Although we sold the boat a few months ago we wanted to share our experience with the Autohelm ST4000 Autopilot. The original belt broke and we tried to get a replacement from West Marine. Although we called ahead and gave them the autopilot model the belt they sold us wasn’t the right size. Autohelm (which was sold to Raymarine and now to FLIR) does not have these belts in stock as these autopilots are old (early-mid 90’s).
Looking online we found a seller on eBay (Polytech Design Inc) who claims to sell the right size of belt for these autopilots. We bough two and installed the first one. The length was correct and the teeth seemed to be right too, but it didn’t work correctly: when the autopilot was engaged and if there was more than 15 knots of wind the belt would slip and when the autopilot wasn’t engaged there was a lot of friction in the system.
When we were in St Croix, getting ready to start our journey back to the US we considered buying a new autopilot because we were expecting to use it a lot in the way back. Just when we were about to decide to order the new autopilot (roughly $1500, without including any installation costs) we found somewhere, a post where someone explained why the spare belts we bought didn’t work very well.
It seems that the belts sold by Polytech are T5-750mm-9mm. That is Trapezoid teeth, spaced every 5mm with a belt length of 750 mm and width of 9 mm.
The problem is that the required tooth pattern is “AT5”, where AT stands for “American Trapezoid”. Funny that all the specs of the belt are in international units (mm) but that the shape of the teeth is “American”.
Wrapping up this story, we bought two belts from New England Belting Company (Berlin, CT), model “AT5-750mm-9mm”, installed one and worked perfectly!
Fair winds!
SoJo Sailing 