Author Topic: Forestay/Jib adjustment  (Read 2406 times)

Brian Mikiten

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Forestay/Jib adjustment
« on: April 26, 2026, 10:02:48 PM »
I don't see much about forestay adjustments and given that there is no backstay, I'd expect to see more. I understand the effect of the shrouds on the tension but wondered if there was a standard (or typical) length of the adjustment loop at the clam cleat by the furler attachment. I seem to have only about 3" of adjustment but remember seeing boats with over 12". Assume no vang is on.

THX

Dean Nelson

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Re: Forestay/Jib adjustment
« Reply #1 on: April 28, 2026, 12:01:46 AM »
The length of the forestay determines the mast rake.  Per class rule 7.4. "The length of the headstay assembly is optional. The recommended total length should be so
that the rake of the mast (dimension R in Figure 3) is between 34′ 9″ and 35′. This measurement will not be enforced and has been kept in the rules as a reference point only."

Brian Mikiten

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Re: Forestay/Jib adjustment
« Reply #2 on: April 28, 2026, 01:24:18 AM »
Good guidance. I'll check the measurements.

Josh Jones

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Re: Forestay/Jib adjustment
« Reply #3 on: April 28, 2026, 02:50:21 PM »
So now that a lot of people are installing adjustable forestays, and this is no longer "enforced", what length are folks using?  Are we really adjusting the forestay regularly based on conditions?

Brian Mikiten

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Re: Forestay/Jib adjustment
« Reply #4 on: April 30, 2026, 07:56:14 PM »
In my case, I had to replace some of the components in the adjustment cleat mechanism and was concerned that I didn't provide enough adjustment. I had seen some boats with almost 12" of available line even if they only used 3-5" of actual adjustment. I realized this was an issue when during the last race we were being very out-pointed by another boat and saw that my jib was quite loose (floppy forestay) and beyond adjustment. I can't imagine doing any on-the fly adjustments but this would be for basic set up and tuning.

Josh Jones

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Re: Forestay/Jib adjustment
« Reply #5 on: May 01, 2026, 01:05:52 PM »
hmm, I never thought to consider that as an indicator of rake measurement

I suppose it would be relevant if all of our jib halyards were calibrated at the exact same distance, but I'm not sure that is the case
« Last Edit: May 29, 2026, 03:44:01 PM by Josh Jones »

Brian Mikiten

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Re: Forestay/Jib adjustment
« Reply #6 on: May 19, 2026, 05:09:31 PM »
To further my education (obsession) on this subject, I pulled my jib (furled) and found that I had about 3" of adjustment on the headstay. This compares to what looks like 12"+ in the original manual. I'm going to confirm that my mast is not WAY forward tomorrow but wondered what other people had for available adjustment. Photo from the manual is shown here.

Dean Nelson

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Re: Forestay/Jib adjustment
« Reply #7 on: May 19, 2026, 10:37:32 PM »
How tight the jib halyard block and tackle assembly is adjusted has secondary/minimal effect on the mast rake.  The length of the block and tackle assembly is simply dependent on the length of the jib halyard.  How tight you want to pull the jib halyard block and tackle is dependent on the wind strength, whether you want any wrinkles in the jib luff and how much curvature you want in the jib luff.  Pulling the block and tackle assembly tight results in the belly of the jib moving toward the luff, reduces the wrinkles in the jib luff and reduces the curvature in the jib luff...all resulting in depowering the jib.  Having the block and tackle assembly too loose results in wrinkles at the luff, the belly moved back and more curvature in the jib luff.  Experience will tell you where the proper jib halyard tension settings are for low, medium and high wind.  Mast rake can primarily be adjusted via: 1) the length of a fixed forestay, 2) the length of the upper furler pigtail, or 3) an adjustable forestay.  Recommended mast rake is between 34'9" and 35'.  On windy days, typically less mast rake is desired.  On low to moderate wind days, typically more mast rake is desired.  Mast rake cannot be adjusted out on the water.

Brian Mikiten

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Re: Forestay/Jib adjustment
« Reply #8 on: May 20, 2026, 10:20:53 PM »
I appreciate the response and understand the purpose which is why I was asking about other boats. Mine has less than 3" of movement which hardly provides any effective change IMHO. I'll look at the 1 and 2 items.

Josh Jones

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Re: Forestay/Jib adjustment
« Reply #9 on: May 29, 2026, 03:38:46 PM »
How tight the jib halyard block and tackle assembly is adjusted has secondary/minimal effect on the mast rake.  The length of the block and tackle assembly is simply dependent on the length of the jib halyard.  How tight you want to pull the jib halyard block and tackle is dependent on the wind strength, whether you want any wrinkles in the jib luff and how much curvature you want in the jib luff.  Pulling the block and tackle assembly tight results in the belly of the jib moving toward the luff, reduces the wrinkles in the jib luff and reduces the curvature in the jib luff...all resulting in depowering the jib.  Having the block and tackle assembly too loose results in wrinkles at the luff, the belly moved back and more curvature in the jib luff.  Experience will tell you where the proper jib halyard tension settings are for low, medium and high wind.  Mast rake can primarily be adjusted via: 1) the length of a fixed forestay, 2) the length of the upper furler pigtail, or 3) an adjustable forestay.  Recommended mast rake is between 34'9" and 35'.  On windy days, typically less mast rake is desired.  On low to moderate wind days, typically more mast rake is desired.  Mast rake cannot be adjusted out on the water.

That's mostly true, but if for whatever reason you have a much shorter forestay and your mast is not raked back properly, that shortened distance *would* affect the slack in the jib halyard.

Lets say his rake is something weird like 35'5" from the transom, this would mean that his forestay is shorter, and the head of the jib would be closer to the turning block at the top of the Furler, and thus less adjustment available at the base.

Josh Jones

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Re: Forestay/Jib adjustment
« Reply #10 on: May 29, 2026, 03:41:13 PM »
Also on windy days MORE rake is recommended (meaning the mast is raked back farther), this would result in a *shorter* measurement to the transom.  But you have *more* rake.
« Last Edit: May 29, 2026, 03:43:02 PM by Josh Jones »

Josh Jones

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Re: Forestay/Jib adjustment
« Reply #11 on: May 29, 2026, 03:45:27 PM »
To further my education (obsession) on this subject, I pulled my jib (furled) and found that I had about 3" of adjustment on the headstay. This compares to what looks like 12"+ in the original manual. I'm going to confirm that my mast is not WAY forward tomorrow but wondered what other people had for available adjustment. Photo from the manual is shown here.

Also how old is your Jib? Perhaps it's just stretched out and tired.

Dean Nelson

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Re: Forestay/Jib adjustment
« Reply #12 on: May 30, 2026, 09:42:31 PM »
There are multiple thoughts on mast rake, which varies by boat design.  For the U20, the recommended mast rake is between 34'9" and 35'.  Here is an AI response to mast rake in high wind:  With high wind, should there be more or less mast rake to a sailboat?  In high winds, you should generally have less mast rake (a more upright mast) on a standard keelboat or monohull to prevent excessive weather helm. However, the exact rule depends entirely on your specific boat class; for example, many high-performance beach catamarans, skiffs, and foiling boats actually utilize more mast rake in heavy air to de-power the rig and drag the boom close to the deck. The mechanical trade-off depends on how your specific vessel balances two opposing forces. Standard Monohulls and Keelboats: Less Aft Rake For traditional monohulls, high winds cause the boat to heel significantly. Heeling naturally forces the boat to spin up into the wind, a phenomenon known as weather helm. The Problem: Raking a mast further aft moves the sail plan's Center of Effort (CE) backward. This generates even more weather helm. The Solution: In heavy air, shortening the forestay to pull the mast more upright (less rake) shifts the sail power forward. This counters the rounding-up effect, neutralizes the steering, and reduces massive rudder drag. Rig Tension vs. Rake: On standard boats, do not confuse mast rake (the static tilt of the spar) with mast bend (curving the middle of the mast). In high winds, sailors crank down on the backstay. While this slightly alters rake, its primary purpose is to bend the mast, which flattens the mainsail and spills excess power. Performance Catamarans and Foiling Boats: More Aft Rake On multi-hulls (like a Hobie 16) and modern foiling classes, the conventional rule is often flipped upside down. The Aerodynamic Goal: In high winds, these boats suffer from extreme overturning lift. To combat this, sailors rake the mast as far back as the rigging allows. The End-Plate Effect: Shifting the mast aft lowers the boom closer to the trampoline or deck. This seals the gap beneath the sail, channeling wind efficiently across the sail skin rather than letting it escape underneath. De-powering the Top: The radical tilt allows the top of the sail plan to cleanly twist out and spill overwhelming wind gusts, while keeping the boat's driving force closer to the water level to prevent a pitchpole (capsizing forward). Any resulting heavy weather helm is physically corrected by raking the rudder blades forward rather than altering the mast.