Discoloration near prop

[Northstar1014]

Hi all,

After haul out this year, I noticed this discoloration near the prop. From the symmetry, it looks like a leak. Or maybe the bottom painter added a extra few coats in this area but I cannot imagine why.

My guess would be some kind of water intrusion is going on in the fiberglass or bottom paint around the prop shaft, but the cutlass bearing looks good with no prop shaft wiggle, and I never noticed any unusual stuffing box dripping last season.

Are those little clam vents ahead of the prop to feed water to the stuffing box, and do they leak? Anyone seen this before?

Ted

[tjr818]

We don't have those clam vents on our 1980 27, hull number 185. I guess they are there to help "lubricate" the cutless bearing

[Wayne Grenier]

I have never seen those "clam vents" on any boat ever in my life. They are not standard on CD's, that's for sure. Normally the cutless bearing is lubricated by sea water as there are longitudinal slits in the rubber. I would explore this further with a professional. I have no idea why anyone would want to introduce seawater into their boat like that. I hope you find an answer.

[David van den Burgh]

I'm curious: Any chance you have an oil leak in either your engine or transmission that is allowing oil to leak down the prop shaft and find its way to the bottom paint? I had a similar "stain" on my Alberg 30's ablative bottom paint after oil leaked down a cockpit scupper. Seemed almost like the bottom paint absorbed the oil. Just a thought.

Another thought...could it be someone used a fairing compound that is porous and, thus, holding moisture?

[Gary H]

It appears that the discoloration may be caused from the exterior. I say this because the paint on the vents is discolored. As the vents are probably metal, it is unlikely that they would be permeable to allow water from inside the boat to get to the paint.

[Frenchy]

Can't really offer an opinion on the discoloration, but I agree that those "vents" are very
unusual. I've never seen them either. I don't think you could go far wrong by removing them
and glassing over, if there's a hole underneath. - Jean

[Northstar1014]

Thanks all for the replies! I will investigate the clam vents further this spring and see where they lead.

The area around the prop shaft on the interior of the bilge is free from oil, so I dont think there is an oil leak causing this. I agree it looks more like heavy coats of bottom paint were added there.

Ted

[Paul D.]

Perhaps moisture under the paint layer from filler patch repairs from the past? Probably not serious but if you haven't a recent moisture reading getting one might be helpful if you are worried about it. Our rudders often are higher in moisture reading than the hulls too.

[Steve Laume]

It seems like those vents were installed to feed water to the shaft log ahead of the cutlass bearing. You shouldn't need these. I would be very surprised if they were not clogged up with some sort of marine growth and non functional at this point.

It looks like the area you are concerned with has all been faired in by a PO with some sort of compound. The only way to know what you have going on under there is to sand off some bottom paint and take a look.

Some spent a lot of time in that area, Steve.

[SAIL1]

to remove the possibility of it being moisture one could use a hair dryer carefully to heat up that area and see if it removes the stain.....

[Wayne Grenier]

Upon further thought I think you should take those photos to a propeller shop or a boat yard. I am puzzled why both vents point forward? Obviously they were intended to direct water in as the boat is moving forward but how does it get out? I would think one vent would face forward and one would face backwards if the purpose was to divert water around the stern tube? Perhaps use some compressed air in one vent and see if it comes out the other one? Is there a funky looking collar or something on the inside?

As of now you basically have 2 holes in your boat under the water line and you have no idea what they do or where they go or if they will sink your boat. I would start exploring.

[Skylark]

Pretty sure, I'll bet, etc. That area was faired and possibly primed differently than the rest. The vent are the introduce water into the Cutless. A custom change nicely done... Alberg 30s have bronze stern tube that does this.