Sonar - where do I put the transducer ?

[Trimix]

Ive got a Garmin 750S and just needed a transducer, so - without thinking too much I orderd a cheap transom one.

But I think that was in haste.

Now Ive had time to thinking about my RIB, its not got a normal transom.

Its a twin engined cat, so the rear sort of looks like a "W", with the two hulls being very, very narrow and of course, two massive Suzuki 175's mounted there.

The middle bit isnt really in the water. So I suppose a transom mounted one wont work will it, or there wont be space to mount it ?

So, do you have to drill a hole in the hull, or fix one inside the hull and it works through the hull. I suppose if there are no air bubbles and the hull is not too thick this would work, wouldnt it ?

(Doh ! I should have thought this through a bit first)

[Chris Caton]

no, don't drill the hull get a thru the hull one, they work spot on

try ebay item 370729437350, Garmin Transducer 50/200Khz Plastic Adjustable In-Hull

[Trimix]

So that will work on a V shaped hull, or does it need to go on a flat bit then ?

[captnjack]

Originally Posted by Trimix

So that will work on a V shaped hull, or does it need to go on a flat bit then ?

it (obviously) needs to be point straight down
You can make a flat spot using some modeling clay and liquid epoxy. Once dry, set the transducer on top and glue in place onto your new flat spot.

[Pikey Dave]

Have you got access to under the deck, to get to the inside of one of the keels?

[MikeCC]

If it's a steep V with little flat area then the depth of filler required to make a large enough surface for the transducer might compromise performance.

You could use the same transducer in an anti-freeze bath. Use a plastic box with a tight fitting lid and bottom cut to hull shape and bond that in. You might want to place it up the hull a little to allow for bilge water to go past it.

The 'official' in-hull one (which works same as above but needs a flat - not horizontal - area of hull to mount) will take up a deadrise angle of around 22 degrees which may be close enough.

[Chris Caton]

Revenger hull is a deep v n it works fine, as long as you can get in the fix it down, we used silkaflex, took 24hrs to go off but has been rock solid for a fees years now, and transducer seems to be reasonably accurate upto 40+k

[Trimix]

In the rear I can get to the bilge areas of each hull easy enough, so I can stick one there. Its the lowest point and about 2 inches of it will be in the water when its up on the hydrofoils. I just need to look at the angles as I see Garmin do various transponders.

I suppose Im really only interested in the depth at slow speed though, say when Im very close to the shore, looking for my dive spot, comming in to harbour etc.

Flat out Im not going to be shallow and certainly ought to be concentrating on where Im going, not my chart plotter

There is plenty of space

[Chris Caton]

I think you will need to fix it as low as possible so it's looking at water n not fresh air, don't forget if you fit as far back as you can it will look at depth at that point, not depth at the pointy end that will find the hard stuff well before the blunt end will, been there n got the tee shirt

[Trimix]

Good point Chris, but can I not calibrate it or set somthing in my Garmin 750S so it sounds an alarm at a certain depth ? I seem to remember reading that in the instruction manual.

Just how far in front will it read ? I imagine the sensor reads down in a cone shape, so the deeper it goes the wider the cone - whereas in a meter or two its not had time to spread out, so I suppose its probably only reading a meter or two in circumference.

[Chris Caton]

Originally Posted by Trimix

Good point Chris, but can I not calibrate it or set somthing in my Garmin 750S so it sounds an alarm at a certain depth ? I seem to remember reading that in the instruction manual.

Just how far in front will it read ? I imagine the sensor reads down in a cone shape, so the deeper it goes the wider the cone - whereas in a meter or two its not had time to spread out, so I suppose its probably only reading a meter or two in circumference.

yes, i guess the 750 will have similar alarms to the 4008, there should be a depth alarm setting in there somewhere, i just dont like alarms n buzzers going off when im out on the rib, i even turn me mobile to silent

as you say, the deeper the water the bigger the cone gets. one thing i have noticed is that shallow silty water does confuse it, so just back right off n take it nice n steady. mine seems to work well, even travelling at a fair speed thru the menai straits it picks up the sudden changes in depth as marked on the chart so im happy with the setup

im looking at a 750 to fit on the SR4, but in no rush to do it yet, waiting to see if there are any good offfers on over the winter

[Pikey Dave]

If you go for the sump fixing option, you need to ensure that there is solid GRP between the txr & the water, no voids, foam, wood etc. It needs to be transducer-solid GRP-water. You can get transducers specifically for the job, as someone already mentioned, they are mounted in a tank of antifreeze bonded to the inside of the hull, this is what I have on BP. If you don't want to got to that extent, then experiment with bonding an ordinary txr. You can try various mounting positions (ooer missus) by filling a bag with water & sitting it on the proposed fixing spot, put your transducer on top of the bag & see if you get a clear echo, the boat needs to be on the water at this point, obviously Alternatively, you can use KY between the txr & hull to test the position, if you're happy with the echo, glue the txr in that position. Personally I'd use epoxy to fix it, but others have had good results using mastic. Time spent now getting it right pays off later, it took me over a day to get my txr positioned & fixed, but I get a faultless bottom trace at all speeds up to WOT, 40kn ish.

[Trimix]

Cheers Pikey Dave, I will certainly be spending the next few months fiddling about with everything.

Ive ordered one that will cope with a deadrise from 2° to 22°, so once ive got it i will have a look in the area I plan to fit it and measure the deadrise.

Fiberglass should be no more than 5/8" thick according to the instructions - no idea if this is the thickness of my boat till I get home.

But as you suggest, i will place it in a temporary way and see if it works properly.

[Chris Caton]

Originally Posted by Pikey Dave

Time spent now getting it right pays off later, it took me over a day to get my txr positioned & fixed, but I get a faultless bottom trace at all speeds up to WOT, 40kn ish.

+1 took us best part of a day to get the position right and get it properly fixed to the hull,but well worth the effort in the end

[9D280]

FWIW the transom mount transducer I got with my (used) plotter was gooped onto the bottom of the previous owner's hull with epoxy.

Another thought:

You say you only really want tio use it at slow speeds. Why not mount it on the transom of one of your hulls - if it's out the water at speed and you don't want to use it - is it a problem if the display shows "err"?

[Trimix]

Well it will look neat and tidy hidden inside, and then I never have to worry abou it - whatever speed I end up doing.