Topic: advice on proper setup of dual transducers on a catermaran with 2 outboards.

[Col]

Can anyone offer some advise on the proper mounting of dual transducers on a catermaran. On each side of the tunnel I have 300mm from edge to center of the motor power leg, thus a total of 600mm for each pontoon. The manual recommends 15 inches (approx 380mm) from the edge of the prop blade, I only have around 150mm to the edge. The second pic shows the 150mm gap from transome to outboard power leg (depiction of view for side image).

[Del]

Looks difficult to me. Maybe something like this is the easiest solution with best results in the end:




At least this should be a way to get a clear SI view.

[Wayne P.]

What unit are you putting on your boat?

[Jolly Roger]

Hello Colin and welcome to the forum!

Good you got the picture attached  .

Stay away from your propellers as far as you can. If you cannot find a far enough place for the transducer at the transom, try to go for a break through transducer set up or go with Wayne's advice.

Regards from Germany and good luck

Harry

[Wayne P.]

You don't need to be concerned with the distance from your propeller with your rig, That only applies to inboards. The water flow across the hull is your concern.
Just need to know if you are going to be using a regular sonar unit or one with the Imaging technology.

[Jolly Roger]

You don't need to be concerned with the distance from your propeller with your rig, That only applies to inboards.

Can you explain why this should be so?

Regards / Harry

[Wayne P.]

Yes, with an outboard, or outboard/inboard rig, the prop is downstream/aft of the transom and a transducer on the transom will not be affected by water flow from the prop.
Only water passing over the hull will affect the transducer.

With an inboard setup, the prop is usually at the transom or forward of the transom, so disturbed water from the prop can pass over a transducer mounted on the transom.
Its one of them simple physics deals.

A common mounting position for a Side Imaging transducer is on a motor jackplate or next to the motor mount pretty much in the middle of the transom from startboard to port. I have mine mounted between the motor and transom for protection from hitting stumps.
On a non-step hull, mounting the transducer next to the hull drain is common.

[Wayne P.]

Additional note: I asked about the sonar unit being mounted on the catamaran because if it was going to be a Side Imaging unit, a dual SI transducer setup is recommended. The two motors and hull fittings are too much to get a single horizontal SI beam past.
The dual SI transducer connection is done with the AS SILR Y cable.

[Col]

Additional note: I asked about the sonar unit being mounted on the catamaran because if it was going to be a Side Imaging unit, a dual SI transducer setup is recommended. The two motors and hull fittings are too much to get a single horizontal SI beam past.
The dual SI transducer connection is done with the AS SILR Y cable.

Thanks for all the input and feedback. It is the 798ci SI unit with 2 off XNT 9 SI 180 T transducers & AS SI LR Y Cable for the split. I don't see a problem with the props either and the 165mm gap from motor to transom looks to be ok but trying to avoid turbulance on this type of rig is very difficult. Thus the aprehension of location. The usual on this type of boat with non SI units is between the tunnel and the   motor

[Wayne P.]

If you want depth reading at top speed, the transducers have to have a smooth water flow across them. If transoms are flat, then anywhere in this area for each side will work fine. You can even put them between each engine and transom if there is enough space. I assume each hull has a drain so it can go by the drain with the face of the transducers just below the hull as shown in the transducer installation instructions.

[Col]

If you want depth reading at top speed, the transducers have to have a smooth water flow across them. If transoms are flat, then anywhere in this area for each side will work fine. You can even put them between each engine and transom if there is enough space. I assume each hull has a drain so it can go by the drain with the face of the transducers just below the hull as shown in the transducer installation instructions.

Excellent I will do so and post the results after testing. Thks Wayne.

[Jolly Roger]

Wayne,

now I understand what you mean and then it makes sense to me. You were talking about the propeller in front of the transducer (not the engine).

But even though: I would prefer to have the transducer as far away from the propeller as possible.
I think it's not only the water flow from the propeller which can cause problems to get a good picture. I think that a transducer too close to the propeller might also pick up noise from the propeller when it is churning through the water.

Another issue that might occur when the transducer is too close to the propeller: Cavitation.
The water (or better air) flow of the transducer can cause ventilation of the propeller. That will give you a real headache when you want to go high speed.

But thanks for clearing up your statement Wayne!

Colin, keep us posted on your results and let's see some pictures  .

Best regards / Harry

[Wayne P.]

This location is where 75% or more transducers are installed on bass boats.

[Jolly Roger]

Thanks for the picture Wayne!

Interesting cable routing on the bracket, I haven't seen it that way before.

Regards / Harry

[Humminbird_Greg]

Harry is right with the possibilities of cavitation from the transducer ventilating the propeller but let’s not forget that the water pick up for some motors is down there too and we have heard from some that have installed transducers in front of the lower unit of their motors that they lose water pressure at higher boat speeds.  No way to know until you install the transducer though.  He is right on about noise from the propeller too but this is a much rarer occurrence and usually does not happen if the prop is in good condition.  Again, the only way to know for sure if you will have problems is to mount the transducer and try it.

Normally if the transducer is mounted on the jackplate or next too it; the transducer is too far (higher) from the propeller and lower unit to cause problems.

[keizerh]

When you have mounted the ducer in front of the prop without problems, please let me know then I will do the same.
Close to the prop or even a metre further forward.

hendrik