Gelcoat

[tunnels]

Originally Posted by fg1inc

One more important point - if I understand you correctly you are considering removing the external laminate and core. Typically, the stronger laminates are external and the thinner weaker laminates internal. Therefore, if you remove external and core you are not going to have anything holding the hull's true shape. It'll distort terribly and all you'll have is a huge mess. DON'T DO IT!

Just to put the record straight ,inner laminates should be the same as or stronger that the outer !!.
Specially if there is a core involved in the construction and also if it was a solid glass hull the inner layers are the ones that take the pounding and banging FROM THE OUTSIDE !!
Having seen rescure craft come apart from that very theory ,its the inner glass that has to absorb the shock of a object hitting the outside trying to be forced through to the inside .
Dont get me wrong here the outer layers are also very important !! every piece of material thats used to make a hull is important and gets stressed in all directions all the time . When a inner skin fractures and puntures then enormous load go on the outer skins untill they finally give way . It is better to make a panel that will flex a little and absorb shock loads and survive and not give way than a ridged panel that has no give at all and will snap at a particular point right when you dont need it to happen .
I learned a lot about flex from making rescue craft for our surflife saving boats on the west coast of New Zealand . Understanding what all the differant types of glasses can do and how they can be used to there best advantage takes years to understand . Making laminates specialy for the purpose of progressive distruction in exstreme conditions is some thing very few people have heard of or even know anything about !!
Human bodies break before the boat do !! the boats always come back and live another day sometimes with no damage what so ever ,where as the driver and the bow man could have broken legs and ankles

Originally Posted by tunnels

Just to put the record straight ,inner laminates should be the same as or stronger that the outer !!.

Same yes, stronger not! That would just waste material.

Specially if there is a core involved in the construction and also if it was a solid glass hull the inner layers are the ones that take the pounding and banging FROM THE OUTSIDE !!

In mass products you more often than not will find the inner layer much thinner than the outer (which has to provide a minimal impact resistance on top of the bending strength).

But be it as it is, the inner layer alone will not hold the junk together and in shape. Stripping the outer skin and core means the boat is gone, just leave it.
Of course everything is possible, but to which extend is it sensible?

The plan to apply a wooden structure (it is no core than any longer) and cover that with glass epoxy is sure possible, but a new build would cost less than half of the $$ needed.

Leave the sampan where it is and find a solid boat, or go the way I recommended in one of my former posts:
Build the same hull, deck in wood epoxy and use the scrap as a organ donor.
You would have a structurally sound and brandnew boat at the same cost than any rather risky repair job would provide.

Regards
Richard

[Herman]

I have only read the last 2 posts, so bear with me.

Inner laminates can be thinner if calculations show that a thin laminate is enough to bear all loads. (enough tensile is reached quickly with fibrous materials). However, this thin laminate can be too thin to bear localised shock loads (bumping into a jetty, for instance) in which case the outer laminate is beefed up for puncture resistance.
One thing to keep in mind then is the shift of the neutral line, and therefore things need to be re-calculated.

About pucture resistance: My racing boat had an outer laminate of 0,5 mm or so, which was more then plenty. Even for puncture. (it was 1 layer of carbon, 1 layer of carbon aramide, totalling 300 grams of carbon and 70 grams of aramide.) Vacuum bagged for low resin content.

[tunnels]

I am glad you live where you do and dont make boats for nz conditions . Carbon is one of the worst materials to us on the inside skin .Kevlar yes but not carbon .
Most times the inner skin is the one that takes all the punishment and holds everything in place specially when you have a core .

Try designing a panel that will progressively distruct and not just go bang and break . You only need 2 differant types of glass and one is csm so what would you use for the other ??

[Herman]

I am glad you do not race boats. You would be scare 100% of the time.

I am confused why you talk without knowing the circumstances. The racing boat I was talking about only raced (still races, actually) in very controlled circumstances. If it decides to self destruct, within the minute either another competitor or a rescueboat will pick you up. Except from collisions, these boats never got damaged, so from a racing point of view, they are still overweight and overengineered.

Off shore racing and touring are a completely different ball game.

See these boats as the Formula 1 (well, perhaps not Formula 1, but definately Formula Ford or similar) of sailing. Would you design a Formula 1 car with spare wheel on the back, a 6 CD player and navigation?
No. Design for the set targets of your audience. If that means that a panel does bang and break, but is a very lightweight structure, and the client totally happy about that, there is no problem. (and as they are solely intended for racing, no CE certification either)

Back on topic: No gelcoat on these boats either. Too heavy (at least 5 kg). A thin shot of PU paint was all it took. 1,5 kg of paint, of which perhaps 0,8 kg stays on. (overshoot and solvents)