>>I'm missing some details regarding how the previous platform stiffness measurements were achieved. Can you explain in detail how the test was performed?

I think I did explain that in my other post. Also I don't know all the details as I wasn't there. I only know what was explained to me.

Goes pretty much like this.

Vertical stiffness :

4 saw horses. Two are right under the very edge of the sterns, two are somewhere under the very tips of the bows.

I speculate that they have checked wether the teh two front saw horse are perfectly level and adjusted them when they were not. It is not critical wether the front and rear saw horses are level. Some small inclination may be present and will only give rise to extremely neglectable off sets.

Than a person lifts one bow till the other bow comes of its sawhorse. Than the person slowly lowers the hull till the other bow just touches the sawhorse. Ever so slighly. Then a second person measures the amount the lifted bow howevers above its sawhorse (or some other calibrated reference point)

The first serie of data (not publized yet) was take with only a fitted platform (no mast etc fitted, just beams, trampoline and related fitting). I think Marcus did the same tests but with the mast etc fitted.


Toe-in stiffness :

Boat rests on supports without forestay tension (or very little)
The distance between the bow tips is measured.
Then two trapeze wires are fitted to the boom and the mainsheet is janked tight so that a tension of 32 on a loos gauge is reached in the forestay.
Now again the distance between the bow tips is measured. The horizontal deflection is of course the difference between the two measurements.


>>With regards to level ground, if you are lifting one hull until the other comes off the ground, level ground is certainly important if that is what they were using to take the measurement between the hulls.

I only know they used saw horses. As basic physics say that any inclination less than 5 degrees only causes less then 0.4 % offset = neglectable. 5 degrees inclination is similar to 3 inches drop every 3 yards. So this is quite forgiving.

The 4 saw horses need not to be in one plane. Only 3 of them need to be, two rear and the one in front. This plane however may be inclined. Also the sawhorse that just touches the other bow must be level with the reference used to measure the lifting of the bow that is held up.


>>Secondly, as I have no idea of the background or aptitude of the persons performing the test you are asking me to assume that they performed the test in a fair and knowledgable manner (and I could have my white lab coat and pocket protector taken away for such an assumption).


Good point. But I also have to trust you to give me dependable numbers. At same point you just have to have faith.


>>>As it sounds thus far, there are some details of how the existing data was achieved that makes acquiring comparable data during Tradwinds difficult...

Not at all, your proposed methode should give comparable measurements.


>>but I'll try to get measurements on some identical boats so we can see how it compares.


Cool !


>>The water level is a great idea! What I propose is


>>upon relatively level ground

certainly helps.


>>locate a pair of cattrax under the sterns centered at a predetermined small distance.

Smart move ! As close to the sterns as you can.


>>We then manually lift and support one bow to achieve roughly the level waterline of the boat.

I would just lift the bow and put a support under its very end and let the whole system come to rest without worrying about any inclination. You have a three point support setup now.


>>Using a poor-man's waterlevel, measure the elevation distance between a similar feature on each bow.

Yes, that would work. I propose to use the very bow tip. Just tape a stiff rod to the top of the lower bow and then move about the other end over the lifted bow till the rod is level. Fix it and measure the drop. It you are handy you just tape the water level to the rod (or plank) making it even stiffer and easy to use.

You can expect distances between 20 mm and 100 mm (4/5 inch to 4 inches) so a simple ruler will be accurate enough.


>>We can easily take a measurement with the other bow supported and average the results to eliminate any twist already present.

Again, smart action.

You can then continue with the toe-in stiffness.


>>Am I missing anything?

No this should give comparable results to what the Aussie boys are doing.

Only thing to take care of it to note down wether the mast was on the platform and wether the rig was pretensioned or not. The latter makes a difference in toe-in deflection. Also wether the mast is on it or not is important from a loading point of view, however I don't expect a 18 kg mast to make much difference on a 130 kg platform. If it does than it'll be relatively small, only some 15 %.

We must also agree on which measurement system we use as the base system, we can convert the measurements later. I propose the metric system because we already have data in that and I don't care much for read outs like 1 + 3/8 inch

This should make for a really interesting article.

If desired I can throw in my excel sheet and determine the ratio's between various contributing factors and explain some of what we are seeing. Like are round beams better than oval beams etc.

Wouter