Follow up
In case anyone is interested:
I have a Raymarine S2G w/ ST6001+ head. I bought both a used Raymarine Type 1 linear drive, and a Simrad HLD350 Mk. II.
The T1 is an electrically driven recirculating ball-nut lead screw; the HLD350 is a dual-acting hydraulic cylinder driven by a reversible electrically driven hydraulic pump.
Surprisingly (to me) the T1 has lower backforce when not engaged. I assumed the hydraulic unit would win here.
To engage, the T1 has an electric clutch, the HLD a normally-open solenoid bypass valve.
As far as interfacing is concerned, the S2G shouldn't know which is which: comparably sized motors, and similar loads for "clutch."
I like the HLD. It seems quite robust, inspires confidence. It seems like it is much better sealed against weather. It seems a lot stronger. The T1 is scary inside - plastic gears, a belt drive, and it's poorly sealed against water intrusion.
Incidentally, Raymarine have a hydraulic linear drive, but it is a larger unit, comparable to the Simrad HLD2000, and it is not integrated like hte HLD350, in that the clinder, pump and reservoir are separate units connected with hoses. A nice feature of the HLD350 is - no hoses! An integral body and reservoir with the motor mountted to it, and one pipe to the other end of the ram.
Both units have rod ends that take 12mm attachement points: a stud, or pin of 12mm diameter. The Simrad manual incorrectly calls 12mm equivalent to 1/2". A 1/2" stud, pin, bolt, whatever, won't fit.
