Transducer placement by trim tabs

[djnward]

Howdy C Brats: I'm currently putting trim tabs and a new fish finder on my 22. Humminbird sticks by it's policy that the transducer must be 15 inches away from props and should be as far as possible from trim tabs. This policy covers Humminbird's butt but it doesn't help me much. I figure I've got 18 inches from the centerline of the (single) prop to the edge of the trim tab (Bennett 120). I notice that DaNag, Tyboo, Jenny B and Alma's Only all have the transducer quite close to the trim tab. Have you or anyone else had any problem with turbulence in that location???
Dick

[TyBoo]

Nope - I have not had any trouble since I set it down deeper into the water. At the recommended 1/16" or whatever it is lower than the hull I would lose the bottom at speeds above 12 knots or so. I set it to a little better than 1/4" below the hull and it rarely loses the depth now. I don't think the need to lower it was caused by the tabs, but am not sure. The position of the tabs when running doesn't seem to have any effect on the transducer.

If you take the time to install a plastic mounting board on the transom and then screw the transducer bracket to it you will be able to experiment without adding extra holes to the boat. If I was mounting another one, it would be screwed on so that the highest point in the range of vertical adjustment was even with the hull bottom so that all the available adjustment was downward. I think they suggest you center the mounting screws in the slots with the transducer positioned at the recommended spot.

Interesting note - I also have a Raymarine depth sounder with a thru-hull transducer and I always have both it and the dual-freq Garmin on at the same time. They do not interfere with each other and are always within a foot of reading the same.

Oh, and you sure picked the right tabs! I had those on my CD22 and it was like they were designed for the hull. You will likely never have them fully down when running, but it is nice to know that the extra is there if needed. The Lencos on my CD25 are all the way down on one side or the other almost all the time, and they still do not quite do the job.

[Sneaks]

Damn, I hate agreeing with Dodge owners but Mike's spot on. I learned all about filling unnecessary holes because I didn't leave enough downward adjusting room. Nevertheless I've not had trim tab turbulence problems with the transducer and it's just under 3" inboard of the trim tab.

Don

[djnward]

Great! Thank you both! Heck, I get a faster response on CBrats that I get at the companies 800 number!
Nothing like other's experience to give one piece of mind. I'm suprised that signals from the two transducers on Tyboo don't interfere unless they are on different frequencies. Smooth sailing...
Dick

[SEA3PO]

I mounted my thru-hull transducer in the center at the back....in the depression by the drain plug... and it works ROTTEN !!! after I drilled the hole I noticed the keel ends a bit forward of that and the water in that area must be terribly turbulent.... so I made a fairing block and lowered it down 3'... helped some but I still loose the signal at any planing speed.

Joel
SEA3PO

[Byrdman]

Joel: Hey Brother!! Stick to picking out shirts that are real bright and have a bunch of big flowers on them man...

I guess deeper is better on our flat bottom boats.

TyBoo/Mike: Where/how did you mount your thru hull? I guess for the transducers hanging down a bit, the trailer is set up as to not let the aft section/stern of the boat come up onto the bunks on the trailer...??

[TyBoo]