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Cat Ketch rigs and Self Steering


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  #1 Howard

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Posted 16 April 2012 - 02:54 PM

One of the percieved benefits of a cat ketch rig is the ability to self steer. With the sails set towards the ends of the boat, vs. bunched in the middle as you would have with a sloop, if the boat wanders off course relative to the wind, the wind acting on one sail with greater force than on the other will create a turning moment that brings it back into equilibrium. At least that is the theory. From what I have read here, that is the practice of some as well. Some guys appear to be able to trim their sails and as long as the wind is not too fluky, the boat will hold a reasonably steady course......sometimes for miles. That is the extent of what I've heard. Don't know if it "wallows" or wanders along a course of it it keeps it on rails. Also don't know if that is just going to weather or if it works off the wind too.

Beyond that, has anyone attempted to perfect this further by use of some means of self steering gear? I assume a self steering vane setup is a bit extreme for this level of boat, but what about sheet to tiller setups? Those can be rigged to hold a good course to weather or off the wind.

Anyone tried it?

Spindrift 10N #529

Princess 26 - Under Construction


  #2 Ray Frechette Jr

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Posted 17 April 2012 - 12:00 PM

I wouldn't call it self steering by and large except for dead downwind.

Steering with sails however is a whole different ball of wax and clearly having the sails separated greatly aids in using sail trim to steer the boat. And do some pretty nifty tricks..

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  #3 Peter HK

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Posted 19 April 2012 - 10:52 AM

I've certainly had mine self steer to windward for 30 mins at a time. Generally the main needs to set fairly tight and the mizzen eased a little so if she falls off a bit the mizzen fills and drives her back up. This is with a tiller control line that holds it in a certain position....getting the right position takes a minute or two. Also everyone needs to stay fairly still so trim doesn't change- the only time I have to adjust anything is when someone grabs another beer.

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Peter HK
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  #4 Hirilonde

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Posted 19 April 2012 - 11:30 AM

.............the only time I have to adjust anything is when someone grabs another beer.


Bah! Tell your crew that they have to fill their old beer can with water and return it to the cooler when they take a new one.

Dave Finnegan

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  #5 Howard

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Posted 20 April 2012 - 07:44 AM

No takers? Will throw out a little more bait for the curious..........

Sheet to tiller systems go beyond the natural ability of a boat to self steer........either by form or by rig. They have been around a while, but the most often recited reference is a book on self steering systems written by John Letcher and published in 1974.

Basic premise of sheet to tiller systems is there is a direct correlation between sheet tension of the sails, sail trim and heading. Trim the sails for the heading you want and if you vary from that heading......above or below the apparent wind.......sheet tension will increase or decrease. You can take advantage of that by connecting a line from the sheet to the tiller and the system will apply weather helm or lee helm as needed to keep the boat on course (boat sailing a heading relative to the apparent wind). Once you figure it out for a particular boat and get a working system, it works amazingly well. Here is an example (I selected this one as it is one of the better examples of how it works.......although his use of a storm jib as his power source is atypical......principle is the same, but most would use the main sheet or jib sheet (main or mizzen on a cat ketch) to power the thing.......depending on heading).



The line from the sheet to the tiller is always from windward and the elastic is to lee. May seem counter-intuitive, but that's how it's done. Elastic tension has to balance the load from the sheet, so that varies with wind strength and how much power the sheets create. You can power them up or down with purchase from blocks. In practice, there is very little tiller movement. Rarely more than a few inches and response to wind shifts is instant. Far better than most helmsman could ever do. Another key feature is the elastic is set to go slack with the tiller amidships or only slightly to lee. You don't want the tiller to make wide oscillating movements.

Steering a heading is accomplished by trimming the sales. Get this right and it will hold a course for as long as the wind blows or you run out of water, whichever comes first. But it is to the apparent wind direction. If the wind shifts direction, the heading shifts with it.

To see how this works, sometime when you are on the water, hold one of the sheets in your hand or pull a bend in a sheet made fast and just hold it. Feel the slack and tension in the sheet as the wind shifts. Imagine that is tied to your tiller and you quickly get a notion for how it could work.

Spindrift 10N #529

Princess 26 - Under Construction


  #6 Ray Frechette Jr

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Posted 21 April 2012 - 05:00 PM

Sheet to tiller steering is different from original query. Original question was regarding self steering due to sails at ends of the boat.

Dead downwind withthe sials forward of the beam the boat self steers nicely with no sheet to tiller set up.

Sheet to tiller would work well also, as would windvane set up.

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