Autopilot drive mounting question

[Guest]

AP

I, like Paul Cossman, have a 7000 Autohelm linear drive AP directly connected to the Edson quadrant. The P42 steering system is pretty robust and I estimate our boat as it sits weighs about 30,000 pounds.

We've sailed Belle-Vie several thousand miles all over PNW waters in all kinds of weather and sea states without incident. Some say having the AP drive shaft connected to a separate tiller arm is better; perhaps. A spare rudder is a good idea, too. Our P42 came with an emergency tiller arm in the event of a steering system failure.

If you feel better about connecting the AP drive shaft to its own tiller arm, do it. I'm happy with our boat and its systems. I inspect and lubricate the steering system each season just to stay on top of any early developing or deteriorating conditions. Some of these I have already corrected.

Listen and sense your boat's operation. It will tell you when something is wrong in most all cases. Stay tuned and nip the little things in the bud before they develop into serious boat issues.

Terry Cox

 

[Rick Sylvester]

Hey jviss,

that tiller arm in the pic I posted is pretty old and it may not even be an Edson but my point remains the same.

It sounds like you've pretty much thought it through so I'm sure whatever you decide to do, it'll be fine. As strong as the quadrant/radial is, I think your concerns about not point loading is valid. You can see the plate I had fabbed up to help with that. It helps greatly with distributing the torquing loads. Is it strong enough? Well, like everything else on Anthem, it is until it isn't.

Oh, and FWIW, I had to move one of my stops so that a rudder slamming over wouldn't land on the drive. My boat has since (for many years) turned harder to starboard than port. Unsafe? Nawww. An annoyance? Once in a great while. I may fix it some day

 

[jviss]

Follow-up and request for help, please!

Great input, thanks to all.

I finally got to the boat this weekend. The position of the Edson radial drive wheel rudder stop is at exactly the right radius for the Simrad drive. I removed the rudder stop assembly (part number 862-2) to re-mount it on the bottom side of the radial drive wheel. First I will turn the pin down to 12mm for the top 1" and drill the end for an "R" clip.

I made a shelf to mount the linear drive. It's mounted to the aft-most internal bulkhead, which separates the aft cabin from the lazarette. I put it on the port side. The shelf is about 7.5" wide (port-starboard), projects aft 12", and has a vertical section with a knee bracket which bolts to the bulkhead, which is also 7'5" wide and 9" vertically. All of the joints will be taped with glass and resin. It seems sold, and while I thought it might not be strong enough in the direction of the drive thrust, which will be athwatships, I feel like I can flex the bulkhead.

Does anyone know if this bulkhead is strong enough for this purpose? How have you fixed the fixed end of linear drives in this vintage C36?

Thank you very much!

jv

 

[jviss]

A new, changed view on this topic.

In the time since I started this thread and expressed my view on what's reasonable and what's not on this topic, I have changed my mind.

I no longer think it's a good idea to connect the linear drive to the radial drive that is used for the cable steering system.

The reasons for this are that:

1. I had the mounting platform for my linear drive break, and it appeared that the stresses on the radial drive might have been enough to break it, if I hadn't caught it when I did. This would be a case of the linear drive wiping out all steering save the (unusable) emergency tiller.

2. After dealing with the steering forces involved I don't think it's a good idea to put this point load on the edge of the radial drive wheel. The design center for the radial drive loads are the cables and rudder post, which are highly distributed loads and presumably accounted for in design. The point load is concentrated (by definition), and not accounted for in the radial drive design.

3. One of the great benefits of a below-decks autopilot is that it offers steering redundancy. In the case of a failure of any component of the cable steering system, the autopilot, via the linear drive, can be used to steer the boat. Driving the radial drive wheel with the linear drive this is not the case.

4. Installation of the drive using the point (as I implemented it) on the radial drive complicates the installation of the linear drive, since drive must be aligned with the pin in a particular way. With a tiller arm, the arm can be rotated within a pretty broad range, and can therefor accommodate more flexibility in drive mounting.

So, taking this all into account, I've installed an Edson tiller arm. It's a very heavy piece, and while expensive, at $429 list, once you heft it you'll appreciate the value. You can order direct from Edson at list, from Defender at $10 less, or find an Internet retailer at less - regardless, it's going to be drop-shipped from Edson. The bore diameter for our C36's is a stocked size, so no charge for boring (usually $70 more).

Now I have a dual-redundant steering system down to the rudder post, and a proper, high-strength connection from the linear drive to rudder.

Highly recommended.

jv

 

[Paul Cossman]

Re: A new, changed view on this topic.

JVISS,

Thanks for giving us the final conclusion here. I agree with you on all counts; you've obviously thought it all through very carefully.

I've spent A LOT of time wondering what would happen if I have a catastrophic rudder failure, and spent a lot of time putting together emergency alternatives. It's one of the worst scenarios I can imagine. Anything that minimizes that eventuality is worth it. Faced with the choice of how to go about it from scratch, I'd go with what you decided.

Cheers,
Paul