Hull Pitting

[ducked]

How concerned would you be about these pits, and what, if anything, would you do about them?

Quite uniform hemispherical depressions. I think I initially took them for barnacles (eyesight deteriorating rapidly) and probably blasted them especially when I did a half-assed pressure wash a couple of weeks ago. I suppose its just possible they were barnacles, and took gelcoat with them when they were blasted off, but most of the hull barnacles were/are very dead (the boat having been ashore for 4-5 years) and quite loose, so this seems unlikely.

Other possibilities are I suppose osmosis (though they seem too shallow) or impact damage, say from a floating baulk of timber with a nail in it.

OR?

I suppose "what, if anything, would you do about them?" is a daft question, since they need filled. "How/what with?" would be a better one

 

[merjan]

Our 40+ y/o GRP hole has pitting as you describe, mostly near the waterline. A few surveyors have seen the photos and dismissed them air bubbles. All suggested fairing and painting over them. As they are numerous, I don't want to remove the paint from inside the craters one by one. I am waiting for the winter when we will have the soda blasted to fair them.

 

[ylop]

Did you mean to attach pictures?

 

[Concerto]

The most likely cause is air bubbles trapped in the gel coat due to poor brushing out during application. My 1980 Westerly Fulmar has patches on the underwater sections of the hull and when I bought her, the surveyor explained it was not osmosis.


These little blisters are 2 to 3 mm across and shows exactly what I am talking about. They can burst, but cause little problem. Gel coat is not 100% waterproof and can slowly enter these cavities and cause them to burst. You can fill them, but more will still appear.

You may find this presentation on renovating Concerto worth looking at. There plenty more via the link in my signature.

https://wiki.westerly-owners.co.uk/images/3/3f/Concerto.pdf

 

[ducked]

Did you mean to attach pictures?

Ｅｍａｉｌhad one of its frequent YOUＡＲＥNOTＩＮTAIWAN panic attacks (which, to be fair, I do myself on these chilly mornings) and wouldnt let me in for a while.

The most likely cause is air bubbles trapped in the gel coat due to poor brushing out during application. My 1980 Westerly Fulmar has patches on the underwater sections of the hull and when I bought her, the surveyor explained it was not osmosis.

View attachment 206509
These little blisters are 2 to 3 mm across and shows exactly what I am talking about. They can burst, but cause little problem. Gel coat is not 100% waterproof and can slowly enter these cavities and cause them to burst. You can fill them, but more will still appear.

You may find this presentation on renovating Concerto worth looking at. There plenty more via the link in my signature.

https://wiki.westerly-owners.co.uk/images/3/3f/Concerto.pdf

Mine look quite similar to the open ones, but a bit bigger/deeper, perhaps 5mm, and there seem to ONLY be open ones.

P[us they are very localised, which is why I thought impact damage.

What would you fill them with?

 

[Concerto]

Looking at the damage I think it is air bubbles in the gel coat like my boat. Looks like gel coat power whisked and immediately slapped in the mould by an untrained person and not brushed out.

To fill I would use Teroson Gel Coat Filler (formally Plastic Padding). This is a polyester based product that is easy so sand smooth. You could use epoxy with micro balloons, but it is harder to sand and more expensive.