Tension gauge accuracy

[allene]

Let me simplify my question. I measured my forestay tension with a PT2 and it says1800 pounds but a PT3 says 1225 pounds at the same time. I then pull on the forestay with 41 pounds 54 inches off the pivot and calculate 824 pounds of tension. Can I assume one of these is accurate? Is there a better way to measure the tension? I don't want to overstress my wood mast but I want less deflection under sail.

A complete write up of what I did can be found at http://l-36.com/loosaccuracy.php

I have contacted Loos and they say they measured a PT2 and PT3 and got 1300 pounds on both on the same wire. I sent my PT2 to them. They seem very professional and helpful but the fact remains that I used 4 of their gauges and got wildly different results.

What is the most accurate way to measure this?

Allen

[Stumble]

Harken makes a digital version of the loose gague that works very well ( http://www.westmarine.com/webapp/wcs...&ci_sku=331218 ) I didn't recommend it too you because it won't work on 1/4" wire. You can do a google search for digital tension meters which will give you a list of some non-sailor in mind gagues out there, though they are likely to be more expensive. I have never thought the loos gagues were very good, but they are common. The trick seems to just use them as a relative scale but other than that I haven't had much luck with them.

[allene]

I made a fixture that puts the forestay on a lever with the other end of the lever on a scale. The lever is attached to the stem fitting. The lever has a 10:1 advantage. As I tighten the backstay, I can read tension off the scale and off the PT-2 gauge. The scale shows that the tension increases very linearly with backstay turns. This is what Hooke's law says should happen so that is good. The PT-2 gauge reads a non-linear sharp increase in tension as the backstay is tightened. My scale reading is very close to a PT-3 reading by the way.

Now the interesting part. I had my PT-2 calibrated by Loos and it was accurate at a reading of 38, which is 1300 pounds but my scale reading says 1150, and the PT-3 says 1075 pounds.

The only difference I know of is that they used 304 1x19 and I have 316 1x19. Could that make a difference in the reading on a PT-2 but not on a PT-3?

My writeup is here: http://l-36.com/loosaccuracy.php

Allen