresses to go, so no differential stresses or cracks. The only trick left is to evenly transmit the stresses along the transition between the old and new areas.

As for using a stronger glass composite material, that really relates only to yield or breaking strength. Basically, if you pulled on both ends of that boat until it broke in half somewhere, it would not break at the patch. But until it did break somewhere, the patch would stretch at the same rate as the rest of the hull.

Now if you were to make the patch much thicker than the original, like the last guy did, or if you somehow glued a piece of steel to it instead of glass composite, you could produce plenty of differential stresses.

So anyway, in my opinion as a structural engineer, what was done could not cause the surrounding area to crack and break.

I oversaw the repair of some concrete shell structures a while back, and got in a big fight with the contractor, who with misguided goodwill wanted to add bunch of extra steel plates to damaged areas of the shell.... the same argument above applied.