TomCat transducer location?

Captain Starbucks · Posted: Thu Mar 13, 2025 10:01 am Post subject: TomCat transducer location?

Hi all,

I've moved my 1,000 watt transducer 3 times trying to pick up the bottom on plane but I can't find the right spot. The 3 in 1 transducer isn't doing any better. It's basically the same spot on the other sponson.

Currently, the big transducer is 5 degrees down relative to the hull and about .5" below the hull running surface.

Just wanted to check with anyone to see if someone has found the perfect spot before I drill 5 more holes in my boat. I think the only logical place left is on the outside of the sponson. My thoughts are that the water is pretty turbulent in the middle of the sponsons so maybe the outside edge would be less bubbly.

ssobol · Posted: Thu Mar 13, 2025 10:18 am Post subject:

Might want to look into a Stern Saver.

https://sternsaver.com/

thataway · Posted: Thu Mar 13, 2025 12:07 pm Post subject:

Don't drill more holes in the boat! I like to make my own 'stern savers'. a long piece of Starboard (or similar). Then you can move to your content. one issue is that your props may be turning outward--on a cat it is preferable to turn inward, to give more stern lift. However since they are on a bracket--that should not make a difference. I have the Lowrance and Raymarine on my current cat, CD 25 and the Tom Cat which I had no problems holding the bottom with. Is there something. causing turbulence forward of that mounting area?

gulfcoast john · Posted: Thu Mar 13, 2025 9:23 pm Post subject:

Mine is placed like your original ducer and does well at displacement speeds. None of our 13 trailer boats in 40 years reliably read the bottom at planing speeds…but by then I’m looking at the charted depths on the MFD display. I always just considered it a fact of life. All my current e-chart chips have shown accurate depths for MLLW if I simply adjust for tides and wind.

I’m curious about why you would care about the bottom 600 ft under your boat…you are not worried about dropping your anchor on a trash bicycle down there. Why do you care? I’m not challenging your concerns, just curious about them.

Stay safe always,
John

C-Wolfe · Posted: Fri Mar 14, 2025 1:54 am Post subject:

I have similar issues with my TC255, but I have not spent much time trying to find the answer, I will certainly working on that this summer, I had much better bottom reading with my 22, completely different system but I’d like to think it is more about the hull design of the tomcat that create interference. I’ll post in here if I find something.

John, I’m not too familiar about your cruising ground but around here, and I’m guessing the PNW is similar, it can go to well over 600 ft to less the 20 in a very short time. Even though the chart plotter tend to be very accurate now a days, its still nice to have a good bottom reading as a second source on info while you go along at 20-30 knot. Some of the area around here have not been sounded since 1940, and we had a big earthquake that change the bottom quite a bit in some spot.

Captain Starbucks · Posted: Fri Mar 14, 2025 9:39 am Post subject:

Thanks for the replies everyone.

SoBelle, I appreciate the link to the SternSaver. The transducer mfr provides 5 lag essentially lag bolts that are 1/4" size. This ducer has a lot of drag. Not sure if the sternsaver would be the best choice.

Bob, I have considered swapping lower units to get the rotation direction you keep mentioning. Maybe next winter when I do the water pumps again. But as far as upstream obstructions, nothing on either hull.

Gulfcoast John, good question about the depth. I'm not concerned with depth so much but I'm looking for any little out of place rock that might hold fish. I fish mostly in the ocean and commonly run 10-50 miles between spots. It would be very nice to be able to see small changes in bottom composition or structure so I can stop and fish. With electric reels, it's nothing to stop up to around 1,200 feet of water and through down the lines just to see what's down there. If I could watch for any anomolies when I'm cruising at 20-30mph would be great. I'm not planning on covering those distances at 7 miles per hour just to watch the bottom.

I do have the very latest in chips that provide up to 1' bottom contours but it doesn't cover everything. And again, I'm looking for that odd boulder or pile of rocks or literally anything different than everything else.

ssobol · Posted: Fri Mar 14, 2025 11:23 am Post subject:

mstrpo · Posted: Fri Mar 14, 2025 12:22 pm Post subject:

I have 2 transducers on my tomcat. One is for a dedicated display I put in the dash. The sensor for this display shoots thru the starboard hull near the forward end of the access provided when you pull the inset cover on the side of the cockpit wall. The corner of the sponson that transitions from vertical to horizontal is solid (tested with sensor in bag of water) so you can epoxy the sensor to the bottom of the sponson. I've seen this sensor finds depth at all speeds.

The fishfinder sensor hangs over the horizontal part of the rear of the starboard hull closer to the corner than yours seem to be. This works well for lower speeds.

Captain Starbucks · Posted: Fri Mar 14, 2025 1:35 pm Post subject:

Edward J · Posted: Mon Mar 17, 2025 3:50 pm Post subject:

I'd sure like to see a photo to and can you share what transducer your using? Thanks Ed Jonson

Captain Starbucks · Posted: Mon Mar 17, 2025 4:25 pm Post subject:

I'm not sure what transducer he used in-hull, but I just ordered a 1,000 watt in-hull Airmar M135M. I'll hopefully get it installed this weekend and get you some images.

mstrpo · Posted: Tue Mar 18, 2025 11:29 am Post subject:

Captain Starbucks · Posted: Tue Mar 18, 2025 12:16 pm Post subject:

Thanks for the info mstrpo. The one I ordered is about 6" diameter so will have to go on the angled part of the hull instead of the small flat part where the vertical meets the horizontal (where is sounds like yours is). That part of our hulls is about 18 degrees, the max for the M135M I ordered is 22 degrees so should be fine. And don't worry about taking your panel off for photos. Once I had mine off it was pretty obvious what was the non-cored solid fiberglass portion of the hull. After a hot water blast and scrub with Simple Green then a 5% bleach solution, looks like new in there again!

Rob

john8lyons · Posted: Thu Mar 20, 2025 4:41 pm Post subject:

I've had adding a 1kw airmar or similar to my TC255 for a while to improve on the current thru-hull transducer that is installed near the back of the port sponson. I saw joechiro30 had done just that on the 2007 that he was selling recently, and he sent me photos of his set-up. It looks similar to your starboard location, but maybe up to the right a bit. Joe had his installed on a block of starboard / transom saver.

Here are links to a couple of Joe's photos:
https://drive.google.com/file/d/1klA62h7yUcRbb-uHdgEAx6W9XhGWgDcw/view?usp=sharing

https://drive.google.com/file/d/1ipW5c6ILWFsFEkfttR7MfYDwUvVR-LTD/view?usp=drive_link