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ST100 and ST550 Transducers

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.

Hull Nut on P17 Housing

Hull Nut on P17 Housing for ST100/ST550
ST100 with Wing-type nut

ST100 with Wing-type nut
ST100 Insert with 33-108 Paddlewheel

ST100 Insert with 33-108 Paddlewheel
ST100 with Anti-Fouling Paint

ST100 with Anti-Fouling Paint
33-108 Paddlewheel with Square Blade Tips

33-108 Paddlewheel with Square Blade Tips
33-109 Paddlewheel with Rounded Blade Tips

33-109 Paddlewheel with Rounded Blade Tips
ST550 Top View

ST550 Top View
ST550 Insert with 33-108 Paddlewheel

ST550 Insert with 33-108 Paddlewheel
ST100/ST550 Blanking Plug 33-414

ST100/ST550 Blanking Plug 33-414
Housing Dimensions

Housing Dimensions
Speed Insert Dimensions

Speed Insert Dimensions
Blanking Plug Dimensions

Blanking Plug Dimensions

Available Parts

Part Part # Description
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.