Thru Hull Transducer on a CD-22?

B

Bill3558

New member
Can anyone give me some advise whether or not a thru hull transducer works ok on a C-Dory 22? I would mount it by the bilge pump.

I plan to keep the boat in the water and it seems to me it would be a lot less hassle to maintain, not to mention installing.

I plan to use it with a Garmin 498 chart plotter.

Thanks for any info.....

Bill
 
Bill-

The 22 has a balsa cored hull and will not allow shoot through transducers, at least without some modification.

The light desity balsa wood does not allow the ultra-high frequency sound waves to pass through it unobstructed. It's like having air bubbles under your transducer.

However, if you do like the through hull idea a lot, you can cut open an area in the inner layer of glass*, remove the balsa core beneath, fill the void with epoxy or polyester filler (like MarineTex), and then mount the transducer above the new solid hull section. (It's usually epoxied down for solid contact.)

The very dense fiberglass resin composition material is transparent to the sound waves. And there'smuch less chance of having air bubbles that disrupt your scanning than if the transducer is at the aft corner of the hull.

I believe the new TomCat 255 has a section of solid fiberglass in the rear of one of the twin hulls intended for this use.

* A hole saw would do a nice job, just don't drill all the way through the outer fiberglass skin with the pilot drill!

Joe.
 
On my 1990 22 Angler I had a thru hull transducer hooked to a 1650 Furuno...WORKED GREAT!!...no turbulance...the only way to go.....mounted in the indent where the bilge pump sets.....Do it!!

Dick
255 TomCat
Orinda
 
A more conservative approach would say be very cautious about punching holes through a boat's hull. If there is a clear and easy alternative to a thru-hull, prudence would suggest to use the alternative.

We like to ask ourselves "What is the risk-reward (ratio) of any action we take?" In this case, the risk of a hole through the hull is, to the extreme, a sinking (particularly if the boat is left in the water for long periods of time, unattended). Now that risk is slight, but it still exists. OK - the reward? Slightly better definition on the sensor. For us, that's a bingo -- not worth the risk.

We have been using, on our CD-22, an externally mounted sensor on our depth gauge for years. It is mounted on the transom, between our twins. We have had almost no incidence of turbulence interupting our readings -- at higher speeds none. At low speed, with little turbulence in the wake, none. The only time we have had 'problem' with accuracy in reading depth is when we have 'plowed' through mud, one engine up, and inches under the hull -- and, I'm sure, a thru hull transducer would have had problems in those circumstances as well.

So we would suggest, from our conservative mindset toward cruising, that a thru hull is unnecessary and for us, at least, not prudent.

If you decide on a thru hull, we suggest you get a wooden cone, tape it next to the thru-hull, so if it ever 'pops out' you can immediately plug the hole and stop the water flow.
 
If you want no holes at all, a very light sand of the transom footprint of your transducer, and JB Weld in place. Mine has been in place four years without need to think about it.
 
Pluto, The nice thing about a transom mount is that you can easily wipe the slime, etc. off it. Much easier than trying to clean the hull outside where you think the transducer is mounted inside.

Special bottom paint is used for transducers, if you use paint on one. You in hull would have to shoot thru whatever outside hull paint you used.

My experience with transom mounts is that you simply rub the stuff that accumulates off them occasionally.

John
 
Bill-

Sorry, I was not clear, apparently, on suggesting only the removal of the innermost layer of fiberglass and the balsa core, not the outer skin itself.

Replacing the balsa and inner skin with a solid filler, like Marine-Tex, would, I believe, leave the hull unweakened and as strong as before.

Then the shoot-through transducer is epoxied to the top of this new section, and nothing protrudes through the hull like in the true through hull transducers which do, in fact, require boring a hull straight through the hull !

Joe.
 
Squidslayer seems to be saying that to mount in the "bilge pump depression" no additional hull work is necessary. That area may not have any balsa in it, hence the depression?
 
Caution!

Anything protruding thru the bottom of the hull in front of the propeller can cause cavitation on the prop!

The bottom of the hull should be smooth from the end of the keel to the transom and within 18 inches either side of the centerline.

Anything that disturbs the water flow to the prop can slow the boat, increase fuel consumption and affect handling at high speeds.
 
Thanks for all the info. I certainly dont intend to put a hole in the hull! I was thinking that the depression where the pump is might be solid glass and work well for a thru hull. I will probably order 2 transducers and see if the thru hull works first. The service manager at wefings marine seems to think it will work but has never tried it. Might shoot an email to the factory as well and see what is in that part of the hull.

Will post what I find out.

Regards and thanks.
 
According to the factory there is an air gap between the bilge pump indentation and the actual hull.

So transom mount it is.

Hopefully the plastic type transducer will be easy to keep clean.
 
We have tested a large transducer for a 22' Angler and the test proved it does work. We did make sure there was only fiberglass under it and no balsa.
There is no balsa by the bilge pump near the transom. However if you put it close to the bilge you might get some interference when the bilge turns on.
 
FacDory Guy,

I hear you, but my boat is a late 2006 and has the molded in deck. I talked to your "technical support" guy today and what he says make sense. I dont have a hard transducer to hull option unless I cut thru the molded part by the bilge pump, and I am not doing that.

It may be something to consider in future models. To have a clear opening to the glass hull right at the transom for thru hull transducer mounting.
 
Good topic. I am shopping for a new Chartplotter/Sounder combo and have been thinking about mounting (epoxy) the transducer in the bilge pump indentation as well. What I think I read in the previous posts is that the indented area near the transom between the fuel tanks is solid glass on pre-2006 boats (mine is a 2000 22 cruiser). Is that correct? If so, then I could mount the transducer with epoxy in that area and have a reasonable expectation that it will work.
 
There's a few other possible complications to this (and I'm not advocating the shoot through hull transducers, just trying to answer a question):

If you want a combination transducer which is also equipped with a temperature sensor and/or paddle wheel for the boat speed, it must be mounted on the transom corner instead.

Also, I would question whether an ultra-wide or side scanning fishfinder would work through the hull.

Joe.
 
It's really easy to tell what result you'll get locating a transducer in the aft bilge/sump area. Just clean the bottom of the sump, fill it with water (that's the really easy part, since it's usually full anyway), plop the transducer in place, and add a sand bag on top to keep it there. If the transducer is a transom mount, have it's front facing forward. What you see is pretty much what you'll get, although you might have to fiddle with the unit's settings to be sure. I use this mount for my back up depth finder.

If you're pleased with the results, leave the transducer in place, drain the water, and mark the location on the fiberglass. Then, rough sand the fiberglass, and mount the transducer using a bed of epoxy. Since standard epoxy doesnt' hold up well in water, I used Marine Tex, which does. Be sure to avoid air bubbles, and if you use regular epoxy resin, use slow cure so the air has a chance to escape before it cures. A temporary dike around the site, via plumbers putty or small pieces of plastic, will prevent the epoxy from flowing out to the sides while curing. Don't use silicone, or other caulks or sealants to mount the transducer, and don't fill in the entire sump - just around the transducer. And, don't plan on using bottom paint on this spot.

Good luck!
 
One way to test a thru-hull transducer (not through the hull) is to put the transducer in a baggie full of water and set that in place to test. This will give you the contact necessary with the hull (assuming no coring in that area). You can move the transducer in the baggie around to find the best location. Then if you don't want to epoxy it in place you can use silicone to mount the transducer puck, just be sure to work out any air bubbles. We've done this on several sailboats with success.

Best wishes,
Jim B.

On edit: oops! I didn't get to page 2 on this topic before I posted... sorry if it repeats much of Alma's Only's advice.
 
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