Shifted overlap stay adjuster.

Here you have the design of a "shifted overlap stay adjuster".

It is cheaper, lighter and smaller then any staymaster or threaded turnbuckle. It also allows you to quickly adjust the stay lengths and rig tension without any tools or measuring. You can always find back your old setting as each setting is unique.

The minimal adjustment incrediment of this adjuster is 5 mm in the given implementation, however every amount is possible by modifying the design in the placing of the holes. I chose 5 mm for the given implementation as I believe this to be a good balance between small incrediments and a total range of adjustment. In addition, this setup is easy to use in the drawings and explanation because it has only a few holes. Systems with smaller adjustment incrediments require more holes to be placed in the strip.

I have had a 4 hole strip system on my own boat the whole 2005 season now and the system held up very well. Season 2005 was pretty windy overhere, halve my races were in 15 knots and over with heavy seaway. This makes the test dependable in my opinion. However I will not accept responsibility for any failings of the given design. A bad choice in materials can significantly cut down on the load baring qualities of the setup.

Is 5 mm a too large minimal adjustement ?

In my experience about 50 kg's on the trapeze wire can put a sidestay 1 hole down (= 15 mm) when it was under some tension orginally. This means a 5 mm adjustment is equal to about 16 kg's difference in tension. When taking everything into account a 5 mm adjustment on both side stays will alter your rig tension by about 30 kg. Typically sidestay tension range from 30 kg to 90 kg on modern catamarans, depending on the conditions. The 5 mm adjustments allow you to cover this range with 30 kg, 60 kg and 90 kg. I think this to be a rather practical range of adjustment. With a similar shifted overlap adjuster of 5 mm steps on the forestay the rig tension can then be adjusted by halve of 30 kg so : 15 kg, 30 kg, 45 kg, 60 kg, 75 kg, 90 kg. This I think to be the maximum number of adjustment (6) you would ever want anyway. More are just to many to use effectively.

I always found 15 mm to be too large an adjustment to find the proper mast rake. Rougly speaking, on a F16, a 15 mm adjustment on the sidestays moves the mast top 180 mm (= 7 inches). With the 5 mm incrediments of the new adjuster this is modified to only 60 mm (just over 2 inches) per incrediment. This in my opinion is pretty close to what you want in the way of mast rake adjustment. In my experience any adjustment under 3 mm (= 36 mm on mast top = 1.5 inch) is useless; you won't be able to tell the difference. These 5 mm incrediments allow a full range adjustment of 65 mm which is 780 mm (= 2 feet 7 inches) of movement of the mast tip. This should be wholly sufficient to rerake your mast from sloop sailing to cat-rigged sailing with some margin to get the right rig tension.


The most simple system is just 3 strips of stainless steel with one strip having the holes at slightly difference interspacing. The best is however a flattened tube with a strip sliding inside it. This way you can also add another 75 mm adjustment by having the eye terminal on the stay go directly inside the tube without a strip. Stuff like that amd the fact that a flattened tube looks better as well adn doesn't have any sharp sides.

In the strip there can be slot in which the pin going through hole E can slide. This pin stays engaged and thus locks up the system so you can adjust it on the water (without any tools) without losing your mast overboard. This feature is also handy when reraking your mast singlehandedly, when adjusting the forestay length and when dropping the mast to trailer the boat. All these activities require you to temporarily slacken the rig tension.

However hole E can also be used to get a slightly bigger adjustement range. The system will work either way, the slot and locking pin is not needed for proper operation of the system. It is adviced to tape it somewhat up so it doesn't act as a pair of clippers, when you are not using the locking pin setup.

Take note : hole spacing is the distance between the centreline of one hole to the centreline of the one above it. It is NOT the distance between the top egde of one to the bottom egde of the other !


I think this covers all.

See the pictures to understand how it works.









In my next post some discussion on how to build them and how to use them most effectively.

Wouter