The ST100 was Airmar's original Speed/Temp transducer. The ST550 was a later version of the ST100 with some visual differences around the pull-ring.
The ST550 has two entry holes in the insert's top with the cable entering one of the two holes. The ST100 has a solid elongated black plastic piece with a directional arrow its full length and the cable enters from the side through the resin (see images below).
Both the ST100 and the ST550 were available with two paddlewheel options: the 33-108 with six 90-degree squared blade tips was for low-speed use, and the 33-109 with six rounded blade tips was for high-speed use. The 33-109 was mainly used by Furuno and Standard Horizon and is no longer available. Most other OEMs used the 33-108 and this can be used as a substitute for the 33-109.
Some early models may have been painted with blue anti-fouling paint.
The ST100/ST500 series did not use valve housings or valve sleeves. The inserts used the P17/B17 style housings (2" OD) with a clean, non-valve, throat and a 0.28" direction keyway notch at the top thread.
Not all original ST100s used the 'wing type' locking nut. Many used the standard round nut 04-004.
|04-400||Plastic Hull Nut for P17 Housing. 2" ID.|
|33-100||Bronze B17 Housing.|
|33-108||Low-speed Paddlewheel (33-109 high-speed version no longer available)|
|33-414||Blanking Plug for ST100/ST550. Overall length 4.21"/107mm.|
|33-417||Plastic P17 Housing|
|405||Bronze Hull Nut for B17 Housing. 2" ID.|