through hull transducer replacement

[rjp]

I'm posting this to Classic Boat rather than PBO as it's a wooden boat problem and I can do without the inevitable 'castor oil in a plastic tube' answers. After 4 years ' restoration (on and off) I finally got Alysia (Buchanan Scorpion 32) launched at the end of June. Everything went like a dream and despite 6 years (at least) out of the water she was pretty tight within days (with the help of some lard to stem the initial inflow). However sod's law dictated that the depth transducer got damaged at some point, probably at or around survey time when the sole was up. There is obvious damage both to the inner end of tranducer moulding and to the cable insulation and I do not seem to be getting any signal at all. Anyway, what would have been easily replaceable a couple of weeks ago is now a couple of feet underwater and of course it's a through hull fitting. I've managed to obtain a replacement depth transducer of the correct frequency, though I have no way of knowing if it's the same diameter and length as the original until I can get the latter out. I also have no idea how the original is sealed in. My tentative plan is to find a convenient wall to dry out against, cut cable and remove nut from the inside of the existing thing. Then I'm unsure whether to pound it out from the inside (possible planking damage?) or somehow try to draw it out from below (drill a hole up though the middle and devise some kind of a puller?) My next problem will be what to do then if the size is different. Also what should I use to seal the new one in. Bearing in mind that everything has to be done within one tide, does anyone have any ideas or advice to offer.

John

 

[tillergirl]

On the diameter, I think you will find that all transducers have one diameter for the whole length. So look at the inboard end where the nut is retaining the tube and measure that for comparison purposes with your new one. You don't say what make of instruments you have but many transducers are made by Airmar (a US company) who have a very good website where the dimensions of all of their transducers can be found.

Removal - underneath the transducer will have a lip and it is usual to bead underneath the lip with some sort of mastic. Undo the nut and gently tap to break the seal and the transducer should come free. If a close fit you might need to 'unscrew' it. Need a smaller hole for the new transducer - I don't think I'd try that on a tide! I'd be glueing in a plug with a overlapping backing pad and redrilling but even with epoxy I'd want it to properly cure.

 

[skipperscouse]

have a softwood plug to hand and a bit of putty , white lead or mastic . tap into hole from underneath . as long as it's a snug fit it'll do for a couple of tides. it will swell up and can be knocked out or drilled out from above.i've used this method a few times without problem.or if you don,t like that use a nut and bolt through the hole.

pete

 

[mainmarine]

Don't forget that in wooden hulls you must use bronze transducers as the swelling of the timber can break the plastic type.
Malc

 

[Mirelle]

Good advice. They cost four times as much, of course!

I found I could remove a plastic one very effectively with a brace and bit...there was not much of it left afterwards, though.

 

[tillergirl]

And last a quarter of the time!!!!

 

[rjp]

Thanks to all for useful information as always. I wasn't aware that you could get bronze transducers, though the existing one is plastic and would seem to have been in place for many years (it's a Seafarer 150kHz type by the way). I've managed to get a replacment NASA 150kHz one which works fine when I dangle it over the side so I'm hoping that will be ok. The diameter of the working end is greater than the diameter of the threaded section on the new one, and from memory this is also the case with the existing one. What I don't know is whether the diameters are the same (though I could check the threaded end from inside the boat and can't believe I didn't think of this when I was on the boat yesterday!) Does anyone have any particular recommendations for mastic?

John

 

[tillergirl]

Forgive my grumpiness on the bronze transducer. Having spent over £200 to get it 4 years ago, I'm a bit miffed to have to replace it because the speed bit has packed up (its a combine triducer).

Mastic - not silicon! I've always used a polysuphide from either Silaflex, Boatlife or Purflex. Is the NASA transducer a flush fit. If you have a Seafarer transducer you may have a faired 'block' under the boat. As I remember the Seafarer had to have a little space around it in the block so it could 'vibrate' or whatever it did. I see NASA do a plastic 'block'. If anything I think you will find the NASA pretty much the same size as the Seafarer, maybe the thread slightly thicker

 

[Sniper]

A few years ago I did exactly the same swap - seafarer for Nasa. I think you will find they are identical. However, the replaced transducer only lasted a season before being crushed by the yard lift. I've since bitten the bullet and fitted an airmar bronze transducer (albeit with a raytheon ST40 head - I don't think airmar make a transducer which is compatible with the seafarer sounder)

 

[rjp]

Ouch! £200? I picked up my NASA one for about £20. Reassuring to hear that NAS and Seafarer are about the same size. I will put it to the test later this week al being well. The transducer is right on the centreline and slightly 'notched' in so is nicely faired as is without need of further protruberences. I'm hoping therefore that I don't need to do much if any woodwork. That's if everything goes according to plan - but does it ever?

John

 

[rjp]

Thinks: Must remember to scribe sling positions onto the toerail! Thanks for the info.

John

 

[ColinHuggins]

I wouldn't dare to contribute to anything about wooden boats BUT . . .

When you've sorted out your bits 'n bobs and how to fit them, consider going over to the Channel Island (or anywhere in the Baie of St Malo) where the range of tide is such that you can stay neaped for days. When I viewed Ebb Tide prior to purchase she was on the beach at St Peter Port and didn't touch water for a week. As a result the surveyor reckoned the hull was too dry for a sensible osmosis reading!

Hope that helps, it could preclude your ending up like that Peyton cartoon of a guy up to his knees still drilling the hole!