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05-06-2013 10:57 PM
Re: Raymarine ST40 speed transducer nearly sunk me

Also sorry for super ranty thread yesterday. I was convinced my boat was sinking and had been doing nothing but "boat launch stuff" for four days straight, all day, every day. Kinda wired.

Thanks for all the help and advice.
05-06-2013 10:55 PM
Re: Raymarine ST40 speed transducer nearly sunk me

I used 4200 to bed the thru-hull and that's not what is leaking. The blank plug leaks too.

I think what happened is this: the hole for the thru-hull is located under the bow, right in the middle where the hull forms a vee. The thru-hull fitting is plastic, instructions say "hand tighten only". I think I overtightened. "Hand tighten" used to mean "tighten as hard as you can with your hands" lol, now I know better. I think the instructions should say "snug", anyway... When that plastic thru-hull was tightened too far it deformed because it's not on a flat part of the hull. The two o-rings on the transducer (and plug) no longer formed a water tight seal. That's my theory.

I happened to have a spare o-ring for the fuel fill, just so happened that it was the exact same size only slightly thicker. I replaced the top o-ring with that and it slowed the leak further. Hmm... I went out and got another o-ring to replace the lower o-ring but couldn't find a suitable size. I ended up using the yellow plumbers tape simply because it's what I had, to build up a layer underneath the original o-ring. It worked. Leak is now stopped.

That doesn't mean I'm not hauling the boat in the next few weeks to replace the thru-hull with raymarine's bronze version.

4200 is fine. You don't need to "glue" the thru-hull into place. The mechanical hold is supplied by the threads etc. All you need is something that'll keep the water out. C&C used butyl tape down there, never once leaked as evidenced by the bare plywood backing plate, bone dry. I used 4200 on the rest of my thru-hulls and they are fine too.
05-06-2013 09:10 PM
Re: Raymarine ST40 speed transducer nearly sunk me

Originally Posted by smp View Post
What do I do now?
Check out your theory on the crack in the thru hull and if it looks OK I suggest you break out a tube of 5200 and re-seal the thru-hull. Relying on the gaskets alone may be the problem.

The 5200 will need time to cure so perhaps it's best to have them block you ashore while you sort it out.

DIY is not without it's costs.

PS I know 5200 is "permanent", but so is the darn thru hull (or at least it should be).
05-06-2013 03:34 PM
Re: Raymarine ST40 speed transducer nearly sunk me

Did you put some of the gel supplied in the kit on the o-rings of the transducer and plug?
05-06-2013 02:50 PM
Re: Raymarine ST40 speed transducer nearly sunk me

Keep a can of plumbers putty aboard. It can be jammed into cracks from the outside in the water and used to seal sudden failed shaft seals etc. It does not harden stays flexy and seals till you can do something.
You do not need to be hauled, you need a diver to jam a wood plug up the opening and seal it with putty. Get rid of that silly knotlog thing.
05-06-2013 02:22 PM
Re: Raymarine ST40 speed transducer nearly sunk me

try removing the transducer and putting the plug in and see if that stops the leak. If not, then take the plug out and put the palm of your hand over the hole with moderate pressure and look for leaks on the sides of the fitting. If water is weeping out of the sidewall you know it's cracked.

When I installed mine I put a thick layer of Sikaflex on the flange and threads where the fitting goes through the hull. Then I loosely tightened it so the sikaflex would form a gasket between the fitting and the hull. Once set I then tightened the fitting further. If you did not use sealant I would suggest hauling the boat, removing the fitting and doing something similar.
05-06-2013 01:33 PM
Re: Raymarine ST40 speed transducer nearly sunk me

Damaged O-ring?? Not likely, I suppose if both plug and sensor leak...
05-06-2013 12:54 PM
Re: Raymarine ST40 speed transducer nearly sunk me

Is this the thru-hull that has a flap inside, to prevent most of the water entry while changing the plug?

Small chance this is the issue, but when Airmar changed the thru-hull for my DST800 transducer to include a flap, the transducer changed too. The new version is identified by a yellow O ring under the cap. Yellow O ring with flap, black O ring without flap.
05-06-2013 07:46 AM
Re: Raymarine ST40 speed transducer nearly sunk me

It is possible when you installed the tube part (Or thru hull) pressure was not even and the tube got out of round. With uneven hull and bilge surfaces this is quite possible. The metal fitting would help but I would check and make sure your mounting surfaces are flat and parallel inside and out. A little tuning with a small grinder might fix the problem. It could also be a part defect or a heavy scratch inside the tube. Take a deep calming breath and look at it carefully. Hopefully a bit of adjusting will solve the problem. Good luck
05-06-2013 05:16 AM
Ajax_MD Probably because the transducer and the blanking plug obscure the view when installed.
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