Osmosis?

[JackFrobisher]

I've just anti-fouled and noticed that I've got bumps on my rudder. Might they be osmosis blisters? I don't recall seeing them before.

It's a Westerly Storm-Cruiser 1989. No sign of similar bumps on the hull.

 

[jon711]

Looks osmotic to me, however, may be an exceptional paint reaction.... My bets are on osmosis...

Sorry

Jon

 

[temptress]

I've just anti-fouled and noticed that I've got bumps on my rudder. Might they be osmosis blisters? I don't recall seeing them before.

It's a Westerly Storm-Cruiser 1989. No sign of similar bumps on the hull.

Yes - that is what they are. However it not too big a problem. You could either live with it, Fix it or replace the rudder.

Fixing is not too difficult but it will re-occur, it is in the design of the rudder. As you seem to be out of the water get a couple of quotes for repair but you could also fix it yourself.

 

[BAtoo]

Might be, but could just be blistering between the gel coat and your primer or epoxy coat (if present). Open one and see.......

Personally wouldn't worry, it's not going to sink the boat or even cause the rudder to fail. Put it on the list of things to do next year at the start of the winter not a few weeks before going back in.

 

[pcatterall]

probably! Prick some and see if some smelly vinegary stuff comes out!
Not the end of the world on the rudder though. ( either to just leave or treat)

 

[JackFrobisher]

Thanks.

Thank you all. I thought it was. As has been observed the rudder is unlikely to 'fail' as a result and the boat won't sink so I'll leave it until next/another year.

 

[boatmike]

Thank you all. I thought it was. As has been observed the rudder is unlikely to 'fail' as a result and the boat won't sink so I'll leave it until next/another year.

The reason you have it on the rudder and not the hull is most likely because the rudder is full of water. The construction is two shells bonded together and most likely filled with foam. The rudder stock probably has 2 or more stainless steel blades welded to it and these are most likely bonded to one shell half and overlaminated before the second half is glassed on and filled with foam. There are several variations on this theme but they all boil down to the same thing. If the seal between the two halves is broken you can get water ingress into the foam and in the worst case it corrodes the steel and breaks the bond. bind the tiller or wheel and give it a good shove in either direction. If it moves on the stock you need to think of a re-build. If not it's safe to launch but I would drill a small hole near the bottom to see if water runs out. If it doesn't and the foam inside appears dry you only have a superficial problem but if it does I would certainly look to rebuild the rudder next year if not this.

 

[ghostlymoron]

May not be osmosis but, as mentioned above likely to be water in the rudder. Drill hole in bottom of rudder and see what comes out. The hole can be sealed by tapping in a 10mm bolt which can subsequently be removed and drained annually. Scrape all paint off and see if the blistering is in the gelcoat or just under the anti-fouling or primer. Also check the integrity of the rudder as corrosion may have taken place which, while it won't sink your boat, might make it difficult to steer!