Self steering (again)

[charliehows]

Originally Posted by Snowpetrel

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

kh25 module 2.5 15/30 teeth $74au

[charliehows]

as far as the cable thing goes - knock yerself out guys. But the cogs work better.

[Jim Cate]

Originally Posted by Delfin

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.

G'Day guys,

I sold that boat and vane a decade ago, and all the drawings for the vane are on I-2 in Hobart and I'm in California for the foreseeable future... hence this is from memory (increasingly untrustworthy these days!).

Anyhow, the tab was about 20% of the rudder width, possibly a bit less. But remember, this was an auxiliary rudder, not the main rudder, and it was semi-balanced. In fact, in the end I kinda reverse-engineered the thing: built the rudder and tab, then adjusted the balance of the rudder to get the response that I wanted. Hanging a tab on an existing main rudder is a different thing entirely.

But, thinking about it a bit, with a longer keel boat that tracks well, your thoughts that small rudder deflections will be all that is required may well be correct. My boat was an old IOR one-tonner and likely a lot less stable in yaw than an H-28. Again from memory, I would see frequent 10 to 15 degree rudder movements as we sailed along off the wind. To windward almost no correction was required, so little rudder movement noted. Remember that with an aux rudder you take out any weather helm with the main rudder and then lock it in place.

Lastly, I don't understand CH's antipathy towards the cable drive systems. The dire friction situations he quotes don't agree with my experience at all, nor the experience of hundreds of AutoHelm users. And I would sure at least give Dyneema cables a try... I think that they would be brilliant!

Cheers,

Jim

[charliehows]

Lastly, I don't understand CH's antipathy towards the cable drive systems. The dire friction situations he quotes don't agree with my experience at all, nor the experience of hundreds of AutoHelm users. And I would sure at least give Dyneema cables a try... I think that they would be brilliant!

Cheers,

Jim[/QUOTE]

I think when i designed a unit based on cable controls i tried to reinvent the wheel - the way i used them didnt work. If you have seen them used effectively then using them in that way will probably work too. What i concluded was that tried and tested systems based on the most commonly used 90* cogs to transfer the drive from the vane to the pendulum werent beyond my ability to fabricate and that is what worked for me in the end. I did a lot of reading at the time and the most common mention of cable systems pretty much graded them as fairly unsuitable, which is what i found in practice. The thing i feel most people dont understand about cables is that when a cable turning through more than a few degrees of directional change is put under pressure the friction effect is distributed over the entire length of the cable and housing meaning it quickly becomes very resistant. So it matters how they are used in the unit.

[Delfin]

Originally Posted by charliehows

Lastly, I don't understand CH's antipathy towards the cable drive systems. The dire friction situations he quotes don't agree with my experience at all, nor the experience of hundreds of AutoHelm users. And I would sure at least give Dyneema cables a try... I think that they would be brilliant!

Cheers,

Jim

I think when i designed a unit based on cable controls i tried to reinvent the wheel - the way i used them didnt work. If you have seen them used effectively then using them in that way will probably work too. What i concluded was that tried and tested systems based on the most commonly used 90* cogs to transfer the drive from the vane to the pendulum werent beyond my ability to fabricate and that is what worked for me in the end. I did a lot of reading at the time and the most common mention of cable systems pretty much graded them as fairly unsuitable, which is what i found in practice. The thing i feel most people dont understand about cables is that when a cable turning through more than a few degrees of directional change is put under pressure the friction effect is distributed over the entire length of the cable and housing meaning it quickly becomes very resistant. So it matters how they are used in the unit.[/QUOTE]

Not quite sure you have the plot outline here, but I believe the OP is looking at mounting a trim tab on an outboard hung rudder, not a servo pendulum design. Driving a tab with gears might be possible, but pointless since cabeled systems work flawlessly for those who actually have them.

[Chrisc]

To clarify, my self steering system currently under build is a trim tab mounted on a transom hung rudder. I have used 90 degree gears on servo pendulum systems that I have built in the past with (some) success. From my experience, the mechanical linkage between the air vane and the servo pendulum or trim tab is vitally important - it really needs to be entirely without play and with minimal resistance, light, strong and with not even a hint of binding through out the entire range of movement. I find all this quite difficult to produce in my antiquated workshop.
I accept that sheathed cables could also be problematic from a friction viewpoint if not laid correctly, however they hold the promise of a fluid, play-free movement from air vane to trim tab - a very desirable attribute.
Since I am a retired person with time on my hands, I am going to have a go at a cable system, mainly because it really piques my interest. Shimano make a very nice sheath for their high end bike brakes that has a teflon core inside a stainless steel spiral and the whole thing enclosed in a uv resistant plastic outer.
Wish me good success.

[charliehows]

Chris, i found a cheap, effective way to build cables was to use black polythene narrow bore irrigation hose - costs absolutely peanuts - and heavy duty fishing line, using ironbark wood blocks bored to take the cable housing ends.
its just one of the things i tried and i mention it because of your post above. I think if its laid out in a straight run over a short distance it works extremely well and because the materials are so cheap keeping plenty of spares aboard is easy. But cables dont like turning corners, they dont like heavy loads, and they dont like pushing, so if you can avoid those things in your design they have the potential to work effectively. Good luck, and keep us posted.

[Chrisc]

Sir - you are a genius!
I know the irrigation hose you mention, in fact I think I have some. This sort of help and advice is what I love about this forum.

[charliehows]

Quote:
Originally Posted by Snowpetrel
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


kh25 module 2.5 15/30 teeth $74au


I just remembered why i chose those - because the bore sizes fit standard s/s round bar so theres no need to turn any shafts down for them, you just build the relevant shafts using that size bar...the other thing i found really useful is; theres two heavy duty s/s pipes that only come in 2 foot-ish lengths that are a nice snug fit inside each other - ideal in strength of material for both pendulum shaft and aux. rudder shaft. they dont usually store that stuff with the round bar, i found it sitting at the end of some shelves...

[akopac]

Originally Posted by 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.

I have an autohelm too and broke a line once. Had spare on board. What kind of #120 line did you use and how did you terminate the end by at the trim tab control arm

[Meandercp]

I just used mono filament fishing line and tied a few half hitches to terminate. The hardest part is threading the line through the little hole on the control arm. I have continued to use this for years. It wears out faster than stainless, but it is cheap and easy to store a spool which is enough for years and years. Having read comments from others, I agree that dyneema might be a good choice. It is usually pretty slippery, plenty strong and chafe resistant. I believe they make fishing line out of dyneema, too.

I have also replaced the tubing a few times with vinyl tubing from a hardware store.

[NevilleCat]

Originally Posted by Chrisc

To clarify, my self steering system currently under build is a trim tab mounted on a transom hung rudder. I have used 90 degree gears on servo pendulum systems that I have built in the past with (some) success. From my experience, the mechanical linkage between the air vane and the servo pendulum or trim tab is vitally important - it really needs to be entirely without play and with minimal resistance, light, strong and with not even a hint of binding through out the entire range of movement. I find all this quite difficult to produce in my antiquated workshop.
I accept that sheathed cables could also be problematic from a friction viewpoint if not laid correctly, however they hold the promise of a fluid, play-free movement from air vane to trim tab - a very desirable attribute.
Since I am a retired person with time on my hands, I am going to have a go at a cable system, mainly because it really piques my interest. Shimano make a very nice sheath for their high end bike brakes that has a teflon core inside a stainless steel spiral and the whole thing enclosed in a uv resistant plastic outer.
Wish me good success.

Maybe it doesn't need to be as free of play and tightly schmic as you think; have you seen James Wharrams designs used on quite a few of his cats? Here
And in use

here

[double u]

along these lines, bike sprocket for adjustments, windvane V-shape frame with cloth covering, very easy to make, a very small amount of "slop" in the "bearings" reduces friction to almost nothing. Made one in 81 in Malaga for our Wharram cat, out of galvanised water tubes & the help of a local "soldatura" (of course in 81 they thought I was some sort of mad inventor...) Gear was very sensitive & steered the boat as well as a windvane could. Moved the tab back from the rudder's rear edge for more power