Ideas? Leaking through-hull transducer housing

[bluedragon]

We've got two Raymarine/Airmar through-hull transducers. After going back in the water, I didn't check they were leak-free because a) I hadn't done anything to them and b) they were not easily accessible at the time. A day or so later I thought I'd better have a look, and to my dismay there is a small amount of seawater in the bilge at this point. Dried it out and over 5-10 mins could just see a tiny amount of seepage around the hull nuts of both fittings. Why this should be I don't know. Perhaps the slings went over this area and disturbed their seals. I also noticed that silicone sealant has been used to "bed" the fittings, which may have been a factor as regular marine silicone is not suitable for total immersion.

So, as a stop-gap measure I've squeezed sealant all around the internal base of the fitting and that has stopped the flow (for now). I've tightened the hull nut beyond "hand tight" but not too happy about that, and it didn't solve the problem. Really they need to come right out and be properly re-bedded, which means another hoist out!! Unless there is a clever way of doing something whilst in the water as a better temporary fix. Securing the fitting then partially unscrewing the hull nuts and re-sealing the internal washer and threads? But what with (?) bearing in mind that some water ingress will occur? Most sealants won't adhere to a wet surface...and I need to get rid of the silicone and other gloop. Other techniques / materials? I did think of an O-ring, but how to get it over the wire of the depth sensor (no blanking plug here). I'd welcome any ideas no matter how wild and/or how others have dealt with this.

 

[angelsson]

I think the only clever solution to permanently put your mind at rest, not to say your insurers, is a lift out and proper inspection of the fitting, personaly I would remove and reset with correct sealants, plenty of those available, any attempt at a temporary repair would be short sighted and possibly disastrous.

 

[bluedragon]

I don't think there's a disaster waiting to happen here. The amount of water was a cupful over a few days and the fittings are secure, but it does bother me. Sooner or later I'll have to re-bed properly (maybe sooner) but in the meanwhile I'd like to improve on what I've already done if that's possible.

 

[Boathook]

Depending on how much beyond hand tight I might possibly worry as these fittings are normally 'plastic'. One option is to undo (not remove) the back nut, clean the underside and hull and tighten back down having used a suitable sealant (I now prefer ArboMast BR for all fittings). This may sort the problem out but also be prepared for the worst and have some 'plugs' ready. The other option is to get some spare fittings and dry out and change them over.

 

[bluedragon]

Yes it's hard to know how tight might fracture the unit. I gripped the nut with a water pump pliers, but just lighty nipped it up. If I'm re-sealing of course hand-tight is fine as the sealant will do the job. My thoughts are along the lines you suggest (inc. getting spare housings). I've used non-curing butyl sealants in the past for fittings I may need to dismantle and with their high body might well work here as a "clamped-up" gasket material - but they do have a tendency to extrude over time. Worth considering though.

The wooden plugs are right alongside already, just in case!

 

[Icarus39]

Hi,

Obviously, the ideal solution is lift out and sort properly. However, as a temporary solution, you can get a product called 'Waterweld' - this is a 2 part sealer in a 'smartie' sized tube. You sqeeze the plasicine like substance together mixing in the catalyst. It is then like putty and can be applied to wet surfaces and will adhere and dry. A fillet of this around your hull fitting in the bilge would most likely sort you out in the short term.

When I bought my last boat (which was almost new) the surveyor made am intersting comment regarding the through hull speed impeller - I paste it below for your reference. This was done prior to launching and guarantees that should the skin fitting fail, you don't get a big leak !
See below and good luck !



Log impeller housing secure. However this fittings is of plastic consisting of a
large threaded body with an external flange and secured in the hull utilising a
large plastic nut located on the body. Fitting secure and flange intact but there
have been a few incidents involving this type of fitting where the external flange
has sheered off allowing the body of the fitting to come loose into the boat
leaving a 1.5” diameter hole. This is rare but all unreinforced plastic such as this
will deteriorate over time and the life of the fitting is largely dependent on the
amount of tension it has endured since being fitted in the first place. It is therefore
prudent to apply a light GRP lamination or epoxy fillet over the securing nut and
onto the surrounding hull surface inside the boat in order that the fitting remains in
situ should the flange sheer off. Obviously the flange should be inspected
whenever the opportunity arises.

 

[bluedragon]

Interesting! In effect that's what I'm doing with sealant at the moment. The only problem I can see is it that if you epoxy the nut in place, how then can you get it off to change the fitting to a new one in the future?? I notice that these fittings are also available in brass and S/S. A safer option I think when I change them, but it seems almost everybody has plastic.

PS - Sounds like Waterweld is good stuff to have on board anyway.

 

[Red Admiral]

NASA stongly recommend that their through-hull fitting is supported inside the hull by a large fillet of glass reinforced resin. Obviously best done when boat is out of water. Don't suppose NASA plastic is much different/weaker than that of other manufacturers.

 

[Icarus39]

Hi Bluedragon,

For sure, WaterWeld is a good cheap thing to keep onboard as a get you our of trouble one. Most chandlers sell it or can be bought online.
When you come to replace a skin fitting that has the epoxy fillet you can soon Dremmel around it to get it out, etc. Definately a good thing to do !

Good luck

 

[bluedragon]

NASA stongly recommend that their through-hull fitting is supported inside the hull by a large fillet of glass reinforced resin. Obviously best done when boat is out of water. Don't suppose NASA plastic is much different/weaker than that of other manufacturers.

I've just read the Raymarine/Airmar through-hull fitting instructions and they don't mention this at all...but it makes sense!