Self steering (again)

[Chrisc]

I recall that a few years ago there was a commercially produced self steering gear where the horizontal axis air vane turned the trim tab by means of a push/pull cable similar to a motorcycle brake cable. Given that a sheathed cable would require regular maintenance to prevent the ingress of gunk from gumming it up, it would appear that having just one moving part (the cable) would be preferable in regard to less friction than linkages, bell cranks, universals etc that make up most systems vane/trim tab connections.
But, if a cable was that good, wouldn't all manufacturers be using it? I must be missing some engineering fine-point here. Advice appreciated.

Chris

[Meandercp]

I believe the commercial vane you are thinking about is the Autohelm from Scanmar. ( http://www.selfsteer.com/products/autohelm/ ). I have one that I bought for my 32' ketch and moved to a 36' cat. I love it. It is amazingly simple. There are no parts that can't be replaced (at least temporarily) with something you can't find in any hardware store in the world.

I never had any trouble with the cables gunking up. When the stainless cable finally broke, I replaced it with a 120# fishing line. I am sure that is overly strong, but about the same diameter as the stainless cable.

My guess is that most systems do not use the cables because the most popular are the servo pendulum type that use the water pressure on a paddle to develop truly large loads (in heavy weather) that can drive the boat's main steering system via the strong gears. The Autohelm uses an auxiliary rudder with a trim tab so that the forces are much smaller.

[charliehows]

yeah, cables in self steering units dont work for two reasons 1; friction and 2; they bind when asked to turn 90 degrees. i put a lot of work into a unit i designed around cables, couldnt get it to work. push/pull cables are particularly uin suitable - the unit i designed used double cables/pull only, to try and overcome that - still didnt work.

[Chrisc]

Thanks for the replies.
I made a basic mock-up of the vane and turret out of cardboard tubes and tried bicycle brake cables and sheaths for the actuating mechanism. It worked really well in one position only - adjusting the vane altered the lie of the cables and introduced friction so, back to the drawing board....

[charliehows]

Engineering trade components supplier - Special purpose engineering products - TEA Transmissions Australia

i bought bevel gears from these guys - i'm trying the hdpe plastic ones at present, seem pretty durable. I'm sure there'd be no probs dealing with them from nz

[Snowpetrel]

Originally Posted by charliehows

Engineering trade components supplier - Special purpose engineering products - TEA Transmissions Australia

i bought bevel gears from these guys - i'm trying the hdpe plastic ones at present, seem pretty durable. I'm sure there'd be no probs dealing with them from nz

These look great, what size did you get, and what price where they? The Stainless Steel or brass look good but if the hdpe ones are big enough it might also work fine (or cheap enough to replace frequently..) I need to build a vindvane for the new boat at some point. Probably an auxiliary rudder with a servo pendulum so I am looking for something like this for the vane to servo pendulum connection.

Cheers

Ben

[Jim Cate]

Originally Posted by charliehows

yeah, cables in self steering units dont work for two reasons 1; friction and 2; they bind when asked to turn 90 degrees. i put a lot of work into a unit i designed around cables, couldnt get it to work. push/pull cables are particularly uin suitable - the unit i designed used double cables/pull only, to try and overcome that - still didnt work.

Hmmm...

I guess no one told AutoHelm (or me) that these cables don't work! There are a lot of AutoHelm vanes wandering about the seas, seeming to steer well.

In my case I designed and built my own similar setup, utilizing teflon tubes and small 7X19 s/s wire as tab drivers. Only problem with that part of the system was eventual wear on the tubes where they went around corners. If I was to try again I would experiment with replacing the s/s wire with Dyneema... less friction by far and so easy to work with.

This home made kluge steered the boat for most of the 87 thousand miles we did in her. I think that this qualifies as "working".

Cheers,

Jim

[Chrisc]

Jim,
You have got me thinking about cables again, especially since I made a prop shaft lock for my last boat which was actuated by 3mm 7x19 wire. For the sheath I used 5mm ID stainless nipple tube, and although it had a couple of right angle bends, worked really well with almost no discernible friction. Now trying to figure out how to adjust vane angle without upsetting the lay of the cables to the trim tab.

[Delfin]

Originally Posted by Chrisc

I recall that a few years ago there was a commercially produced self steering gear where the horizontal axis air vane turned the trim tab by means of a push/pull cable similar to a motorcycle brake cable. Given that a sheathed cable would require regular maintenance to prevent the ingress of gunk from gumming it up, it would appear that having just one moving part (the cable) would be preferable in regard to less friction than linkages, bell cranks, universals etc that make up most systems vane/trim tab connections.
But, if a cable was that good, wouldn't all manufacturers be using it? I must be missing some engineering fine-point here. Advice appreciated.

Chris

As you are blessed with an outboard hung rudder you can easily do what I did on a Cape George 36. I mounted the Autohelm on the stern rail, built a bracket that mounted on top of the rudder and held a 1" shaft on which I built a trim tab. The bottom of the shaft rested inside a socket attached to the bottom of the rudder. Cross bars on the shaft provided what was needed for an attachment point for the Autohel steering cables. This setup steered the boat on all points of sail in all winds with zero wear or fuss for 20,000 miles. I also built a 12" tiller that could steer the trim tab and attached a small electric autopilot to that tiller. Because the force required to turn the tab was very small, this dinky autopilot also worked for years without trouble.

IMHO this arrangement was far simpler and more robust than any other I saw.

[Chrisc]

Yes, exactly the arrangement that I have in mind, in fact the rudder currently resides in my garage where I am trying (without much success) to dry the darn thing out so I can fibreglass it. I have already built the trim tab and am just now welding up the bits and pieces to attach it to the rudder. I was planning on posting photos as the self steering job progresses.

Chris

[Jim Cate]

Chris, does the H-28 rudder have any balance area? I can't remember. If not, it will take a big tab to drive it adequately.

The hardest part of getting my homebrew vane to work was getting the balance of the aux. rudder right. I did lots of calculations using the NACA data for the foil shape that I used and they were WAY off!. I finally just C-clamped the gudgeons on, hung the rudder on, ran the engine to provide prop wash and played with it, adjusting the balance a bit at a time until it "looked right". That proved successful if a bit inelegant!

Good luck with your project. As I have posted before, designing and building that vane was the single most satisfying boat project that I have ever done.

Cheers,

Jim

[Delfin]

Originally Posted by Jim Cate

Chris, does the H-28 rudder have any balance area? I can't remember. If not, it will take a big tab to drive it adequately.

The hardest part of getting my homebrew vane to work was getting the balance of the aux. rudder right. I did lots of calculations using the NACA data for the foil shape that I used and they were WAY off!. I finally just C-clamped the gudgeons on, hung the rudder on, ran the engine to provide prop wash and played with it, adjusting the balance a bit at a time until it "looked right". That proved successful if a bit inelegant!

Good luck with your project. As I have posted before, designing and building that vane was the single most satisfying boat project that I have ever done.

Cheers,

Jim

Jim, like you I ultimately just did 'eyeball' engineering on mine. My tab was only 6" deep and the rudder on the Cape George is pretty hefty. One concern I had was whether the rake of the rudder would complicate things, but if it did I never noticed. The one thing I do remember is the importance of getting the tab to be as close to the trailing edge of the rudder as possible. I think mine was separated by only 3/16" or so. Worked like a charm, and what I especially liked was how simple it was. Nothing to chafe and nothing humungous handing off the stern.

[Delfin]

Originally Posted by Chrisc

Yes, exactly the arrangement that I have in mind, in fact the rudder currently resides in my garage where I am trying (without much success) to dry the darn thing out so I can fibreglass it. I have already built the trim tab and am just now welding up the bits and pieces to attach it to the rudder. I was planning on posting photos as the self steering job progresses.

Chris

If its wetted with sea water, drying it may not be possible. Have you soaked it really, really well in water, preferable with a bit of 'Salt Away' mixed in with it? Then a trip to Death Valley might be in order.

[Chrisc]

The rudder on the H28 is not balanced and is quite large. However, I have been impressed with the vessel's handling - even if you haven't paid much attention to sail trim the helm is always light, never more than a finger or two required on the tiller to keep her on course. So I think a balanced trim tab at approx 20% of rudder immersed blade area will be sufficient.
Regarding glassing the rudder, I burned the paint off (it is built of heart Kauri) and then waterblasted it for a good couple of hours. I talked with the in-house technical genius at a firm called Adhesive technologies who are the agents in NZ for West System and they didn't forsee any problems with glassing a piece of timber than had been in seawater so long as it was dry. I have noticed that in the last day or so that the rudder is starting to check, particularly around the end-grain so it must be beginning to dry out. I need to find a friendly house builder with a moisture meter.

[Delfin]

Originally Posted by Chrisc

The rudder on the H28 is not balanced and is quite large. However, I have been impressed with the vessel's handling - even if you haven't paid much attention to sail trim the helm is always light, never more than a finger or two required on the tiller to keep her on course. So I think a balanced trim tab at approx 20% of rudder immersed blade area will be sufficient.
Regarding glassing the rudder, I burned the paint off (it is built of heart Kauri) and then waterblasted it for a good couple of hours. I talked with the in-house technical genius at a firm called Adhesive technologies who are the agents in NZ for West System and they didn't forsee any problems with glassing a piece of timber than had been in seawater so long as it was dry. I have noticed that in the last day or so that the rudder is starting to check, particularly around the end-grain so it must be beginning to dry out. I need to find a friendly house builder with a moisture meter.

My Cape George had a completely unbalanced rudder as well. I'm afraid I can't remember the exact % of my trim tab, but one thing to remember is that with a wind vane, you really are not trying to move the rudder a great deal - just enough to stay on course. As a result, you don't need huge amounts of power in the tab, and I found that even my small one generated more than enough. As a guess, I would think that 15% would be fine, and on your vessel a 4 to 5 inch tab should work fine. I would be curious to hear what size Jim Cate's was and whether he agrees.