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Author Topic:   Montauk Transducer Mounting - How far from centerline?
Divedog posted 01-22-2005 05:23 PM ET (US)   Profile for Divedog   Send Email to Divedog  
I know this topic is all over the Forum and I've read several treads before posting. I just have to ask before I start drilling holes. What's the best location?
I noticed from a previous thread that Knot at Work and Jim D mounted their transducers quite far to the starboard side (just inside the starboard strake). I'm curious if anyone has mounted a transducer closer to the centerline as the instruction on my Garmin 178C note. I know you need to stay out of the prop area but looking at the hull, it seems like just to the port side of the starboard drain hole would be ideal. Centered but not in line with the prop.
Any one try this? Any input?
Thanks for indulging me!
fairdeal2u posted 01-22-2005 11:37 PM ET (US)     Profile for fairdeal2u  Send Email to fairdeal2u     

I have a furuno transducer mounted on the starboard side.

It works great there. Be sure to put a little angle on it so that the end is a little lower than the front of the transducer. I can run the montauk at full speed and still get a good picture. There is a a little static just before the boat get on plane. Other than that the picture is perfect.

By the way, the furuno 582 is on sale now for around 1000.00
boat show special that Boaters World will sell for.

fairdeal2u posted 01-22-2005 11:47 PM ET (US)     Profile for fairdeal2u  Send Email to fairdeal2u     
Hello again

I just went and measured the position.

The middle of the transducer is 10 inches from the starboard corner.

The bottom of the transducer is even with the bottom surface of the boat. Use a long ruler to match the bottom of the transducer to the bottom of the hull. Again, I have the rear of the transducer tilted slightly lower than the front.

Be sure to keep the transducer level to the ground. Don't be fooled by the deadrise angle of the transom.

Hope that this helps

fairdeal2u posted 01-22-2005 11:54 PM ET (US)     Profile for fairdeal2u  Send Email to fairdeal2u     
hello again

Sorry, about this info. I didn't realize that I was on the post classic forum. The measurements are for my 1987 montauk.
It will be different for your new montauk 170. Better to wait to hear from someone with the same boat as yours.

As a comparison without actual measurements. My transducer is sitting just port of the outer strake on the starboard side of the boat.

Moe posted 01-23-2005 12:39 AM ET (US)     Profile for Moe  Send Email to Moe     
The 150 and 170 hulls are pretty much shaped the same, so I followed Barney's advice to mount just inboard of the strake. Works great on our 150 Sport.


Divedog posted 01-23-2005 06:14 PM ET (US)     Profile for Divedog  Send Email to Divedog     
Thanks for the input. I can drill with a little more confidence.
gotaway posted 01-23-2005 10:04 PM ET (US)     Profile for gotaway  Send Email to gotaway     

My transducer is on the starboard side about 2-3" port of the speedometer spinner. Don't mount your transducer there.

I tried a Matrix 10 and a Piranha 20 and both can't read depth above 30mph with the transducer located where I have it.

I've adjusted the transducer all different ways with no luck. I was worried that the speedo spinner was kicking up too much foam but when I look at the water trail at 35-40mph it seems clear.

So, I'm not sure what's wrong with my set up, but learn from my mistake!


Divedog posted 01-24-2005 05:11 PM ET (US)     Profile for Divedog  Send Email to Divedog     
Thanks for input but where is your speedometer spinner? I don't have one on my boat. Could you describe the transducer location in relation to the hull?
Matthew posted 01-24-2005 06:59 PM ET (US)     Profile for Matthew  Send Email to Matthew     
My Garmin transducer is located 8 and 1/2 inches towards the centerline from the starboard strake or about 2 and 1/2 inches from the middle of the drain hole towards the centerline. Both measurements relate to the starboard side of the transducer.

I've had good luck, but will occasionally drop the bottom in 350+ feet of water, at cruise in the chop.

gotaway posted 01-24-2005 10:21 PM ET (US)     Profile for gotaway  Send Email to gotaway     

I don't have a picture to show you now. I'll see if I can find one to email to you.

Basically, the speedometer paddle wheel transducer as Smartcraft calls it, is located almost directly below the starboard edge of the motor well. If you go to, you can look at the PDFs of the 2004 Whalers and see the Dauntless transom. I think this PDF is the best one:

You'll see a strake below the starboard motor well edge. I believe the speedometer paddlewheel is located on the flat of this strake. My transducer is 2-3" more to the center of the boat.

Although the directions from Humminbird indicated you should not mount the transducer behind a strake because you could see bubbles etc, I think for the smooth hull of the fiberglass boat, the strake water path is probably a good spot. The water line is flat meaning the transducer will cut the water less and surf more...which is what I think you need.

I'm still learning myself on this one so get more opinions.


bigjohn1 posted 01-27-2005 08:03 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     

I don't mean to hijack your thread but rather than starting a new one (since there are so many already), I want to add some additional questions. In the process, it will hopefully be info you can also use.

I have reviewed the reference article in detail but still have questions. I have an '05 170 Montauk and will be installing my brand new NAVMAN Trackfish 6600 next week. A few questions I hope someone can answer follow:

1. Transducer cable routing. I take it the best way to run this aft is through the rigging tunnel. Given the potential interference I may encounter from the engine's electrical cables running in that same tunnel, what else can I do? One idea I have that I think has merit is to first run the transducer cable through a long length of RF shielding then run it down (through) the rigging tunnel. This shielding cable safely protects military electro-explosive devices (EED's) that are highly sensitive to outside RF sources of radiation. I figure if it works there, it would prevent the engine electrical cables from introducing RF energy that will effect my chartplotter.

2. Drilling holes for transducer mounting. I am a bit confused when they say to drill oversize holes equal in diameter to the shank of the screw (to prevent gelcoat cracks). I always thought the way to prevent cracking would be to first drill a tiny "pilot" hole then re-drill progressively larger holes till I achieve the size of hole I need for the screws. I am confused on this statement so anyone feel free to "show me the light" on this hole drilling process. The last thing I want is cracks because I drilled improperly.

Big John

davej14 posted 01-27-2005 08:43 AM ET (US)     Profile for davej14  Send Email to davej14     
Big John,

It is a good idea to progressively increase the size of the hole you are drilling. The point of the instruction is to make sure your final hole diameter is slightly larger than the shank of the screw so that when the screw is installed it will not crack the gelcoat. From my experience you will be more likely to break the screw than crack the gelcoat if the hole isn't large enough. This material is very hard and if you experience extreme resistance when installing the screw, back it out and enlarge the hole. Be sure to install the screw with sealant rated for below the waterline.

Another suggestion is that before you drill the holes, make sure the boat is on the level and use a level to mark the starting locations for the holes. The deadrise of the stern makes it dificult to get it right by eye.


Divedog posted 01-27-2005 04:18 PM ET (US)     Profile for Divedog  Send Email to Divedog     
Happy to have you further the discussion.
I'm not sure about interference from the engine electronics but Whaler has installed pull string for you to route the cable through the same raceway. I don't know if you've seen it or not.
Regarding drilling the holes, it's my understanding that you want to oversize the hole just at the gelcoat level (very beginning of the hole). The rest of the length should just be pilot hole. Basically you have two sizes of hole. At the surface it's larger than the screw but the rest of the hole is smaller.
davej14 posted 01-27-2005 05:00 PM ET (US)     Profile for davej14  Send Email to davej14     
Divedog makes an interesting point, but I would still drill the hole the same size to a depth slightly longer than the screw. the diameter should be larger than the screw shank and slightly smaller than the screw threads. Get it too small and you will twist it right off. If you are really that concerned with the gelcoat then I would suggest using a countersink bit to flare the top of the hole. That would be easier than trying to stop a larger bit from feeding too deeply into a smaller pilot hole.
gotaway posted 01-27-2005 07:52 PM ET (US)     Profile for gotaway  Send Email to gotaway     

Big John,

The directions on some depth finders say EMF could be a problem so your idea of shielding is interesting.

The Trackfish 6600 seems to have the ability to hook into the SmartCraft bus. You'd get all your gauges to show up on the Trackfish screen. That's got to be a pretty nice set up!


jimh posted 01-28-2005 01:14 AM ET (US)     Profile for jimh  Send Email to jimh     
Advice to drill the hole larger than the screw shank applies only to the gelcoat layer, which is probably only about 0.2-inch thick. You just want to enlarge the hole so that the gelcoat layer does not crack by having the screw shank forced into it.

Under the gelcoat will be a layer of laminated material that is probably 0.5-inch thick or more. This will be the material into which the fastener threads must obtain purchase. Do not drill this portion oversize.

erik selis posted 01-28-2005 05:23 AM ET (US)     Profile for erik selis  Send Email to erik selis     
I agree with Jimh's last post and also what Divedog said.

I would also like to add a small piece of advice concerning the string in the cable tunnel. Be sure to attach a second string to the transducer cable when pulling the cable through the tunnel. This way you will always have a string to attach to any cables to in the future.


timsr posted 01-28-2005 08:12 AM ET (US)     Profile for timsr  Send Email to timsr     
I am also looking for the same advice on installing a transducer on my new Montauk. Jimh when you say that after drilling through the gelcoat there will be a layer of some type of material a 1/2" thick, is that the fiberglass or is that the encapsulated plywood. When the manufcaturer provides mounting screws for the transducer are these machine srcews or some type of self tapping screws that would screw into the plywood and usually hw long are they?

On another topic I had seen a recommendation about attaching a piece of starboard to the transom and then mount the transducer to the starboard. Is that the best method?

One last question. When mounting the transducer should it be paralell to the water line? In the above thread I interpeted someone's post to mean that the transducer should be paralell to the bottom of the boat? I always thought the transducer was paralell to the water line.

Thanks in advance for the advice.

This is a fantastic forumn.

davej14 posted 01-28-2005 08:28 AM ET (US)     Profile for davej14  Send Email to davej14     
Since the transducer functions by receiving sound waves reflected from the bottom, you definitely want to mount it parallel to the surface of the water and NOT aligned with the bottom of the boat.
Backlash posted 01-28-2005 09:15 AM ET (US)     Profile for Backlash  Send Email to Backlash     
After drilling the small pilot holes for the screws, use a counter-sink bit to flair the gelcoat ONLY - to prevent cracking. My experience using a larger diameter bit to accomplish this has often resulted in recessing the holes TOO much. The counter-sink bit will allow you to make fine adjustments to the recess.


Backlash posted 01-28-2005 09:18 AM ET (US)     Profile for Backlash  Send Email to Backlash     
Sorry, Dave...didn't read your previous post.
bigjohn1 posted 01-29-2005 09:24 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
Thanks to all for clarifying in great detail about how to drill those holes. Its redundant for some but man, I just want to be sure as drilling into a new hull is scarey to say the least. On the RF shielding for the transducer cable, I am going to do this as I really feel that it will make a difference. Basically, the shielding will tightly cover the transducer cable - its woven in such a way as to "tighten" - or get much smaller in diameter - when pulled tight; simple zip ties will keep snug on each end of the cable.

I'm sure the next bit of information I'm about to share will put me on some sort of FBI internet watchlist but here goes for those who don't understand the concept of protection from EMR - or electromagnetic radiation. Certain types of explosive devices are susceptible to accidental detonation by induced EMR. A Laymen's example follows...for those who have driven on the interstate through mountain blasting zones, you have likely at some time encountered signs that say to switch off two-way radios. This is because the radiation emitted by the transmitter antenna CAN cause the blasting cap in the
dynamite to blow up accidentally...thereby killing the poor dude working as a blaster for the mining company. I say "can" rather than "will" as many factors come into play, frequency of the transmitter, the number of watts being pushed thru the antenna, the initiation charactaristics of the explosive device in question, topography, etc. Basically, any device that is electrically initiated is to some degree susceptible to potential sources of EMR. Many devices that are highly susceptible to EMR (usually small blasting cap type devices), have RF shielding kits installed to shield them from this EMR. Many of the kits are not much more than simple metal shielding that goes over the cable. I am a federal explosive safety specialist so this is something we deal with on a daily basis.

The thing I do not know is the EMR being emmitted from an outboard motor's power cable running through that rigging tunnel the type that would be blocked by simple metal "cable shielding". I will try it nonetheless and report back on the results.
Big John

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