1969 Cobalt GT500 Hull

Questions about boat repairs with our resins and fiberglass: hull patches, transoms and stringers, foam, rot etc.
rustnrot
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1969 Cobalt GT500 Hull

Post by rustnrot » Sun Apr 19, 2009 11:59 am

This boat is a splash by Cobalt Boat Company of a Donzi Corsican built at the same time but this hull is laid up differently.

It is 18 feet long, 7 feet wide and will be powered by a 310 hp efi Ford V8 and have a Pulse Drive surface drive installed in lieu of the outdrive installed originally.

The factory installed stringers were 3/4" pine installed on top of the following:

gelcoat
3/16" layer of matt fibers (I cannot discern the individual layers of matt perhaps it is chopper gun?)
3/8" balsa core
some layers of heavy woven roving topped off with matt

The rotten stringers and rotten balsa core are being removed. However a broken piece of the hull reveals that all we will have left is a 3/16" shell for the entire bottom (up to the chines) with sides of matt and woven roving, no core. The gel coat is also all cracked and will have to be mostly if not completely removed at some point.

Before I go further I would like some advice as to what we will be left with can be built upon or not. I show a piece of this outer 3/16" layer that is broken off. It is (was) quite wet but appears to be drying out. It also appears to be resin starved to some extent but I am no expert. Obviously careful blocking and leveling of the hull would be in order prior to building it back.

The Donzi boats this was copied off of were not balsa cored. I would prefer to go back with a laminate that does not require a core but need your opinion on that also.

Thanks for any and all assistance and opinions.


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TomW
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Re: 1969 Cobalt GT500 Hull

Post by TomW » Sun Apr 19, 2009 1:12 pm

Honest answer I would trash the boat and build the Mangusta plans from here. You will spend less and have less time involved in it and less headaches than if you try to rebuild your Cobalt. Some boats are worth rebuilding some are not. By building the Mangusta the designer Jacque has already set up the parameters for an inboard/outboard drive and can help you with your installation.

Where did the broken off piece come from out of curiosity.

I'm not saying it can't be done it's what I would do, as I would then know I had a solid boat under me that would last me forever or almost. My .02 worth .01 tomorrow. :D

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rustnrot
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Re: 1969 Cobalt GT500 Hull

Post by rustnrot » Sun Apr 19, 2009 1:42 pm

The piece that broke off is actually a piece centrally located in the bottom where a crow bar went thru prying off the core.
Last edited by rustnrot on Sun Apr 26, 2009 9:25 am, edited 1 time in total.

TomW
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Re: 1969 Cobalt GT500 Hull

Post by TomW » Sun Apr 19, 2009 9:28 pm

No reason you couldn't do that deck on the Mangusta. It is just a matter of determining the camber and cutting the frames. Thats the nice thing about these boats as long as the hull or framing spacing are not changed just about any other change can be done.

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Re: 1969 Cobalt GT500 Hull

Post by Cracker Larry » Sun Apr 19, 2009 11:25 pm

I have to agree with Tom. Scrap it, it's gone.
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Re: 1969 Cobalt GT500 Hull

Post by Daddy » Mon Apr 20, 2009 9:46 am

One more thumbs down on rebuilding. :(
Build new :)
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Re: 1969 Cobalt GT500 Hull

Post by tech_support » Mon Apr 20, 2009 11:06 am

re-coring can be tricky and its going to be a lot of work. The alternative is to just lay in new glass until you have built up enough thickness (something around 3/8" glass, maybe more depending on factors we can calculate later if you decide to move forward)

Besides the re-coring its a pretty straight forward rebuild.

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Re: 1969 Cobalt GT500 Hull

Post by tech_support » Mon Apr 20, 2009 11:07 am

re-coring can be tricky and its going to be a lot of work. The alternative is to just lay in new glass until you have built up enough thickness (something around 3/8" glass, maybe more depending on factors we can calculate later if you decide to move forward)

Besides the re-coring its a pretty straight forward rebuild.

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Re: 1969 Cobalt GT500 Hull

Post by rustnrot » Mon Apr 20, 2009 11:25 am

For now, let us take out some more of the inner glass and core and see what we end up with. We'll get back to you.

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Re: 1969 Cobalt GT500 Hull

Post by Matt Gent » Wed Apr 22, 2009 4:13 pm

I don't see why this boat can't be saved.

Get it completely stripped, but preserve as much of the outer skin as possible.

You could choose to re-core it or build up the skin and add some more stringers & bulkheads.

Looks like a neat boat!

EDIT - I had a few wayward incidents with the air chisel too. Easy enough to repair since you are in there glassing anyways. Mine is getting re-cored (using ATC core-cell). The worst part about that is there is no way to really know you have a good bond. I'm vacuum-bagging it in place, and it has perforated weep holes for the resin, so there is at least and indication if it is dry over a large area.
Last edited by Matt Gent on Wed Apr 22, 2009 4:48 pm, edited 1 time in total.

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