Pushmi-Pullyu; a Proa for All Oceans?
The fact that a 48 ft cat rigged boat finishes 45 minutes behind a 40 ft stayed sloop rigged boat in a 5 hour race tells me something.
I assume this is a typo; the unstayed cat boat finished 45 mins ahead of the raceboats, thus the entire fleet, not behind. She was first to finish.
Dave
My apologies .....
Pushmi will do very well with a catcoat rig or a balestron rig but maybe better with a stayed sloop one if you could get it to work.
Nothing more to add.
Rob
A little devil’s advocacy…
Why do you think that the Atlantic Proa has not lived up to the potential implied by its bitchin’ RM and light weight?
Its not for lack of a brilliant designer, or big budgets.
What do you think?
Why do you think that the Atlantic Proa has not lived up to the potential implied by its bitchin’ RM and light weight?
I propose it’s because in a box rule (which we had for some years, in the ORMA 60s) transverse righting moment is not the limiting factor. The ORMA trimarans already had more transverse than longitudinal righting moment. When the recent boats were released from the box rule, they became longer, not wider. A proa of the same length as a trimaran would have less longitudinal stability because the centre of gravity is in the middle (unless you add ballast aft and lose weight advantage), and hull and foil shapes are not optimised for the current direction of travel. I don’t see a proa being competitive in a box rule class. Proas might rule a claiming race class. I am pretty sure a $100 000 boat could race offshore, and would be cheaper than the Minis (box rule again, I think they always end up being expensive for what they do).
The current crop of racers seem limited by the size of rig the crew can handle. It seems less clear cut to me where the advantage lies, but people more knowledgeable than I am still go for trimarans. The “rebuild” of Geronimo for Thomas Coville seems to have kept only the beams and some foils. They probably could have built a longer proa for the same money and with the same rig, but chose not to. Come to think of it, the proa would lose out on cost, aerodrag and weight by needing two of each foresail. At that size and weight, moving them from one end to the other would cost too much time, even it it can be done. Perhaps that’s what prevents proas from being competitive.
Has anyone answered Marco’s concerns about “pitch instability”? I am assuming this is a reference to “hobby horsing”, which seems like a problem with fore and aft symmetry, which is a defining characteristic of proas, whether Pacific, Atlantic or Pushmi-Pullyu.
Has anyone answered Marco’s concerns about “pitch instability”? I am assuming this is a reference to “hobby horsing”, which seems like a problem with fore and aft symmetry, which is a defining characteristic of proas, whether Pacific, Atlantic or Pushmi-Pullyu.
As I read it, Marco’s comments refer to longitudinal stability per se, not hobbyhorsing, which is more to do with pitch damping. Robert Biegler’s comments above deal with the longitudinal stability issue. Hobbyhorsing was discussed in the ‘A better proa hull?’ thread: http://proafile.com/forums/viewthread/408/
In either case, it can’t be stressed enough that the proa advantage is that you can get a longer boat for the same cost, all else being equal. The proa should gain back any loss of pitch stability due to the extra length. Comparing a proa with another configuration of equal length is a flawed comparison. As Robert states above, box rules don’t favour proas.
Mal.
it can’t be stressed enough that the proa advantage is that you can get a longer boat for the same cost, all else being equal. The proa should gain back any loss of pitch stability due to the extra length. Comparing a proa with another configuration of equal length is a flawed comparison. As Robert states above, box rules don’t favour proas. Mal.
Would not a 1/3 lighter boat, on the same length hull as the heavier boat, be functionally equivalent to having a longer boat, at equal displacement? In a sense I believe I’m restating Mal’s point, just a different POV. Proas’ “singular” advantage being length for weight, rather than length for cost. I’d use this same argument with Robert’s box rule conclusion: The boat needn’t “fill” the box; it can be narrower (lower roll moments less stress on the structure) It can be lighter (lowering the sail CE, reducing the amount of pitch stability needed; beneficial spiral allowing further decreases in mass, increases in specific strength of structure, reduced cost overall), yet have identical Bruce numbers and even more extreme length/displacement ratios.
As to hull shapes, 1) we just went through a fairly lengthy thread suggesting (and not disproven) that over some given L/B ratio, cross sectional shape becomes moot—almost no advantage/disadvantage regardless of what one does. Taking 1/3 the mass out of equal-length hulls will have far, far more effect on boat speed than a transom stern versus double-ended stern will. 2) There have always been “healthy” double-ended designed hulls which performed well. (Pat’s Boat and WhiteWings, just to stick with Newick. Names escape me, but many, many offshore tris had/have double-ended aft waterlines on their amas. This assists them in not slamming quite so hard in sloppy conditions.) 3) There is a great deal of fashion in boat design; for the immediately foreseeable future there will be many multis with shapes and sections reminiscent of the recent AC; whose shapes are strictly the result of compliance with a complex set of rules and not at all to optimize shape. Match racing, let alone AC match racing, is not a place to look for transferrable optimization. The whole point of that style of racing is to beat your opponent by 6’, not 6 miles.
Boards and proas; Tris have two asym boards and/or two asym foils, so does the proa. There is no difference here at all; one board/foil/rudder gets raised and the other lowered with every tack; it’s identical with the Atl proa. Pushmi-Pullyu adds additional complication, so take him away and scoot a pure Atlantic back in his spot. Maximum high-wind performance remains significantly better than the tri. Put Pushmi-Pullyu back and you’ll excel in light wind as well. My contention all along has been that the (small) sacrifice in complication and mass of doubling rudders is more than offset by the (large) gain in wind range within which one can fly a hull.
A little devil’s advocacy…
Why do you think that the Atlantic Proa has not lived up to the potential implied by its bitchin’ RM and light weight?
Its not for lack of a brilliant designer, or big budgets.
What do you think?
I think it’s for lack of brilliant designers and big budgets, myself. Atlantic proas frightened the status quo quite badly in the 70’s and early 1980’s; there was much protective activity, number one. 2) the capsize issue was never addressed, Proas could and did tip over—regularly. This was a marketing shortfall, not a physical one, Newick proas (the two built to designer’s spec) repeatedly capsized and self-righted; something the tris of that day (and this) cannot replicate. The bad press was then was used by the opposition to beat them to death. I expect a “modern” atlantic proa would require masthead floats or similar, just to get into the races. 3) [a well-known Frenchman] more or less single-handedly managed to push the boat type far beyond healthy limits, had no controls on his ego or budget and managed to get them successfully banned in all oceans (first time this has *ever* happened in sailboat racing, I believe) before more than 2-3 designers’ boats ever saw water. Cheers had 260 sq ft in both mains, plus another 100 in her jib. Her bruce numbers, s/d ratios, strength of materials were all pathetic, even by standards of the day. Save for the functionally quite successful harryproas, there has been zero development work done on the type since, save for [a well-known Frenchman’s] circus freaks, now more than 40 years in the past.
(bracketed remarks redacted because, well, he’s still alive.)
Dave
My contention all along has been that the (small)
sacrifice in complication and mass of doubling rudders is more than offset
by the (large) gain in wind range within which one can fly a hull.
Dave, are you talking about a racing situation here?
the capsize issue was never addressed, Proas could and did tip over—regularly.
It is a really good thing no race-boat (mono, catamaran or tri) has ever capsized since then. This whole capsize thing is only for proas, soo lets ban then from racing!!!
First page of a google picture search of “racing trimaran”.... First page!
http://i.telegraph.co.uk/multimedia/archive/02597/SPINDRIFT2_2597852b.jpg
Don´t search for “race boat capsized”!!! We might have to ban monohulls, catamarans and trimarans if this out!
As moderator, I’ll ask other members to not respond to any of Dave’s many points until after I post a reply sometime tomorrow. Thanks.
Dave Culp is no longer a member here at Proafile. It is not our policy normally to announce the removal of a member (which thankfully has been a rarity) but as Dave has been very active lately and engaging a lot of members in discussions in multiple threads, it would seem very odd if he suddenly disappeared without any explanation.
In his last post (which I have now removed) on this thread, Dave contravened the “Terms of Use” in multiple ways. I initially rejected his application for membership of the Proafile forum because of the debating tactics he employed on the Yahoo proa group. He appealed my decision and I agreed provided he understood he would not be granted the latitude other members could expect. He made assurances that he would abide by the different rules here. He repeated these assurances to me personally only a couple of weeks ago.
In his last post he insulted some members by misrepresenting a situation that has a long history and that he was part of. This may not be apparent to those who do not know this history but, never-the-less it, was a serious breach not only of the Terms of Use but also of our agreement.
This thread is now closed. If any members wish to contact me by Personal Message regarding this, please feel free to do so.