Lower rudder bearing housing leak, B37 2006

[umu]

Recently noticed a tiny leak on the lower rudder bearing housing (see picture, yellow tape and paper towel was applied to locate the water source).
Initially I thought it might be condensation while the boat was still in cold Atlantic waters but that can be exluded with the recent water temperatures.
The strange thing - it is just between the top of the big lock nut and the larger upward housing extension. No water seeping out underneath the nut.
Bearings had been changed three years ago, found only tiny pitting inside the housing. Always used non-copper antifoul around the bearing housing
Anybody experienced the same?
Any way to fix this apart from swapping out the housing (saw that Jefa has spare parts, but getting the housing out seems like a major pain).

[Yngmar]

Those fine droplets of water do look like mostly condensation. Or possibly salt attracting moisture from the air. I assume you cleaned it up thoroughly already?

The bit on the right with the foam on it could be an actual leak. It's near a corrosion spot and the pitting may have gone through. That's how our stainless cockpit drains started seeping before we replaced them.

If so, you can patch it up with sealant from the inside for the season and then go about dropping the rudder in winter. Maybe you can patch up the housing and tube (there's a lot of space in there) for another couple years, but eventually it'll have to be replaced if that is indeed corroded through. Do make sure though, else it's a lot of work for nothing

[umu]

Yup, had cleaned the area several time with fresh water and the water reappears. I was also hoping for condensation but over the last days the water is 22-23 degrees inside the marina and the dewpoint is around 16 so not much hope left in that direction.
I like the idea of sealing a potential corrosion from the inside. What would you use for this? Filler like Watertite or rather sealant (Sika or Polymer)?
But after looking at the replacement housing specs I am still trying to make complete sense of what I see and if it is actually corrosion that causes the leak or if the aluminium tube that is glued to the top of the housing might have worked loose/broke the seal.
Attached is the Drawing from JP3 for the housing and the large nut. What wonders me is that on the photo taken from the leak you see no thread on the inside of the nut or gap between nut and tube. So my guess is that the tube that extends upward on the photo is flush with the nut and thus covers the thread/gap.
Which in turn means that the nut is sitting pretty high up on the housing and also that the contact area between the extension tube and the housing can only be minimal (about 1cm?).
My setup has no gaiter, but a lip seal sitting in a (fairly stiff and short piece) rubber tube clamped to the alumnium rudder tube. Could the normal slight flexing of the rudder shaft over time be an explanation?

[Yngmar]

We have the exact same setup with the rubber tube extending the aluminium part and a lip seal on top. It's not a flexing issue, the rubber tube is really just a short piece of large diameter exhaust hose, extremely tough, but still somewhat flexible. It will easily absorb what little movement there is (and there isn't much to begin with).

I'm not sure how the aluminium tube is attached to the top of the housing. Maybe it's actually threaded onto the remaining thread above the nut? On ours no thread is visible either. Not sure how much JP3 diagrams can be trusted

Either way it looks like you now have crevice corrosion and likely pitting from the leak, which can only be fully treated from the outside (with the rudder out). Depending on how severe it is, you might have to replace the housing or might be able to patch it up with epoxy. Until you can haul out, I'd meanwhile clean and dry it best you can and apply a thick bead of MS polymer sealant between the top of the nut and the tube, going for a large surface area to adhere to. This has lasted us 6 months when we had a small trickle (from the last metal through-hull, not rudder) before we could haul out and fix it properly. Epoxy based filler will not work well with the water leaking in (it's great in the other direction though - outside the boat, but you'd have to drop the rudder for that!).

[umu]

I had the boat lifted and the rudder pulled.

Looking at the inside of the bearing housing I found only one corrosion spot which was even close to the height of the leak. My hope this is the root cause for the leak was dampened after grinding it down to fresh metal without breaking thru to the outside (see pictures) BTW: What would be the best way to fill this ? Epoxy/watertite?

Next step was to split and remove the 100mm aluminum tube on top of the housing.
First thing that surprised me is they did not use Sika or the likes but polyester (or epoxy?)  to glue the tube to the housing (yellowish on the pictures).
The tube and the housing have several areas where the corrosion (or dried out saltwater, hard to tell) goes all the way down the glueing area (see pictures)

I now tend to believe the leak came from between the housing and the tube.
Which would relieve me to bite the next bullet and swap the entire housing which is a pain to get out.
But would really appreciate views/comments/opinions.

[Yngmar]

That housing looks absolutely fine! Fill the pit with Watertite if you can get a small tub of it and done. Make sure you fair it sufficiently so the bearing ball doesn't get stuck. It does look very much like the leak came from between the tube and the housing and just came out the bottom there. Perhaps not enough glue applied or someone on the production line elbowed it before it had cured through.

What will you replace the tube with? A new tube or the Jefa flexible gaiter?

[umu]

Thank you for the feedback.
I will go for an Aluminium Tube (to get safely above the water line) plus Gaiter. Jefa has the matching parts in stock.

Concerning the glue - I was thinking to use flexible Glue (Sika or some MS polymer), but wonder since the factory used Polyester to attach the tube to the housing if that would be to better/appropriate material?

[Yngmar]

Sounds sensible to go with tube and gaiter on top.

Good question about the glue. I've used PU based Sika and MS polymer below the waterline without issues, but they won't be anywhere near as strong as epoxy or polyester. It's unlikely the tube will see significant forces applied though, so that's probably not an issue. I think the biggest deciding factor would be adhesion to the aluminium. I've seen adhesive sealants detach from mild corrosion on aluminium when water gets under the edge. So personally I'd use epoxy or polyester glue to to attach the tube. It's what worked originally, apart from perhaps being insufficiently applied (we have the same tube and bearing and never had any leakage problems).

Make sure you apply enough so it beads out of the space between, then bevel it with a stick from the top of the tube That way, no water should be able to get between tube and housing to start corrosion again.