Raymarine ST60 tridata and Airmar ST800 speed calibration

[jtsai]

Ardea is on jackstands for bottom paint, a chance to investigate the faulty speed/temperature sensor. The erroneous temperature reading is a known problem on the Airmar ST800 analog sensor and I can live with it. The speed paddle wheel rotates freely, but it displays a suspiciously low speed. The attached picture is the highest speed shown with me flicking it like a spinner fidget wheel.

The Raymarine ST60 has calibration instructions, but it does no good with the boat on the jackstands. Has anyone had success with speed calibration?

This is the chance to replace the unit if the calibration procedure doesn't solve the problem. Is pulling the wires from the sensor to the cockpit bulkhead a PITA project?

Yes, I know the chartplotter and the Navionic app both show speed. Just want to solve this mystery.

 

[Loren Beach]

The Raymarine ST60 has calibration instructions, but it does no good with the boat on the jackstands. Has anyone had success with speed calibration?

Yes. I have done so by motoring at constant rpm, both directions because we boat on a river with current. Using the GPS plotter to give me both speeds to average was our method.
Back in Ye Olden Days... there was a measured mile at several places along the river with shore marks. Boats used to calibrate their meters by motoring both ways -against and with current - for same minutes and then averaging the result. Those shore marks have slowly vanished, as have the wooden cabin cruisers and older skippers have diminished as well.
Sic transit gloria, or something like that.

Your instrument kind of looks more like the ST60+ model, to me.
And also, our marvelous plotter does not display boat speed, only SOG. Useful, but variably related.....

 

[peaman]

Is pulling the wires from the sensor to the cockpit bulkhead a PITA project?

Three years ago, I upgraded my electronics to NMEA2000. The cable for depth and speed instruments ran through a plastic hose "conduit" (3/4" or 1" I.D.) from just forward of the mast step, back to the nav table at the outport (port) hull. Had a heck of a time getting the old cable out because there was a corroded BNC connector deep inside of the conduit. Once that was out, running a new cable was no problem. There are two other conduits at the nav table. One comes from the port chainplate area, accessed through a round access port. Another runs from nav table aft to the rudder post area. To get to the "cockpit bulkhead", you might want to get to the nav table and then down across the fuel tank and up within the engine compartment to where ever you want your instrument.

Replacing the speed sensor was pretty easy. First, I made an adapter to remove the interior flange from the through hull fitting. Then, I cobbled together some plywood bits, a PVC pipe coupling, and a "Pony" clamp. Assembling the parts as in the third image, applying steady pressure was all it took to remove the old through hull fitting. The new through hull fit in the hull opening with no modification.