Tuning the mast

[James Sherk]

Hi guys, put my boat in the water couple weeks back. This is the picture of it after I brought it into the marina from 5 miles down the road.
When tuning the mast with a proper gauge, you want the rig between 14 and 15% breaking strength of the rod rigging , if it is set up correctly, the rig will sing at 9 kn. Make sure the mast is straight up and there is no rake to our boats to talk about however, when you do use your back stay, you will get rake.
Want to thank the group for talking about the pedestal
I took mine apart this spring and found out it was all rotten ordered the parts from the manufacturer and rebuilt it before I put the boat in the water.
Mine was so bad that I couldn’t imagine sailing it after seeing it
to use it again this summer
The other thing that I found when I pulled out my fuel tank and cleaned it got all the sludge out of it. I noticed that the exhaust hose was leaking from the engine. I changed it when I put the tank back in the boat. I found that it rocked back-and-forth, I decide to move the exhaust hose around the tank to the port side and back out to the back of the boat, which did solve that problem in the process, I changed all the hoses from the engine compartment to the back of the boat. They seemed to be in bad shape.
James Sherk
Pegasus

[Francois Rivard]

I generally agree except for rake, also there's pre-bend to consider depending on your main's cut and shape.  For example: My cruising main is designed for 3 inches of pre-bend. 

About rake: Rake = whole mast angled backwards = power in the rig and weather helm. The boat's keel and rudder foils are designed for a small amount of weather helm. For racing: Rake for light air should be adjusted to be more pronounced than rake for heavy air.

Rake is controlled by the lenght of the forestay, think about it... If the forestay lenght doesn't increase how can the the mast go backwards? Simple grometry. 

The backstay does nothing for rake, it's designed to increase pre-bend, flatten your main,  and therefore improve the ability to point and lessen heel in heavy air.

How does it work? Think about a bow ( as in bow and arrows) given that the forestay lenght is fixed, cranking on the backstay will cause the last few feet on the top of the mast to angle back and go down, causing the mast' center to bow forward (like pulling the string on a bow) , effectively pulling the middle of the main's luff foward and decrease the airfoil's thickness. ( sail belly). Be assured that from about 3 feet down from the top, the mast doesn't go backwards when the backstay is tensionned, in fact: it goes forward from the bowing effect. 

Long story short: Heavy wind = less rake for less weather helm and less power/heeling.  Light wind = more rake for more power and some additional desirable weather helm. 

For general cruising, my rake is set for a neutral helm around 10 knots apparent. Seems like a happy medium to handle 1-20 knots of apparent wind without having to fiddle with the pain in the butt turnbuckle adjustment built into my old original Harken furler. 

I hope that clarifies things.  

François Rivard 

1990 34+ "Take Five" 

Lake Lanier, GA 

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[Francois Rivard]

Ps. As per C&C's instructions, my "happy medium" rake setting is 10" from the gooseneck. 

How to measure? Take a pail or some other object with some weight and attach to your main halyard, the object should hover about 10 or so inches back from the gooseneck. It's all explained in details on the C&C site. 

-François 

[David Knecht]

I disagree with Francois on one point about the mast.  I agree that forestay length controls the rake.  But we don't have carbon masts and they don't bend much with backstay tension.  So while there is some effect on the main, in my mind, backstay tension on our boats is the primary method of controlling forestay tension.  A "slack" forestay curves off to leeward.  Increasing backstay tension increases rake and prebend slightly, but mostly it increases the tension on the forestay therefore reducing the tendency of the forestay to curve to leeward, ie making it straighter.  This has the effect of flattening the leading part of the genoa, improving pointing but also depowering the genoa.    Dave

David Knecht

S/V Aries

1990 C&C 34+

New London, CT

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[Helen Tacha]

You're spot on about backstay tension's role in controlling forestay tension on boats with less flexible masts. Here's how it breaks down¹:
- *Backstay Tension's Primary Role*: Increasing backstay tension indeed increases forestay tension, reducing its curvature to leeward. This straighter forestay flattens the genoa's leading edge, enhancing pointing but depowering the sail.
- *Effect on Rake and Prebend*: While backstay tension does slightly increase rake and prebend, its primary impact remains on forestay tension and genoa shape.
- *Mast Stiffness Considerations*: Unlike carbon masts that can flex significantly, stiffer masts require more precise tuning. Backstay tension becomes crucial for fine-tuning forestay tension and sail shape.
- *Tuning Priorities*: When setting up your mast, consider these priorities:
    - *Prebend*: Aim for 2-4 inches of prebend, depending on wind conditions and sail shape.
    - *Headstay Tension*: Balance tension to achieve optimal genoa shape and pointing performance.
    - *Rake*: Adjust forestay length to control rake, ensuring neutral helm.

To achieve optimal performance, consider the following dynamic responses:
- *Backstay Tension*: Use it to fine-tune forestay tension and genoa shape, especially in varying wind conditions.
- *Sideways Bend*: Minimize excessive sideways bend to maintain efficient sail shape and pointing.

Some general guidelines for tuning include:
- *Uppers Tension*: 27-29 on the Loos gauge for moderate conditions, increasing to 35+ in heavy winds.
- *Lowers Tension*: Looser than uppers, with windward lower tightening during sailing.
- *Spreaders*: Max aft sweep to achieve desired prebend and support for the spinnaker.

Keep in mind that specific settings may vary depending on your boat's design, sail plan, and sailing conditions. Experimenting with different settings and monitoring performance will help you find the optimal setup.

To view this discussion visit https://groups.google.com/d/msgid/cc-3436/385FC658-DF1F-456F-93E3-723E8A6F679B%40gmail.com.

[Peter Griffin]

Thank you responding to my query. My last boat was a J120. With a carbon fiber mast. I am finding Kuleana a bit  tricky  to set up. 

This is all very helpful. 

 Pete G

Sent from my iPhone

On May 24, 2025, at 6:04 AM, Helen Tacha <helen...@gmail.com> wrote:



You're spot on about backstay tension's role in controlling forestay tension on boats with less flexible masts. Here's how it breaks down¹:
- *Backstay Tension's Primary Role*: Increasing backstay tension indeed increases forestay tension, reducing its curvature to leeward. This straighter forestay flattens the genoa's leading edge, enhancing pointing but depowering the sail.
- *Effect on Rake and Prebend*: While backstay tension does slightly increase rake and prebend, its primary impact remains on forestay tension and genoa shape.
- *Mast Stiffness Considerations*: Unlike carbon masts that can flex significantly, stiffer masts require more precise tuning. Backstay tension becomes crucial for fine-tuning forestay tension and sail shape.
- *Tuning Priorities*: When setting up your mast, consider these priorities:
    - *Prebend*: Aim for 2-4 inches of prebend, depending on wind conditions and sail shape.
    - *Headstay Tension*: Balance tension to achieve optimal genoa shape and pointing performance.
    - *Rake*: Adjust forestay length to control rake, ensuring neutral helm.

To achieve optimal performance, consider the following dynamic responses:
- *Backstay Tension*: Use it to fine-tune forestay tension and genoa shape, especially in varying wind conditions.
- *Sideways Bend*: Minimize excessive sideways bend to maintain efficient sail shape and pointing.

Some general guidelines for tuning include:
- *Uppers Tension*: 27-29 on the Loos gauge for moderate conditions, increasing to 35+ in heavy winds.
- *Lowers Tension*: Looser than uppers, with windward lower tightening during sailing.
- *Spreaders*: Max aft sweep to achieve desired prebend and support for the spinnaker.

Keep in mind that specific settings may vary depending on your boat's design, sail plan, and sailing conditions. Experimenting with different settings and monitoring performance will help you find the optimal setup.

On Fri, May 23, 2025, 08:17 David Knecht <davida...@gmail.com> wrote:

I disagree with Francois on one point about the mast.  I agree that forestay length controls the rake.  But we don't have carbon masts and they don't bend much with backstay tension.  So while there is some effect on the main, in my mind, backstay tension on our boats is the primary method of controlling forestay tension.  A "slack" forestay curves off to leeward.  Increasing backstay tension increases rake and prebend slightly, but mostly it increases the tension on the forestay therefore reducing the tendency of the forestay to curve to leeward, ie making it straighter.  This has the effect of flattening the leading part of the genoa, improving pointing but also depowering the genoa.    Dave

David Knecht

S/V Aries

1990 C&C 34+

New London, CT

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[Francois Rivard]

It does tension the forestay, but if you go in the cabin and you look up the porthole that's next to the mast you'll see that the top of the mast moves about 4 inches when you tension the backstay.  

My mast does bend and it's the same as yours.  

-JF

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[Francois Rivard]

Here's a video on how it works.  It really does work that way and as mentioned if you look at the top of the mast from the small port hole in the cabin you'll see the top of the mast move 4-6 inches back as you tension. 

https://www.youtube.com/watch?v=9GDro9i1ye0&ab_channel=AlexandreKossack

Check it out, you'll learn interesting stuff... 

-Francois

[David Knecht]

Hi Francois- Sorry- I found this email from a while back and realized I forgot to respond and keep this discussion going.  

As usual with sailing rigs, the situation is complicated and there are multiple things happening.  I agree that tightening the backstay moves the top of the mast back.  What I am saying is that with a carbon mast, that would significantly bend the mast, thereby removing draft and flattening the main.  That also happens to some extent on our stiff aluminum masts, just not as dramatically.  But in either mast type, it will also tension the forestay and I think that is the greater effect in our boats.  If you try to move the forestay side to side, the amount it moves will decrease dramatically as you tension the backstay.  So as it gets tighter/straighter, it will decrease the lateral curvature of the forestay, which depowers the genoa and changes the angle of attack.  Since the genoa is the main source of power on our boats, I think that will be the most important effect.  See the links below for a more complete analysis.  Dave

David Knecht

Emeritus Rear Commodore/Thames Yacht Club

Emeritus Professor/University of Connecticut

Basketball Capital of the World

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