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Buoyancy tank - lack of stiffness?

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Buoyancy tank - lack of stiffness?

Postby jkilpatrick » Sat Sep 19, 2015 10:06 pm

Hi all,

I am renovating an OY Albacore, hull no. 7851. I have managed to successfully address a few small areas of de-lamination between the hull and the tanks by chipping out the original bonding material and replacing with an epoxy/microballoons/colloidal-silica slurry. So, having completed this repair, I noticed that the aft port-side buoyancy tank has a region about 2 feet long where there appears to be a significant lack of stiffness in the top and side of the tank. I have no idea how the tanks are constructed, but I am guessing that there is a core material which backs the outer skin of the tank, and it has somehow also de-laminated (there are signs of stress crack on the top surface of the tank). The aft tanks only permit a 4" inspection port in the side of the tank, while the top of the tank would permit a 6" port.

My question is - does anyone have any useful knowledge regarding this lack of stiffness? I hate the idea of putting a port in the top of the tank (looks a bit unsightly to my eyes) but the larger port would be helpful to permit me to repair the area, and I guess I could whack a barney bag in the port and gain some useful storage.

My thoughts were that several layers of glass and epoxy applied to the inside of the tank would add the necessary stiffness, but I guess you could also stiffen the tank by epoxying in some stiff wooden battens on the underside, and maybe screwing into these as well with stainless fixings and 4200 sealant.

Any other suggestions appreciated.
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Re: Buoyancy tank - lack of stiffness?

Postby townsend » Mon Sep 28, 2015 11:07 am

I've seen this in other OY albacores of that vintage, but don't know what causes it or how to address it. Your hypothesis about the cause sounds likely, but without opening it up it's hard to say for sure.

Since you don't (or shouldn't be) sit that far aft it may not be that much of a problem.
Paul Townsend - Albacore 6040 - Michigan Albacore Fleet
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Re: Buoyancy tank - lack of stiffness?

Postby JimE1 » Thu Oct 01, 2015 1:25 pm

I would probably just leave it.
Mark where it changes from stiff to flexible and see if it moves forward over time.

No change, I would leave it. If it changes, I would go in and fix it.
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Re: Buoyancy tank - lack of stiffness?

Postby jkilpatrick » Sun Oct 04, 2015 1:12 am

Thanks guys! Glad to hear two similar opinions.

John
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