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Old 19-04-2014, 22:10   #1
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Sheet to Tiller Steering

Given recent controversies about reliance on technological steering aids, I thought it was worth distilling a few key points from Letcher’s book, “Self Steering for Sailing Craft”

I have always thought of vanes and autopilots as convenience features, and where possible I prefer to use the inherent characteristics of the boat. This greatly reduces the workload for the technology when it is in use (and power consumption, for a pilot). Plus I find it more satisfying to have the boat “wanting” to go in the desired direction, like a horse getting a sniff of home.

If there is a breakdown, it’s a simple matter to intensify measures to do with course stability which were already partly in place. Even if they weren’t, they’ll be well understood in relation to the hull and sailplan.

I’m just taking the opportunity to re-read Letcher. I’ve had his book since I was young, and some of his insights I had forgotten, others I had mistakenly thought I had discovered for myself.

But what I noticed most was this: having acquired some worldly familiarity makes me much more impressed with Letcher’s advice and explanations this time round. It’s a work of genius.
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Old 19-04-2014, 22:13   #2
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Re: Sheet to Tiller Steering

Here’s some of his key insights, as I see them.

The first two are self-evident, but their significance runs deep, and the underlying reasons for the statements in brackets seem widely misunderstood, including in a sticky on the topic of weather helm on this forum.

1) Sailing on the wind tends to be inherently stable because of heel (luffing decreases heel, which corrects luffing)

2) Sailing off the wind is inherently unstable because of heel (luffing increases heel, which intensifies luffing)

3) Stability is enhanced by oversheeting sails carried forrard, and undersheeting aft, even off the wind.

4) Compensation for wind-strength changes is by taking some part of the running rigging, with or without changing the mechanical advantage, to pull the tiller to windward. This will exceed the required weather helm; the difference (and some of the adjustment) is provided by elastic cord set to pull the helm to leeward.

5) The relaxed length of the elastic cord should coincide with tiller amidships or slightly to leeward. The variable to play with is stiffness (ie number of cords, and/or diameter). Use rubber tubing, or synthetic (solid) stretchy cord, not braid-covered traditional bungee cord.

6) Simplest way of stabilising close reaching: hitch a line pulling sideways on midpoint of standing part of mainsheet tackle to sense wind strength, lead that to windward side of tiller; set up bungee in opposition as in 4).

7) Simplest way of stabilising broad reaching: exaggerate point 3: if necessary, improvise a long bowsprit and set a jib on it, sheeted flat. (If there is no mizzen: consider setting up a riding sail, particularly if there are twin backstays, on the windward stay: undersheet when on course).
Use a staysail sheet to sense luffing: lead that to windward side of tiller; set up bungee in opposition as in 4), but using stiffer rating than in 5).

8) Simplest way of stabilising square running: twin headsails on poles, sheets led to tiller on each side.
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Old 19-04-2014, 22:15   #3
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Re: Sheet to Tiller Steering

Letcher does not mention the twistle pole arrangement, which is a proven way of preventing the rolling which twin headsails generally promote (which he DOES mention). AFAIK, the twistle is a more recent invention.

He does mention that friction is a major enemy. It will pay to use high quality, rolling element (ball or roller) blocks. The sails and sheets and blocks should be identical and disposed symmetrically. If increasing wind causes decreased steering accuracy when running, try easing the sheets.


There is no shortage of sailors who will tell you none of this “sheet to tiller stuff” will work, or that you’ll spend more time fiddling to make it work than you save from not being stuck on the helm. Tere are also those who will say it only works on traditional hull/keel combos. *

It seems to me what they’re really saying is that they haven’t been able to make it work for them.

Possibly they didn’t have access to all (or possibly any) of the insights above.

If they’re given to dispensing advice on things which won’t work on the internet, I would suggest it’s likely they’ve never even tried.
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Old 19-04-2014, 23:31   #4
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Re: Sheet to Tiller Steering

Easy on a small yacht, harder on a big one. The second picture shows attachment to the staysil sheet. This was last year: (yes that is an old bicycle rim cost 1 usd)
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Old 19-04-2014, 23:51   #5
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Re: Sheet to Tiller Steering

Indeed, Newt.

Everything's harder on bigger boats.

Except, perhaps, holding formal dinner parties, intimidating stand-on vessels into yielding, ....

And convincing people to go to sea who really shouldn't ...

Nice setup, BTW
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Old 20-04-2014, 00:11   #6
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Re: Sheet to Tiller Steering

Newt, great idea about the bicycle wheel. Now I finally know why we got the kid that new bike!
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Old 20-04-2014, 00:19   #7
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Re: Sheet to Tiller Steering

I used sheet to tiller steering on my Westsail 32 and it worked great as long as i was not sailing direct downwind. I loved it. I could never get it to work on my Privilege 39 catamaran which had wheel steering.
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Old 20-04-2014, 00:26   #8
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Re: Sheet to Tiller Steering

Quote:
Originally Posted by Andrew Troup View Post

There are also those who will say it only works on traditional hull/keel combos. *
The most traditional of all cruising boats, Josh Slocum's Spray, had such awesome directional stability that she would hold course on any point of sail with nothing more than a lashed helm. A fact that was verified by my friend George Maynard when he built an exact Spray copy (not a Roberts) and sailed her around the world.

Don't know about modern boats but as a schooner, Panope self steered with staysail sheet to tiller steering perfectly (when my father selected the Saugeen witch design, a major factor in the decision was the ability to self steer without windvane or autopilot).

Certainly hull/rig type must be a large factor with successfull sheet to tiller steering. I wish I was savvy enough to explain why.

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Old 20-04-2014, 00:33   #9
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pirate Re: Sheet to Tiller Steering

When the student is ready, the teacher appears.

Outstanding work Newt. Real sailor stuff.

I had a serious case of the hots for the Aleutka all those many years ago and ever since. Letcher walked the walk. Right with Guzzwell IMO.
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Old 20-04-2014, 01:35   #10
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Re: Sheet to Tiller Steering

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The most traditional of all cruising boats, Josh Slocum's Spray, had such awesome directional stability that she would hold course on any point of sail with nothing more than a lashed helm. ......

Certainly hull/rig type must be a large factor with successfull sheet to tiller steering. I wish I was savvy enough to explain why.

Steve
Letcher alludes to Spray in particular and long keels in general: he points out that, while a fin keel has a LOT less yaw resistance than a long keel, when a fin is combined with a decent sized rudder, positioned well aft, the combo has an overall length dimension not significantly less than most 'long' keels from the cruising fleet. (Where the rudder is often some distance in from the stern, and the forefoot often cutaway - although not in Spray)

The fin/rudder combo is obviously more efficient (in the same way that a plane develops more lift from a separate wing and tailplane than if they were joined)

and being able to develop lots of lift in the desired direction with little drag is a good thing from the point of view of active yaw control, (as with a decent wind vane or autopilot) but does not tell the whole story for passive yaw control (sailing with helm lashed)

The fact that not all the intervening space is filled in, means that there is not the same degree of passive damping against external yaw-inducing forces.

Letcher says of modern underbodies "such boats are quicker to turn off-course when the helm is simply let go, and have less ability to damp out oscillatory yawing that might be induced by self-steering gear."

nevertheless, all his experiments were conducted in fin keelers, and he says

"it has been amply demonstrated that boats with short keels and separate rudders can be made to steer themselves quite adequately by windvane or sheet-to-tiller gear, so length of keel for self-steering ability need not be a consideration in the choice of the design of a voyaging yacht".

(Which I'm not alone in loudly endorsing)

Elsewhere he points out that the points I numbered 1) and 2) in my early post are less applicable to beamy boats. He doesn't add the qualification which in recent times I think becomes important : PROVIDED they do not take advantage of their beam to fit a tall rig.

I say this because his points 1) and 2) presume that the primary cause of weather helm from heel is what I think of as the "spanner" effect, due to the drive on the sails being applied far out to leeward because of heel, 'screwing' the bow up into the wind.

I think he's right to point out that this predominates (and he had done formal research into that exact question); most sailors have been misled to believe that weather helm from heeling is entirely due to the immersed shape of the hull being so lopsided.

While I believe this is not true for the general case of cruising boats, it may be a significant contributor for very beamy boats which nevertheless heel enough to make the underwater shape very asymmetrical when on the wind (eg most modern racing sailboats).

Returning to Spray, I would imagine that Joshua sailed her pretty upright, and because of this, point 2) would not be much of a factor, and the hull form would be more like a cruising catamaran in terms of being course-stable downwind.

Secondly, Joshua had a very long bowsprit on Spray, AND fitted her with a mizzen (purely to assist steering) shipped as far aft as it could go, on the taffrail IIRC - and this complies as well as any boat could with Guzzwell's point 7) about exaggerating the spread from foresail to aftmost sail.

Thirdly, the rudder was probably very heavily built. Letcher doesn't talk about this in relation to Spray, but Wanderer III was an enigma because she sailed thousands of miles in varying windstrengths (admittedly, with the main reefed more than would normally be the case) with the tiller free, not even lashed!

Letcher reckons this could have been an accidental happenstance: when the boat heeled, gravity acting on the rudder swung the helm to weather in proportion to the amount of heel.
I've considered trying a pendulum on a more modern boat to simulate this effect, but it occurred to me it would have to be well damped.

The rudder on Wanderer III would have been well damped by the water immersion and flow, and (althought Letcher does not mention this) the rudder rake, while not as considerable as on Wanderer V, would have added a tendency to self-centre with gravity, which I reckon would have been valuable in light winds, which generally defeat 'free rudder' attempts (unless the boat is capable of a decent turn of speed in drifting conditions).

So a subset of these characterisitics is probably sufficient to plausibly explain Panope's coursekeeping with sheet to tiller (the short, divided rig must have helped in her original guise, and the long keel would still)

and to me the whole nine yards certainly explains why Spray was such a smug pussycat in that department, requiring no assistance.
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Old 20-04-2014, 01:47   #11
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Re: Sheet to Tiller Steering

There's one other design characteristic Letcher mentions for positive yaw stability: he points out that the centre of gravity needs to be forrard of the hydrodynamic centre. *

And that, I think, is partly why we saw forefoots cut away on long keel yachts as designers got more attuned to the characteristics of small vessels, more than the aft extent of the keel was shortened.


Some salty little offshore boats like the Vancouver 27, 32 and 36, spring particularly to mind.

* He doesn't draw the analogy with the yaw stability of a dart when thrown correctly as opposed to backwards, but I think that this is applicable, albeit a gross exaggeration.
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Old 20-04-2014, 02:55   #12
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Re: Sheet to Tiller Steering

Andrew, interesting thread, don't want to drift it but you used the expression "the whole nine yards" do you know the origin of that saying?
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Old 20-04-2014, 03:04   #13
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Re: Sheet to Tiller Steering

rs

I used to assume it referred to nine cubic yards of concrete (given that you never expect to use the entire amount you've ordered)

Or possibly cloth, perhaps from the days when you had to 'send to town' to make up clothing for the entire tribe ...

But I've heard other explanations and I think it's been around a long time. One explanation was that the ammunition belts used by early machine guns were 27' long...

I heard another story about American football, but any sort of football is mystery to me, particularly that sort...

Sorry I can't help; I've a feeling it might be one of those expressions whose origins have been lost.
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Old 20-04-2014, 05:42   #14
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Re: Sheet to Tiller Steering

Ned- I loaned you my copy of this book twelve years ago. Please return it when you are finally done reading it. I believe you promised that you would. Thank you.
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Old 20-04-2014, 05:56   #15
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Re: Sheet to Tiller Steering

Andrew you were correct in the ammo belts. The American ammo belts in their fighter aircraft were 27 feet long. When the pilots returned after a sortie and the ammo boys were reloading the aircraft and found the belt completely used up, Wow, he gave them the whole 9 yards. So the expression is not that old. Good for you for knowing. No I'm not an American.
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