how to fit dual depth sounders

[Jassira]

I have a sailing boat with a vee'd steel hull that has twin Nasa depth sounders fitted either side of the vee. When I brought the boat it had what I assumed to be a mercury switch that activated only the transducer to leeward. For reasons that now escape me I thought it would be a great idea to have a second display and run both transducers at the same time. The problem now seems to be that transducers interfere with one another, I was going to just refit the mercury switch but I seem to of lost it. I guess I have a few options.

In order of preference.

a) Fit a transducers that runs at a different frequency, possibly connected to a fish finder or similar
b) Buy another mercury switch... the old switch was in the transducer cables but now I have two displays I don't see why I couldn't just switch the power to the whole unit.... anybody know a supplier of a switch that wouldn't bounce in and out to much. ?
c) Find another use for the second transducer hole in the hull
d) Weld up the second hole and forget I ever had 2 transducers

Any other suggestion would be appreciated..


Thanks
Nigel

 

[pvb]

d)

 

[Twister_Ken]

My Twister had twin transducers. The two lots of wiring came to a box mounted out of harm's way on the centreline, tucked in under the companionway. One set of wires to port, t'other to starboard. Inside the box there was a pendulum. On starboard tack it would connect the port transducer's wiring to the gauge, vice versa on port tack. Box was made by Stowe, but I'm sure other manufacturers did them as well.

PS - may still be available…
http://www.stowemarine.com/gravity.htm

 

[Seajet]

Nigel,

my grp boat had twin transducers in oil baths inside the veed hull forward, and like you I found they conflicted.

I moved the saloon depthsounder transducer to the relatively flat hull aft of the keel and now they seem to co-exist happily; OK I lose a nonoseconds' warning if about to go aground, but this matters little if anything in reality - I use the cockpit Nasa Clipper display when sailing, and the saloon Garmin fishfinder one with the aft transducer with shallow & deep alarms set for overnight anchor watch.

 

[Seajet]

Nigel,

my grp boat had twin transducers in oil baths inside the veed hull forward, and like you I found they conflicted.

I moved the saloon depthsounder transducer to the relatively flat hull aft of the keel and now they seem to co-exist happily; OK I lose a nonoseconds' warning if about to go aground, but this matters little if anything in reality - I use the cockpit Nasa Clipper display when sailing, and the saloon Garmin fishfinder one with the aft transducer with shallow & deep alarms set for overnight anchor watch.

I much prefer having the redundancy backup of two separate systems compared to one with a repeater.

 

[William_H]

Yes inevitably they will conflict. Especially so if both sounders are the same make and model. It is the sounder it self that determines the frequency of the pulses not the transducer which simply must match the sounder. (transmitter/receiver).
So definitely one running only at a time. I can only suggest that Seajet having 2 running at once they are on different frequencies of sound and probably different pulse rates and then spacially removed from one another. It is likely at close range that even on different frequncies they will interfere. So OP will have to switch one off at any given time if they are similar machines.
I think a microswitch with a pendulum attached to the operating arm and then mounted at such an angle that heeling will operate or not the switch. The flip flop function might minimise erratic switching from one to another although you might need an over ride switch for level operation in a lumpy sea. The microswitch switching power to the appropriate sounder. However if it takes too long to power up each sounder then best you resort to a manual changeover switch.
If you go to a mercury or microswitch wired in the cable to the 2 transducers. (Going to just one sounder and head) then it is likely that the system could cope with frequent changes from one transducer to the other without missing a beat (or too many). Only experimentation will tell.
Best and simplest one sounder one transduce on flat bottom. good luck olewill

 

[Sandy]

Can't for the life of me think what use they would be.

What is your draft? How far down the Vee are they sited?

It might be worth mocking up a wee diagram and seeing how little change there is in depth as you heal one way or other.

Ideally you only need one fitted that should work on both tacks.

Call or drop an e-mail to NASA they will be very helpful.

 

[Twister_Ken]

Can't for the life of me think what use they would be.

A transducers sends its pulses out in a cone. When it's not possible to fit one transducer on a flattish portion of the hull in such a position that the cone will hit the bottom underneath the boat no matter what the angle of heel, then two are used so that the 'downhill' one that is pointing most closely at the seabed is connected to the instrument head. Obviously an automatic switchover is desirable, else it might be forgotten.

I think twin transducers are now an 'old boat' solution as most modern hulls have a flattish underwater sections.