transducer loosing deep over 12 Knots

C-Wolfe

I have a newish to me TC255 with a very new to me Raymarine system. I had or install Garmin on all my previous boat, I have nothing against Raymarine but I am not very familiar with it and I’m trying to adapt to my new system. One problem I have, and probably have nothing to do with brand, is that I get good deep reading at slow speed but always loose it as I pass the 10-12 knots mark. My first thought is it might have something to do with the angle but that seems to my untrained eye to be about right. my second thought is location, but I’m not familiar enough with my new boat to know where to start. I have 2 transducer and they both have the same issue and also are both set on a very similar location.

Flashyfish · Posted: Fri Jul 12, 2024 10:15 am Post subject:

My experience with externally mounted transducers is that they lose bottom over a certain speed. Only a transducer mounted inside the hull that shoots through the hull will keep bottom at higher speeds.
Rough water, turbulence, prop wash, air bubbles all affect the transducer mounted on the transom.

ssobol · Posted: Fri Jul 12, 2024 10:41 am Post subject:

thataway · Posted: Fri Jul 12, 2024 1:07 pm Post subject:

The Raymarine is not as intuitive as the Garmin. I had RM on my last 25 and put it on my Caracal Cat more recently. If it has the latest MFD, it is a very good system. Also the techs are more responsive--or they were..RM was sold a few years ago.

I agree with the two posters above, but it is difficult to see the transducer because of the outboard bracket on the Tom Cat 225.

The round transducer on Starboard looks to be too deep, and the longer, more oblong transducer also looks a bit too deep-but is closer. You might do better with the transducers closer to the center.

The good news is that both of the transducers seem to be screwed into HDPE (Starboard) type of blocks, which allows movement of the transducers without putting more holes in the hulls--that is also the bad news, since they cannot be moved without putting in new blocks.

On my TC 255 I put the Starboard Block in the center exactly flush with the bottom. Where you have the transducers there is an issue because of the "U" of the hulls and the depth of the bracket)--making the Starboard one at least to be difficult to raise any further. Where the hull is deeper in the center, this is resolved. Also in the center of the hulls there will be much less turbulence from the chines of the hulls.

If you can't raise the transducers slightly and resolve the issue, then put new HDPE blocks in the center, and place the transducer in the center, just even or a couple of MM above the bottom of the hull. My best guess is that you will have to move them to the center.

C-Wolfe · Posted: Fri Jul 12, 2024 1:37 pm Post subject:

Bob, if I understand well, you are recommending that I move the transducer in centerline of the pontoon that will put it also in line with the outboard?

for reference, I have a CPT-100 (the long cigar shape on port side) and a Arimar TM260 on starboard side. wondering is one will be better for higher speed use?
I added a few picture of my set up in my photo album

thataway · Posted: Fri Jul 12, 2024 4:07 pm Post subject:

Yes, I do suggest in the center. The increased turbulence to the outboard prop is minimal. You will get less turbulence around the transducer than nearer the inner chine.

The TM 260:

mstrpo · Posted: Sun Jul 14, 2024 12:38 pm Post subject:

I have 2 transducers on my boat that I installed last summer. One is on the starboard hull just where yours is in the pics. I had to do a little adjusting to enable always-reading functionality. The other shoots thru the hull with a dedicated gauge on the dash. This transducer is epoxied inside the starboard hull at the forward end of the removable inset in the cockpit. If you pull that inset out, you can reach down into the bilge area and epoxy the transducer on the inside bottom of the hull near the outside vertical part of the hull (near the corner). You can find a good spot by putting the transducer in a plastic bag with enough water inside to cover the transducer and then laying/taping the bag to the inner hull. Then connect the transducer to the gauge and verify proper depth reading. Hard to describe so will try to post some pics when I get a chance.

Captain Starbucks · Posted: Mon Jul 15, 2024 10:04 am Post subject:

I've been struggling with this as well. I've moved my transducer a bit deeper, but after more consideration, I think it was a mistake to mount the transducer inboard of the drain plug. I believe mounting it outboard of the drain plug would have been a better bet by getting less turbulent water. The water between the sponsons is very turbulent.

C-Wolfe · Posted: Mon Jul 15, 2024 1:50 pm Post subject:

Captain Starbucks · Posted: Mon Jul 15, 2024 3:17 pm Post subject:

I assumed it was factory but have no idea now that you mention it.