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Old 26-08-2018, 07:41   #1
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Rotary drive autopilot

Hiya
Looking at installing a ray marine type 2 rotary drive autopilot.

Can these be installed direct onto the rudder shaft and if so how do I calculated the correct gear ratio?

Install under the pedestal is going to be a pain - the drive unit will be in the engine bay and will need a lay shaft installed so trying to avoid if possible.

Thx

Winf
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Old 26-08-2018, 07:51   #2
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Re: Rotary drive autopilot

I have a rotary drive. Mine all fits in the pedestal.

But you are trying to install it in a way it isn't really designed for it sounds. Why would you do that instead of using a linear drive?
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Old 26-08-2018, 08:06   #3
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Re: Rotary drive autopilot

Quote:
Originally Posted by Winf View Post
Hiya
Looking at installing a ray marine type 2 rotary drive autopilot.

Can these be installed direct onto the rudder shaft and if so how do I calculated the correct gear ratio?

Install under the pedestal is going to be a pain - the drive unit will be in the engine bay and will need a lay shaft installed so trying to avoid if possible.

Thx

Winf
Short answer: NO! They do not have the torque to drive the quadrant directly. That's why they make a linear drive. (a great piece of kit, by the way!)

As an option, you can put a length of chain in the existing cable and use that with a couple idler sprockets to connect to the output of the AP chain drive.

But, if you are DETERMINED to connect to the quadrant,

Calculate the gear ratio you would use to connect to your wheel.

Now calculate how many rotations of the AP output shaft that is going from lock to lock.

Figuring your rudder swings 45deg each way, you need to rig up gearing so you get that many rotations of the AP drive with a 90deg swing of the rudder.

On my boat there are 6 full rotations of the 3 inch diameter AP drive sprocket from lock to lock. You would need a gear ratio of at least 24 to 1 to get 6 rotations of the AP drive in 1/4 rotation of the rudder shaft if you are connected directly to the quadrant. That's a drive sprocket of 72 inches (Yes, 6 FEET) in diameter. Sound practical to you???
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Old 27-08-2018, 03:01   #4
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Re: Rotary drive autopilot

Settle down fellas, not determined on installing anything anywhere just yet, just askin so I don't screw up. So rotary on the quadrant clearly out. Thanks for that.

Have looked at linear drive. Couple of problems is 1) I won't get the full +/- 45 degree rudder movement and 2) can't fit the linear drive in the space available without lots of mods.

Hmmm. I am starting to see why the PO went wheel drive but it just doesn't have the oomph in any weather.

Still thinkin!

Winf
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Old 27-08-2018, 03:35   #5
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Re: Rotary drive autopilot

If you use a hydraulic ram, the body can be mounted on the quadrant, and the end of the rod to a bulkhead. This minimises the space needed, and is what has been on my boat for the last 30 odd thousand miles, trouble free. The ram was custom made, but cost less than the off the shelf units!
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Old 27-08-2018, 06:35   #6
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Re: Rotary drive autopilot

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If you use a hydraulic ram, the body can be mounted on the quadrant, and the end of the rod to a bulkhead. This minimises the space needed, and is what has been on my boat for the last 30 odd thousand miles, trouble free. The ram was custom made, but cost less than the off the shelf units!
I'd second that... If you have serious space issues, a hydraulic unit can fit in odd places because the pump can be separate from the ram. Like any quadrant drive, you do need to be SURE you have something strong enough for the ram to push against.

Downside is: They are a lot noisier, in my experience, than the linear drive. I have a linear drive under my berth, and through the mattress you hardly know it is on. My old boat had an Octopus hydraulic drive. Work a treat, but was rather loud.
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Old 17-12-2019, 04:32   #7
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Re: Rotary drive autopilot

Winf - what did you end up doing, if anything? An SC36 I am looking at has a rotary drive and I'm considering new options for extended offshore passages if the existing unit is near the end of its life. You say the Raymarine Type 2 "doesn't have enough oopmh in any weather" - can you elaborate?

As an aside, I rate the linear drives. I fitted a Raymarine linear drive to a previous 36-footer I owned and it was brilliant across a full Pacific crossing (with the Evolution computer).
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