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Full Version: [DG] Rotary Drive selection
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I have a defective type 1 rotary drive unit, and have some questions on proper replacement. Sailboat is 40', 22,000 lbs. Existing rotary drive is type 1. All new Raymarine electronics a few years ago, including ACU 200, EV1, driving an older Autohelm Type 1. Drive has maybe 10,000 miles on it. On recent trip back from Bermuda, while sailing on a constant heading with wheel nearly neutral, motor started singing, and wheel locked up. Uppon return home, found that the sun gear is worn to a nub. All the planet gears are fine. Looks like it simply wore out. We sail offshore a lot in heavy seas, so the unit gets a work-out. It's been suggested that I go to a Type 2, but I have some reservations. The old Autohelm type 1 and 2 ran at different speeds (18rpm and 28 rpm). The new Raymarine units operate at 33 rpm for either type. I need gears that will last. Are the gears the same on both a type 1 and a type 2? Can an ACU200 be converted to an ACU400? I'm on the break-point in displacement. Current stop to stop is 1 3/4 turns. chain ratio is 3 to 1. I can go 4:1. How do you reconcile desired 10 second hard over to hard over times in your manual, when the Type 1 and type both run at 33 rpm, but you show different chain ratios for each?
HI Hg1
Thankyou for your enquiry.

Given the vessel displacement, for offshore work a T2 Rotary drive would be the best option as it would give plenty of power in a heavy sea, where the T1 would struggle and need to have the mainsail reefed and helm load eased.

The T2 rotary drive would require an ACU400, although the control unit, rudder reference unit and EV would remain unchanged.

The gear ratio will need to be changed, the calculation is achieved by measuring the turns of the steering gera shaft at the point the rotary drive is going to be connected to from hard port to hard starboard. Once you know how many turns you need - this is referred to as the Driven shaft.

I have attached a graph that can be used to now identify the correct reduction ratio required based on the number of turns of the driven shaft and the T2 Drive. this will identify the correct reduction ratio and the size of sprockets required.

I hope this helps?



I fully understand the curves. I have had no problem with the power of the unit. My problem was a mechanical failure of the gears. As I said, the old Autohelm units used different gear ratios, and the drives were physically different in overall dimension. The new Raymarine drives are of identical size, and identical gear ratios.

My question is this. Are the gears the same inside a new type 1 and a type 2 unit? I'm afraid that more power will equal more stress on the gears. It's important for me to understand from an engineering perspective since a gear failure can lock up the steering system, but a motor failure will not. My steering did lock up while offshore, but luckily, we were able to free it. In tight quarters it would have been a problem. Is there a designer I can talk with?

HI Hg1

Thank you for your feedback.

The new style drives have the same type of gears inside, bear in mind all drives now use the heavy Duty gearbox as standard and so compared to the older drives which just used plastic gears, all drives now have strengthened gearboxes and so are significantly more robust than the older drives.

If you have specific design queries, you are welcome to PM me.
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