Transducers: should I glass them in?

[LadyViolet]

I installed two ST40 transducers through the hull of my Red Fox trailer-sailer two years ago, using Sikaflex. So far, (touch wood) no leaks have occurred. But I think I saw an article somewhere (was it in this forum?) that said that transducers should be glassed in. This is beginning to disturb my sleep, as the hull, being flat bottomed, comes into contact with solid items (such as the trailer, mud-berths etc) more than is usual for most boats. With the season nearly upon us, should I glass them in now? If so, how? Would it suffice just to put the resin around the flange on the insides of the hull or should I take them both out and reinstall them with resin instead of the Sikaflex? Any suggestions gratefully received.

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[colvic]

Leave them as they are, but glass the threaded section to the inside of the hull.

Make sure you really clean the area around the transducers then apply a good fillet of epoxy paste or use matting and resin to build a collar up the fitting.

This is done to try and ensure that if the external flange is knocked off then the rest of the fitting stays in place. Our boat had one and it obviously wasn't glassed in very well as it broke free whilst at sea. Almost lost the boat as there is a hole over 2inches in diameter letting in water!


Phil

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[Evadne]

I'd agree, a transducer of length 4-6 inches being held in by the hull skin alone is not mechanically very strong. My (rather old) grp boat has a wooden teardrop attached to the outside of the hull that supports the e/s transducer laterally. A GRP support on the inside as described by colvic will do the job more elegantly, with less drag and less likelihood of the transducer being strained laterally in the first place. And you can make it much beefier if you want to. The only advantage I can think of of my arrangement is that the transducer is held away from the hull, so is in a cleaner flow.

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[AvanLoon]

What a coincidence! I installed a ST40 set myself this weekend. The install instruction only suggests to 'glue' the snesors with Sikaflex or so, by putting it in a layer of about 2 mm on the flange and that part of the shaft that touches the hull. Turn on the nut handtight and there you are. Do you think Americans take any risk with their responsability? No doubt.
Actually I saw this evening in an install instruction of a NASA log that the shaft could be covered by some polyester layers. Maybe that is the source of your nightmares?
Let's mae a calculation: the surface of the hole is approx. 3/4 x 52 x 52 mm2 = 21,22 cm2 The opening is about 50 - 60 cm under water, so there is a waterpressure of 0,06 kg/cm2. The whole force to press the units into the hull are then 1,27 kg! Anxious that the flange OR the Sikaflex can't cope with that force?
Don't worry, sail happy, and think about another nightmare. For instance: why shouldn't you buy a set of wooden taps to drive in the holes, 'just to be sure to be sure'?


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[vyv_cox]

I replaced a depth transducer last weekend. The previous one had been installed for about 5 years, using only Sikaflex. There is a wooden spacer inside the hull simply to add some thickness to ensure that the nut fits down nicely. Never leaked or gave any trouble. The replacement was installed exactly the same way. Doesn't ever come into contact with anything, but would glassing it in make a significant difference if the hull weight was resting on a trailer?

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[roger]

I think you've got the answer there. The NASA log housing is plastic and would leave a very big hole if broke away. I certainly feel happier having wugged mine in place with polyester. Incidentally I used "bonding" filler. Its a mixture of resin and shortish glass fibres. Its very convenient to use.

<hr width=100% size=1>Roger