Through-hull v. transom mount FF transducer

slowbuilder2005 · 03-27-2006, 03:06 PM

As you can see in my link below, I am building a boat... hoping to splash it this summer sometime. At some point, I'm going to have to decide on a through-hull or transom-mount fish finder transducer. Which is better and why? Doesn't the deadrise (the 'V') of the hull make a difference since it would aim the transducer off to the side? I'm afraid of just going for it ...is there much risk that I'd pick a bad spot that has bad waterflow or anything? The boat has a keel skeg and about 15" off to either side, a side strake. Otherwise, it's all pretty smooth. The deadrise at the stern is 12 degrees, and about 17 degrees amidships. The boat is epoxy fiberglassed plywood. Where would you put the transducer? Do you cut a hole and mount it flush? Or does it bond on the inside of the hull? I know that I can do a web search and read up on this stuff, but I'd like to hear some real-life experiences ...both positive and negative.

Thanks,
Brian

Reelentless · 03-27-2006, 05:12 PM

You can get high performance through hull, shoot through, or transom mount transducers. All have their pros and cons.

The through hull transducer gives you better performance at higher speeds (unless its installed wrong). You can flush mount it in a pocket on the very bottom. However, since your boat has the keel, that probably isn't an option. Another way to mount the through hull is off center. You can use a fairing block to clean up the water that flows around it. Its big and can affect the performance of boats less that 28' or so. I believe the transducer is shimmed so it is shooting plumb.

Another option is the shoot through. No holes and a little less performance than a good through hull (10% or so), but much better than a transom mount. The only caveat is that you cant have wood or foam (air) between the transducer and the water. It must be solid glass with no air bubbles. This is the route I went with. My boat is cored with balsa so I had to cut the inner fiberglass skin and chisel out the wood. It works great.

Transom mounts are the easiest. They make a high performance 1kw model that mounts on a bracket. The big drawback with putting it back there is that the water is usually turbulent when you get to about 15 knots. When the transducer shoots through the turbulent water, the image quality is reduced and you tend to lose bottom.

Go to the link below for a lot more info. Airmar makes almost all transducers. I emailed them about my application and they gave me their recommendation. Whatever you do, dont buy a $1000 Furuno fishfinder and hook it up to a $60 transom mount transducer. That would be equivalent to putting a Corvette engine in a Chevette. :smile:

http://www.airmartechnology.com/airm...in.asp?LinkID=

Metal Manipulator · 03-27-2006, 06:10 PM

I don't think a shoot through will work on a wood hull as there is air in the wood. Comparing a transom mount to a through hull the thru hull will beat it hands down in every detail. Get the dual frequency with speed and temp you won't be sorry. If you don't want any thing hanging down below the hull then you can put in a flush mount well, a lot more work but well worth it if you trailer alot.

Beer Waggin · 03-27-2006, 06:53 PM

I have a B260 w/ the high-performance fairing block and I've yet to see any performance issues with my boat after the install.

If you plan on trailering, and I do every weekend for fuel, you must make sure the boat buck hanging under your boat has clearance. I have a bunk trailer and have no issues.

slowbuilder2005 · 03-28-2006, 08:22 AM

I think I'll take Reelentless' advice and contact Airmar and describe to them my application. Nothing like having an expert who wants you to have a successful experience with their product to get to an answer quick.

I kind of hate to have junk on the transom and would like to put trim tabs on if I decide that I need them. A speed sender would be OK 'cuz it's small. I'm perfectly willing to bore large holes in the hull and back-fill with glass/epoxy. And I'm perfectly willing to try it first then someday switch to something else if it didn't go so well ...if it gets junk off the transom. And I'd really like to have reliable sounder info when at speed, on plane. I'm kind of tired of having to slow down, take a read or take a look, then speed back up again ...repeat. :smile:

Brian

Onokai · 03-28-2006, 09:22 AM

The deal with all transducers is the best -the bif brass thru hull-2nd best shoot thru hull-the worst -hang off transom. I have 2 of the hang off transom and am getting the shot thru hull for my furuno nav net system. The key to making the hang off transom's work ar speed is put the down in the water column. they trow up a roster tail but read at speed. Mark

Just got off the phone with Boston whaler-there is no single glass spot to put a shoot thru hull transducer on any whaler. They do have a putty box for a thru hull but I am unwilling to do that on a trailer boat. -Bummer

Nalu · 03-28-2006, 09:43 AM

I have the same Airmar B260 w/ high speed fairing that Beer Waggin has. Reads at speed and no performance issues. I also have a bunk style trailer.

Onokai · 03-28-2006, 12:25 PM

Hey Mike is that baby stuck down with 5200 caulk??. I'm starting to warm up to drilling that hole thru the hull for better transducer porformance. My furuno nav net black box puts out 1 k so I think I'd even be able to see tuna -something I have never seen on the screen before. I have a furuno tube fishfinder (backup) in the overhead electronis box as well.. I'd have to add a temp sensor for my old eyes. Mark

Nalu · 03-28-2006, 01:42 PM

Mark,

Yes, plenty of 5200. 5200 on the underside where it mates to the hull, 5200 inside the fairing, 5200 on the threads, 5200 inside the boat where the penetration is.

Woo-hoo 5200 everywhere!

I already had a through-hull for the original transducer, I just needed a new one. The old Si-Tex 106mkII works like a champ again!