Hydrodynamic Peel

[Morgig]

In January’s issue of Professional Boatbuilder the was an article on damage tolerance by Bruce Pfund. One part of the article that particularly interests me is the part about “Hydrodynamic Peel”. For those of you who have not seen the article this is where a FRP hull structure looks like it has literally had outer layers peeled off, being associated with high speed craft and minor damage. The article seemed to indicate that if not common, any one working with high speed boats should have experienced it at some point. This surprised our office having worked with high speed craft for a number of years and not seen a boat damaged in this way. I would therefore like to ask if any one else has experience of this mode of damage and how common is it?

[ClarkT]

We've seen this (though nothing as dramatic as Pfund's photos) after a boat hit a submerged piling at high speed, then continued running at high speed for some time.

[gonzo]

As a surveyor investigating insurance claims, I've seen several. They ranged from a couple of square feet to almost the whole bottom.

[Morgig]

Thanks Gonzo & ClarkT the response. Can you give me any more info on these incidents, i.e. speed of the vessels, hull laminate, lay-up procedure – hand or vacuum bagged etc. In other words what I’m looking for is any pattern that can be avoided.

[gonzo]

The main problem is defective interlaminate bonding. All the failures I've seen show shiny spots where the fiberglass ripped off. Also they were bubbles or voids. I think it is mainly because the resin cured before the other layer was laminated on. There is no other explanation I can come up with. If the resin had failed, it would show fractures, but there are always these slick areas.

[ClarkT]

I'm certain the hydrodynamic peel we saw was just a byproduct of the massive damage from a collision. The delamination did not extend beyond the impact zone, and then it was limited to the aramid delaminating from the E-glass. It appeared that some water was forced into the hole, and the aramid and skincoat were separated by the water pressure.

The outer skin in question is as follows

400g CSM
400g biax aramid
800g E-glass
300g CSM
400g biax aramid
800g E-glass
300g CSM
400g biax aramid

[Morgig]

Thanks again for your replies

Regards

The delam was likely at the interface of the aramid. This interface is the weak link, as the aramid does not wet out well like E-glass and works somewhat like peel ply. I have had experience with safety capsules on tunnel boats in which once damaged, we were able to continue the delamination by pulling on the exposed composite. The bond beteween the aramid and the next layer in the laminate is the weak link.