Thru Hull or Transom-Mount Transducers

[Abby Normal]

I'm looking at various chart/GPS/depth or depth/speed combo systems. Some come with transom-mount transducers or options for through-hulls or even pod-type transducers that sound through the hull which to me doesn't sound like it would be that accurate.Is there any particular problem with transom mount transducers on sailboats? I know through-hulls are generally specified to mount ahead of the keel for least water turbulence, and I would imagine close to centerline as possible due to heeling. Some transducers by different manufacturers do not recommend through hull for trailerable boats. My boat is a Mac 25 and is trailered maybe two to three times a year and otherwise stays in the water during the season.I'd like opinions on through hull and transom and pluses/minuses for either set up.

 

[Ross]

The biggest con with the transom mount is

vulerable to bumps and bangs. I made a skeg and mounted a transom mount transducer on Bietzpadlin. It is at the stern and some have questioned the placement but my feeling is that fifteen feet isn't going to make much difference.

 

[Rob Hessenius]

Transon Mounts

Abby- I think the biggest problem associated with a transom hung ducer is that your transom is raised above the waterline. You will also have to off-set to one or the other side. When heeled the ducer will be out of the water and be useless to you. I dont think your concerns should be about the fifteen feet aft location. Rob Hessenius

 

[Abby Normal]

Waterline

Actually, the waterline on my transom is submerged about 2 to 3 inches w/o pax(MacGregor 25). But of course, under sail, one side or the other will likely be out of the water. Other problem I've got is with an OB rudder needing clearance on either side of that.Curious about the skeg mount that Ross mentioned. Got a drawing or photo to share?

 

[Ross]

No drawings but simple enough. The skeg

is in my case a long wedge that is attached to the hull with the skinny end in front. The bottom surface is horizontal and the wedge is about three inches wide and about 18 inches long. The advise that came with the system was that it should be kept away from propeller turbulence. The position of the transducer is about a foot forward of the transom and entirely under water. Heeling has never been a problem but floating rafts of vegetation make it go crazy.

 

[BarryL]

puck type

Hello,I have never seen a transom mounted transducer on a sailboat.I bet there are some out there, but it just seems wrong tome to have the wires running either through the boat orup and over the side. I mounted a puck / pod type that shoots through the fiberglasshull. It was very easy to do and works great. You lose some range,but since I only care about how shallow the water is, not howdeep it is, I was willing to lose a little depth. With thetransducer inside the boat there are no worries about breakinga wire, hitting the transducer, or putting another hole in theboat. To be honest, for solid fiberglass hull boats I thought that ashoot through hull transducer was the only real choice.Barry

 

[Ross]

BarryL , You simply have to get creative

to make it work. Mounted it in '99 and have not had any problems.

 

[r.w.landau]

Abby, the thru the hull depth finders

are acurate. ( pucks in the hull with out holes thru the hull)You won't get fish finding but the depth is on the mark.Mount it forward of the keel. I watched my depth go from 30' to 2.5' in about 6 seconds one afternoon. I was only moving at about 1 knot, I knew it was coming, but that was a rough grounding.It was sand but we stopped real quick!.Depth finders should be mounted as far forward as possible.r.w.landau

 

[Bill Roosa]

Use the transom tranducer as a thru hull

As a member of the "cheap brothers society" I'll offer that you can make a well in the hull with a piece of PVC tubing and then fill it with water. Set the transducer into the water and provided that you have a solid hull it will shoot right through the hull with only a little attenuation.The only restriction on placement is that it can not be over the keel.

 

[Ross]

R.W. The angle of repose of sand will not

permit a twenty-five foot gradient in ten feet. (1knot in six seconds)

 

[r.w.landau]

Ross, I sail on a man made lake.

I am saying that I knew the bottom structure but I missed going around this point by 10'.This was farm land that was flooded. The depth at the area I was speaking of actually goes from 30' to 2.5" in a horizontal of about 10'. If you are getting technical, ask my wife when I said hang on , I missed it...as we stopped dead in the water.Ross you are right, most of our sand is a sand clay compositer.w.landau

 

[jimq26]

The archives have tons of information on this!

nm

 

[Ross]

WoW, I stand corrected! we have a place

where they dreged for a pier that goes from twenty to two or three feet almost vertically.

 

[r.w.landau]

Ross, My lake is not like the the mighty Susq.

or the Chesapeak with tides and major water flow. The area is almost flat and was historically a Moraine from the glaicers. That is why it is named Moraine State Park. The lake has many features like old road beds and railroad tracks with the old cable guide rails and even old structures.When fishing, you find alot of the old structure, but where else can you catch a 28" stripper or 54" muskie on an inland lake?It is a great place but it is just a little small! I would love to be on the Bay or near the Erie Islands.r.w.landau

 

[Ross]

R.W. Sounds like they flooded a river bed

I watched them do that in Connecticut in the middle 50's. Made a nice lake, ruined a nice wild river. Ya give a little and ya get a little. If you ever see a chance to come east, give me a heads up, I will make you welcome.

 

[Abby Normal]

No Fishing

I'm not concerned about fishing, only how shallow the water is. If the pucks are accurate enough without going through the hull, then that's all I care about.

 

[Ross]

R.W. I went to "Topozone" and

pulled moraine state park PA and Lake Arthur. The gradient lines are quite close together around the edges of the lake. It must get very thin quite suddenly around the edges.

 

[Abby Normal]

Read The Archives...

I went to the archives and read up more on the topic. Should have done that from the git-go. Since, according to some here on the general board, my Mac is constructed with a flimsy hull and inferior materials, an in-hull transducer should work just fine as long as I don't have a lot of air in the laminate. )I'm also going to make a stretch and assume that several layers of epoxy and ablative bottom paint won't affect the sensor terribly?

 

[jimq26]

It'll work fine !

Just make sure there are no air bubbles in the epoxy. That's why they recommend the slow cure - no air bubbles. The signal from the transducer puck to the lake bottom must be a straight shot with nothing containing air in between.

 

[Abby Normal]

Plastic Bag

Well the idea of using a water-filled and de-aired plastic bag to find the optimum location makes a lot of sense to me. Just move it around the hull till I find the best spot.This all makes me feel a lot better about not having to cut a hole in the boat or drill some mount holes at the transom.