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      Abbreviated rules   07/28/2017

      Underdawg did an excellent job of explaining the rules.  Here's the simplified version: Don't insinuate Pedo.  Warning and or timeout for a first offense.  PermaFlick for any subsequent offenses Don't out members.  See above for penalties.  Caveat:  if you have ever used your own real name or personal information here on the forums since, like, ever - it doesn't count and you are fair game. If you see spam posts, report it to the mods.  We do not hang out in every thread 24/7 If you see any of the above, report it to the mods by hitting the Report button in the offending post.   We do not take action for foul language, off-subject content, or abusive behavior unless it escalates to persistent stalking.  There may be times that we might warn someone or flick someone for something particularly egregious.  There is no standard, we will know it when we see it.  If you continually report things that do not fall into rules #1 or 2 above, you may very well get a timeout yourself for annoying the Mods with repeated whining.  Use your best judgement. Warnings, timeouts, suspensions and flicks are arbitrary and capricious.  Deal with it.  Welcome to anarchy.   If you are a newbie, there are unwritten rules to adhere to.  They will be explained to you soon enough.  
QBF

Sailrocket 3 - The Offshore version

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DubTray, I do not, as it happens, but you have prompted me to ponder an important question. A recent proa thread http://forums.sailinganarchy.com/index.php?showtopic=183030 which I had the strange experience of reading, gives some background on the bizarre conflict between certain Pacific and Atlantic proa people. What is particularly striking is the seemingly very small number of proas that have ever been built so that arguments are all based on literally one or two boats ever. DL comes in for all sorts of criticism for not building anything but the good news is everyone else is building and progressing so at least we're not arguing about 1976.

 

Meanwhile, Paul Larsen goes and builds what I suppose is a foiling Proa, and maybe I missed all this but he didn't seem bring out the crazies all that much. My question is, does proa crazy cancel out foil crazy? Or does actually building a thing tend to make everyone shut up. Or am I crazy?

 

Good luck with making the force aligned sailing boat models. It seems like a really good procrastination activity at work.

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DubTray, I do not, as it happens, but you have prompted me to ponder an important question. A recent proa thread http://forums.sailinganarchy.com/index.php?showtopic=183030 which I had the strange experience of reading, gives some background on the bizarre conflict between certain Pacific and Atlantic proa people. What is particularly striking is the seemingly very small number of proas that have ever been built so that arguments are all based on literally one or two boats ever. DL comes in for all sorts of criticism for not building anything but the good news is everyone else is building and progressing so at least we're not arguing about 1976.

 

Meanwhile, Paul Larsen goes and builds what I suppose is a foiling Proa, and maybe I missed all this but he didn't seem bring out the crazies all that much. My question is, does proa crazy cancel out foil crazy? Or does actually building a thing tend to make everyone shut up. Or am I crazy?

 

Good luck with making the force aligned sailing boat models. It seems like a really good procrastination activity at work.

 

Anyone who criticizes me for "not building anything" is an uninformed idiot. Just look at my gallery here and on boat design -and thats only part of the model and fullsize boats I've designed and built.......

 

http://forums.sailinganarchy.com/index.php?showuser=30

 

http://www.boatdesign.net/gallery/showgallery.php?cat=500&ppuser=31218

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Does anyone else here compulsively google sailrocket 3 while compulsively making small models of force aligned proas or flip tackers or canting mast trimarans or some other dream of a force aligned sailing vessel?

 

You bet! I got it so bad that I built a canting rig for my 12m/40' proa. Still getting the bugs out of the rest of it, but will try the canting "soon".

 

Foiling Optimist:

There are enough proas built and sailing to know what works and what doesn't. I have been building them for 20 years, still get abused every time I post (down to one or two people, from a high of about 20, so things are improving), so building does not seem to prevent the crazies. Not everyone who reads the threads thinks they are a waste. The interested people contact me direct to avoid the abuse and idiocy.

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DubTray, I do not, as it happens, but you have prompted me to ponder an important question. A recent proa thread http://forums.sailinganarchy.com/index.php?showtopic=183030 which I had the strange experience of reading, gives some background on the bizarre conflict between certain Pacific and Atlantic proa people. What is particularly striking is the seemingly very small number of proas that have ever been built so that arguments are all based on literally one or two boats ever. DL comes in for all sorts of criticism for not building anything but the good news is everyone else is building and progressing so at least we're not arguing about 1976.

 

Meanwhile, Paul Larsen goes and builds what I suppose is a foiling Proa, and maybe I missed all this but he didn't seem bring out the crazies all that much. My question is, does proa crazy cancel out foil crazy? Or does actually building a thing tend to make everyone shut up. Or am I crazy?

 

Good luck with making the force aligned sailing boat models. It seems like a really good procrastination activity at work.

 

Anyone who criticizes me for "not building anything" is an uninformed idiot. Just look at my gallery here and on boat design -and thats only part of the model and fullsize boats I've designed and built.......

 

http://forums.sailinganarchy.com/index.php?showuser=30

 

http://www.boatdesign.net/gallery/showgallery.php?cat=500&ppuser=31218

 

 

 

Now look what you've gone and done FO!! :( :(

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*bump*

There is a bit about the project on CNN. Looks like Paul had enough sailing in a straight line. Why sail for a mile if you could try tor the Blue Ribbon instead?

[source]

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On 7/6/2017 at 1:08 PM, Chasm said:

*bump*

There is a bit about the project on CNN. Looks like Paul had enough sailing in a straight line. Why sail for a mile if you could try tor the Blue Ribbon instead?

[source]

I heard "asymmetric boat"...

A proa?

 

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On 08/07/2017 at 9:52 AM, Laurent said:

I heard "asymmetric boat"...

A proa?

 

I heard that too.

The ultimate weather gamble, an asymetric boat!

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12 hours ago, Jethrow said:

I heard that too.

The ultimate weather gamble, an asymetric boat!

If it is an asymmetric tacking boat, like a trimaran with different boards on the ama, or a rig permanently tilted on one side, or a MASSIVE tacking canoe (one long main hull with an ama on one side only), then YES; it is a weather gamble...

But if it is a "true" proa, shunting from one tack to the other, then it is not.

It would be interesting to see how a 150 ft long shunting proa, in archimedian mode, not weighting more than the current ultim class trimarans, would perform...

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So, a tacking outrigger Malagasy style ?

For a NY -  Lizard record could work , around the world I would prefer a proa, shunting, unless one has to pull off the number of tacks that Coville had.

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20 hours ago, Laurent said:

If it is an asymmetric tacking boat, like a trimaran with different boards on the ama, or a rig permanently tilted on one side, or a MASSIVE tacking canoe (one long main hull with an ama on one side only), then YES; it is a weather gamble...

But if it is a "true" proa, shunting from one tack to the other, then it is not.

It would be interesting to see how a 150 ft long shunting proa, in archimedian mode, not weighting more than the current ultim class trimarans, would perform...

Fast.  At 150+ feet it would be extremely fast.

 

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On 11 July 2017 at 8:23 AM, Laurent said:

If it is an asymmetric tacking boat, like a trimaran with different boards on the ama, or a rig permanently tilted on one side, or a MASSIVE tacking canoe (one long main hull with an ama on one side only), then YES; it is a weather gamble...

But if it is a "true" proa, shunting from one tack to the other, then it is not.

It would be interesting to see how a 150 ft long shunting proa, in archimedian mode, not weighting more than the current ultim class trimarans, would perform...

Using data from Wikipedia, the current Ultime tri's are around 40 metres long, so a 45 m Proa for the same displacement, wouldn't be worth the effort. Only two ways to go really, and that is a 40 metre Proa and make it as light as you can or use the same displacement and make it as long as you can. And the Archimedean numbers are:

Banque Populaire: L 40m, Displ 23t SA 720m2 Base (average) Speed: 29.40 knots

40m Proa: Displ 18t SA 720m2 (if it can carry it) Base (average) Speed: 31.28 knots

60m Proa: Displ 23t SA 720m2 Base (average) Speed: 36.00 knots

Match the displacement and maximise the LWL and a Proa will always win the theoretical Physics argument.

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15 minutes ago, Tropical Madness said:

why the veil of secrecy?

Copyright, intellectual property and Patent rights ..... Just look at Hugh Wellbourne and DSS.

Better still to keep it patent pending as long as possible so no one knows what you are really patenting and everyone else is hamstrung from progressing similar developments further for fear of ultimately breaching. 

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A 40 metre version of this minimalist 6.5 metre foiler with double luff main and D shaped mast would be as light as a proa, probably faster (or as fast) and be easier to tack/shunt?

frog7copy.jpg

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^ It certainly has the same attribute as a Proa in that you don't need 3 full length hulls and therefore can get a lot more LWL for the same (Tri)  displacement. And it should tack faster than a Proa could shunt.

But it doesn't work so well in the Archimedean state.......

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7 hours ago, carcrash said:

I first did what Hugh calls DSS as research for my Westlawn studies in the mid 70's on a 5o5. Intellectual property protection is weird.

You should compare notes with Mr Wellbourne. You might be in luck. There must be quite a few projects paying him a fat licence fee.....

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10 hours ago, carcrash said:

I first did what Hugh calls DSS as research for my Westlawn studies in the mid 70's on a 5o5. Intellectual property protection is weird.

It boils down to protecting your IP.  Whether music or boat design or whatever.  

Cruel but fair, I guess....

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19 hours ago, carcrash said:

I first did what Hugh calls DSS as research for my Westlawn studies in the mid 70's on a 5o5. Intellectual property protection is weird.

well if any of it was published it could be used to challenge Hugh's patent as it would be considered "prior art" and would invalidate his patent

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Further to the information regarding early "DSS" - before it was invented; there was a superb Murray Ross monohull named M1 in Auckland, owned by the Hull family (Simon Hull, very well known owner/skipper of the ORMA 60 Vodafone/Frank/formerly Michel Desjoyeau's Geant), well, 15 years ago, maybe more, we were beating up the Waitemata in my trifoiler and going the other way was M1 .... with angled leeward foil exiting just below waterline and set at around 30 degrees, maybe even less. Later I talked to NZ designer Brett Bakewell-White who was horrified that the Hulls had butchered the famous Ross design. Not an advanced thinker BB-W, just joking. Apparently the foiled M1 didn't work as well as the hydrodynamicist Hull father intended and later the two foils were removed and the boat became the classical M1 again. But it seemed to sailing okay when we saw it. My point: was this boat ahead of the Wellbourn DSS?  And I'm sure there are other stories of near horizontal foils attached to monohulls. And of course the French were putting inverted Y and T foils on multihulls in the 1980s.

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On 7/11/2017 at 2:40 PM, r.finn said:

Fast.  At 150+ feet it would be extremely fast.

 

I wonder how fast?

I got to wondering as I was looking at the projected track of TD 8. It's puttering along off the east coast, but next Tuesday it's apparently going to take off across the Atlantic at a speed of around 40 knots. So if you could grab hold of it and go 40 knots and take the resulting pounding...

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I know I tried it on half a dozen models when I was a kid and it didn't work as well as putting weight on the high side. 

Of course where I lived, it blew hard almost all the time, and ithe only reliable way to make one of my sailing models go faster was to put shifting ballast on deck, or in many cases further to windward on outriggers. This was the only way I ever got my free sailing models to plane upwind. Which WAS pretty cool when I got I got it right, about once a year ........

SHC

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14 hours ago, carcrash said:

Length is not an advantage if the boat is not dependent on Archimedes........

 

Totally agree, but an offshore foiler still has to carry its load and be stable in the static state, when hove to in really bad weather at sea and until it has lift off from a standing start. And if foils break or their control mechanisms irreparably fail, it still has to get safely home without external assistance?

Looking forward with great interest to see what Paul Larssen comes up with....

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14 hours ago, carcrash said:

Length is not an advantage if the boat is not dependent on Archimedes.

Only if you ignore the effects of waves, which is silly in the ocean.

The water surface gets proportionally smoother as the boat gets longer which is a good thing.

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1 hour ago, carcrash said:

Foils have always, and continue to suffer from damage.

Perhaps we should learn from nature, and just fly low over the water using wing-in-ground-effect, rather than hydrofoils......

...........The Albatross and Pelican are great examples of using a single foil (on each side of course) and still dealing with waves of arbitrary size.

Totally agree, but an offshore ground effect craft (Ekranoyacht?) still has to carry its load and be stable in the static state, when hove to in really bad weather at sea and until it has lift off from a standing start, which is harder to do because air provides far less lift for a given wing area and fluid velocity.

If one were to go down the ground effect path, it probably would have to be some form of Atlantic Proa, which would only have a ground effect wing on the leeward side to provide lift and counteract heeling moment? Although if it were a tri, with both wings adjustable, it could have the leeward one in uplift mode and the windward one in balance/down lift mode and not lose the ability to tack. Both wings could be in uplift mode then whilst the boat slows through the tack. And if the wings break or their control mechanisms irreparably fail, it would still has to get safely home without external assistance?

I know of a Pacific Proa which has an inverted wing to provide extra righting moment in itself plus usable deck area and storage space to windward to carry crew and shift heavy equipment when necessary and stay dry.....

Looking forward with great interest to see what Paul Larssen comes up with.... 

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The Russians have a long history of ground effect craft or Ekranoplans..... Link below might amuse you:

http://englishrussia.com/2015/10/23/awesome-soviet-ekranoplan-aircraft-carrier-project/

And FWIW, SailRocket 3 is a partial Ekranoplan. The horizontal part of the wing to leeward is in lift mode. 

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On 7/11/2017 at 8:23 AM, Laurent said:

If it is an asymmetric tacking boat, like a trimaran with different boards on the ama, or a rig permanently tilted on one side, or a MASSIVE tacking canoe (one long main hull with an ama on one side only), then YES; it is a weather gamble...

But if it is a "true" proa, shunting from one tack to the other, then it is not.

It would be interesting to see how a 150 ft long shunting proa, in archimedian mode, not weighting more than the current ultim class trimarans, would perform...

It would get hammered, partly due to all the development that has gone into maxi tris compared to maxi proas, partly due to it being grossly overweight.  

If Bank Pop is 23T with 720 sq m sail, and you removed one of the floats, 75% of the main hull (ie 10m instead of 40 and 2 kgs per sq m instead of 8(?)), made the daggerboards steerable so you didn't need the rudders and kept boa the same, it would weigh less than 10T.  To get the same power to weight (Bruce Number) as BP (2.4), the proa would need 425 sqm of sail.  The proa would still get hammered on the development front, but might be faster in some conditions due to lower wetted surface and drag, easier to handle rig, etc. 

If you were "unconstrained", the weight could be appreciably less.  

Are you still in SIngapore?

Gary,

Looks good.  Frog, I presume?  What does it weigh?

Rob Z,

What is "Base (average) Speed"?  

According to your numbers (below) reducing the weight by 22% ((23-18)/23) results in a speed gain of 6% (31.3-29.4)/29.4).  

Does this mean a Tornado cat with 2 x 70 kgs crew (300 kgs, 22% lighter) will be 6% faster than one with 3 crew (380 kgs) ie, if the 3 crew sail at 10 knots, the 2 crew will sail at 10.6?

And increasing the length by 50% ((60-40)/40) results in a speed gain of 22% ((36-29.4)/29.4).  In which case a 30'ter wiil sail 22% faster than a 20'ter, weight and sail area being the same?   

Seems to give an unduly high benefit to length and unduly low benefit to weight savings.

If 50% longer is 22% faster, is it reasonable to assume 12.5% ((45-40)/40) will be 5.5% faster?  In a 40 day trip round the planet, that would make the 45m boat over 2 days quicker than the 40m.  Well "worth the effort", I think.  

Using data from Wikipedia, the current Ultime tri's are around 40 metres long, so a 45 m Proa for the same displacement, wouldn't be worth the effort. Only two ways to go really, and that is a 40 metre Proa and make it as light as you can or use the same displacement and make it as long as you can. And the Archimedean numbers are:

Banque Populaire: L 40m, Displ 23t SA 720m2 Base (average) Speed: 29.40 knots

40m Proa: Displ 18t SA 720m2 (if it can carry it) Base (average) Speed: 31.28 knots

60m Proa: Displ 23t SA 720m2 Base (average) Speed: 36.00 knots

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RobD,

Basic physics. You get roughly double the increase in Base Speed by going for (say 10% extra) length as opposed to saving (say 10%) weight. It isn't rocket science. You can check the numbers your self. Not hard. http://www.multihulldynamics.com/news_article.asp?articleID=226

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Rob.

Frog with rig and foils weighs 126.5 kgs ... without sails. But the new increased float size will push this figure up a few kgs.

Main hull and dagger weighs 56 kgs. Hence we could do the stealthy/sneaky early morning shift.

Beam weighs 28.5 kgs

Platform beam overall is 7.4m. counting the outfacing foil tips.

D mast is 9.57m tall. Double luff main will be full mast height.

frog6 copy.jpg

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On 8/13/2017 at 7:58 PM, Groucho Marx said:

Further to the information regarding early "DSS" - before it was invented; there was a superb Murray Ross monohull named M1 in Auckland, owned by the Hull family (Simon Hull, very well known owner/skipper of the ORMA 60 Vodafone/Frank/formerly Michel Desjoyeau's Geant), well, 15 years ago, maybe more, we were beating up the Waitemata in my trifoiler and going the other way was M1 .... with angled leeward foil exiting just below waterline and set at around 30 degrees, maybe even less. Later I talked to NZ designer Brett Bakewell-White who was horrified that the Hulls had butchered the famous Ross design. Not an advanced thinker BB-W, just joking. Apparently the foiled M1 didn't work as well as the hydrodynamicist Hull father intended and later the two foils were removed and the boat became the classical M1 again. But it seemed to sailing okay when we saw it. My point: was this boat ahead of the Wellbourn DSS?  And I'm sure there are other stories of near horizontal foils attached to monohulls. And of course the French were putting inverted Y and T foils on multihulls in the 1980s.

Didn't M1 have a configuration with square beams that extended out of rotatable housings in the topsides with skimming planing board things on the end? They could be extended to leeward and the planing surface would provide lift which was adjustable by changing the aoa by rotating the housings and beams. 

Looked heinus. 

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11 hours ago, Alcatraz5768 said:

Didn't M1 have a configuration with square beams that extended out of rotatable housings in the topsides with skimming planing board things on the end? They could be extended to leeward and the planing surface would provide lift which was adjustable by changing the aoa by rotating the housings and beams. 

Looked heinus. 

You know more about M1 than I do, Alcatraz. Wish I'd taken a photographs when we saw her. I thought the foil (one or two, I don't know) exited near the waterline - but then M1 was heeling over when we crossed and i couldn't figure out the foil setup. Maybe, thinking back, there was only one asymmetric foil that slid across the boat at/near WL? Would be educational if Simon Hull would enlighten us. Maybe they're embarrassed? But seeing the boat definitely got our attention.

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17 hours ago, Groucho Marx said:

Rob.

Frog with rig and foils weighs 126.5 kgs ... without sails. But the new increased float size will push this figure up a few kgs.

Main hull and dagger weighs 56 kgs. Hence we could do the stealthy/sneaky early morning shift.

Beam weighs 28.5 kgs

Platform beam overall is 7.4m. counting the outfacing foil tips.

D mast is 9.57m tall. Double luff main will be full mast height.

frog6 copy.jpg

Cool.  Bit heavier than a 25' harry, but with more "accommodation". When is the first sail?

Scaling this hull so that it was 40m long but only as wide and high as necessary would be lighter than the Ultimes main hull, which seem to be winding the design spiral towards heavier and more powerful rather than lighter and more easily driven.  Let's hope it does not have the same result as the ORMA's which were also length limited.

RobD,

Basic physics. You get roughly double the increase in Base Speed by going for (say 10% extra) length as opposed to saving (say 10%) weight. It isn't rocket science. You can check the numbers your self. Not hard. http://www.multihulldynamics.com/news_article.asp?articleID=226

Thanks for the reference.  No need to be snarky.   

That formula was devised by the very  clever Richard Boehmer to relate the race results of a group of boats in the 80's and 90's, none of which were longer than 50' and including cruisers and racers, good sailors and bad.  In 2001 he wrote (MHML) that it did not apply to ORMA 60 type multis.

Consequently,  I agree with you.  In regards to 40m tris and proas, it is not rocket science.  Nor is it physics, basic or otherwise.  Nor is it of much use comparing the two.

It is similar to the formula used by both Texel and the MYCQ, both of which are pretty good for similar boats, but not so hot when they get dissimilar.  

Given the unlikeliness of the samples i gave in my previous posts, I would treat it with care.  Unless you think that the samples I gave are reasonable results?    

A 5m extension of the waterline on a 40m tri would knock 2 days off the RTW record?  A 3 person Tornado will only be 6% slower than a 2 person?   

Another one: What is the "basic physics" explaining this year's Transpac where the ORMA 60' beat the MOD 70's?  Same sail area and crew ability, the 60 is15% shorter.  "Roughly double the increase in Base Speed by going for (say 10% extra) length as opposed to saving (say 10%) weight")  implies it would have to be more than 30% lighter to justify being quicker?   

Boats which are as different as 40m tris and proas do not answer to simple formulae, at least not to any that are known at present.  Part of this is the lack of experimental evidence to test them with.  

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3 hours ago, harryproa said:

Cool.  Bit heavier than a 25' harry, but with more "accommodation". When is the first sail?

Scaling this hull so that it was 40m long but only as wide and high as necessary would be lighter than the Ultimes main hull, which seem to be winding the design spiral towards heavier and more powerful rather than lighter and more easily driven.  Let's hope it does not have the same result as the ORMA's which were also length limited.

Thanks for the reference.  No need to be snarky.   

That formula was devised by the very  clever Richard Boehmer to relate the race results of a group of boats in the 80's and 90's, none of which were longer than 50' and including cruisers and racers, good sailors and bad.  In 2001 he wrote (MHML) that it did not apply to ORMA 60 type multis.

Consequently,  I agree with you.  In regards to 40m tris and proas, it is not rocket science.  Nor is it physics, basic or otherwise.  Nor is it of much use comparing the two.

It is similar to the formula used by both Texel and the MYCQ, both of which are pretty good for similar boats, but not so hot when they get dissimilar.  

Given the unlikeliness of the samples i gave in my previous posts, I would treat it with care.  Unless you think that the samples I gave are reasonable results?    

A 5m extension of the waterline on a 40m tri would knock 2 days off the RTW record?  A 3 person Tornado will only be 6% slower than a 2 person?   

Another one: What is the "basic physics" explaining this year's Transpac where the ORMA 60' beat the MOD 70's?  Same sail area and crew ability, the 60 is15% shorter.  "Roughly double the increase in Base Speed by going for (say 10% extra) length as opposed to saving (say 10%) weight")  implies it would have to be more than 30% lighter to justify being quicker?   

Boats which are as different as 40m tris and proas do not answer to simple formulae, at least not to any that are known at present.  Part of this is the lack of experimental evidence to test them with.  

RobD

As you well know, it is not the first time I have mentioned Base Speed nor is the first time I have given a reference in other threads that we both have been involved with. And I am well aware that Base Speed has been used or adapted for many handicapping systems including Texel, MOCRA and OMR.

An earlier poster mused at what kind of Archimedean speeds a 150 ft (ish) Proa might be capable of and I and I gave a fag packet answer. It is a rule of thumb limited to basic physics because there are so many other variables in the real world not to mention the human factor in the way a project is prepared and executed and what weather conditions prevail during any race/record attempt. We are musing about something on the very extreme edge in terms of multihull size and hydrodynamics. So who really knows?

i look forward to seeing what Paul Larsen comes up with.

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On 15.8.2017 at 3:01 AM, Rob Zabukovec said:

RobD,

Basic physics. You get roughly double the increase in Base Speed by going for (say 10% extra) length as opposed to saving (say 10%) weight. It isn't rocket science. You can check the numbers your self. Not hard. http://www.multihulldynamics.com/news_article.asp?articleID=226

That link contains something else than basic physics, including elementary errors. It gives a formula for SA/D and then makes a false claim it has units of square feet / cubic feet. Yet it is a mathematical fact it is dimensionless as given. D/(2/3) has units of square feet, not cubic feet. SA/D = 16 * Bruce number squared by the formulas given, hence both are dimensionless.

The text portion does not even explain that stability speed is proportional to (and indication of) apparent wind speed when all but lee hull begin flying, nothing to do with boat speed.

If it is supposed to be an explanatory text it does a bad job, just hope the formulas are correct even though not worth too much for performance prediction anyway even if the are correct.

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On 14.8.2017 at 4:15 AM, carcrash said:

Length is not an advantage if the boat is not dependent on Archimedes.

It is if you include pitching moment, even for full foilers. And even if pitch stability is controlled by aerodynamic wings, rather than foils in the water or hulls on the water. Beam is similarly advantage for rolling stability, even when narrow boats and foilers like moth work just fine.

Length between tail and wings is an advantage even for airplanes, but that doesn't mean there is anything wrong with a flying wing design like https://en.wikipedia.org/wiki/Northrop_Grumman_B-2_Spirit 

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1 hour ago, NotSoFast said:

That link contains something else than basic physics, including elementary errors. It gives a formula for SA/D and then makes a false claim it has units of square feet / cubic feet. Yet it is a mathematical fact it is dimensionless as given. D/(2/3) has units of square feet, not cubic feet. SA/D = 16 * Bruce number squared by the formulas given, hence both are dimensionless.

The text portion does not even explain that stability speed is proportional to (and indication of) apparent wind speed when all but lee hull begin flying, nothing to do with boat speed.

If it is supposed to be an explanatory text it does a bad job, just hope the formulas are correct even though not worth too much for performance prediction anyway even if the are correct.

If you read through the various sections on the website, you will also find that there are two differing formulas for Base Speed.

Nevertheless, for minimal input, to get a ball park comparison, as an interested amateur, I have found it useful. And more helpful than just calling something "fast" or "really fast" as a comparative.

Any alternative suggestions??

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On 22.8.2017 at 6:48 PM, Rob Zabukovec said:

If you read through the various sections on the website, you will also find that there are two differing formulas for Base Speed.

Nevertheless, for minimal input, to get a ball park comparison, as an interested amateur, I have found it useful. And more helpful than just calling something "fast" or "really fast" as a comparative.

Any alternative suggestions??

Not anything simple.

Most VPP are not perfect either, but do a much better job at performance prediction, while being substantially more complex. But it's also possible to do simplified VPP for boats not having too much wave resistance that do work without computers with a little more errors, which still might be useful enough for ball park comparisons and much better than any single formula ever can. The biggest improvement over any single formula comes from treating separately situations where boat is not powered up and when they are powered up, ie treating stability to carry sails as it works in real life, affecting sail area and/or trim, and not directly to speed like some formulas try to do it. Max sail area to be ignored when powered up, as it's not used, and replaced with stability criteria to predict effective sail area used in real life to predict performance. In light air stability has practically no effect in aerodynamics, but might have some relevant effect on wetted area, but it depends on type of boat, so no one single formula for all kind of boats can exist to take that effect into account. Either each type needs own treatment, or it must be ignored too losing accuracy. Any treatment of wave making resistance requires computers, but for a light boat for it's length, the errors for not taking it into account are rather small if all hull resistance are treated like it where due to wetted area.

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I also forgot to mention with regard to Base Speed, if you are talking about correctness of applying units etc, how do you get to knots without a time element in the equation? 

And no doubt you have spotted the inconsistencies/errors in Shuttleworth's Stability formula and Frank Bethwaite's Sail Carrying Power formula?

Nevertheless, I reckon Base Speed is a fast simple indicator to get a ball park idea. To give an example:

I calculate the Base Speed of Jester 2, a Proa designed by Paul Bieker to be 11.6 knots, which gives it a top speed of 23.2 knots and a top upwind speed of 11.6 knots. All in flat water of course. Below is Bieker's VPP for the boat. Check out the maximum Up and Dn Vs......

Multihulls of the size we are speculating could be a different can of worms...... Even for sophisticated and complex VPPs.

I totally agree that sail carrying power is important, but if you are talking  about maximising average speeds over long distances, you need grunt for light weather as well, as a lot of RTW racers have found out.

 

 

image.jpeg

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2 hours ago, NotSoFast said:

Not anything simple.

Most VPP are not perfect either, but do a much better job at performance prediction, while being substantially more complex. But it's also possible to do simplified VPP for boats not having too much wave resistance that do work without computers with a little more errors, which still might be useful enough for ball park comparisons and much better than any single formula ever can. The biggest improvement over any single formula comes from treating separately situations where boat is not powered up and when they are powered up, ie treating stability to carry sails as it works in real life, affecting sail area and/or trim, and not directly to speed like some formulas try to do it. Max sail area to be ignored when powered up, as it's not used, and replaced with stability criteria to predict effective sail area used in real life to predict performance. In light air stability has practically no effect in aerodynamics, but might have some relevant effect on wetted area, but it depends on type of boat, so no one single formula for all kind of boats can exist to take that effect into account. Either each type needs own treatment, or it must be ignored too losing accuracy. Any treatment of wave making resistance requires computers, but for a light boat for it's length, the errors for not taking it into account are rather small if all hull resistance are treated like it where due to wetted area.

Agreed.  

An example, which ties in with your comments about max sail area and stability is the other Beiker proa, Team Pure and Wild, which was actually built and raced, as opposed to Jester 2 which was neither.  Perhaps Rob Z could calculate TPW's Base Speed and compare it with what was actually achieved?  

Rob Z,

I have indeed been on other threads where you have used this formula, but never considered it important or relevant enough to test it with real boat numbers.  When i did, (see previous posts), it appears to be flawed.  

As well as examples of unbuilt boats that agree with your formula (perhaps because the VPP uses the same inputs?), maybe you could comment on the real world examples i gave above, where it doesn't?  

Do you know the parameters of the Jester 2 VPP?  ie, hull flying or not, water ballast or not, crew location, sail plan, etc. These are just some of the elements that make proa speed (and behaviour) predictions a difficult task.  

What are the errors in the Shuttleworth and Bethwaite formulae?   

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RobD

Built or unbuilt, the point was that you can put in a lot of work on VPPs or wade through a Texel calculation and come up with similar answers. If you have a stack of real world numbers, then happy days for,you.  Do you have VPPs for Bucket List? And how does it match reality? I seem to recall that you were pleasantly surprised by the Base Speed numbers I gave you in private Email correspondence years ago. How do they compare?

Shuttleworths formula gives the heeling arm as the distance from waterline to CE, whereas it should be CLR to CE. The formula implies a result in TWS whereas it should be AWS, and gives it in statute mile per hour. When was the last time you used wind speed in statute mph?

Nothing wrong with Bethwaite's SCP formula other than it is over complicated. It you check the maths,  the same SCP number can be derived by just dividing righting arm by heeling arm and expressing it as a percentage.

The point was that there are a lot of formulas about and they all have flaws and need to be taken with a pinch of salt, but I still use  them, in the absence of anything else, especially when it comes to proas.

No one is obliged to use or agree with Base Speed. Just sharing and trying to be helpful. Nothing more to say on this.

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On 24.8.2017 at 5:01 AM, Rob Zabukovec said:

I also forgot to mention with regard to Base Speed, if you are talking about correctness of applying units etc, how do you get to knots without a time element in the equation? 

There is another document on the site on the subject: http://www.multihulldynamics.com/images/analysis2011/CHM Analysis and Comparisons of CRUS MULTHULLS2013.pdf

The base speed formula can have knots as an answer, just assume the constant multiplier having appropriate units. in the above pdf page 17/60 the constant is 1.7 with unspecified units to make the result as knots. There is also S-number in the following page. If you multiply S-number with lwl^0,41667 (or sail area^0.20833), the result scales the same as base speed, but with differing results when boats have sailarea, weight and length scaled very differently. The interesting part is that for boats extremely light for their length, the S-number has almost no correlation with length, it becomes only Bruce number related, but for heavier boats, the length is far more dominant. Same with reality, wave making is almost irrelevant for extreme light for their length boats, and dominates drag for heavy boats. I have no idea how well that formula would predict performance in general terms compared with all those base speed type formulas of differing names and differing constants.

The article also have a lot of errors in mathematics and basic reasoning:

As an example on page 24/60 Stability Index for boats over 40 ft has wrong formula, but the correct one is included in appendage at the end. For both SI formulas / sign is missing. For a lot of places in the PDF sign is used instead of / sign, and parentheses is missing quite often there they should be. Stability speed obviously uses wrong units, not the ones Shuttleworth intended. The results in the graphs would suggest all cruising cats as well as racing ones could capsize in light winds quite easily. As a guess they are off by factor of 3.

Without all those errors, most of them not mentioned here, any formula giving only single number for performance prediction would most likely indicate increasing max sailarea increases boat speed. In real life more sails in a higher mast does so in light air, but if 2 otherwise same boats have different mast height and sail areas, and there is enough wind for the boat with a shorter mast to reduce power, it will be faster than the boat with a taller mast, not slower as those formulas indicate, because it has lower center of gravity and less windage. No formula producing a single number can catch that fact. A VPP can and it should, if not, it's worthless.

Quote

I totally agree that sail carrying power is important, but if you are talking  about maximising average speeds over long distances, you need grunt for light weather as well, as a lot of RTW racers have found out.

It seems to me those RTW racers (or rather record chasers) have all reduced their mast height from the original, Spidrift has shorter mast than original BP5, and similarly IdecSport during recor by Joyon&co has shorter mast than it had as Groupama3. The new breed of G-class seems similar to those shorter masted modified boats in that area.

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The point was that there are a lot of formulas about and they all have flaws and need to be taken with a pinch of salt

Exactly the point I was trying to make. :)

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