Replacing thru-hull transducer housing

[Tony Button]

Hi, I bought an Airmar ST800 paddle wheel speed sensor to replace the sonar transducer which failed (surprise, surprise) The new unit fits in the old housing, but the housing supplied with it has a spring-loaded valve which should reduce the salt water fountain which occurs when the unit is removed, so I would like to use it. (I remove the sensor after every sail to minimise growth on the paddle wheel.) How do I remove the old housing ? Is it simply held in place by the plastic collar or are they generally glued into the hull ? I will be slipping the boat in a couple of weeks so I'd like to know in advance. Thanks for any help.

[C420sailor]

There is (should be) sealant.

That collar should unthread, and unless a strong adhesive sealant was used, you should be able to tap the old housing out without much trouble. I usually use a short length of 2x4 and a mallet. Remove all the old sealant thoroughly, apply new sealant (3M 4200, Sikaflex, etc) and install.

I seem to remember those housings being directional, but could be wrong. Regardless, follow the Airmar instructions—-they’re usually pretty good.

[Shelter]

You can find your original Airmar documents for reference here: https://www.boatclick.co/product/1841 and many more useful information on various products.
You would have to register first in the following link https://www.boatclick.co/signup

[hoolie]

In my experience if it's been fitted with Sikaflex it won't just "tap out". You may well have to cut out the old fitting in bits. Allow plenty of time to do it!

[roverhi]

steady pressure is the best way to get a through hull out sealed with adhesive sealant after unscrewing the collar. Standing on the fitting or somehow using leg strength to force the fitting out works best. Failing that, using a piece of wood or pry bar as a lever to pressure the fitting out may work. Pounding on the fitting has little effect as the elastic caulk absorbs the blows unless you have a really big hammer. If all else fails, use a hacksaw blade or narrow bladed saw to cut the fitting into pieces.

[Cadence]

Return the paddlewheel speed sensor. Do you wish to go sailing or doing constant maintenance. If you're a competition sailor it may be worth it, if sailing for pleasure there are enough other important things to maintain.

[Tony Button]

Thanks very much for all the suggestions; I guess I won't find out how difficult it will be until the boat is out of the water. I'm happy to use a mallet or bodyweight to break some sealant, spending hours with a hacksaw blade removing slivers of plastic, not so much. Maybe I just need to work on my chamois technique !

[Flatswing]

Usually the sealants are pretty adhesive and many use 5200 below the water line so pushing it out may be almost impossible. There is a fast way to cut it out-same technique as used for old bronze through hulls. Wedge in a cone of soft wood into the outside of the thru hull fitting, cut the wood off flush or close to the "mushroom" flange and mark/ center punch it's center. Then use the appropriate sized (for your new thru hull fitting) bimetal hole saw (pilot bit centered in the wood plug) to cut through the mushroom flange then through the threads/ hull interface. Once the mushroom flange is cut off on the outside, there is not much holding the thru hull in place if you have backed the inner nut off

Disclaimer: I have not personally done this on a thru hull. I have used the technique to enlarge existing hull openings (where there is no existing substrate for the pilot bit). The vids cutting thru bronze thru-hulls are most convincing and I can't see why it wouldn't be easy with your plastic fitting.

[lk240]

this method worked for me in removing 2 plastic thru-hulls that had old depth and speed sensors.

https://www.youtube.com/watch?v=lx_Zu9sW_Qk

Best,

LK240

[hoolie]

With all due respects, the complete lack of sealant/adhesive on the through-hull fitting in your video suggests it wasn't thoroughly installed in the first place; not enough adhesive or the wrong type.

No way can you just withdraw a fitting as easily as that when it is properly bonded to the hole in the hull.

[hoolie]

ps Thinking about it I'm possibly being a bit unfair as the video is probably just a demo, not an actual through hull fitting being extracted.

[CAR54]

Removing the through hull depth sounder that was threaded and sealed with 5200, I found a product called debond using this product with lots of ventilation because of VOC’s on 5200 turns the sealant into a jelly like substance. You score the surface spray and repeat a little at a time on the inside and go as far as you can while scraping the old 5200 away.

Then on the outside of the hull where the mushroom head on the depth sounder is flush to the hull I used a vibrating saw with a smooth blade to work around the flange which was made of plastic and sprayed debond again.

Returning back inside, I sprayed the fitting again with debond and left it over night

The next morning I put a pipe wrench on the threaded fitting and got it to budge, then sprayed it some more let it set while ventilation continued for a few more minutes, put the pipe wrench on it again and it started to turn a couple more times, by this time I could turn it by hand and thread it out.

Debond turns 5200 into a jell like substance and is easy to remove.

5200 as far as I’m concerned has met it’s match!