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Author Topic:   mounting transducers and bait pump to transom
Eric posted 08-24-2001 09:27 PM ET (US)   Profile for Eric   Send Email to Eric  
I've got to mount two transducers (depth and speed/temp), as well as the pump for the baitwell. These will go on the transom of my Nauset. I cut a couple of pieces of 1 inch starboard with the intention of mounting them to the transom, then attaching the parts with 3/4 inch screws. The bracket for the depth transducer must be horizontal. Without the starboard, the screw holding the lower end closest to the bottom of the boat would be in the edge of the glass rather than into the wood. I suppose that the speed/temp transducer would work better with the part on an angle matching the deadrise of the hull. This also may apply to the bait pump as well, as it's the type that should pick up water when underway, without running the pump. Other factors to consider are which side to mount each of these items on. Considering prop rotation, is the water less disturbed from the prop on the starboard or port side of the motor? This might be a factor in depth finder performance. How deep/close to the motor should these go?

I really hate doing things over, so any tips would be greatly appreciated.
I'm sure that all the input from the other members of the forum is a big factor in the admiration my boat got last week (see "unveiling"). Thanks to all.

simonmeridew posted 08-25-2001 08:41 AM ET (US)     Profile for simonmeridew  Send Email to simonmeridew     
I think the most important thing when mounting the depth transducer is staying free of an air bubble/turbulance area which can come from the prop but also bubbles etc which follow aft from the chines and strakes on the hull. You should get down and look at the boat bottom from back and down far enough to sight where the chines and strakes come back to the transom. Stay away from this area as bubbles will come from the bow and work backwards along the bottom and mess up your reading if the transducer is in the way.
I don't think the speed/temperature transducer is as sensitive or critical of the bubbles though I might be wrong.
In any event, on my Montauk, I mounted the depth transducer 8 inches to the port of midline, and the speed/temp paddlewheel 3 inches from the midline, again on the port side.
The depth sensor works perfectly here, at any speed my boat will go.
BTW I thought of using a piece of starboard to mount my transducers, Cabela's sells a piece just the right size. But then I said, Keep It Simple Stupid, I just drilled and screwed directly to the transom. The transom is not perfectly flat, especially nearer to the bottom you go,(try it with a straightedge, so the star board would not be lying perfectly flat and there would be a gap of probably 1/4 inch somewhere. Besides I spend quite a bit of time looking /thinking about this before hand and figured if it didn't work out well and I got turbulance etc. I wouldn't be able to come up with an alternative location anyway. I picked what I thought was the best spot and drilled.
Mort posted 08-25-2001 05:06 PM ET (US)     Profile for Mort  Send Email to Mort     
Could you give some more details on where you mounted the transducer on the Montauk? Mine does not give me a good reading at higher speeds. You said it is 8" from the center line. Is that measured up from the very bottom of the hull or form a line drawn from the bottom of the hull to the top of the transom? I need to move mine and any info would help.
FISHNFF posted 08-25-2001 08:06 PM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
On my Montauk, the Kodiak bait pump is mounted on the starboard upward sloping part of the transom centerline of the inverted V. The S/T sensor is about 8' inboard of that. The transducer for my Lowrance X-70 is on the Port about 15" from centerline measured along the hull (the boat is currently moored so exact measurement not possible). With my Merc 75 2-stroke I got great readings at all speeds. Now with my Merc 90 4-stroke I get sometimes eratic readings and poor high speed readings. Coincidence, bad unit/transducer, different ignition system, or hull sitting lower in the water causing different turbulance?
NWflyfisher posted 08-25-2001 11:16 PM ET (US)     Profile for NWflyfisher    
If you go back throught the previous posts/threads, you'll find the overwhelming majority here recommend mounting transducers to the stern's port side. I mounted a new depth/speed/temp transducer for my Furuno 1810F on my '78 Montauk following Furuno's recommendation to mount it on the starboard in spite of the sage wisdom. I've not noticed any adverse impact from that mounting i.e. no surface clutter. For reference purposes, I have a '78 Mercury 700 as the main engine and a '88 Mercury 15hp mounted on the starboard transom. Neither seem to affect the readings while operating.
simonmeridew posted 08-26-2001 08:34 AM ET (US)     Profile for simonmeridew  Send Email to simonmeridew     
I went back out to the boat this morning to remeasure. I guess you were asking
if I measured from a perpendicular along the centerline of the boat, through the
drainhole to the top of the transom. Yes, I did, and as it happens, I placed the
depth transducer of my X-85, 8 inches to the port of the drainhole, centerline to
centerline. And the speed/temp transducer I placed between the drainhole and the
depth transducer, measuring 3 inches from the cl of the drainhole.
Looking at my 84 montauk, from the stern most of the bottom appears like a
smooth parabolic curve , until you go way laterally to the sponson area on port
and starboard. But on my boat there is another structure, if you look way
underneath, I'm sure I'm calling it the wrong name, but let's call it a strake;
anyway this starts from the bow area and comes aft but stops about halfway
back on the bottom of the boat. This looks to be maybe 13-14 inches from the
centerline drainhole although you can't directly measure it. Anyway the reason I
mention this thing is that I wanted to avoid any bubbles which might trail off
behind this and bother the transducer, so I figured put the transducer 8 inches
from the drain, rather than 13 inches which would have put it right behing the
I have no surface clutter up to my top speed which is about 35-36 mph. I will
say that with the 20 degree transducer I have, when the water gets deeper than
225 feet the display itself gets progressively weaker and fainter, but this is true
whether I'm moving or not. The digital readout is correct however. Perhaps
switching to one of the 7 degree, or is it 9 degree transducers might work better
at extreme depths.
I really needed to recalibrate the speed unit, you do this within the software
menu program. I needed to correct by a factor of(-.87) if I remember correctly.
THe indicated speed is not linear however, that is there are inaccuracies at each
end of the scale so you need to pick the speed you want accurate. I tested with
Garmin GPS 12.
BTW, The directions to the X - 85 said to run a separate wire back to the
battery to avoid electronic interference. They said the unit has some sort of
automatic suppression of interference which would diminish sensitivity, but I didn't
notice anything myself. I connected it directly to the bus bar in the console. It
works fine, same whether engine on or off. The engine is a '99 Johnson 70.
Hope this helps.
dgp posted 08-26-2001 09:05 AM ET (US)     Profile for dgp  Send Email to dgp     
Eric, you might want to read this also
Eric posted 08-26-2001 11:08 AM ET (US)     Profile for Eric  Send Email to Eric     
Thanks for the reference to Jim's article. Very comprehensive, and answered some of the remaining questions I had.
Mort posted 08-26-2001 07:50 PM ET (US)     Profile for Mort  Send Email to Mort     
Thanks for the reply, that should be a big help.

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