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Old 31-03-2011, 11:03   #1
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Changing a thru-hull depth sounder in the water

Has anyone done this? We were just in the boat yard with our Allied Seawind doing a quick bottom job and clearly should have dealt with our depth sounder then, however we didn't and it started seeping in water when we splashed the boat. (it never did this before, but it hasn't worked in a couple of years either) First we thought it was the seal around the block and tried using 5200 in the water, and also underwater epoxy. After these didn't work, we discovered, by sticking a knife into the block on the inside of the hull, that the block is completely saturated with water. So the rotton blocks are absorbing water and slowly seeping into the inside of the boat. This has probably been happening for many years since the block inside is completely covered with 5200 and it just recently worked its way through. I suppose we could do the same thing again or try hydrolic cement on the outside covering it completely until next year when we haul again but I would prefer to buy a new depth sounder and replace the blocks and the sounder. Does anyone have any advise for me?
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Old 31-03-2011, 11:53   #2
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Re: Changing a thru-hull depth sounder in the water

Greetings and welcome aboard the CF, SeawindGirl.

Haul the boat, remove wood blocking, waterproof the hole edges, replace the blocking /w plastic [impermeable], and reinstall the sender.
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Old 31-03-2011, 12:15   #3
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Re: Changing a thru-hull depth sounder in the water

If it was just a simple change out, you could do it in the water but because of the backing block integrity compromised, I agree with our resident Oracle, Gord May. You should plan on a haul out to remove all the soft soaked wooden backing block, check the immediate hull area for signs of water intrusion in to the hull laminate and dry out completely with a hair dryer or electric heater, install new backing block and seat with bedding compound before installing the new sounder sending unit. Waiting and hoping that no further water intrusion occurs is asking for a bigger problem down the track IMHO. By the way, welcome to CF... cheers, Capt Phil
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Old 31-03-2011, 12:35   #4
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Re: Changing a thru-hull depth sounder in the water

Third that! Trying to fix this in the water will be a waste of time.
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Old 31-03-2011, 12:52   #5
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Re: Changing a thru-hull depth sounder in the water

If what you really want to do is not haul for a year, 5200 is not what you want to apply underwater. Use polysulfide, 3m 101 or life calk. I'm not saying it's a great fix, it'll be messy, but if the sounder is exposed and not covered in paint you may be able to smear it with some polysulfide and seal it up temporarily.
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Old 31-03-2011, 12:57   #6
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Re: Changing a thru-hull depth sounder in the water

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If what you really want to do is not haul for a year, 5200 is not what you want to apply underwater. Use polysulfide, 3m 101 ...
Why polysulphide 101 vs polyurethane 5200?
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Old 31-03-2011, 13:07   #7
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Re: Changing a thru-hull depth sounder in the water

I'd haul, repair the wet area, glass it over and set up the new transducer to shoot through an uncored section of the hull. I've had good results with transmitting through the hull and it it's always nice to reduce the number of holes in the boat.
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Old 31-03-2011, 13:24   #8
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Re: Changing a thru-hull depth sounder in the water

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Why polysulphide 101 vs polyurethane 5200?
It has been my experience that water speeds the cure of polysulfides also.

A long lasting, permanently flexible marine polysulfide sealant which can be sanded, painted***, and used above and below the waterline. Tack-free in 1 to 3 days, excellent resistance to teak oils, gasoline, and diesel fuel. Ideal for teak decks, to bed deck and hull hardware, seal thru-hull fittings, and underwater seams. Will bond to fiberglass, wood, metal, glass, and itself. Cures to a firm flexible rubber seal with excellent waterproofing and adhesion qualities. Can be applied underwater for emergency repairs. Can be applied to damp surfaces
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Old 31-03-2011, 13:35   #9
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Re: Changing a thru-hull depth sounder in the water

The whole hull is uncored so I am hoping there is no damage to the integrity of the hull. The threaded pipe that goes through the hull is 3/4". I would like to replace it with one that could use the same pipe, however I'm not sure they make them that size anymore. Reducing the number of holes below the waterline would be nice though. The hull is approximately 1" thick uncored fbg at this spot, would a transducer that shoots through the hull work well? Thanks for the thoughts.
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Old 31-03-2011, 13:46   #10
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Re: Changing a thru-hull depth sounder in the water

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Originally Posted by SeawindGirl View Post
The whole hull is uncored so I am hoping there is no damage to the integrity of the hull. The threaded pipe that goes through the hull is 3/4". I would like to replace it with one that could use the same pipe, however I'm not sure they make them that size anymore. Reducing the number of holes below the waterline would be nice though. The hull is approximately 1" thick uncored fbg at this spot, would a transducer that shoots through the hull work well? Thanks for the thoughts.

Our boats are virtually idendical, our was also weeping through the wood wedges with no damage at all to the layup. Last month we hauled and I replaced the transduer and the wood, but our ducer was 1.5" not the 3/4" variety. check airmar for transducers.
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Old 31-03-2011, 15:00   #11
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Re: Changing a thru-hull depth sounder in the water

How long was it weaping before you hauled and replaced it? Wow the airmar transducers are expensive - but looks like it would be perfect. Thanks for your help
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Old 31-03-2011, 15:34   #12
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Re: Changing a thru-hull depth sounder in the water

I looked at the airmar site and most of the transducers that I'm interested in show a 2 inch diameter transducer. I have a 25 year old boat with an Impulse depth finder which I'll replace one day soon. It's a thru hull transducer and in the Impulse Instructual Manual it says to drill a 2 1/16 hole so I assume that is the size of the hole that is in the boat now. The airmar site does not give (as far as I could find) the diameter to drill in the boat for their 2 inch dia transducers so does the 2 1/16 hole sound right? That way I can use the existing hole without having to drill another.
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Old 31-03-2011, 15:40   #13
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Re: Changing a thru-hull depth sounder in the water

Do not bother to replace it.

Many new transducer/depthsounders can be placed in and work fine from inside the hull. Nothing special needed.

Buy a new Depth Sounder with a transducer. A $200 Lowrance will work fine.

Find a spot in your bilge as far forward as possible. This spot must be pure glass to the outside, no coring, not too thick and no ballast.

Test this spot by pooling water there and putting the transducer down in solid contact with the fiberglass (maybe a weight on top of it). When you find the spot that works...clean, dry, the put the transducer down with epoxy.

It should work just fine. Modern tranducers can shoot right through the hull, pretty much no problem.

It is worth a try, if you are having problems.

Hope this helps

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Old 31-03-2011, 15:49   #14
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Re: Changing a thru-hull depth sounder in the water

Quote:
Originally Posted by SeawindGirl View Post
The whole hull is uncored so I am hoping there is no damage to the integrity of the hull. The threaded pipe that goes through the hull is 3/4". I would like to replace it with one that could use the same pipe, however I'm not sure they make them that size anymore. Reducing the number of holes below the waterline would be nice though. The hull is approximately 1" thick uncored fbg at this spot, would a transducer that shoots through the hull work well? Thanks for the thoughts.
You shouldn't have any trouble with 1" of glass, but using John Drake's approach to testing can confirm it for you. Try to find a spot with limited turbulence. Bubbles will cause more disruption than solid GRP. I put our transducers under a quarterberth on our Tartan 34. I would have preferred a spot a bit further forward, but couldn't find a convenient location. I had an inexpensive Lowrance with the transducer mounted in a short section of PVC pipe glassed to the hull and filled with water. I replaced my instruments with a Garmin 740s last year. It came with a transducer made to be shot through the hull and worked like a charm.
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Old 31-03-2011, 15:51   #15
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Re: Changing a thru-hull depth sounder in the water

The transducers for the typical digital depth sounder are 3/4". Just installed a Raymarine ST60+ and that was the transducer that came with it. An upgrade was a removable transducer that required a much larger puka like 1 1/2" or so. The problem with doing the replacement in the water is making the fairing block because of the angle of the hull. You'd have to remove the old transducer, measue the hull, cut a new fairing block, make sure it's cut to the right angle, redo if necessary, and then install the new transducer and fairing blocks. Not a lot of fun in the water especially if you're paying a diver to hang around while you're making the blocks. It wasn't a lot of fun out of the water, can't imagine doing it in the water.
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