Transom-mounted Transducer ?

[GoldenDawn]

I am planning to install a transom-mounted transducer on my Kadey Krogen 42 and would welcome comments on previous experiences with such a set-up, especially suggestions on where to mount and issues with weed, etc collecting on it.

The reason for this configuration is to add a Humminbird side-scan sonar transducer, which is not offered as a thru-hull. I already have the Humminbird side-scan system on my skiff and find it really useful. With a transom-mounted transducer on the KK, I can just move the deck unit back and forth.

 

[caltexflanc]

I'd consult the manufacturer for mounting requirements. The issue with transom mounts is the propellor is in front of them, thus harder to get "clean" water. They tend to be much more popular on outboard and sterndrive type boats. I'd guess Humminbird will want you to mount well off to one side, and not in the downstream path of any stabilizer fins or existing transducer protuberances.

 

[tpbrady]

John,

I mounted a Lowrance side scan on the transom of a 38 foot trawler and didn't see any issues due to the prop. I did mount it on port side as the prop wash would offset slightly to starboard although I don't think that would really matter that much. I didn't notice any problems on the screen looking port or starboard while underway. I flipped on the macerator pump (outside the 3 mile limit) and could even see the output on the display as it passed the transducer.

Tom

 

[GoldenDawn]

Tom

Exactly the type of advice I was looking for.

And to date you haven't had any hassles with weed collecting?

 

[tpbrady]

Never had an issue with weed collecting. There really wasn't any place for weeds to get hung up. I had it mounted far enough outboard that I could reach it from the swim step. That was useful for cleaning off the moss and other things that liked to grow on it when we weren't underway.

Tom

 

[Jetstream]

Tom I had a Lowrance Structure Scan transducer transom mounted on my last runabout. From memory Lowrance suggested mounting it on the starboard side on a single outboard boats transom to keep it out of the prop wash but it would depend on the direction of prop rotation. As others have said mount it where you get a clean undisturbed water flow for best results.
Also something to look at might be the Stern Saver type of device that glues onto your transom so you don't have to drill holes directly into it. I did pick up a little weed on the transducer sometimes but it normally fell off once we stopped or gave it a little reverse.

HomePage | THE STERN SAVER

Cheers

Brett

 

[tpbrady]

Brett,

On a slow boat like my trawler or a KK42, it probably doesn't matter. I didn't notice any degradation on the side scan transducer to the starboard while running at 4-5 knots. The side scan coverage was from the surface down to a 45 degree angle. The turbulence caused by the prop could only affect a small area of the side coverage to the starboard side as the prop was about 36 inches below the transom. The downscan transducer likewise only had a small area that could be affected. In practice I didn't see any indications that the prop wash affected the sonar operation. At higher speeds prop wash could be a factor due to the air bubbles created by a rapidly spinning prop. I haven't looked at prop wash from a trawler, but I suspect a large prop turning at 400 rpm doesn't create as many small bubbles as a smaller outboard prop turning at 2000 rpm.

Tom

 

[Jetstream]

I think your right Tom and the thru hub exhaust on most outboards could cause a problem that wouldn't exist with a shaft drive vessel. I'd like to install the new Simrad 3D Structure scan when we get our new boat but at this stage there is no through hull for it so I might be looking at the same problem,

Brett

 

[Larry M]

On the several transom mounted transducers we've mounted, I've found that there is a sweet spot that works under most conditions and at any speed. I'd temporarily mount the transducer on a piece of flat stock or a suction cup and play around with the positioning till you find it. Your swim platform may make that a little more difficult but you only have to drill holes once.

 

[Nomad Willy]

The only transducer we had on our Albin 25 was on the transom. I think it was a Lawrence and it worked fine. It was installed by a PO and I was always amazed how well it worked through the turbulence at the transom above the bottom line.

 

[Mako]

Wow Brett, I thought I was looking at a picture of my own 20' CC. Exact same unit and mounting location. Works perfectly. The transducer needs to extend below the hull about 1/2+ inch, but I have never had a problem with snagging weeds or debris. The only issue is that when I run up on the beach I need to be port side to the beach otherwise the transducer bounces up and down in the sand.

GoldenDawn, you bring up a great idea. I really hate the idea of drilling a hole in the bottom of my steel hull 5 feet down for a transducer. Would rather attach it to a small welded bracket under the stern and run the cable up to the waterline boot stripe where it can pass through a watertight seal.

This is much better than risking a leak in the hull. Damaging a $100 - $400 transducer is still cheaper than one dry dock to repair a leak in the hull.

Thank you for the great idea!

 

[GoldenDawn]

I appreciate the comments/suggestions. As Larry suggested, I can play around with a temporary mount rigged from the swim grid, then install it permanently during my haul-out. I like the idea of adding a mounting block - I wonder if just bedding a block with 5200 would suffice?

John H
Golden Dawn KK 42-83

 

[Mako]

What type of waterproof grommet do you propose for sealing the wire as it passes into the hull? I would not want to just rely on bedding compound/silicon, especially down at the waterline.

 

[GoldenDawn]

I will run the transducer cable to above the waterline, just above the swim grid. Not 100% sure of the fitting I will use on this.

 

[FlyWright]

Good advice here. Using a transom board to mount the transducer saves drilling into the transom. 5200 should work fine to attach the board.

I had a similar setup on my SeaRay runabout. I bought a small clamshell cover to protect the cable hole. Filling the hole with something like Boatlife or SikaFlex would work well. I'd even consider butyl tape as a plug in the cable hose.

Before I passed any cables through the new hole, I'd seal the new edges with a coating of 5200 to keep the transom water tight.

 

[koliver]

Tom:

I did exactly what you are contemplating, but for a regular fishfinder, so had a sounder head that went back and forth between the Flybridge and the dinghy. It worked as long as I had that dinghy, but when I sold it with the sounder, I would have replaced everything with a better one, but couldn't easily get a long enough cable in the better brand unit, so I put the transom mount unit in the bilge, alongside my shoot thru transducer for the wheelhouse sounder. I epoxied a piece of 3" or 4" (can't go look just now) ABS cut to the angle of the hull, mounted the transom 'Ducer inside the pipe, added some light weight oil, and have had a top performing Flybridge sounder ever since. In the dinghy, I epoxied the transom mount Ducer directly to the inside of the hull, at the right angle, and again, top performing sounder in the second location. The dinghy was easier, as I could locate the transducer in the V at the bottom of the hull. Not possible in the engine room of the big boat, so I mounted it about 2' off centre. If you can get to the flat bottom of your hull just forward of the place on your transom where your outside mount would have been, you can mount it without fear of seeing the keel or of fouling, and without screw holes below the waterline.