Major delamination & foam core options

[Will001]

I recently bought a home made / designed trimaran. It seems my survey skills have a lot of room for improvement...
The main hull is 21ft mostly polycore sandwich with glass and epoxy.
It looks like most of the lower part of the boat has delaminated. Revealing a variety of foam cores on the outside of the polycore...
It looks like the foam was used to created a wider profile at the waterline. But it has not adhered to the paint? underneath.
I know this will all need to be removed and the paint ground off to allow a new bond to be made. But im trying to get an idea of just how much work there is to do.
Can wet foam be dried out and re-bonded?
Whats the foam that looks like polystyrene?
Should i get all new foam and re-shape the profile from scratch?

 

[rwatson]

You guessed it.
It's a complete removal and rebuild job.
Looks like someone wanted some extra buoyancy down low.
I bet they had nose-diving problems with the original hull.

 

[JSL]

I have seen situations like this before... very unfortunate.
As unpleasant as it sounds, you might want to assess the entire boat and situation prior to investing more time & money. Avoid a 'good money after bad' situation.

 

[JamesG123]

I sadly concur with JSL. I hope you didn't pay much for it.

 

[Will001]

Thanks for the replies. Bit of food for thought there...
Anyone know a good surveyor in Newcastle NSW?

 

[fallguy]

That will be a bit tricky to repair. The foam they used looks like it had no shear strength or as you said; the ?paint? sheared.

The repair would not be too horrific in my opinion, but it will take some time. I wouldn't bother fixing if the whole hull is that way.

It would be a vac bag job.

 

[JamesG123]

Do you have the plans? You'd probably be better off building a new hull and transferring the hardware over to it.

 

[JSL]

A marine surveyor may not be able to address all the design and construction 'issues' you have.
It's a homemade design & build: taking into account the modifications needed to 'correct' the structure and design, you might be better off to get a proper design and build new.
You should also review the suitability of the 'old' hardware & any outfitting.

 

[tpenfield]

If the hulls are not too water logged, you might be able to set it on fire . . .

 

[JamesG123]

That would release a lot of rather toxic gases into the air. This would not endear him with his neighbors nor the authorities.

 

[fallguy]

Do you have the plans? You'd probably be better off building a new hull and transferring the hardware over to it.

Might be easier to use the old hull as a jig if it doesn't have any reverse curves.

 

[JamesG123]

Maybe, but considering the hull's poor finish (if you can see how lumpy it looks on the Internet...) it might be less help than by creating a new jig and strongback. I would not be surprised if that hull was completely asymmetrical.

 

[Will001]

I do have some very basic plans. Pretty much just a few cross-sections. I don't like the idea of starting over if it can be avoided.
The rest of the hull is made from polycore panels (polypropylene? hex core) with glass/epoxy. The panels seem to be solid with no delam (tap test).
The hull does not seem too assymetrical, I measured from the front down both sides and it is within 5mm. Not to say the profile is necessarily the same both sides.
I had a more thorough look over the hull tonight, and noticed the bulkheads are not well tabbed in most cases. The major bulkheads (under the front and rear beams) look well fibreglassed into the sides of the hull and sometimes to the false floor. But it looks like none of the bulkheads are properly attached to the bottom hull panel...
I assume it's not normal to attach the bottom of the hull last and not tape the join on the inside? Seems pretty critical to me?
I am currently working through Dave Gerr's Elements of Boat Strength. It's great how quickly you get useable data for recommended glass thicknesses etc.
I also contacted the guy who made the boat to try and confirm what lay-ups have been used in different areas.

After reviewing this info I will try to decide if it's worth rebuilding.

I think the easiest way to tape the bottom hull join and the rest of the bulkheads will be to cut out the false floor and reinstall later. Any other ideas?

Thanks for all your replies (except the one about starting a fire, haha)

 

[Will001]

My other question is should a hull like this have stringers?
It has 6 bulkheads along the length (6.5m), but no stringers.
I guess he was hoping the polycore panels would provide enough stiffness?

Also any design books relating directly to trimarans or multihulls?

 

[rwatson]

Rebuilding from scratch is a bit "over the top"
Also, "symmetry" is a minor issue. It's a rare boat that is perfectly symmetrical and usually doesn't make any discernable difference in performance, speed or control.

With a bit of luck, the main hull will be sound enough to get some use out of it. At least with foam and glass, repairs don't entail major technology.

As far as stringers go, monocoque foam hulls are entirely possible, but if the "designer" wasn't qualified, you have no guarantee of structural integrity. But, running around adding strengthening without a plan is just adding weight. You really need a professional opinion, or at the very least plans of a similar hull, as you requested.

Boats and Motorcycles can be the most problematic of secondhand, owner altered things to buy.