[Public-List] Stern tube

[David Fay]

Hi Gerard,

First, you should know that normally water shouldn't be able to get between the outside of the stern tube and the thiokol packed around it. The water should be prevented from going there by the seal between the cutless bearing housing flange and the hull. (In my case, that seal was good, but the threaded joint between the cutless bearing housing had failed so water was able to get from the inside of the stern tube -- which always has water in it -- to the outside of the stern tube.)  Assuming you don't have a problem like mine, it's likely that the sealant between the cutless bearing housing and the hull on your boat has failed. This allows water to seep through the joint and then travel along the outside of the stern tube and into the boat. This is a relatively easy fix but it does require you to haul the boat. You need to: (1) unscrew the two bolts that hold the cutless bearing housing on; (2) unscrew the housing from the stern tube (be sure to keep the stern tube from rotating while you're unscrewing the housing); (3) clean up the surface of the housing flanges and the hull; (4) apply a waterproof sealant/adhesive to the flanges (for example, 3M 4200, but some people prefer 3M 5200 or Sikaflex); (5) put everything together.

This is the most likely failure path, but there are others. For example, your stern tube itself may have failed, allowing water to get from the inside of the tube to the outside. In this case, you'll have to replace the stern tube, which is what I ended up doing on my boat. That's a much bigger job because it involves taking apart the drive train, putting in a new stern tube and cutless bearing, and then re-aligning the prop shaft and engine when you're done. Let's hope you just have to put some sealant on the housing.

David

> On May 28, 2020, at 11:32 AM, Gerard Kuperus <gkuperus at hotmail.com> wrote:
> 
> David,
> 
> That is very helpful, although not necessarily good news: it is indeed leaking from the Thiokol. Since I do not plan another haulout right now, what would be my best options to stop the leak for now. Could I use a sealant on it that can be applied to wet surfaces? Some underwater epoxy? 
> As far as I could tell when I replaced the cutlass bearing is that the stern tube is in good shape. I think that because of the movement with removing the bearing a weak point in the Thiokol (at the bottom there is only a thin section, less than a 1/2 inch, at the spot where I saw water, probably a 1/4 of an inch) gave up. Maybe that is wishful thinking, but I hope I can simply fix it, at least for now with an adhesive that works in wet conditions and sticks to fiberglass and Thiokol. I can then again assess at the next haul out. 
> 
> Suggestions?
> 
> Gerard