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Old 02-10-2018, 03:41 PM   #1
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Through hull transducer

I am hoping to put in a through hull transducer in a sailboat.Is that a good/bad idea? I have a 7ft keel so if I just deduct 7 from the depth will that be ok, or is there a better way. I dont want to pull the boat out. Thanks for any input.

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Old 02-10-2018, 03:59 PM   #2
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The depth finder will have an offset for the depth of the hull, once you program the offset it will read depth to the bottom of your keel (more or less).

I can't imagine putting in a thru hull while the boat is in the water... There are "shoot thru the hull" transducers available. Do more research!

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Old 02-10-2018, 04:52 PM   #3
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Look into the Airmar P79.
It mounts in the hull and the transducer sits in a liquid. I think it was antifreeze.
I had one in a few boats that I did not want a through hull and had good success with the P79.
It was good for depth up to about 200'.
They are fairly inexpensiveness as far a transducers go.

To get it to read the correct depth you will need to go into the settings of you MFD and change the draft of the boat to the depth below water line the transducer is mounted.
If you want to spend some money look at an aimar M260. You will be able to watch the fish on the bottom as you are crossing oceans.
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Old 02-10-2018, 06:03 PM   #4
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Iíve got a new P79, never installed for sale. PM me if interested
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Old 02-10-2018, 06:58 PM   #5
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Keep in mind that the steeper the angle of the hull where the transducer is mounted, the thicker the fiberglass it has to look through, and the greater your chances are of getting an unsatisfactory picture through all that.
Most fiberglass boats have generous overlaps of plies at the centerline, so mounting a foot or more off the centerline could advantageous too.
Personally, I wouldn’t buy a shoot thru transducer, but I’m an avid fisherman and insist on the best bottom information I can get from my machine, at the cost of having to jump in the water to clean it frequently.
You can lead a horse to water,
But you can't make him ski...
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Old 02-10-2018, 07:09 PM   #6
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Joe, I successfully installed a transom mount transducer as a "shoot thru the hull" in my boat,f/g hull around 3/4-1" thick,no "pocket" design for it. Installed in a piece of plumbers drainage pipe filled with silicone, got it vertical using a small builders level. Takes a little longer initially finding the bottom, fine after that, same readings as the thru hull one(I`ve 2 transducers, one for each sounder).
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Old 02-10-2018, 07:15 PM   #7
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Test possible shoot through the hull locations by putting the ducer on top of a baggie filked with water.

Putting a thru hull ducer in while the boat is in the water is done all the time, but by people who know how to do it and have experience doing it.
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Old 02-10-2018, 07:17 PM   #8
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You can and should test the location for the Airmar P79.
Look up the installation procedures and it should give you the directions.
2008 MS 34 HT Trawler
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Old 02-10-2018, 08:07 PM   #9
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I get good bottom readings beyond 600 ft shooting through the hull, two separate sounders, one with a t'ducer designed for shooting thru, the other a transom mount, inside a length of 4" ABS sewer pipe cut to the angle of the hull and epoxied in place. Both are filled with light oil, haven't needed a top up in over 10 years.
I also have a transom mount t'ducer epoxied to the inside bottom of the RIB hull, works as well.

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