Self Steering - Sailing downwind

[Nicholson58]

Originally Posted by Captain Graham

I sail in Lake Erie it is 200 miles west to east and is very shallow.
So even with just a 15 MPH wind the waves can build a good chop.

I like to balance my sailboat and setup self steering.
Going into the wind and waves no problem but going down wind I have always had problems.
This has been a problem with the 5 sailboats I have owned.

The issue is when a large wave catches up with me it picks up my stern and pushes it to one side.
Then the wind catches the sails and I round up.

Well this weekend I kind of found a solution.
The weather was great 10-15 MPH winds and a normal good chop.
I sailed upwind closed hauled at a about 5 mph with self steering for about 3 - 4 hours.
Very relaxing.

But when I started my return I tried sailing with just my jib but still the same old problem.
The wind had picked up a little to 15-20 MPH

Well I got a little tired from hand steering so I wanted to heave too and take a break but I was too tired to put up the main.
So I tacked and back winded the jib but did not put up the main.

Too my surprise my sailboat started to sail almost down wind and stayed on course well.
I did have to make a few adjustment but it worked.

So with jib only and hand steering I was sailing at about 5 mph
With the jib back winded and self steering I was sailing at about 3 MPH.
The course was not directly down wind but good enough for me.

I sailed this way for 2 hours without touching the tiller.

Has anyone else done this?

Typically done in rough stuff in the ocean. Seas toss the transom everywhere. Powered up aft sails spin the boat around. The best solution is double head stay tracks. Raise a second head sail and pole out. Often, the boats carry two poles. Sometimes there are two identical jibs so tac the same side covering one another or down wind, separated. No main. Prime example is an Amel.

[CarinaPDX]

There are a few posts here that are just wrong. To understand what is stable downwind (any point of sail actually), and make your own good appraisal, you should understand how to use force vectors to model your boat, its Center of Effort (CE) and Center of Lateral Resistance (CLR), plus the rudder effect necessary to counter any imbalance. The Power Squadrons had (and I suppose still has) an excellent sailing theory course that cover this well (I taught this course in the late '80s). There are also some good books for racers that explain the same material.

The most stable DDW sail plan is a twin headsail: identical sails set on opposing sides of the bow. The wind just pulls the boat straight downwind, regardless of gusts. Just leave ample maneuvering room to get them down at the end of the run. The next best thing is a staysail and jib opposing one another, using a small jib or storm jib to keep the sizes similar - this is what I mostly used on the westbound Atlantic crossing. Next is the jib alone, which will also pull the bow down and will still be resistant to broaching although some steering effort may be needed to maintain course because the CE is to the side of the CLR. After these, things get far less stable and should be used with caution if gusting or quartering seas are anticipated. Wing-and-wing (poled out jib opposing the main with preventer) is useful in stable conditions and light to moderate wind when greater sail area is desired. However, it is rare to be able to get the CE lined up with the CLR so a gust will put a torque on the boat that can require a significant correction. Because the CE is further aft and closer to the CLR then the previous sail plans the tracking is much less stable. In this case if the boat starts to yaw and backwinds one of the sails the likelihood of a broach increases greatly. So use wing-and-wing judiciously. Finally, in what I would call the lazy fool approach, I see sailors that furl the jib when the wind pipes up and use the main only because it is easier to furl the jib than drop the main. This puts the CE near or behind the CLR (very unstable) and far off to the side (requiring steering compensation). So in steady wind the rudder is over, countering the yaw moment and acting like a brake as well. If a gust hits, the CE from the sail spikes, requiring an immediate and large steering response. Often the rudder is simply unable to provide enough force to counter the yaw and a broach ensues. Self-steering and autopilots are simply not smart enough to counter this foolishness; this is a recipe for breaking things. Don't do it.

The problem with self-steering and sheet-to-tiller systems downwind is that the apparent wind can be so light (in light winds) and thus can provide very little input force for steering. Letcher got around that by using the staysail for the sheet-to-tiller, thus using a large sail area to provide steering force (the staysail was not used to provide drive for the boat in that case).

Again, a plea to all to learn the interplay of forces on a boat: it explains so much.

Greg

[Don C L]

Originally Posted by CarinaPDX

The problem with self-steering and sheet-to-tiller systems downwind is that the apparent wind can be so light (in light winds) and thus can provide very little input force for steering. Letcher got around that by using the staysail for the sheet-to-tiller, thus using a large sail area to provide steering force (the staysail was not used to provide drive for the boat in that case).

Greg

Yes, and Letcher actually says that Skidmore used that from "a close reach to a very broad reach," not DDW. (Page 46)

[barryglewis]

My first singlehanded voyage was non-stop Cape Town to Sydney in a 32 ft steel sloop in1974 to 75. Took it easy, dropped down to 41°30'S, took 86 days.
Aries pendulum wind vane, roller reefing and hanked on jibs, a very long fin, could ha e been "long keel" and skeghung rudder.

A lot of the time I was under close reefed main only, before going to bare poles. Used to adjust the course in bad weather so as to minimise slewing from waves / swells from SW and NW .

Moral,
1) beware pundits
2) what can work on one style of boat and approach to sailing isn't necessarily good for different type.

PS, during the 50,000naut miles we've done in Risky Business (see avatar pic), an Alloy Adams 13, we've frequently run nearly dead down wind under electric autopilot and any of main only, reefed, or jib only, or barepoles. We find as the SAES get up we have to reduce sail to keep A/P from being overwhelmed, keeping speeds below 8knots, below 6knots in strongest blows.
Very different boat to the steely, Risky is 13.5m by 3.1m beam by 3m draft, 2.7 ton lead in bulb, 9 ton in world voyaging trim(lots of spares and tools).

[Woody]

One of my boats was set up with twin headstays and two sets of symmetrical jibs, one set for light and another smaller pair for heavy air.
There was also a dedicated set of poles mounted at the spreaders on the mast. The sheets were led to a set of snatch blocks mounted on the rail athwart the tiller. A pair of simple cam cleats on the tiller allowed easy connection and adjustment.


Another boat I owned had a self steering windvane, which would steer the boat when running in 10 knots or more, but this simple sheet to tiller setup worked far better, in much lighter wind.



The boat was an Aleutka, designed by John Letcher. A pdf of his book (out of print) on self-steering is available online here. Its a unique book and a must read.



I sailed that boat across the Gulf of Mexico twice with no autopilot, hand steering or using stt setups the entire way.



Pictures attached are a diagram of the arrangement from his book, the sails, the sheet to tiller setup, and the boat.

[Woody]

Attached a photo of of Letcher's original Aleutka, steering with twins on headstays.