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#87869 - 11/08/06 04:58 PM Re: Good start would be ... ***** [Re: Robi]
Wouter Offline
Carpal Tunnel

Registered: 06/16/01
Posts: 9582
Loc: North-West Europe


I think my Taipan hull is 0.34 mtr wide at the widest point; shall we start at 0.35 mtr.

Again the hulls volume must at lead be 500 liters or it will sit to deep in the water. I think 550 liters is the total volume of the Taipan hull and that one is a bit to deep in the water when sailed by crews heavier then 145 kg. So lets start for our project with a total hull volume of at least 600 kg. That would be a good start also.

Can you tell that I've done this before ?

Ohh, lets decide to ONLY use SI units like mtr. kg, liter, newtons and no US or imperial units. Till save alot of work and miscalculations.

For example under SI the displacement of a volume is simply the product of the volume in mtr^3 times 1000.

Wouter
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Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands

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#87870 - 11/08/06 07:29 PM Re: Good start would be ... [Re: Wouter]
Robi Offline
Carpal Tunnel

Registered: 07/08/04
Posts: 2718
Loc: St Petersburg FL
I agree, we should use only one measuring system.

So far
Non canting
600kg total volume.
Hull width of .35m
Hull length of 5.0m

Hull height What would be a good starting point? Maybe .46m??

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#87871 - 11/08/06 07:54 PM Re: Good start would be ... [Re: Robi]
Scarecrow Offline
old hand

Registered: 07/05/06
Posts: 907
Loc: Melbourne, Australia.
I'm not going to get overly involved in your project as its not my class (and there is an F18 kit boat on my "drawing board" at present). But can I recommend starting out with a discussion of LCG, LCF and prismatic coefficient. The rest of your hull design will follow.
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#87872 - 11/08/06 07:56 PM Re: Good start would be ... [Re: Wouter]
Mark P Offline
old hand

Registered: 05/08/06
Posts: 953
Loc: Mumbles Y.C Wales U.K
Quote:



Looking at how well Matt/Gina did at the Alter Cup qualifier I say that uncanted/uncanted is probably a very good place to start our Open source project.

Wouter


Not taking anything away from Matt & Gina but aren't we forgetting that IF they were sailing a Cat with canted hulls etc they might have won and Qualified? A's have been a development class for years longer than F16's and nearly all the top designs are canted hulls. Lets not fall into the Tiger Trap. Tigers have won the F18 Worlds on nearly every occassion but IMO this is can be attributed mainly to Hobie buying the right crews and not necessarily designing the optimum F18.
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#87873 - 11/08/06 08:39 PM Re: Good start would be ... [Re: Mark P]
Wouter Offline
Carpal Tunnel

Registered: 06/16/01
Posts: 9582
Loc: North-West Europe

Quote:


Not taking anything away from Matt & Gina but aren't we forgetting that IF they were sailing a Cat with canted hulls etc they might have won and Qualified?





Good points Mark,

I will further support my proposal. And it is just that, a proposal.

I propose uncanted hulls and uncanted daggerboards because ;

-1- No clear quantizied advantage of canted can be shown as of yet. I would elaborate but it will be much easier to ask to other side to provide actual data that canting is faster. I, for one, have over the last 5 years not been able to quantize its effect, either positive OR negative. I propose to not include complexity adding components to a design UNLESS their is a clear and quantizied advantage to doing so.

-2- Canted hulls are best implemented by making assymetrical hulls. Not something a homebuilder appreciates. You can't make both hulls from one mould or deck jib anymore. Therefor canting adds cost in building the boat. Same can be said, but too a lesser extend, with respect to canted boards.

-3- Canted hulls and boards appear to be a drawback in conditions where you can't luff your windward hull. Often this is the region where most people do poorly. I must rather trade in some "overpowered weather" performance for good "underpowered weather" performand then the other way around. Such compromises will have to be performed more often during the design. You can design the perfect craft for 10-15 knots and end up with a total dud in 0-10 and 15-25 knots. Lets not design the cats equivalent of a "single gear race car".

-4- Which way do you cant it ? In or out. For a time outward cant was popular in A-class now inward canting is. If you decide on inward canting the will stick out to the side and could become a very nice shin basher when you are trapezing in rought conditions. An uncanted board has the advantge that it is well out of the way there in the middle of the hull.



Now allow me to reply to the other statements.

Quote:


A's have been a development class for years longer than F16's and nearly all the top designs are canted hulls.





True, however on this forum a few years ago, Jim Boyer himself wrote that the only difference they found with canting was that the boat steered a little better in the mid range winds, something that was found advantagious when wildthinging the boat. No noticeable speed advantage was reported beyond improved control that in turn allows to maintain top speed better. AHPC had just put out the mark 4 Boyer A-cat which was effectively a Mark 3 but with canted hulls. In F16's we don't do much of wildthing at all. Under spinnaker the way the boat behaves is different from a boat without that does the wildthing.

I'm argueing that this could be a case of where a thing that works in A-cats might well not work in F16's. And there are alot more of these things. I won't elaborate but A-cats and F16's are remarkably different craft. The A-cat designs operate under a very different set of balances and specification, often to such extend that data acquired there is not easily transferable to F16's.

I can also state here that I spoke to 3 different A-cat builders/designers about this and all said that they didn't think that canted hulls would help much at all on boats that carried a crew of two. I won't elaborate so you can dismiss this point I you want.


Quote:


Lets not fall into the Tiger Trap. Tigers have won the F18 Worlds on nearly every occassion but IMO this is can be attributed mainly to Hobie buying the right crews and not necessarily designing the optimum F18.





The Capricorn F18 is uncanted in both boards and hulls : 2006 world champions
The Cirrus F18 is uncanted in both boards and hulls : 2002 world champions

All other world championships ever held were won by the Hobie Tiger (uncanted/uncanted)

So no worlds was ever won by a canted/canted design.

Note how no new F18 has canted boards anymore, only a few have canted hulls. I think only the Nacra Infusion has canted hulls as one of the newer F18 designs. I think we can regard the F18 as a development class of long standing as well.

I refer back to my original point; unless it provides a clear and quantizeable advantage then I wouldn't propose making the design more complex then necessary.


However having said all this, I propose that is people are committed to canted hulls and daggerboards then lets open up a parallel design path where the alternative design has them. Then when both are done we can look at which is the most attractive when balancing performance potential to things like production considerations and cost.

Wouter
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Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands

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#87874 - 11/08/06 09:41 PM Re: Good start would be ... [Re: Wouter]
Scarecrow Offline
old hand

Registered: 07/05/06
Posts: 907
Loc: Melbourne, Australia.
Quote:


Note how no new F18 has canted boards anymore,
Wouter



Canted boards are not legal under the F18 rule. The boards must be located on the centre plane of the hulls.
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#87875 - 11/08/06 09:59 PM Re: Good start would be ... [Re: Robi]
Erez Offline
member

Registered: 09/17/05
Posts: 104
Loc: Israel
I already said that I'm not an engineer
So what ever I write is not based on calculations.
I'm very curious as for hull shapes
I have been looking at the hull shapes of every beach catamaran I could find trying to figure out it's concept
and what the designer was trying to achieve,
The more I looked I was able to see things I could not see in the beginning.
I'm very excited about this Open Source Project and I can't wait to find out all the things I don't know that I don't know.

As for the hull width I suggest 0.4m where the water line is,
and then play with the deck width to achieve total hull volume of at least 600 kg.

more volume = more weight
carbon = less weight
carbon = $$$


Quote:

However having said all this, I propose that is people are committed to canted hulls and daggerboards then lets open up a parallel design path where the alternative design has them. Then when both are done we can look at which is the most attractive when balancing performance potential to things like production considerations and cost.




We can design a part that will be placed between the hull and the beam and make the hull canted,
or not canted with a different part,
I am not talking about one part with two positions.

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#87876 - 11/08/06 10:11 PM Re: Good start would be ... [Re: Erez]
Robi Offline
Carpal Tunnel

Registered: 07/08/04
Posts: 2718
Loc: St Petersburg FL
Erez I am trying to get a box measurements and then concentrate on where it should be wider, narrow, taller, shorter etc etc.

Volume - 600kg
Length - 5.0m
Width - .35m
Height - ????.45m .46m .44m????

After we get this box dimensions, we can play with placement of the values. For instance how far back will the tallest, widest thickest point be? Rocker placement, crossbeam positions and everything else.

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#87877 - 11/08/06 10:47 PM Re: Good start would be ... [Re: Wouter]
ncik Offline
old hand

Registered: 10/18/05
Posts: 951
Loc: Brisbane, Queensland, Australi...
wouter, displacement is volume multiplied by 1025 if in salt water...1000 if in fresh water.
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#87878 - 11/08/06 10:56 PM Re: Good start would be ... [Re: ncik]
Wouter Offline
Carpal Tunnel

Registered: 06/16/01
Posts: 9582
Loc: North-West Europe


Quote:


wouter, displacement is volume multiplied by 1025 if in salt water...1000 if in fresh water.




well we want the boat to also float in fresh water so lets err on the right side and stick to 1000.
_________________________
Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands

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