http://www.fiberglasssupply.com/Product_Catalog/Core_Materials/core_materials.html

"here's what I propose to try and measure at Tradewinds:

(?) Anybody else willing. Hobie Wave?"

Kathy Kulkoski just won the Nationals walking away with a boat the flexes terribly (3 feet maybe) at least. At one time the Panthercraft Tornadoes were the fastest around and were referred to as "Flexible Flyers."

Sounds like an interesting test, nonetheless.
Rick

Agreed - I don't know what we're proving, but it's got to be something.

That is what I was told by a befriended boatbuilder just days ago. I said something like the H16's are about 10.000 Euro's (price of 2001 converted to Euro's) and he replied :"No, the H16 have gone up in price as well lately. They are some 12.000 to 12.500 Euro's now."

I am certain they were about 10.000 in 2001 add 3 years of 3 % inflation and you also come out at 11.000 euro's as a minimum. So now you know the same as I and make up your own mind.

With the Euro to US exchange rate a US H16 would cost about 8000 Euro's incl shipping an taxes; that is if the 7000 number is correct

Wouter

>>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

$7,000 is correct +/- the hagling or particular dealer.

>>I've been thinking about measuring the platform stiffness on my Nacra, but I have an issue with how the above test was performed. Several factors may influence the results

Lets run through them

-1- the ground may be slightly uneven

How would that impact on the results in a significant matter ?

The platform during measuring is layed up on a, what is called, three point support. It therefor WILL rotate untill all supports carry their portion of the load as determined by a simple balance equation. This means that all boats will look for an find a comparable loading sitaution as all boats are governed by the same balance equation. In addition, how bad is say a 1-3 degrees rotation of a platform when compared to a perfect level other measurement. It would cause an offset of less than 0.1 % and therefor be neglectable when compared to the manual measuring accuracy of about 1 or 2 mm of a 50 - 100 mm deflection.

But the measurements where not conducted on the ground but using 4 saw horses. Two supporting the sterns and two acting as a layup when resting the boat. During measuring the two front saw horses did not support the platform. Only the human lifting one bow and the two stern saw horses did. I trust the measurers made sure that their reference point was calibrated.

I know data of one person and he used exactly the same setup for his measurements of 3 boats so here the relative ratio between the measurements is accurate even when in absolute sense larger offset may be present.


-2- were the boats all tested in the same exact spot?

Does this matter ? Again during testing we have a point support situation forcing comparable loading on boats of same length and weight (and easily scaled loading on boats of similar length and weight). We may assume gravity to be constant over the earth surface when looking at our manual measureing accuracy.

Slopes or uneven ground below saw horse that are less than 5 degrees produce are neglectable offsets in the end results. Cosine (5 degrees) = 99.62 or the offset in loading is less than 0.4 %. And 5 degrees is a noticeable slope. A rise of 3 inches for every 3 yards. No body would use such ground for testing.

Then the way of measuring, lifting one bow till the other comes free of its supports, garantees that pre-flexing or such plays no role in the final measured flexing. Again think of the 3 point support situation.

Last point is that the centre of mass is always located behind the mainbeam and thus behind the halve way point along the hull when looking from the stern supports. Therefor the boat will always be leaning on both rear supports and a little less on the supported bow. This makes sure that the hull doesn't fly itself on just two supports at a perfect balance. The reason why the centre of mass is where it is is because of that 3 - 5 kg rearbeam.



-3- The boats themselves may not be perfectly flat and may have some pretwist in it -

See my comment at point -2- the way of lifting goes a long way in prevent ofsets with this cause. BUT yes the reference point for measuring must be calibrated.

I would say that the use of a plank or wooden beam and a waterlevel tool will do wonders here. I do not know where such a thing was used by Marcus. But you can when measuring the boats are tradewinds.


-4- were the measurements taken from each side and then averaged?

I don't know.


>>Truthfully, even before I seated my beams, 95mm (3.74 inches) of deflection simply by lifting an opposite bow sounds unrealistic on my nacra...it's SO much stiffer than my 6.0 was (I would believe it on my 6.0).

If you just lift your boat by the bow when it is on the beach you will get smaller deflection readings. Because the fulcrum can be significantly ahead of the sterns. Mast and stays will probably stiffen up the platform as well when pretensioned.

When laying on the beach I had rougtly 50 mm on my 1975 Prindle 16. When I lifted it with two people where one took the stern and another took the diagonally opposite bow then it did flex alot more.


>>Instead of doing the test as described above, I propose that we perform our own independent test. We should start by loosening the rigging substantially so the rigging doesn't help support the hulls and beams adding a variance to different width boats.

I understand. Just make sure we can still compare the data to eachother.

Also width will always be a factor in what ever way you measure platform stiffness. And absolute platform stiffness (at a the real width) is the only thing important while sailing. However, using theoretical means we can normalize the data to a fixed width. The formula's for this situation are not that difficult.



>>Then we support the boats by both sterns and one bow and measure the height of the unsupported bow from the ground.

You can do that and arrive at much the same situation as the way the Aussies measured the stiffness. Just make sure your measurement reference point is calibrated somehow.


>>Then apply, say, 10kg to that unsupported bow and measure again.

You will tip the boat of its supports by doing that and no longer have a stable 3 point loading.


>>That will give a more accurate indication of vertical axis platform stiffness and would also remove some of the ground level variance and most effect from any preexisting platform twist.


You can exclude pre existing twist more effectively by measuring on both sides and than averaging the results.

10 kg weight may well be relatively little and only produce a small deflection requiring very accurated flex measuring to get enough accuracy. What is the extra flexing is 10 mm ( alot !) than a measuring error of 1 mm (not alot) constitures a 10 % offset already. Alot worse than say 1 mm out of 50 mm (2 % offset)

You must think this one through very carefully.



>>Of course I probably won't have access to the Blade F18, or any Tornados soon, but would very much like to see the results there too. Can someone help with that?

Probably. We are all interested in acquiring good data. For designers such data is golden.


>>>Mary, if you're still putting up with this thread, can we submit a Catsailor article on the test results? Perhaps we can do some testing at Tradewinds. Wouter, want to co-author it?


Ohh yes, it'll be my pleasure. You know I'm a sucker for this stuff.

Wouter

Jake,

I'm willing to ask for clearance to publize some Taipan data. Here comparison between glass and ply is very good as the designs are identical. I know it but I need to get into touch with the source of this data to declassify it.

With luck you guys can put Matt McDonalds Blade F16 on the bench as well as get his data. He is planning to be at tradewinds.

Maybe measure a Inter 17 R as well and a FX-one if they show up.

If we work out a good procedure than measuring at different times and places should not be a problem

Wouter

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

As it sounds thus far, there are some details of how the existing data was achieved that makes acquiring comparable data during Tradwinds difficult...but I'll try to get measurements on some identical boats so we can see how it compares.

The water level is a great idea! What I propose is; upon relatively level ground (Gilbert's concrete slab where the warehouse used to be will be great if we can find a spot without a boat or trailer on it!) locate a pair of cattrax under the sterns centered at a predetermined small distance. We then manually lift and support one bow to achieve roughly the level waterline of the boat. Using a poor-man's waterlevel, measure the elevation distance between a similar feature on each bow. We can easily take a measurement with the other bow supported and average the results to eliminate any twist already present. Am I missing anything?

>>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

Rhodysail

I talked to a dealer and he said the new Hobie 16 was around 9,000 and an F18 was 13,000 to 14,000. Who is selling new Hobie 16's for 7,000? My first boat a Hobie 16 was 5,800 and that was in 1985 and did not come with any options.

Agreed....if I can find a metric ruler...

Sorry to take this thread on such a tangent.
I think I paid about 7k for my boat. I cant find the paperwork. I did find some prices listed on the internet. When you consider that buying a boat through a dealer is like buying a car I think you should consider these prices to be the high side.


http://www.waterventures.com/prods/31.html
Water Ventures
Price:7475.00

http://www.sail-s.com/MAIN/cart-s/Hobie_Cats/Hobie_Cats.htm
Self Awareness In Leisure
Price 7,995

http://www.marina42.net/cgi-bin/p/m42p-listing.cgi?d=the-anchorage&id=675
The Ancorage
Price: 8,195

http://www.theboathouse.biz/boat_hobie_price_list.asp
The Boat House
Price: 7,995.

I think most of you are missing the point with what Marcus did with the blade and where most boats fall down. Firstly there is minimal difference in the flex of the actual beam, there is also minimal difference in the actual hull flex. The BIG thing is the mounting of the beams to the hull. It is almost irrevelant the type of beam and its construction (within reason) Consider this, if the beam can move 1mm at the beam landing what does that mean at the extremity of the boat??

I have a Taipan 5.7 which is now 10ft wide, it is actually stiffer at 10ft wide than it used to be at 8ft2" wide. The main difference is how I attached the beams to the hull. I have been able to reduce the amount of movement to almost nothing. Now the boat is stiffer than a Marstrom Tornado.

Some time ago there was a discussion down the same lines on the Aussie F18 bb and I made the same comments, I heard that some of the class "legends" were taking the piss out of me for those comments at a regatta, anyhow then Marcus comes along and builds the Blade and the bloody thing is quick straight out of the box, first weekend with home made sails and hulls that are not to the designers spec (shape is wonky) the biggest thing about the Blade is that the platform is very stiff. Watch out for the next Blade which is being built and will have the correct shape, better sails etc. I think we will see that the main improvement in the F18's will be along the platform stiffnes route.

I think you have to be very careful comparing the stiffness of different boats. Comparing an F18 to a T such as above has to many variables. ie width, length and weight not to mention age. I know that Marcus has re beamed his Marstrom. Was this done before or after the test. This is a 12 year old boat that was in need of some TLC before Marcus bought it. The front beam was also riddled with holes from moving fittings around. If you wanted to test the stifness of the Marstrom, it would have been allot better to use a new or near new platform.

Also the Reg White used was a 17 year old boat with the small beams. Hardly a fair comparison with a brand new F18.

This test was only ment for a rough personal guide for the guys and should be taken as that.

You may want to measure the toe-out of the gudgeons/pintels as the bows toe-in.
This shows what happening from bow to stern.
Obviously fractional in-out or twist at the stern affects rudder alignment.

This is all a little meaningless as a measure.

Were all the dolphin strikers at the same tension? Same rig tension ? All beam bolts at the same torque, was the ambient temperature the same ?

All the above will have significant effects on this.

The measurements at tradewinds are a great Idea.

It may be useful to measure toe out as well as it will be the worst case, i.e toe in will be stiffer due to the due to the contribution of the trampoline.

Any one have experience of design of experiments? I studied it years back but have forgotten most of it. It is a useful statistical technique for isolating the contributions made from various bits and to finally end all the speculation of which part is most important.

Gareth

You are also sure that these aren't the boats that were used during the 2004 Hobie 16 worlds ? The chartered boats.

I must confess 7000 US$ is not alot of money for a catamaran.

Wouter

Does that include TAX. In Ireland we would pay 21% VAT on to that.