Where to mount transducer on stepped hull?

[Cannondale]

Howdy y'all!

I've got a 2000 Javelin 17' F&S, which has a stepped hull. Trying to mount the rear transducer for a Hummingbird 598ci HD SI. But there is an issue...maybe. Or maybe I'm just too old to figure it out.

Hummingbird, in the unit's install instructions, states that the transducer is to be positioned 15" to the side of the prop. It also states that is to be mounted on the step of a stepped hull, which my boat has, not on the transom behind the step.

So, here's the issue, and let me illustrate first with these:




You're looking at the rear of the boat, a better view of the stepped transom, and a closeup of the transom with some measurements.

The step measures on average 6 7/8" deep (from transom to step) and averages 2 1/2" tall.

Now, in the pic with measurements, the red measure is the distance from centerline or prop---ends at a strake (?), the distance recommended to offset the transducer from the prop. The black 9" measure is the next distance from strake to strake, where I'd automatically put the transducer....but therein lies the problem.

The beginning of that above measured 9" section is where the step begins to angle back instead of parallel to the transom...makes a roughly 20 degree angle rearward. As seen above in the pic, the depth/setback of the step begins at 6 7/8" and tapers down to 3 3/8" at the end of the measure.

I can't put the transducer at an angle like that and have it function properly, can I? And where I'd put it is exactly where the bunk on the trailer hits the hull.

So, I'm stuck and open to suggestions as to where to mount the thing.

 

[rothfm]

Re: Where to mount transducer on stepped hull?

I have the same transducer...I can only add that I just installed a Humminbird 1 Model down from yours. Really like the unit. Was careful in my install, left the locking screw out of the mount until "dialed-in". I have a Deep V 20'. Followed all the recommendations, and have a clear mounting location. I made many test runs while adjusting multiple ways.

Its perfect under a couple MPH, but giving throttle produces erroneous soundings. I can read the bottom ok, and depth. But lots of "clutter" in the water column. I've tried everything.

I'm considering an In hull type for comparison. Seems these things should be able to produce a clear picture above 5 mph?

Good luck, Just thought I'd share

 

[dingbat]

Re: Where to mount transducer on stepped hull?

What is the best type of transducer mounting for a stepped hull?

Choose a thru-hull or in-hull transducer and mount it just forward of the leading step. The steps on the underside of the hull create a lot of aeration. For a transducer to work, it must be mounted just in front of the first step, before the source of aeration.

NOTE: A transom mount transducer should never be installed on a stepped hull. When mounted on the transom, the transducer receives all of the aerated water generated by the step(s). A transom mount will perform poorly above 8-10 kn (9 - 12 MPH) on a stepped hull.

Airmar FAQ - What is the best type of transducer mounting for a stepped hull?

I fought with a transom mount for almost a year before giving up and going with a shoot thru design. I first tried gluing the transducer to hull. No "noise" but an unacceptable loss of sensitivity. I then went with a tank design. The sensitivity was satisfactory in that configuration.

When I got the new boat I went with a thru hull right out of the blocks. Absolutely no comparison in performance. I will never go with a transom or shoot thru again. The thru hull is that good.