Thru-hull or not?

[MacD68]

I guess this is one of these questions that comes up again and again, but I thought I would solicit some fresh input /forums/images/graemlins/smile.gif
I am about to fit new depth/speed instruments to a 32ft yacht, where previously there was only a speed transducer.
For depth, the options seem to be:
1. Cut a hole through the hull for the transducer
2. Fit the transducer in the hull
3. As I'm replacing the instruments/transducer, purchase an instrument type that supports a combined speed/depth/temp transducer (tri-ducer??), so that I only use the hole currently in place for the original speed transducer.

I would like to avoid number 1 if at all possible.
Number 2 seems the best option to me, but I have heard that it will not function well with a thick hulled yacht.
Number 3 could be an option, but from what I've seen so far, it seems to be a limited number of these multi-function transducers and instruments available, and all beyond my planned budget.

Any thoughts/experience welcome.

MacD

 

[hightech]

In hull can be very succesful, you just need to pick a good spot, unless the boat is old, modern hull thickness is not too great and for depth only purposes will usually work fine. Only if you want fishfinding signal quality do you have to go through the hull.

Airmar do a combined plastic triducer that looks like a standard speed transducer and fits in the same hole, this is marketed by a few of the usual instrument makers in their standard packages.

Addtional holes in hulls need not be feared, the fitting just needs to be well positioned and properly sealed.

 

[samwise]

You don't need to cut another hole for the depth transducer. Epoxy a short length of plastic pipe to the hull in the appropriate spot i.e. out of the way of bubbles that might give a false reading. Drop in a bit of oil or other liquid ( I can recommend KY Jelly) so that the sensor can read through the hull , insert your instrument ( O this is getting worse!) and it should work fine. Do check that the transducer is suitable for in-hull intallation, some are not. We have had an installation like this for three years, no problems. The existing hole could be used for the log impeller, although having lost two paddlewheels and tackled the dreaded waterspout when the thing clogs up and has to be pulled out and cleaned, I would consider one of the newer units that don't have a wheel or any vulnerable bits poking out from the hull.

 

[Aeolus]

Consider whether you need a thru hull speed instrument. You could rely on a GPS speed reading instead. Then you have one less thru hull requirement to worry about.

 

[MacD68]

Thanks for the feedback.
I guess using the current hole for depth, and relying on GPS speed is an option that I hadn't thought about, and would be worth considering. It's interesting, but not essential, to compare log speed with GPS speed, to get a feel for what the tides doing, but I guess I can live without that info.
The boat is from 1982, and I guessing it has a fairly thick hull.

 

[graham]

I took advice on here and stuck my NASA depth transducer to the inside of the hull with silicone. Works fine. Use a bit of chewing gum to temporarilly check if your chosen position is ok. (I tried bluetack first but it didnt work, chewing gum worked first time).

 

[Caer Urfa]

The less holes underwater the better!
For the depth finder it needs to read straight down (not at an angle) and make sure it is not reading through the keel!
Remove any bilge paint back to the original hull then I used the old Blue Tack and just stuck the transponder to it for testing best position in various spots.
Finaly with the aid of good old sikaflex stuck the transponder permanently,(just move it a bit when sticking to remove any traped air),THEN, when its dry build more up around the sides to make it more secure.
Works every time (well twice on last two boats)

 

[Spuddy]

Just done the same as Graham and it's worked a treat. I'd guess that hull thickness might only affect sensitivity to deep, deep depths. I tested for a good spot by putting the transducer in a plastic bag of water with the neck tied.

 

[ebbtide]

[ QUOTE ]
You could rely on a GPS speed reading instead.

[/ QUOTE ]

Rollocks! That really isn't what navigation is about!

As for' holes' I fitted Raymarine BiData but soon replaced with separate log and depth instruments 'cos not enough info displayed when wanted.
No probs, cerainly no damaged paddlewheel, and that waterspout is miniscule.