Transom mount transducers on catamarans

[Jon - Raymarine - Moderator]

Choosing the best position and mounting type for transducers on catamarans, especially trailerable catamarans can be a challenge.

As a rule of thumb a through hull transducer ([censored] in the hull to fit transducer) is the best choice, secondly is inhull (transducer mounted inside the boat inside a wet box) mounting transducers and thirdly transom mounting transducers (transducer mounted on the transom).

When the catamaran is powered by outboard or sterndrives the distance between the drive leg and transducer mounting in most cases is insufficient. This means that mounting it close to the leg to avoid disturbed water makes it very close to the leg which can give false returns. Conversely mounting it as far from the leg tends to place it in disturbed water.

Raymarine mounting location guides for transducers are general in their nature and may not always be practical for all applications. An example of this is the mounting of a transducer between the outboards or sterndrives in a twin drive system. This might work for a mono hull but not for a catamaran. Treating each hull as an individual monohull as a starting point then considering other factors might help. Some factors to consider

In most cases the best solution is to mount the transducer through hull or inhull which will allow the transducer to receive the least disturbed water forward of the drive. Selecting between through hull and inhull will depend on the mounting limitations of the hull (including hull material, hull type and suitable position) and physical external influences such as trailer and lifting points.

Adding to the transducer question is the best solution for an RV type transducer where we need to consider the two downward elements for Downvision and Sonar and the two side elements (port and starboard) for Sidevision, the combination of these is Realvision. In a catarmaran this can be effectively achieved by a single through hull transducer which can be mounted in either hull on a zero degree surface (consider the position of this for trailers and lifting points) or by using a tilted element pair 12 or 20 degrees with one element in each hull. The RV transducers are all wet faced so there is no RV inhull option.

If the hull design or trailer does not allow for through hull RV transducers then the transom mounted RV transducer can be used with some limits to consider. Accepting the waterflow and drive limitations on the Downvision and Sonar with transom mounting on this type of application it is foreseeable that returns from Sidevision can be reduced to the side nearest the transducer. To clarify this further the transducer ideally on a catamaran with outboards would be starboard mounted on the starboard side of the starboard motor, mounted as far from the motor as possible and as deep as possible. In this mounting arrangement the Sidevision to the port side will be reduced by the outboard motor. Sea trials have demonstrated a reduction in this effect by trimming the motor upwards.

RAYFAQ#