Shoot Thru Hull Transducer

[rocinante33]

Ericson 27 is a solid fiberglass hull. No core.

[Gust14882]

I installed a standard transom-mount transducer as a shoot-thru by epoxying it to the center of the hull, just forward of the keel. It works great and was much cheaper than the "made as shoot-thru" units Aft there is too much turbulance and to either side of the keel creates dead spots when the boat heels. If you are finding gelcoat on the inner surface, it's probably still part of the liner. The inner surface of the hull is usually a bit rough and will often show texture from the glass fibers beneath the resin.

[Nicklaus]

Thanks for everyone's help and advice.

I'll be back out there Saturday with my sandpaper, epoxy, and ziploc bag.

Will keep you posted...

[tspooner]

[QUOTE=RobGallagher;862467]I just picked up a Lowrance 5 chartplotter/fishfinder at a boat show.

I want to install mine forward of the keel but the factory rep at the boat show said to put it aft as there was too much turbulence forward of the keel. It this accurate?

RG - I think I got the same chartplotter/fishfinder at a boatshow. Mine is an Elite-5 by Lowrance but the rep told me to ensure it was mounted forward of the keel where there was LESS turbulence. He also said the keel would impede the sonars forward beam if mounted aft of the keel. The transducer I have is external however I don't see that making much difference.

[mitiempo]

Forward, ahead of the keel in a sailboat, aft on a powerboat.

[FlyNavy]

I'll also recommend the forward position. You want to know what the depth is before you hit bottom, not after.
I installed my shoot through hull transducer under the V birth on my San Juan 7.7. Bought a section of PVC clean out pipe with a sufficient I.D. to hold the transducer puck and not much more...3 1/2 inches or maybe 4 inches I believe. Did the water baggie test as a transducer needs a uniform surface to shoot through in order not to send erroneous signals... no cored hulls, no bubbles. Once I found the sweet spot, I siliconed the clean out to the hull, let it dry…very important, filled it with water, did a leak test, dried it out, laid the transducer in, filled the clean out with mineral oil, (doesn't freeze, doesn't bubble, doesn't go rancid) and screwed the clean out cap on leaving a small notch for the transducer wire. Put a dab of silicone on the notch.

[travlineasy]

Flynavy,

Putting the transducer in front of the keel doesn't provide you sufficient time to react to a grounding. By the time you hear the alarm sound you will already be hard aground. Now, depending upon the boat, there could be more turbulence up front than aft. Much of this will depend upon the hull design and weather conditions. In rough seas, there's a lot of bubbles created as the bow crashes into the waves, many of which are dissipated along the sides before reaching the stern. Consequently, it's important to test the transducer sites while underway, preferably in rough sea conditions--times when you need accurate depth information most.

Good Luck,

Gary

[FlyNavy]

So Gary, my comment about knowing what is ahead of me was somewhat tongue in cheek as I'm sure that if you aren't aware of your depth until you run aground it really won't help but.... how is having it behind your keel going to help at all?
Turbulence can certainly be a problem and giving it a test drive in different locations should minimize that.

[travlineasy]

The big difference in having the transducer aft V/S forward is:

1. Less distance to route the wire to the display, which is usually in the cockpit.

2. Most turbulence is produced in the forward section of the boat, thereby providing some distance for the bubbles to dissipate before making it to the transducer location.

3. The hull is usually a bit flatter near the stern, thereby less offset of the signal cone and a more accurate depth reading.

I'm sure there are other reasons, but I just can't think of any at this time. As for the position relative to running aground, it really doesn't make any difference. If you're skimming along at 5 to 7 knots, not paying a bit of attention to your location, and encounter a sharp channel edge, you're more than likely going to run aground, regardless of where the transducer is positioned.

All the best,

Gary

[kwaltersmi]

I installed my shoot-thru transducer under the v-berth, in front of my fin keel. It's offset to one side, so I needed the manufacturer provided base plate to be able to mount it level. The display unit (Uniden QT206) also has sensitivity and depth adjustments to account for the distance between the transducer at the bottom of the hull and the surface of the water.

The base provided with my transducer provides a cavity sealed with an o-ring screw-on lid. I filled the base with mineral oil, per the manufacturer instructions. I've had no problems in the 2 years since I've installed it.