Replacing a log transducer tube

[Sinc]

I'm about to replace the plastic tranducer tube for the log. The original had a mangled thread when we bought her.
The tube is an Airmar product and they have supplied a spare - very good service by the way - which should be a direct replacement. The log is a Raymarine ST50.
I just wondered if anyone had done this and had any tips? I suspect removing the old one will be tricky, especially getting a clean surface inside the hull. It's not glassed in but no doubt the sealant is solid and I expect to have to break it out in some way.
I was planning to use Sikaflex as the new sealant - any advice on which one?
Thanks, Graham

 

[alahol2]

Can't help with the removal, and this may not apply to the Airmar product, but for the refitting NASA recommend normal silicon sealant. I believe there are some sealants that will make the plastic brittle. They also recommend using glass fibre filler to build up a fillet over the fixing nut and part way up the thread. See here.
Airmar may have their own recommendations.

 

[David2452]

As it's plastic it will be fairly easy to reduce it to "kit form" to get it out if needs be, I sometimes use a piece of cheese wire between a couple of short dowels to Saw through sikaflex and other sealent interfaces between the outside hull and transducer flange with good efffect. Sika 292 is very good for through hull transducers but a pain to remove when properly applied, once the thing is out then you may need to use a scraper to remove the residue and then an abrasive an finally acetone and possibly sikaflex primer before replacement, let it go off a bit before the final half turn or so on the collar. The Airmar fitting instructions are available on the web site if they haven't included them with the replacement part.

 

[Sinc]

Thanks both for your helpful comments. Always a bit apprehensive about making holes in the hull!

 

[swifty]

I have just done this job, firstly I carefully chain drilled the fitting nut and then split it off the through hull fitment. I then sat under the boat with a hacksaw blade, which I had marked with a line that compared to the thickness of the fitment (measurement taken from new fitment). I then used the blade to weaken the fitment every 20 degrees being careful not to cut into the hull area. This weakened the fitment and I removed it by carefully breaking it down.

The recommended sealant is Sikaflex 291.

Good Luck