Depth sounder with no thru-hull?

[jr438234606]

I have heard from Sailnet articles and other sources that some depth sounder transducers can be installed inside of a hull in such way that you don't have to drill a hole in it. The requirements are that the hull not be cored in the area you locate the sounder, and that you permanently afix the device using epoxy.

My existing depth sounder, which uses a thru-hull mount for the device, has stopped functioning. As it is a very old unit, I want to replace it. However, I'll need to haul the boat to do it. I don't plan on hauling the boat until the coming winter, but I also don't want to be without a depth sounder until then. Hence, I was hoping I could use this technique to put one in now. (I can't use a transom mount due to the shape of my stern.)

Can anyone comment on the pros and cons to this? I was thinking of using Raymarine's ST40. Anyone know if the technique would work with this unit? If not, is there a particular unit that it would work with?

Thanks in advance for your feedback.

[camaraderie]

Yeah...it will work. You need to encase the transducer in mineral oil for best results. Won't any other depth sounder transducer fit your existing through hull? Most of them just unscrew and pop back in without haul out required.

[sailingdog]

I'd try and get a replacement transducer that will fit your thru-hull first. BTW, you do lose quite a bit of power on a through-the-hull setup, and it can be seriously affected by the hull material. If the hull is cored, it won't work. If there are any voids or bubbles in the laminate below the transducer, it won't work, etc...

[Gene T]

It's easy, I have installed 3 of these. You can test the spot on the hull first by using vaseline to hold it in place. If it works, and I have never had a problem with any spot I have chosen, then clean all the vaseline off with alcohol and glue it in place. I have used epoxy but I prefer simple RTV, put a blob in the center of the puck and make sure there are no bubbles in it, then push it down on the spot so that the RTV pushes out on all sides. I don't like epoxy because you have to mix it up without any air getting in it, which is difficult. I know people who cut PVC pipe an angle in order to compensate for the angle of the hull, then use mineral oil to put the puck in. Very messy and unnecessary if you ask me. On the last boat I bought a fish finder with a transom mount transducer. I cut the mounting tabs off and glued it to the hull under the nav station on about a 10% hull angle and it worked great. This isn't rocket science and it is easy to test the spot first. Shooting at an angle is the only consideration as you might not get the best reading when healing the wrong way. But the beam angle is pretty wide and I don't think it is a big issue.

[Ronbye]

I installed a Uniden digital depth sounder with a shoot thru the hull transponder. It is excellent. Just follow the manufacturer's installation instructions and you should not have any problems. You might want to look at a fishfinder unit. Quite a number of boats in our area have installed these.

[sailphoto]

Another way to do a quick test on a shoot thru transducer is to fill a ziplock baggy with water and hold the transducer against the hull through the bag. If you can find a spot low and ahead of the keel it will usually give you a good angle. Anchor or hang on a mooring, measure the depth with a leadline and check what the transducer tells you. Remember that some depth sounders may need some manual calibration ( refer to the manual). Do this in varying depths until you are confident that it is working. Mount the transducer and repeat to confirm calibration.

[captnemo2]

GENE (re the quote below)
1. probably a dumb question but what is "RTV?"
2. Do you cover the whole bottom part of the transducer that sits on the hull with vaseline/epoxy/RTV, not just the edges of the transducer?
"..then clean all the vaseline off with alcohol and glue it in place. I have used epoxy but I prefer simple RTV, put a blob in the center of the puck and make sure there are no bubbles in it, then push it down on the spot so that the RTV pushes out on all sides..."

[sailingdog]

Captnemo-

1) RTV—Room Temperature Vulcanizing, usually a silicone sealant of some sort, generally used for making gaskets and such.

2) The whole bottom part of the transducer should be immersed if you are doing it for real, the whole bottom should be covered for testing.

Generally, I don't recommend silicone, but putting the transducer in a piece of oil-filled PVC pipe that has been glassed to the hull. But that's just me, and the way I learned to do this.

[Sabre66]

Originally Posted by sailphoto

Another way to do a quick test on a shoot thru transducer is to fill a ziplock baggy with water and hold the transducer against the hull through the bag. If you can find a spot low and ahead of the keel it will usually give you a good angle. Anchor or hang on a mooring, measure the depth with a leadline and check what the transducer tells you. Remember that some depth sounders may need some manual calibration ( refer to the manual). Do this in varying depths until you are confident that it is working. Mount the transducer and repeat to confirm calibration.

Ditto! The ziplock works like a charm.
You cant have any air between the puck and the hull. When I installed mine I thickened the epoxy slightly then used duct tape to hold it in place until it dried.

[svchareta]

I second Gene T's recommendation. I have used this method on two boats and it has worked very well for many years.