Transducer Location

[Rex Delay]

About to install all new instruments. Currently boat has speed transducer foreward of the keel, I intend to put new one in the same location. Aft of that is an in-hull depth. New instrument package says that depth aft of speed causes problems from turbulence. Current setup also has 2 transducers to starboard of the mast. Could I use one of those for depth even though it is beside the keel? Remove and fill the other? All new transducers looking to use existing holes in the hull.

[Orion Jim]

How about something like the Airmar DST800 depth, speed, temp. Do away with some of those hull penetrations.

[Rex Delay]

The holes are already there. Question is if putting the depth transducer beside the fin keel would reduce it's function.

[ChrisseH]

Originally Posted by Rex Delay

About to install all new instruments. Currently boat has speed transducer foreward of the keel, I intend to put new one in the same location. Aft of that is an in-hull depth. New instrument package says that depth aft of speed causes problems from turbulence. Current setup also has 2 transducers to starboard of the mast. Could I use one of those for depth even though it is beside the keel? Remove and fill the other? All new transducers looking to use existing holes in the hull.

I had the depth transducer installed in front of the speed transducer and the outcome was that the speed measurement became unlinear. When calibrating the instrument at 6 knots it showed (compared with the GPS) more than half a knot wrong at 3 knots. And if I calibrated the instrument at a lower speed the inaccuracy at higher speeds became a problem. The only rational explanation for this is that the depth transducer in front created turbulence which had an effect on the speed measurement. Solved the situation by replacing the depth sensor with a DST800 and putting a plug into the old speed transducer hole.

[GordMay]

Originally Posted by Orion Jim

How about something like the Airmar DST800 depth, speed, temp. Do away with (by plugging) some of those hull penetrations.

Clean water flow over the face of the transducer is critical to the proper operation of the system, and is the single most important parameter in selecting a mounting location. When mounting alongside of a keel, it should be far enough away from the keel, so that the keel will not be detected within the transducer’s beam angle.

[Rex Delay]

"Clean water flow over the face of the transducer is critical to the proper operation of the system, and is the single most important parameter in selecting a mounting location. When mounting alongside of a keel, it should be far enough away from the keel, so that the keel will not be detected within the transducer’s beam angle."

Good point. Perhaps put the depth in the bow and speed beside the keel?

[Sailmonkey]

Originally Posted by Rex Delay

"Clean water flow over the face of the transducer is critical to the proper operation of the system, and is the single most important parameter in selecting a mounting location. When mounting alongside of a keel, it should be far enough away from the keel, so that the keel will not be detected within the transducer’s beam angle."



Good point. Perhaps put the depth in the bow and speed beside the keel?

That would be my choice

[ChrisseH]

If possible, the best location for the speed transducer is on the boat's center line at least 1 meter in front of the keel. Here the flow is still laminar and you will avoid getting different readings on different tacks. Further forward will (depending on the boat size) increase the risk for getting the transducer in rough seas above the water. And depending on the hull shape the depth transducer could then be installed either just abaft the speed transducer or a bit to the side, but still in front of the keel.

[Rex Delay]

This was brought up by the package I got from Raymarine which stated "do not put the depth transducer aft of the speed transducer"

[ChrisseH]

Originally Posted by Rex Delay

This was brought up by the package I got from Raymarine which stated "do not put the depth transducer aft of the speed transducer"

Exactly like that the yacht manufacturer had installed the transducers of my Raymarine Tridata setup when my yachy was delivered as new in 2007. But as mentioned this resulted (at least in my case) in a non-linear speed measurement. Did not test the other way around, but my gut feeling is that the ultrasonic echo sounding is less sensitive to turbulence. Anyways, my Airmar Triducer DST800 has worked well for both speed and depth since 2012. Please note that I ripped off also the Raymarine Tridats display as it no longer was compatible with the DST800. Instead I today use a PC based system where all NMEA sensors are connected through a ShipModul multiplexer to the PC running OpenCPN and SeaMODE Speed Lab.