through hull transducer placement

[hoga]

is the best place to mount it in the center of hull

[scottar]

What hull? What transducer? The "best" place is a spot with good clean uninterrupted water flow. On some hulls the positions that work can be quite surprising. On others you can't see any reason for a transducer not working

[hoga]

its in a glass hull and using the proper brass transducer in a wet box but getting good reading at idle but put a few reves on I have to wind the gain right back but get a good reading at speed

[scottar]

Your issue may be interference/noise being caused by the prop as against actual transducer location. Typically the answer to your question is yes - as close the centre line and towards the stern of the vessel is the correct place to allow a transducer the best access to clean water in all but the roughest conditions. I have on occasion found however that the best results can be achieved by mounting the transducer further away from the propeller. It becomes a balancing act - go too far forward or too far towards the sides, you run the risk of the transducer getting into aerated water or the area of the hull physically leaving the water. The beauty of wetbox installs is that it is fairly easy to test an area for suitability with the use of a wet plastic bag and a good mate. The downside is when you don't have easy access and need to start cutting holes to get it.

In the past I have experimented with wetboxes under bunks in the halfcab of a couple of boats - a V17C that works pretty well - gets a bit of break up when choppy but good enough not to bother with further experimentation and a Cruisecarft 625 - worked well up to 3000 revs at which stage the hull started to lift and the transducer came out of the water. I did do another 625 by cutting access into the false floor in the cabin - worked better than under the bunk but still eventually came out of the water. In all of these cases there was a marked increase in the amount of gain that could then be run without picking up propeller noise - if it could be picked up at all.

Unfortunately, unless someone has experimented with your exact combination of sounder/hull/engine/prop , getting a definite answer probably isn't going to happen. Just out of interest - what brand/model or sounder and boat.

As a side note - I have seen instances where different props produced variations in sounder noise - if you can borrow a different prop to try it may present another avenue to rectify the problem but I wouldn't shell out for a new one without testing.

[Fed]

Give it a rev in neutral.

I'd start with a dead boat (everything off).
Turn up the gain until you see garbage or it's on maximum, whatever comes first then back it off until the screen is good.
Then start the motor and see what effect it has if any, back off gain accordingly.
Then rev it in neutral and see what effect it has if any, back off gain accordingly.
Then put it in gear and continue as above while incrementally increasing speed.

It's really only common sense, in a perfect world you would be able to run the gain at the dead boat gain setting.

[hoga]

thanks for inpout sounder jrc ff50 h h 620sf the old b&w lowrance x70 worked well in same spot but just glued to hull no wet box should have sorted this out ages ago

[scottar]

Part of the problem is that the FF50 is a lot more sensitive than the X70 was. It was with FF50's /Plot 500's that the experimentation was done with the Cruisecrafts. You can also make an adjustment to the STC that will clear up the clutter a lot but it will also get rid of fish echos.

[hoga]

looks like I have found a transom mount will try it do you think it would be better prefer through hull as beach launch at fraser a bit I always thought it was because it was more powerful but was told by experts that it should not make any difference thanks 4 your help

[scottar]

There are some differences in echo returns between transom mount and bronze through hulls but not enough to worry about. If it fits in your wetbox you could try it there before you drill holes. I have seen one boat (Cruisecraft) where a transom mount didn't give as much noise as a through hull but you won't know until you try it