# Depth sounder with no thru-hull?



## jr438234606 (Apr 25, 2006)

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.


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## camaraderie (May 22, 2002)

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.


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## sailingdog (Mar 19, 2006)

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...


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## Gene T (May 23, 2006)

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.


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## Ronbye (Nov 16, 2005)

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.


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## sailphoto (Apr 26, 2006)

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.


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## captnemo2 (Jun 28, 2005)

*How to test in-hull transducer before installing?*

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..."


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## sailingdog (Mar 19, 2006)

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.


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## Sabre66 (Feb 3, 2007)

sailphoto said:


> 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.


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## TSOJOURNER (Dec 16, 1999)

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


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## rlevy (Feb 3, 2008)

Does the power or frequency of the transducer affect how well it will shoot through the hull?


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## T34C (Sep 14, 2006)

I WOULD NOT RECOMMEND USING EPOXY OR ANY TYPE OF SILICONE for this application. I have installed units in this manner in my last 4 boats and will say that it works very well. All of the advise above is spot on with the exception of what material to secure the "puck" in place with. Silicone/RTV is designed to be flexible. It will absorb some of the signal that you are trying to shoot thru the hull. Epoxy will hold very solidly, but if you ever need to remove it, it aint gonna happen. I would recommend using polysufite caulk when attaching the puck to inside of the hull. apply nice (1/2") glob to bottom of transducer covering entire puck, making sure there are no bubbles, and press firmly into place. caulk will squeeze out the sides. Let sit for 24 hrs. before use. The caulk will remain somewhat pliable in case you ever need to remove it, but does not exhibit the flexibility of silicone based products. Obviously some have used RTV with success, so it is certainly doable, just not what I would recommend.


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## SailorByFate (Feb 6, 2007)

I have an in-hull transducer that I installed myself. The old transducer could not be removed without a haul out, so in-hull was the obvious choice. I was quite surprised to find that it can reliably give us a depth reading to 500 feet here in Puget Sound. Most of the time we get a solid reading to 600 feet.

Ours is a 1972 (I think) Cascade hull, non-cored of course. Fiberglass compositions vary, so I don't know if you will get the same results.


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## wchevron (Oct 19, 2007)

how do you know if your hull is cored or not. should you call the manufacturer?


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## TSOJOURNER (Dec 16, 1999)

If you need a depth sounder for just the season, go with the Prirana Max Fish Finder. I epoxy the puck to the inside of the hull and works great. All for about $60. When you haul, put in the system you want. I even spliced the tranducer cable to get it to my helm. Easy to do. It's a 2 wire signal cable that I soldered. It reads to 600'. When I am heeled over I do get some false readings on fish hits about 10' off the bottom at depths over 100'. I ignore these. Couldn't be happier for the price.


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## sailingdog (Mar 19, 2006)

The only problem is if the boat has a cored hull or a void in the layup. Either will stop a transducer dead.


Maddog046 said:


> If you need a depth sounder for just the season, go with the Prirana Max Fish Finder. I epoxy the puck to the inside of the hull and works great. All for about $60. When you haul, put in the system you want. I even spliced the tranducer cable to get it to my helm. Easy to do. It's a 2 wire signal cable that I soldered. It reads to 600'. When I am heeled over I do get some false readings on fish hits about 10' off the bottom at depths over 100'. I ignore these. Couldn't be happier for the price.


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## TrueBlue (Oct 11, 2004)

wchevron said:


> how do you know if your hull is cored or not. should you call the manufacturer?
> __________________
> wchevron
> 
> ...


I believe the '78 Catalina 30s were built with solid fiberglass hulls below the waterline - at least according to a friend who has one. But, check for certain with either the mfgr, or the C30 owner's association.


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## artbyjody (Jan 4, 2008)

And for more information Don Casey's How TO


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## sailingfool (Apr 17, 2000)

wchevron said:


> how do you know if your hull is cored or not. should you call the manufacturer?


The Catalina should be all solid glass.

You can identify core areas, in either a hull or deck, by the change in laminate thickness where the core is present, the laminate gets thicker, producing a sharp ridge at the transistion point. If you look around the underside of any cored deck (which would inlcude about 99 out of 100 decks), you will see the core ridge, usually several inches in from the toerail. Hopefully far enough in soy the stanchions bolts go only through the non-core laminate.


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## artbyjody (Jan 4, 2008)

Actually, it may be cored - my 1980 C-27 has a plywood cored bottom that tapers off at the waterline to the deck as solid GRP... I installed my own ducers so pretty positive on that one...


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## roline (Apr 7, 2000)

I've installed a ST30 in my Santana525 and a ST60 in the Cal 9.2. Both are epoxied to the inside of the hull and read to the max depth of the lake. While sailing on a Cal 2-30 in the SF Bay, it also had an older flasher style depth system with the puck glued to the inside of the hull. You can use water, grease, etc to couple the transducer to the inside of the hull to verify the sensitivity/ reliability of the system prior to committing to gluing it in place.


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## scottyt (Jul 19, 2008)

i did a replacement on an older system on an IP and just used 4200, works fine

my boat has a fish finder and i used gel coat paste, and waxed the transducer first in case i ever need to get it loose


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