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  Topic Review (Newest First)
08-24-2012 02:04 PM
Should not take you too long.

Originally Posted by Trinidoc View Post
Ok you have sufficiently worried me to redo the project. I'm still out the water and only rushed to get the stern tube down so that my new engine can go in. I will pull it apart tomorrow and start over. Thanks.
The good news is that the tube will be easy to remove once you get the bolts off as the butyl rubber is pretty easy to remove.

Once you get the stern tube removed. Rough both the bottom it's flange and the hull interior with 100 grit sand paper, soak a rag with rubbing alcohol to remove the sanding dust, and then follow it with a thorough cleaning with an acetone soaked rag. Allow the acetone to fully evaporate (pretty quick) before bonding. Butter both the stern tube flange and hull with the adhesive (Sikaflex 291 or 3M 4200) about 1/8" thick, position the flange onto the hull, bolt tight an clean excess adhesive. Run your finger along the edge of the flange and hull to get a nice smooth transition of the adhesive. Go under boat and remove excess adhesive that may have squeezed out into the cylinder where the prop shaft will go. Should take no more than 30 min start to finish.

I know that I lot of folks on this forum think the butyl rubber is the best bedding agent because it flows well, is sticky, and is easy to apply and remove. But because it really has no adhesive properties nor structural strength, it isn't a good material for thru hulls and other below waterline fittings nor as the primary means of fastening something to another surface. It is also very easily degraded by organics like diesel, oil, and gas. "

Folks have to remember that adhesive doesn't necessarily mean something that is tacky/sticky. Honey and syrup are sticky/tacky, but have no significant structural adhesive properties. The best way to think of Butyl Rubber is a soft and deformable "o-ring and use it in in areas where a item like that would be okay.

08-24-2012 01:28 PM
Re: Resealing the Stern Tube?

Ok you have sufficiently worried me to redo the project. I'm still out the water and only rushed to get the stern tube down so that my new engine can go in. I will pull it apart tomorrow and start over. Thanks.
08-23-2012 05:15 PM
Butyl Tape for Below Waterline

I am not sure I would have gone that approach.

I have no issue using Butyl Rubber above water line for deck hardware, but for I would never use it below waterline for thruhulls. I would have used Sikaflex 291 or some other Brand Name of that type of material. Butyl rubber has NO tensile strength and weak adhesion, so all of the load on your stern tube is now on the bolts. Also, since the rubber has weak adhesion, if any there is any really poor bonded areas, water can push past it. Unlike deck hardware which has no water pressure, the stern tube has the pressure of the water holding up the boat. With an adhesive, like 3M 5200/4200 or Sikaflex 291, the the adhesive you have much more adhesive properties and the adhesive distributes the load across the bonding surface.

If I was you, and the boat isn't launched, I'd rebed the stern tube with Sikaflex 291 or 4200. If it is in the water, keep and eye an one it and replace it at the end of the season.

08-21-2012 04:41 PM
Re: Resealing the Stern Tube?

looks like butyl tape. Stays pliable forever.
08-21-2012 04:07 PM
Re: Resealing the Stern Tube?

Ok I managed to get the stern tube down over the weekend. I used a bedding compound that came in a roll. I don't know the name of it as a friend gave me some and I don't think even he knows that correct name. Basically you roll it out and bolt down the tube over it. It compresses out like Plasticine and can be easily removed in the future as it remains pliable. I used a small amount of 5200 to seal the bolt holes as I will fibreglass those in on the outside so they will be water proof anyway.
08-20-2012 10:02 PM
Re: Resealing the Stern Tube?

I'm not too sure about 5200 under the waterline. I once sandwiched some additional ballast on a boat with a fiberglass covered wood keel, connecting the two ballast pieces by through bolting them. I gooped the bolts up with 5200. The boat sat for another couple of weeks before I launched her. About two years later I decided to replace the bolts. Lo and behold, they came out very easily. The 5200 was soft in consistency, like it had never set up properly.

Another time, I saw a fellow recaulk his boat (about 35' plank mono) using 5200. When launch day came his boat had to sit in the slings for 3 days before the leaking slowed down enough for his multiple pumps to keep up with it. Pretty mad yard owner too.

I'm not an expert on this subject, just food for thought.
08-19-2012 02:28 AM
Re: Resealing the Stern Tube?

I think thru hulls is one of the places you probably would want 5200. Easy to get to for the most part when the boat is out of the water, and very sad if they let go :-)

It's one of the only places we use it at work. Otherwise it's 4200 or a specific goop for the specific job.
08-18-2012 08:38 PM
Re: Resealing the Stern Tube?

Originally Posted by JimsCAL View Post
Are you talking about the bearing? If so they are either held in place by set screws or it just a press fit.

FWIW, never use 5200 on anything you might want to remove in the future.
No not the cutlass bearing - I already changed that (with lots of swearing). It's the bronze tube to which the dripless seal attaches.

The general consensus seems to be not 5200. I will look around for that Sikaflex. I guess I shouldn't use 5200 on my thru hulls either then as I'm about to change all of those as well.
08-18-2012 01:06 PM
Re: Resealing the Stern Tube?

I used Sikaflex 291 or 292, can't remember- the fast one, because I wanted to be able to remove it again someday.
08-18-2012 11:39 AM
Re: Resealing the Stern Tube?

5200 will work, but that's kind of like welding spark plugs into a gas engine. Works great, until the time comes to get them out -- and then you're talking about a real chore.

Listen to your friends, and use something less permanent than 5200. I'll even go a step further and suggest that you give away whatever stocks of 5200 you may currently have aboard so that the itch to use it in the future will not be easily scratched.
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