Epoxy, is it the greatest or what?!

[Rockter]

I had a few blisters in Houston, in the warmer water there. Back here, where the water is very much colder, I never seem to get them quite so much. One or two little ones appear from time to time, but none of the 3" stuff I used to have when I bought the ship.

Temperature seems to be a big player in this osmosis game. Cold water really seems to slow it radically.

[boatpoker]

Rockter is correct. The three main external issues that exacerbate blisters are moving water, fresh water and warm water. The worst location I have ever seen for blisters is my own harbour. We used to have a power generation plant next door that exhausted their turbine cooling water into the harbour. I've seen more blisters in this harbour than anywhere including two one year old boats that the builder states were built with vinylester gelcoats (no way to know for sure without lab tests, I never trust builders).

[yellowwducky]

So is there issues with builders doing different parts of the boat in different materials? For instance, Outremer mentions "the hulls are indestructible - monolithic vynilester and multiaxial e-glass - hand laid up fiberglass to prevent catastrophic osmotic delamination as experienced in many high stress areas of sandwich hulls"

Sounds 'good' to me as a non boat builder but does that mean the whole of the boat is done with the same material below the rub rails where the seam of the 'deck' is attached on top? You wouldn't do one part of the hull (say the outside facing part) different from the inside facing parts would you?

[xort]

poker
fresh is worse than salt? Because of the larger salt crystals?

Why would moving water be worse?

Thanks

[boatpoker]

Repeated tests by several resin mfg's and Professional Boatbuilder magazine have confirmed that warm, fresh and moving water exacerbate blisters. I believe the fresh and warm parts are due to the lower density of water in this condition being able to penetrate the resin at a faster rate. I don't know why moving water has that effect but all tests confirm the condition.

If you don't get it now you should subscribe to Professional Boatbuilder magazine. It is the best marine mag around and subscription is free and you can subscribe on line.

[yellowwducky]

Moving water would likely be more able to force its way through/into microscopic imperfections would be my guess.

[sailingdog]

One correction Gramp—

Kevlar doesn't really add stiffness. You can't PUSH ON A ROPE. It does add significant impact and abrasion resistance. Often, kevlar is added to areas where impact is likely, since it will often prevent complete failure of the laminate in case of impact.

Originally Posted by Gramp34

Let me jump in here and add a few words to what's been said.

We're talking about hulls made from composite material. That just means there are two components in the material, the reinforcement fiber (glass, aramid/Kevlar or carbon fiber) and a resin (polyester, vinylester or epoxy).

[Jeff_H]

One correction SailingDog,

Assuming that Gramp34 is using the term 'stiffness' in the usual structural sense of of the term, i.e. reducing deflection, Gramp is right, kevlar does add to the stiffness of the structure. While you are correct that kevlar does not add to the compressive strength of the structure, it does greatly reduce tensile elongation as compared to fiberglass reinforcing fabrics. This helps both in bending applications when the Kevlar is on the tensile face of the structure and in axial tension, such as where shrouds attach to the hull.

This means that a properly designed kevlar reinforced boat is likely to flex less and so, using the term 'stiffness' in the structural sense, the boat therefore will be stiffer.

Respectfully,
Jeff

[Gramp34]

Yes, I used the word "stiffness" in the structural sense, as Jeff describes.

Interesting you mention Kevlar in the tensile face of panels, Jeff. I've seen a few builders advertising a layer in their hulls. The most extreme case must be Hunter:

Hunter Kevlar® Technology

Hunter adds the extra strength where you need it most. From the stem to the keel sump, Hunter has added a Kevlar® laminate to give you added protection against collisions. This is the most likely area for damage or penetration and Hunter provides an extra level of security.

I took their tour a year ago, and saw the single layer of Kevlar cloth going into a hull mold right on top of the gelcoat.

The two things Hunter fails to mention are that:

1. In a collision, the outer side of the hull panel goes into compression. The Kevlar's compressive strength is way less than that of the layer of fiberglass it replaced. You'd be better off with the Kevlar on the inside of the hull rather than the outside.
2. People may think of Kevlar protecting against penetrations in bulletproof vests, but that's Kevlar 29. Hunter is using Kevlar 49, which doesn't offer much ballistic protection.

I expect Kevlar cloth on the outside of the hull would provide much better abrasion resistance than glass, but abrasion doesn't seem to be what their claimed "extra level of security" applies to.

This is what my Pappy would have called a Gimmick.

Cheers,
Tim