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Old 11-03-2016, 09:59   #1
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Wheel de-clutch during autopilot operation?

Hi Folks-

I'm moving from a CPT wheel pilot (soon to show up in the for sale section) to a below decks L&S hydraulic actuator. Damn pricey switch, but I want reliability.

The steering system is the classic Edson chain-> wire (sheathed with greasers)-> quadrant, pull-pull cable, setup. This means of course, that when the autopilot is on, the movement of the quadrant gets translated back through the wire to the wheel, which will turn on its own in the cockpit.

During operation on the new autopilot actuator, If the wheel is jammed (by, for example a child or guest's leg, a balled up jacket, a coil of line or an errant winch handle), then whatever force the autopilot actuator needs to generate to move the rudder will be generated - up to the max output of the actuator (relief valve pressure).

This applies forwards and backwards - so if the system is being driven by a ram capable of outputting 1400lbs on a 12" lever (same radius as quadrant), and the wheel is jammed, then we could have 1400 lbs tension on one of the pull cables as a result.

There is a significant gear ratio in all steering systems - for example if my wheel is 36" in dia, and the chain sprocket is 3" dia, then a 20 lb force on the rim of the wheel results in a 12 times (or 240lb - neglecting friction) force on the pull cable. This works forwards and backwards, so in the preceding example of a jammed steering wheel while on autopilot, the actual force (at the rim of the wheel) required to jam the wheel is 1400/12 = 116.7 lbs (again, neglecting friction). The ratio drops quickly (by the radius) if the jam occurs not on the rim of the wheel but in the spokes - which means the force required to jam goes up proportionately. It's not hard to see bone-snapping forces being generated quite easily here.

As well, quite apart from th safety question, these are very large numbers for a typical steering system - I wouldn't want to see this ever happen if I could avoid it; but unless the wheel is de-clutched from the shaft somehow, it seems that this is not easy to do.

There is also the loading from the wheel inertia itself (remember it's a stainless hoop 36" in diameter) which is putting unnecessary cyclic tensile loading on the steering cables during normal, un-jammed operation. As an engineer, I know this is bad... and it can add up to a lot of cycles over time.

I'm concerned about this, and wonder how/if anyone has dealt with this by putting in a de-clutching mechanism on the wheel shaft? discussion with Edson engineers revealed they have no solutions to offer.

I may have to design my own declutching hub.

Or - am I being paranoid/delusional and making a problem where there isn't one? Surely I'm not the first guy to worry about this?

thanks for your thoughts!

bg
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Old 11-03-2016, 10:07   #2
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Re: Wheel de-clutch during autopilot operation?

Make up an easy to remove wheel nut. Then just remove the wheel.
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Old 11-03-2016, 10:20   #3
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Re: Wheel de-clutch during autopilot operation?

You're not paranoid--if the autopilot is engaged you want to stay away from getting an arm broken. Yep. It was one of the first things I was advised by the manufacturer of our autopilot. I wouldn't be designing a declutching hub, I'd just be careful and have all aboard be careful.

You don't want to remove the wheel--you want to be able to very quickly resume manual steering if you need to.
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Old 11-03-2016, 10:23   #4
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Re: Wheel de-clutch during autopilot operation?

Quote:
Originally Posted by steamgoat View Post
Make up an easy to remove wheel nut. Then just remove the wheel.
Edson makes a very pricey wheel hub with a knurled knob.

Please, do NOT consider it.

We have the standard Edson wheel nut. If you grease the threads on the shaft, that nut will be very easy to remove anytime you want or need to do so.

I greased mine 18 years ago when I first bought the boat and it still moves easily all these years later with no further grease.
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Old 11-03-2016, 10:56   #5
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Re: Wheel de-clutch during autopilot operation?

I believe my wheel nut is plastic.
If mine weren't so small I'd remove it and hang it on the rail just to get it out of the way and free up space in the cockpit, when we are at anchor.

From a reliability standpoint, I'd keep the CPT, leave the pulley on the wheel, remove the rest and store it below, that way it's a 5 min job to re-install if your primary ever breaks.

On edit, surely the pressure relief valve is adjustable, so you can turn the pressure down enough so that you still have steerage, but not so much it would break something?
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Old 11-03-2016, 11:14   #6
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Re: Wheel de-clutch during autopilot operation?

I think if you ease the regular wheel nut (that seems to work by tension/friction on many boats) then the shaft will spin while the wheel will free wheel thus you will get some wear on the shaft/hub interface, unless the shaft is conical.

Another factor is that people walking around the wheel tend to grab the wheel when the boat lurches. If the wheel is free to turn, these people end up at least badly bruised (by not finding support where there is normally some).

And so I would just leave the wheel fully locked on the shaft and accept the fact that it follows the AP ram. Which is actually what I did on all AP driven big boats I have crewed or skippered. (PS some had carbon wheels though).

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Old 11-03-2016, 11:21   #7
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Re: Wheel de-clutch during autopilot operation?

Thanks for the immediate feedback.

On my system the wheel is on a keyway on a straight shaft, so no loosening works - you have to remove the keyway to have relative motion between the wheel hub and shaft. And - there are 2 set screws, one bearing on the keyway and one bearing on the shaft at 90 degrees too.

I'd thought of removing the wheel, but it is problematic. First there is the keyway that drops out (and of course will fall down the cockpit drains). Then there's the loose wheel nut, set screws and the bitty 1/8" Hex key used to release them. then there's the bloody great round wheel thingy that rolls around and needs a home (I have images in my head of losing it over the side and steering for the rest of the trip with a pair of vise grips clamped on the shaft!). And then - if someone falls overboard, it simply is not an acceptable delay while you fuss with putting it back on to regain control of the boat.

No, what I'd like is a wheel hub retrofit clutch, where I can do some action like flip a lever, push a button, or pull a knob, and the wheel toggles between freewheel and locked modes... That would be perfect.

Anyone else want this?

bg
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Old 11-03-2016, 11:59   #8
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Re: Wheel de-clutch during autopilot operation?

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Originally Posted by NSboatman View Post
Anyone else want this?

bg
Well, yes of course, something like the "clutch" on the CPT would work, you know the ring you pull that disengages the two steel pins? Course unlike the CPT, maybe you would want those pins strong enough so that you couldn't shear them.
I have never thought about it as the CPT if you jam the wheel, the belt just jumps on the wheel, but a hydraulic unit of enough power could be dangerous.
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Old 11-03-2016, 12:08   #9
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Re: Wheel de-clutch during autopilot operation?

I've never considered this as a problem......it's a knowledge/Darwin sort of thing to me. Then again I work in an industry that is rapidly moving to Borg hive mentality for simple decision making. The Borg try to engineer so much risk out of day to day operations that soon poodles will be doing the work.


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Old 11-03-2016, 12:12   #10
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Re: Wheel de-clutch during autopilot operation?

Have heard nothing but praise for the CPT. Why do you thing it's unreliable??? Is it the size of your boat??
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Old 11-03-2016, 12:16   #11
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Re: Wheel de-clutch during autopilot operation?

I understand what you want. I do not think it exist. All though the risk of injury exist, I think the risk of actual injury is quite low and acceptable. Under normal circumstances the wheel is moving very little, 1/8 turn port, 1/8 turn starboard. With a big following sea it moves much more.
After awhile at sea under AP control it become a non issue as you step about the moving wheel. If the risk is to much for you then maybe mitigate some of the risk by installing a smaller wheel with the spoke areas filled in plastic of some sort attached with zip ties so that limbs and things are less likely to become trapped between moving spokes and stuff that does not move.




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Old 11-03-2016, 12:45   #12
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Re: Wheel de-clutch during autopilot operation?

Quote:
Originally Posted by Schooner Chandlery View Post
You don't want to remove the wheel--you want to be able to very quickly resume manual steering if you need to.
^^^^^^^^^^^^^^^^^^^ This

AP may fail, power to AP may fail, input data to AP may fail - at any time, and Murphy dictates it will be at a most inconvenient one. You want to be able to take over immediately, not spending time looking for a clutch nut, or taking the wheel out of storage..
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Old 11-03-2016, 13:05   #13
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Re: Wheel de-clutch during autopilot operation?

Hey Roverhi- the CPT was initially very cantankerous, but I sent it back to them and they rebuilt it completely, upgraded it and tested it out. It worked much better after this, and we did run with it for a while. The experience with CPT the company was great.

The unit is a bit touchy to set up at times though, as you do end up tweaking the dial a bit to match the setting to the direction you actually want to go; and after that I found it necessary to really play with the gain and deadband settings a lot to get a reasonably stable course. It hasn't been - at least for me - a "push the auto button and hold a course" type of pilot. Maybe I've been doing it wrong all along, but I have given it a fair shake.

Beyond that, my issues with the CPT relate to the way we use the boat. It is a big boat, and a very 'lively' hull in terms of course stability, particularly when motoring or motorsailing. She can really wander off rapidly if you're not paying attention. This was a surprise to me - I come from traditional rigs and long, straight keels where walking away from the wheel for a few minutes is ok... I'm working on this as well with changes to the rudder aperture and prop, but I don't expect miracles there. It is what it is.

We frequently sail short-handed, and with children and non-boaty guests aboard. last season one child managed to get his fingers caught under the drive belt (we weren't even on autopilot at the time, I was steering and he just reached out and stuck his finger under the belt suddenly as I was turning the wheel! he howled pretty loudly, but no real damage was done). I considered building a shroud for the belt, but then I realized that the whole setup is more exposed and takes up more room in our already cramped cockpit than I like.

So - I'm giving the below-decks, full-on approach a try. I do like the simplicity and robustness of the CPT - I had it apart a couple of times before sending it back and it truly is 1980's technology, in a good way. The PO said he got good use out of it, and equipped it with the wind sensor, the remote heading adjustment switch and related goodies. I also got the whole cruisers service kit when it was rebuilt, so I'm not walking away from it lightly.

Brantleychuck -that is good feedback. i'm wondering the same thing - is it just going to be 1/4 turns this way and that, and if so, then it's probably ok... but I'm still a bit concerned in the long term.

The CPT clutch is the sort of thing I had in mind, just machined into the hub, and with probably a lot more than 2 pins (if I used pins - maybe splines) - certainly something that I can't break.

thanks folks - appreciate the ideas and comments.

bg
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Old 11-03-2016, 14:05   #14
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Re: Wheel de-clutch during autopilot operation?

No reason you can't have what you want. But if it isn't a standardly available off the shelf item (and there are a great many very good things that aren't) then the path to get what you want is to design and fab the part. There are several ways to achieve what you want. As A64 said, you can use a removable pin to lock or unlock the shaft to the wheel. Hard to imagine a simpler approach. Pin diameter will need to be large enough to take the largest load you will ever apply to the wheel. And this will require a shaft of adequate diameter to take the pin.

There are other approaches possible - a dog clutch would work well.

There are many things on boats that can be improved if you're willing to take on the task of doing them yourself - and this includes hiring someone else to do the work it it's not an area you're comfortable with.
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Old 11-03-2016, 14:07   #15
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Re: Wheel de-clutch during autopilot operation?

Very first thing I learned when dealing with AP equipped boats
was Never Ever stick my hands through the wheel.
A quick and easy solution is to leave the wheel cover on when on AP
It will turn with the wheel, prevent arms and fingers between the spokes,
And can be quickly and easily removed.
In an emergency you could grip right thru it, also.
Cheers
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