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Old 13-12-2018, 02:32   #1
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Replace depth sensor without taking out of the water?

this is probably an insane question, but is there any way to replace depth sensor without taking out of the water?

its a raymarine airmar sensor, one that is hardwired into the hull unfortunately, not the removable sleeve type like the speed sensor is.

i was wondering about sending a diver down to remove the old one and insert the new one, but besides the obvious problem of maybe sinking the boat, i think basically impossible without soaking the new depth sensor in seawater.

but maybe there is a trick i haven't thought of?

thanks
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Old 13-12-2018, 02:46   #2
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Re: Replace depth sensor without taking out of the water?

Yes and we have described it before on here, but it is not for the faint hearted. Buy a bucket and put thick pipe insulation around the rim. Put the new sounder and wire in the bucket and give it to a diver to take down and place over the old transducer, the insulation foam makes a water tight seal. We then tied the bucket in place with ropes each side of the hull. Next drop the old transducer through the hull into the bucket. Using a wire coat hanger fish the new transducer wire out and lift into place. Squirt sealant as best you can and screw down the lock nut.

It worked and saved us a fortune not having to lift a 80T fleet tender, but we had a full team of experienced divers on board in case it went pear shaped.

If you have a choice or a tidal area, I would lift or dry out the boat and do it in slow time.

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Old 13-12-2018, 02:55   #3
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Re: Replace depth sensor without taking out of the water?

ingenious, worth a shot as it costs about $800 to lift the boat here, just for an hour

i love the idea, i'm thinking connect an air line from a spare scuba tank to the bucket to keep a positive air pressure in there, and a one way bleed valve in the bottom, as a way to expel any water leaking in. kind of like making a mini diving bell

thanks a lot
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Old 13-12-2018, 04:54   #4
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Re: Replace depth sensor without taking out of the water?

actually, i think the mini diving bell idea will not work because as soon as the old sensor is out, the pressure will equalize with the atmospheric pressure in the boat so pumping air in will be pointless.

but maybe i put a little bilge pump in the bucket to be on the safe side
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Old 13-12-2018, 05:52   #5
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Re: Replace depth sensor without taking out of the water?

What will be your Plan B if the diver thing does not work and you are left with a 1” hole in your boat?
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Old 13-12-2018, 05:53   #6
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Re: Replace depth sensor without taking out of the water?

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Originally Posted by steveh2112 View Post
ingenious, worth a shot as it costs about $800 to lift the boat here, just for an hour

i love the idea, i'm thinking connect an air line from a spare scuba tank to the bucket to keep a positive air pressure in there, and a one way bleed valve in the bottom, as a way to expel any water leaking in. kind of like making a mini diving bell

thanks a lot
Adding air won't help, what you need is the water pressure to hold the bucket onto the hull to help form a seal. Even 1 metre down will do as the pressure inside is atmospheric pressure once the old transducer is knocked through into the bucket. If you add air the bucket will fall off or leak.

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Old 13-12-2018, 05:56   #7
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Re: Replace depth sensor without taking out of the water?

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Originally Posted by Woodland Hills View Post
What will be your Plan B if the diver thing does not work and you are left with a 1 hole in your boat?
From memory the Raymarine needs a 52mm hole so stand by with scuba mask, wooden mallet and a large bung to fit from the outside.

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Old 13-12-2018, 06:00   #8
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Re: Replace depth sensor without taking out of the water?

Pete7, 2 more great points, thanks
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Old 13-12-2018, 07:26   #9
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Re: Replace depth sensor without taking out of the water?

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Originally Posted by steveh2112 View Post
this is probably an insane question, but is there any way to replace depth sensor without taking out of the water?

. . .
Most depth transducers that are made to be installed through the hull will also work if installed to shoot through a fiberglass hull. To try this, connect the cable from the transducer to the instrument. Your helper holds the transducer against the inside of the fiberglass hull while you watch the instrument. The bottom surface of the transducer must be in contact with the hull or some liquid such as water must fill any small gap between the bottom of the transducer and the hull. You should see the depth reading on the instrument.

The transducer must be clear of the keel. If this is a forward looking (or side-scan) sonar sensor it will not work inside the hull.

If this simple test works, you should be able to make an installation that will work until you have the boat hauled for other work. There are lots of suggestions on the web for installing depth transducers inside the hull.

Since depth transducers send sound waves through the water to echo back from the seabed, you don't want an air gap between the bottom of the sensor and the hull. I know some use silicone sealant between the bottom of the sensor and the hull. Others make a small container that holds liquid (water, antifreeze and biocide) to fill the gap between the transducer and the hull.

The depth range will be reduced with the sensor inside the hull.

Paul
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Old 13-12-2018, 07:32   #10
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Re: Replace depth sensor without taking out of the water?

Paul, that's very interesting, i'll check it out tomorrow
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Old 13-12-2018, 07:37   #11
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Re: Replace depth sensor without taking out of the water?

I recently drilled a 1.5" hole through the bottom of my boat for a head discharge thru hull..and the boat was in the water!

As well as having a number of back-up plans in place what also worked for me was the following...

As I drilled the hole, my mate was outside in scuba gear with a rubber toilet plunger. As the hole opened, he inserted the plunger, handle first from the outside and the pressure sucked it up and sealed it very quickly with not even a dribble coming in. After my heart-beat had slowed down, we tried to insert the mushroom thru hull. I coated it with 5200 (fast cure) and sent it down with my mate. There is really not that much pressure forcing the water into the bilge, but it was sufficient to dislodge the 5200 and it quickly became a mess. The plunger went back up the hole and we tried again. Swapping the thru hull with the plunger only took a few seconds so only a gallon of water at most got inside, easy enough for the bilge pumps.

This time I coated the thru hull in 5200 and left in in the sun for a few minutes until it skinned over slightly. The second time the diver went down, the thru hull went in without fuss and we secured it from the inside.

I had the added complication of the fact that the thru hull is also a hole in itself. I overcame this by first blocking the hole in the thru hull with a plastic lid. I had found a lid from a hair gel tub that sat nicely over the outlet and silicone'd it in place to block the hole. You wont have this complication as your thru hull is solid.
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Old 13-12-2018, 08:13   #12
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Re: Replace depth sensor without taking out of the water?

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Originally Posted by .Paul. View Post
Most depth transducers that are made to be installed through the hull will also work if installed to shoot through a fiberglass hull. To try this, connect the cable from the transducer to the instrument. Your helper holds the transducer against the inside of the fiberglass hull while you watch the instrument. The bottom surface of the transducer must be in contact with the hull or some liquid such as water must fill any small gap between the bottom of the transducer and the hull. You should see the depth reading on the instrument.

The transducer must be clear of the keel. If this is a forward looking (or side-scan) sonar sensor it will not work inside the hull.

If this simple test works, you should be able to make an installation that will work until you have the boat hauled for other work. There are lots of suggestions on the web for installing depth transducers inside the hull.

Since depth transducers send sound waves through the water to echo back from the seabed, you don't want an air gap between the bottom of the sensor and the hull. I know some use silicone sealant between the bottom of the sensor and the hull. Others make a small container that holds liquid (water, antifreeze and biocide) to fill the gap between the transducer and the hull.

The depth range will be reduced with the sensor inside the hull.

Paul
===============================================aas described by Paul,an inexpensive depth finder with transducer included can be purchased,some even describe on specs that can be used in this way.
When I had my old Tartan and not liked to drill a new hole I installed it inside the boat,worked for the 4 years we cruised.
Is recommended the use of mineral oil but not fond of having oil leaking just replaced with water that could top when needed.
The ONLY problem is what kind of bottom your boat has,if is cored WILL NOT WORK as the transducer will fail to transmit,but again the whole unit is inexpensive enough to try out.
cheers
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Old 13-12-2018, 08:17   #13
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Re: Replace depth sensor without taking out of the water?

you are in a popular cruising area,some of the cruisers might have a spare set you could borrow to try,since there is no need for permanent install,just run a spliced set of 12 volts wires and you are set
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Old 13-12-2018, 08:31   #14
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Re: Replace depth sensor without taking out of the water?

Paul's method works well as a test if you put the transducer in a thin plastic bag with water, then you can move it around the hull to find a good spot whilst viewing the screen. Once selected a blob of sealant applied carefully so no bubbles or gaps works well.

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Old 13-12-2018, 08:34   #15
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Re: Replace depth sensor without taking out of the water?

A temporary solution could be to lash/secure the transducer to a pole (we used a spare stainless steel stanchion and hose clamps) and attach the pole to the side the boat somewhere, possibly aft or on the transom, we used a 3 cockpit drain for a few years.

When you next haul out you can sort the problem properly
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