Catamaran Deck to hulls, glass bond or fasten

[mfoh69]

Hello everybody,
I have an old 19' Cougar cat that is a tunnel design having a hard open deck. The deck is presently fastened to the hulls at the perimeters. The deck overlaps the top edges of the hulls which have a step at the top edge so that on the outside surface the deck and hulls are flush. The fasteners are aluminum pop rivets every 6" or so between the overlap. I am in the process of re-gelcoating her and want to make her as strong as possible and so I am asking, should I leave the design as is or fiberglass them together. Is there wisdom in letting them "give a little" under stress or not. The joint at the leading edge of the tunnel was bonded, not fastened or glassed, possibly glued. It separated some and so needs to be repaired and so got me thinking about how I want to fix it.
Sorry this has been so long but I wanted any boat builders to know what I have so they can advise me well.
Thanks,
Mark

[mfoh69]

I wanted to add some pictures.

[a64pilot]

I’m not a Cat owner, nor a boat builder, but maybe my post will bring some out.
It’s my opinion that boats are usually bolted together and not glassed together because it’s much easier and maybe faster to bolt them together and it works well if the join is properly designed, it’s done for ease or expense, not because it’s better.
However I believe that if it were properly glassed together it would be stronger and if it’s not done after the fact but done during manufacture, it may be lighter also.
I don’t believe there is ever any intent for the join area to flex and if it did then surely it will leak and that’s a bad thing.

I would fix any disbonded areas you may have and maybe use a better fastener than pop rivets, but unless your real good with glass and have a good plan I don’t think I would glass it, although if it were done that way when manufactured I think that may be better.
It can certainly be done, some boats hulls are glassed together in the middle as they were two halves.

Actually looking at the pictures they way it’s overlapped, and how thin it appears to be, I think I would glass it.

[mfoh69]

That's what I was thinking. Thanks for your post.
Mark

[Glassdog]

I agree and my thinking would be that if you could drill out the pop rivets and open the hull/deck joint enough to inject some 5200, I would then re-fasten with stainless bolts/washers/nylock nuts. That should keep the old girl together!

[motion30]

offshore racing powerboats almost always have the hull deck joint glassed together on the inside.

[Slainte1]

Bond and glass inside and out. Much stronger and looks better

[Cheechako]

I would glass them together if it's reasonable to do so.

I assume it's bonded with 5200 or something like that already. On a small cat it's possible they put it together with something else though... marine Bondo? If not, your plan of separating and using bolts and 5200 etc would be good, but beware that many mono makers did it that way and many get leaks around the perimeter into the boat.
The problem is likely that all the bolt holes, which are hard to seal are not 100% waterproof.

[flyingfin]

Many of the old school V-hull Offshore teams would join hull to deck with 5200 and use a few rivets to keep the deck in place or pull wide seams together, then cover the exterior of the joint with a rubrail. You can go back with 4200 later if you have any wide gaps that did not make waterproof seals. But you wont get it apart again, even with a backhoe!

[Chotu]

Glass it.

[Matt Johnson]

I doubt you're going to be able to fiberglass that tight of an area from the inside. That bow area is really tight.

Matt

[mfoh69]

I've decided to glass it. Glassing on the inside would not be very strong as there is no vertical surface on the inside of the deck where it meets the hulls, only the horizontal surface of the bottom face of the deck, so glass there would be trying to pull perpendicularly away from the under surface of the deck. The outside glass will be strong since almost all the forces on it will be in line with the fiber. I'm planning a 4" wide strip having a 2" lap down from the top edge of the hull side and a 2" lap up and over the edge of the Deck. I believe my boat will be stronger and DRYER that way.
My original fear was that it might be too strong like the mighty oak which breaks vs the willow which just bends.
Thanks everyone,
Mark