(DG) Replacing ST50 or ST50+ masthead Transducer

[Derek - Raymarine - Moderator]

The original masthead wind transducer used by the ST50 range has not been available for many years, it's part number was D168 and was identified by the vertical tube at the outboard end and the angular 'squarish' style cups.

The current masthead transducer, R28170, is identified by the 'egg' shaped body and the hemispherical cups for the anemometer. The R28170 is contained within the E22078 pack, which also contains a new 30m cable and masthead mounting block.

The two masthead units are operationally the same, and both use the same type of 5 pin plug and socket at the top of the mast, however the early masthead transducers did not have a key on the plug to locate the pins correctly in the mounting block sockets which could lead to bent or damaged pins if carelessly inserted.

The later style masthead transducers had a moulded key on the plug and a keyway cut in the socket to ensure the plug and socket were correctly aligned before the securing nut was tightened and so ensured no damage was done to the pins.

It is possible to remove the key to allow later masthead transducers to be fitted to early style mounting blocks, but this is not recommended since it risks damage to the pins; we would recommend replacing the masthead cable and mounting block at the same time as fitting the new masthead transducer

We would point out that the hemispherical cups are more efficient and will rotate faster than the older angular cups, giving a wind speed over reading of 30%. The later ST60 and ST60+ instruments have a wind speed calibration and so this over-reading can be corrected out. The ST50 and ST50+ displays did not have a wind speed correction and so they will over-read the wind speed by 30%.

We would advise to fit the new masthead cable, (we would recommend this is replaced due to the likely age of the old one - cable can fatigue over a period of time) and the new masthead Transducer and it will work with the existing ST50+ wind display, except the wind speed will over read by 30%.

RAYFAQ#