Stern gland bedding mastic

[Flossdog]

My new prop and stern tube refurbishment is coming along nicely and it is now time to think about bedding compound for the stern gland. Popped into a well known South Coast chandlery on Friday and asked for non setting bedding mastic and was told that they didn't stock such a product and why not use Sikaflex 291? I told the guy that this would be fine until I had to, in the future, replace the cutless bearing or other such job and the thing (stern gland) would be stuck there giving me grief trying to remove it! What do others use in such situations? Non setting mastic seems to be hard to get.

Incidentally, the previous owner, or maybe the builder (Northshore) used non setting mastic and the stern gland came away from the hull quite easily (to my surprise).

 

[wee_niall]

what about this kinda thing?

https://www.idealsealants.com/butyl-rubber-sealant-grey-310ml-idealseal_c119p225.php

 

[Flossdog]

Thanks wee_niall, I didn't find anything like that but this looks to be just what I am looking for. Many thanks.

 

[Flossdog]

Just heard from Ideal Sealants and they don't recommend their butyl non setting rubber sealant for continuous underwater applications and in fact they cannot recommend anything in their range. What do others use?

 

[martinaskey]

Last item on the page ............ not used this for sterntube (only used for fittings etc) but might be OK - worth a look.
It is very sticky stuff !
Martin

http://www.tradboats.com/caulkingandseamfillers.htm

 

[vyv_cox]

There seems to be a strange belief that Sikaflex 291 doubles as welding! It's just a polyurethane adhesive/sealant with moderate strength. I have removed hundreds of fittings sealed with it, including windows with light aluminium frames. OK, it's a pretty good adhesive but it most definitely does not make a permanent joint. I use it for just about every sealing job on board, above and below the water line and it never fails to do a good job.

 

[sailorbaz]

When I bought my boat two years ago the PO told me that the stern gland needed nipping up as there was a drip which let in about a litre a week. In spite of tightening it I still had the leak and didn't want to open it up with the boat in the water.
I had the boat in the yard during our winter and opened up the stern gland - there were 8 pieces of packing in there! Looks like the PO had kept adding a piece to stop the leak.
The rubber tube onto the stern tube only had one hose clip on each end and it turned out it was that leaking. I sealed it with Sikaflex 291 and two hose clips on each end. I still have a dry boat after 6 weeks in the water.
Sailorbaz

 

[Tranona]

My new prop and stern tube refurbishment is coming along nicely and it is now time to think about bedding compound for the stern gland. Popped into a well known South Coast chandlery on Friday and asked for non setting bedding mastic and was told that they didn't stock such a product and why not use Sikaflex 291? I told the guy that this would be fine until I had to, in the future, replace the cutless bearing or other such job and the thing (stern gland) would be stuck there giving me grief trying to remove it! What do others use in such situations? Non setting mastic seems to be hard to get.

Incidentally, the previous owner, or maybe the builder (Northshore) used non setting mastic and the stern gland came away from the hull quite easily (to my surprise).

Suggest you use a polysulphide such as Boatlife Boatcaulk or Arbokool 1000. Have been using this sort of sealer for underwater fittings for years. Always works and comes undone easily.

 

[Neil_Y]

The stern tube should be considered a permanent fixture that is rigidly held, the shaft bearing should be removable from the stern tube/bearing carrier. You might have to destroy it to remove it though. The stern tube should be well supported (good fit in the hull) otherwise it won't support the bearing or may move, so there is only a very thin layer of any bedding material (less than 1mm) and even epoxy at that thickness doesn't bond to the surface but it will support it. Commercial vessels will use an epoxy such as Chockfast from ITW, but equally araldite 2011 will do the same job.

292 is a sealant adhesive, but 291 is just a sealant and not an adhesive sealant, but as Vyv says it's not that strong and would do the job, just make sure any soft/rubber sealant isn't gap filling as this may allow the stern tube to move.

 

[Flossdog]

Thanks guys for the words of wisdom

 

[PlankWalker]

I'll second what Tranona says, polysulphide is the stuff to use.

Plank