>>naahhh - I'm with you. I'm being argumentative too but don't mean anything by it either.


Good ! Lets continue this then. I'm enjoying this.


>>Seriously though, if you're trying to measure the difference in stiffness of the plywood hulls vs. the composite glass hulls, why are you fooling with all the beams inbetween?

You are correct with regard to vertical stiffness, With regard to toe-in stiffness I can proof to you that the beams do not give cause than more than 15th of the total toe-in flexing, this (7 %) is negelectable. We are talking 2 mm iut of 35 mm here. You'll be lucky to be able to measure the flexing at 1 mm accuracy.

So I say to compare ply hulls with glass than the toe-in stiffness is a good, dependable and easy to execute test.

Tell me if you care for the proof ! It does involve some mechanics of material stuff and "Formulations I gleaned up at university"



>>That's what I meant about being scientific about "hull stiffness". You're measuring "platform stiffness" which has very little to do with the actual hull stiffness that we've been discussing.


Well we started out discussing how homebuilding a ply platform could produce a platform with superior stiffness. After that we drifted away to discussing the comparison between glass and ply directly.


>>In other words, most of the platform movement you show in your measurements does not come from the hulls but instead from the beams and beam joint in between.


Yes we knew that, the between both our viewpoints is that the beamlanding in the hull is important. Of course it dependent wether you categorize the beam landings as part of the hull or part of the beams.

But in principle we are in agreement on vertical stiffness. (And vertical stiffness only as I has a different opinion about toe-in stiffness)


>>>A horizontal measurement would be a little more difficult with the boat assembled but I'm sure you see what I'm saying.

Not needed, in the horizontal plane the beams act as nearly inflexible supports.

There is a reason why the test were done in the way they were. Afterall as a designer and sailor you eventually want to know what it all means for a platform while sailing. The test as performed approximated this the best. We know as a result of the test that the Blade F18 platform will noticeably flex less than most other F18's. If we preformed the test you propose we would indeed have a number directly comparing glass to ply, in a more scientific way, but we wouldn't know how it would impact directly on a sailing platform. Indirectly we could establish that but why not measure it directly.

There are some more consideration in this testing and yes we must take care not to compare very dissimilar boats to eachother. For example I know the Taipan glass and Taipan ply numbers as well. But these platforms are so much lighter then the F18's that they are arguably tested at lower loads and therefor produce smaller deflections. However when looking at Blade F18's, other F18's are as good as identically tested and the Tornado is similar in weight and not to dissimilar in length. We can easily conpensated for that roughtly. The compensated numbers fore the tornado to make it directly comparable is 49 mm and is therefor about halve of the mainstream F18's.



>>>However, I am impressed with the platform stiffness of the Blade F18 compared to the other boats.

I actually believe most of the people that were told in the beginning didn't believe it. I know that I was taken back by it a little. Also by how much the other boats flexed. I expected less. So I did some rought testing myself and then grew more confident of the number provided.

Please note the test were designed to give large deflections, You would not actually see your F18 platform flex 93 mm while sailing. Large delfections give more relative accuracy. Maybe the F18 only flexes some 20 mm I real life sailing but as a result of these test we expect the Blade F18 to flex only some 5 mm in the same conditions while sailing.


>>While Phil may have not glued in the beams, I bet his beam socket was a bit more refined than what I had on my Nacra. I'll see if I can get a measurement on mine soon.

Please, I love real life data like this. And I'll always use such things somewhere down the line, in some technical model or rating system model.


>>I thourghouly waxed the beams prior to joining them with the hulls hoping that that would aid in future removal if ever necessary.

Okay so you improved on the fit of the sockets and didn't really glue the in permanently. Both the Blade F18 and home-builded Taipans and Blades seat their beams like that, also allowing them to be removed later.

I spoke to one Blade F16 builder here in Netherlands and his fitting was so tight that he could lift the hull of the ground even when the bolts were completely removed. The fitting stuck to the hull but a short sharp blow released the beams. He said he had no worries about platform stiffness after this. Of course the Blade F16 beams (production version) the hull wraps around halve of the rounde 80 mm by 2 mm beams. So this will give a clinging grip when tight.


>>>The beam and hull union was NOT a good one from the factory - the socket in the hulls was not smooth and had bumps in it. While sailing, even after putting in as much 'grunt' as I dared to the bolts, I could see movement between the hull and beam while under sail. I sailed the boat before and after this operation and the difference was very noticable.


I think we have found here the reason for the high numbers of some of the tested boats. And also proof that the design and quality of the beamlandings are important. Mind you the Blade F18 also uses 4 bolts on each side of every beam. With the right design of the hull skin around the beamlanding you'll end up at these low platform deflections.


Wouter