Forestay tension

[allene]

This is probably asked 100 times but perhaps not this way. I have a wood mast (spruce box 5x7 at cabin top made of 1x and 40.5 off the deck, keel stepped). The boat is an L-36. The forestay is 1/4 inch wire and the boat has a new mast step with 5 new floors and is solid. I race a guy with a L-36 with an aluminum mast and know I cannot match his forestay tension, which is very high. He always beats me (I get 2nd) and he told me this is one of the reasons although there are many. I was advised by my sail maker to set the forestay to 18% of the breaking strength or 1300 pounds and bought a PT2. But I get a lot of forestay sag. I don't want to just crank things tighter and hurt my rig. Because the backstay tension was less than 1/2 the forestay tension and I calculated it should be 2/3, I questioned the accuracy of my gauge.

I bought a PT3 which is also calibrated for 1/4 wire. Both the PT2 and PT3 are rated at 3% accurate but I saw a 26% difference between them when measuring the same tension. I bought another PT2 and it read the same as mine. Loos has been helpful and is going to calibrate my gauge but I got to thinking I could measure the tension by pulling on the forestay itself. So, I pulled on it with 41 pounds, observed a 2.4 inches deflection and calculated 825 pounds of tension. This at a setting where the PT2 said 2000 pounds and the PT3 said 1250. I don't know what to believe.

The bottom line is I think I need more forestay tension but I don't want to hurt my mast.

I can provide more detail on any of this if asked.

What should I do?

Allen

[Stumble]

Allen,

A few quick questions.

Are you always measuring the forestay tension with the backstay off? If not this can radically change the forestay tension.

When you measure with the same instrument in the same place on the wire do you get the same or different measurments? Moving the gague can induce different results, and if the gague is reading differently on different measurements then it isn't a calibration problem it is a repeatability one.

What points of sail does this guy beat you on, all the way around the race course or just upwind or downwind?

Is your pre-bend and rig placement right? Either of these can alter the headstay tension if you set it initially by length.

[allene]

Answers below:

>Are you always measuring the forestay tension with the backstay off? If not this can
>radically change the forestay tension.
I adjust the forestay tension with the backstay. The last set of measurements I took with 14 turns (1.4 inches) in addition to the fairly slack in the dock setting.


>When you measure with the same instrument in the same place on the wire do you get
>the same or different measurments? Moving the gague can induce different results, and if
>the gague is reading differently on different measurements then it isn't a calibration
>problem it is a repeatability one.
The gauges are repeatable as long as you make the measurement the way they suggest. There does seem to be some resistance in the wire so you can get different readings if you measure differently but as long as you follow the instructions, it is repeatable.

>What points of sail does this guy beat you on, all the way around the race course or just
>upwind or downwind?
He beats me upwind, my boat is faster on all other points of sail. I have pulled away from him 4 boatlengths in a mile sailing on a close reach. That makes this all the more frustrating. Our race course is mostly reaches but I lost a huge amount on the beat by being out pointed. Like I said, several reasons and I am addressing them all. This is just one factor but it is a factor.

>Is your pre-bend and rig placement right? Either of these can alter the headstay tension if
>you set it initially by length.
Not set by length. I had the initial set done by a rigger when he put the new wire on. This was done when the new mast step was put in as that raised the mast up and all the wires had to be made longer.

Allen