best adhesive for underwater work?

[Chubby Bunny]

With all of the debris floating around in Puget Sound I've already managed to tag my transom-mount transducer and break the flange of the plastic bracket in which it fits. Last night, a failed superglue attempt let me know that I need something more serious. Should I use epoxy?....Silicone?....Something else?

[Sneaks]

If you have the Airmar transducer like most of us, you can buy the mounting bracket kit separately.

Don

[Sea Wolf]

chubby bunny-

Are we talking about

1.) using a glue in air that holds up under water, letting it cure in the air, or

2.) actually using the adhesive under water, where it has to cure with the water all around it?

Most adhesives require the presence of air to allow the escape of solvents and vehicles that allow the adhesive to harden up once they are gone.

Epoxies and a few other adhesives are catalytically hardened by the chemical reaction of a two part system where the two parts polymerize into a new compound, sometimes without the release of vapors. A few of these can be used under water. MarineTex epoxy is one such adhesive/filler.

Joe.

[Chubby Bunny]

Joe - I'm talking about #1: making the repair on land, letting it air dry, then having it be underwater when the boat is in the water.

[acustis]

Well The best way to seal/bond something is with a marine grade sealant as 5200 bostik. It acts as an adhesive as well as a sealant. If you can get it out of the water use an epoxy but make sure to scuff and clean the fiberglass where you are appling the glue.

[lloyds]

I don't know about the other options but I do know marine-tex is really good stuff. Super tough.

[mikeporterinmd]

3M-5200 is generally considered the best sealant for attaching underwater components
to the hull. However, it is very difficult to remove anything that has been
attached with 5200. Often times, the gelcoat will come off instead. There
are now 5200 removers, but I've never used one. 5200 also takes a number
of days to cure. I think seven, but check the directions. I don't recall how
soon you can re-lauch after applying it.

There is also 4200 which has a 24 hour cure period.

Neither of these will fix a broken flange on a depth sounder unless you are
attaching a decent sized piece of plastic to the hull. Neither would do a plastic,
edge to edge type of joint in my opinion.

Probably need a new flange.

Mike

[stevej]

Quick trick for removing something that has been bonded with 5200 or the like.

Use a thin very flexible putty knife, get it started under the part to be removed then use a hammer to drive the putty knife through and break the bond. Works every time without damaging the glass work.

I use small wire brushes to scrub off the residual adhesive. Soft stainless one if I am concerned about the finish, If not I use copper pipe cleaning brush (very stiff) to remove.

sj

[acustis]

They do have a fast cure 5200 3m bostik. I believe it is tack free in 1hr and full cure in 24hrs. I do know its expensive about 12$ a tube =)