thru hull vs. transom mount transducer (depthfinder) - The Hull Truth

familyof5forhim · 11-01-2006, 10:12 PM

I just bought a 1991 22' Grady White and I'm putting a new 225 yamaha 4 stroke on a motor bracket. The question I have is: When I put my depth/fishfinder in, how should I mount the transducer? Should I mount it on the stern or epoxy it in the bilge and have it shoot through the hull (no hole in bilge)? Will there be too much turbulence if I mount it at the stern and give false readings?I've heard good and bad for both.

Thanks in advance,

Joey

prockvoan · 11-01-2006, 10:55 PM

Mounting it on the transom,as you run,you will pick up air pockets,giving you false readings in ruff seas.Mount it inside the boat and shooting thru it,it will do just about the same think.Chop sea = air= false readings when under way.For a tranducer to work right,it needs to be in contact with the water or shooting thru the hull which stays in contact all the time with the water.That is why a good thru hull that sticks out pass the bottom of a boat reads the best most of the time.Problems with those is if you hit something,you can break it.If you do go that way,buy a good bronze one,not one of those plastic ones.
Now in your case,try to mount it inside the bilge first using some silicone to hold it in place.If you have a hollow core boat,it will not work that good at all by mounting it inside the bilge and must be mounted on the transom.If you go that way,read the instructions that come with the ducer.

jawz · 11-01-2006, 11:14 PM

personally,i like the transom mount 'ducers...if it's installed correctly,they will read perfectly even at full speed...i've installed countless numbers of these style 'ducers and i've yet to have a problem....
not to change the subject...but....
with those older gradys,it's not allways the best approach to repower with a 4 stroke-due to weight concerns...on a bracket the problem is much more compounded,due to the fact the grady drive bracket has a realitivly small "tub" therefore,it provides little or not flotation...end result can be the boat sits way low in the water-as in the scuppers will be below the water line...not a good thing,considering,abyc codes state "any thru hull fitting at or below the water line must have a positive shut off valve"...there are no shut off valves on the scupper hoses....
just something for you to bear in mind......

familyof5forhim · 11-01-2006, 11:50 PM

Thanks for the replies!

Jawz,

I have been around and around about the weight thing with the 4 strokes. Will 90 lbs. make that much difference? I looked at the 200 hpdi 2 stroke as well but the motor dealer said a 4 stroke shouldn't be a problem at all but did recommend the scuppers with the ping pong ball inside. Still debating on what motor.

jawz · 11-02-2006, 12:06 AM

Quote:

familyof5forhim - 11/1/2006 10:50 PM

Thanks for the replies!

Jawz,

I have been around and around about the weight thing with the 4 strokes. Will 90 lbs. make that much difference? I looked at the 200 hpdi 2 stroke as well but the motor dealer said a 4 stroke shouldn't be a problem at all but did recommend the scuppers with the ping pong ball inside. Still debating on what motor.

contact grady white,you will get the same advice...they don't reccomend 4 strokes on the older models...

dnunez · 11-02-2006, 12:15 AM

just sold my 25 sailfish cause i couldn't find a good pair of used 200 hpdi. from lee at gw (lots of good advice) the older gw can't hold up the weight and boat won't float right. but that was my 25 sailfish, call up gw in nc and ask for lee or neil.

Hawkeye · 11-02-2006, 09:26 AM

A transom mounted transducer installed right should read just as good or better then a thru hull. A shoot thru hull is not imune to air bubbles either. Most problems with transom mounted ducers are they arent in the right place or they are set too shallow. I have set many transome ducers up and all have worked clear up to 35 mph and very little interference up to 45 mph. Never had a bot to run over 45 so I dont know about any faster.