Most Weatherly Schooner

Discussion in 'Hydrodynamics and Aerodynamics' started by sharpii2, Aug 26, 2021.

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Which of these three design strategies is going to be most effective?

  1. Strategy 1

    1 vote(s)
    100.0%
  2. Strategy 2

    0 vote(s)
    0.0%
  3. Strategy 3

    0 vote(s)
    0.0%
  1. Robert Biegler
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    Robert Biegler Junior Member

    I think there is a better experimental test than your three configurations, especially if you would be interested in contrasting your proposal with mine: make two sails with different spans. If you are right, then placing the shorter sail aft, where its shorter span keeps it out of the wing tip vortex of the taller forward sail, would be faster than putting the short sail forward. A cat ketch would point higher than a cat schooner. I predict the opposite, especially if you let the aft sail twist a little more, because the foresail's wing tip vortex increases the angle of attack of the upper part of the aft sail.

    That idea gave me a keyword for another search (tandem wing), and I found this paper: AIAA Aerospace Research Central https://arc.aiaa.org/doi/10.2514/6.2021-1823 Judging by the abstract (the whole paper is behind a paywall), their results support my interpretation of the situation, though it would be more convincing if they had made the comparison outlined above. Abstract is below, the added emphasis is mine:

     
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  2. sharpii2
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    sharpii2 Senior Member

    How so?

    Enlighten me.
     
  3. sharpii2
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    sharpii2 Senior Member

    I'm trying to understand this theoretical aircraft.

    The piece said that there was a propeller above each wing.

    Does this mean there were four propellers?

    I would think that this would be a fairly dangerous machine. The high AR aft wing would be more likely to stall first. That could lock the plane into a nose up attitude.

    This could be especially ruinous if the aft wing engines should suddenly quit.

    One of the reasons for this thread is to tease out whether the Bernoulli principle is responsible for lift, or if it's actually the Coanda effect that causes it.

    My vote is with the Coanda effect.

    This is why I think design strategy 1 is the best.

    It would best guarantee that the airflow on the aft sail would follow its cross section all the way aft to the aft edge.
     
  4. CT249
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    CT249 Senior Member

    I assume it's the interplay between the leading edge of the aft mast and the leach of the foremast, but Tom Speer and Mikko and othere here know incomparably more than I do about that.

    With respect, your experience isn't really enough to indicate that all the rulemakers for about 150 years, just about every raceboat designer and many years of racing experience are wrong, and that schooners aren't slower upwind. Even one of the world's most successful racing schooners, Pen Duick IV (?), was converted to a ketch.

    I'd love to have a schooner in many ways, but over a century ago they were rated as 12% slower around a course than an equivalent sloop. That was in the grand days of big-budget schooner racing with boats like Westward and Ingomar. I've recently been doing a lot of looking at old race results, trying to compare the speeds of the great schooners with the 130' cutters of the 1800s, and it's apparent that even the big racing machine schooners were dramatically slower than the cutters.
     
  5. CT249
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    CT249 Senior Member

    Uffa didn't join the two masts together. They were, from memory, about 12" apart at the head. Fair point about the pitching.

    I've never sailed a properly rigged sloop where we couldn't properly control the twist of the mainsail, at least in light or medium conditions, so I can't see that as a factor. On my fairly typical 36'er, for example, the mainsheet led to a twin-speed winch each side, about as big as the headsail winch. There was zero problem with excessive twist, and that's the norm in racing boats.
     
  6. Will Gilmore
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    Will Gilmore Senior Member

    Just to be clear, I was only saying our schooner did well, not better, not even a well as other designs, only that it did a reasonable job of sailing to windward for a cruising sailboat. The J44 was clearly a faster boat to windward, for example.
     
  7. sharpii2
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    sharpii2 Senior Member

    I didn't notice any claim to superiority or even equal performance to a sloop.

    What I did notice is a statement that the schooner went to windward well enough.

    Well enough implies to me that it went to windward well enough to satisfy its owner, not necessarily well enough to beat a sloop.

    I think there is a problem with some members of the racing community. They seem to think that what is best for them is best for everyone.

    Though it's true that there have been vast improvements in performance in the racing community, this doesn't mean that these improvements translate well to the cruising community. In some cases they do. But in others, they have little relevance.

    I think there is a confusing of 'speed performance' with 'operational performance'. The two can be quite different. And a prospective owner may well choose the latter over the former--and for good reason.

    Some traditional schooners, for example, had a huge operational advantage over other rig types. This was that they could temporarily anchor while leaving the largest sail up. If the vessel made frequent stops, this could well make up for lesser windward performance when it comes to completing its journey. It may well be able to get the job finished sooner than the more weatherly sloop would--even if the course is dead to windward.

    Another operational advantage a schooner may have over other rig types, is that the Sail Area can be distributed along the length of the hull. This can improve natural course keeping without the need of self-steering vanes and auto-pilots. Ocean voyaging schooners, during the last years of sailing cargo ships, were noted for the small amount of crew they needed. This could be a major reason why. These schooners were often different from their coasting sisters in that the aft sail was a much smaller portion of the overall sail plan.
     
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  8. gonzo
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    gonzo Senior Member

    At the end of the era of sail, speed was not as important. Sailing ships could not compete with steamers in speed. Therefore, sailing ships only got the cheap cargo that was not time sensitive. Those cargoes could not pay for the full crew of a ship. The result was to switch to fore and aft rigs that are slower but need smaller crews.
     
  9. philSweet
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    philSweet Senior Member

    Also, the steam powered windlass was available, so you could pull as hard as you wanted. This resulted in a strong motivation to reduce the number of running rigging lines, and fore/aft beats full-rigged hands down in that department. Sails got bigger and controls got fewer. And you didn't need 60 guys to bring up the best bower or run the chain pump for three days.

    And steam tugs got you in and out of harbors.

    Those developments facilitated smaller crews as well.
     
  10. CT249
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    CT249 Senior Member

    If you're aiming your remark "I think there is a problem with some members of the racing community. They seem to think that what is best for them is best for everyone" at me, then you've ignored much of what I have written in discussions with you and others here. I've repeatedly said that I don't think anyone should tell someone else what is good for them. In light winds, one of my boats is probably the least weatherly of its design afloat, so I don't even think that being the most weatherly all the time is even the most important thing for me.

    I got into the thread in response to Robert's note about cat rigs pointing higher, and noted that in craft of the type you proposed that is not normally true. I also mentioned sloops to illustrate the importance of jibs, and the importance of aspect ratios. That was not to say that schooners were inferior - it was to throw some more bits of info into the discussion about how to make the most weatherly schooner.

    I (wrongly ) assumed that Will was trying to bring up an example that showed that the schooners were as quick and high upwind, as a point of data to throw in to compare with my notes that small classes had moved away from schooners. I'm sorry that I got his inference wrong.

    The basic point was that if one actually analyses the issues with schooners' upwind performance then one can probably do a better job of optimising it. If you don't compare and contrast the weatherliness of various types, then how can one try to achieve what you claim to want to achieve?
     
  11. Robert Biegler
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    Robert Biegler Junior Member

    Translating that into the corresponding rotation axes of a boat, that is a worry about whether the boat self-steers without a rudder in the water. That is a question different from whether the forward wingtip vortex spoils flow over the aft sail.

    My understanding is that the Coanda effect needs an airstream blown over a surface faster relative to the surface than the surrounding air. A sailing boat lacks a pump or propeller to create that fast stream, but perhaps it could be created by ram air pressure. Perhaps that is what people think of when they talk about the slot effect. I don't see how it could apply to a boat with a soft sail in anything but wind so light that tension holds the sail fabric well enough to let it act like a solid wing. Once the wind picks up, any attempt to create a funnel between two sails would result in the aft sail luffing. I have only ever let that happen to decrease, not increase lift.

    Is that why one of your design strategies emphasises overlap?

    Either for practical research or even just thought experiments, I prefer to separate variables as much as possible. For your first question, on wingtip vortices, I still think the most informative comparison is that of cat ketch and cat schooner, differing only in how they order the sails. To find out whether the Coanda effect has anything to do with sailing, find a way to measure speed over the mainsail as a function of the angle between jib and main. Does that speed increase as you close the slot, and does that increase L/D? If yes, can you still do this with a soft sail?
     
  12. rangebowdrie
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    rangebowdrie Senior Member

    Insofar as yachts, as opposed to commercial craft, John Alden is probably the most noted.
    A study of the evolution of his schooners shows that as time went on he kept increasing the sail area of the foresail and fore triangle, and reducing the proportion of the mainsail in regards to total sail area.
    Starling Burgess also comes to mind, his schooner designs have been shown to be weatherly and easily handled without a large crew.
    Caveat; I'm a fan of schooners, if I wanted a boat that was large enough to require 2 masts it would be a staysail schooner.
    Ah yes,, sailing thru Polynesia with a schooner, a cargo of copra, trading beads and baubles with the islanders,, probably doesn't get any better.
    At least in my dreams,, Adventures In Paradise.
     
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  13. CT249
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    CT249 Senior Member

    I didn't know that about Alden's rigs. At the height of schooner racing in the UK (late 1800s) the tendency was the other way; towards big mainsails. That may have been a reflection on sail technology at the time, which made foretriangles less effective.

    I'm fairly sure that either Loomis or Hoyt say that Nina, at any rate,was a good upwind performer but a crew-intensive boat to work.
     
  14. CT249
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    CT249 Senior Member

    Think you'll find that CFD and empirical measurements show that the "funnel" between two sails slows the airflow in that area, rather than accelerating it as the old theories went.

    There's quite a few boats that go faster with the mainsail luffing along the mast, even in fairly light winds. It's not hard to see why; you may lose 5% of effective area but the wider sheeting angle etc can increase the drive by more than the amount that is lost. Actual lift may not be increased, but the vector seems to be more efficient.

    I've been lucky enough to sometimes sail with various America's Cup and world championship winning sailmaker/trimmers (Grant Simmer, etc) a bit. They tend to consider the rig as a whole and will sacrifice the theoretical efficiency of one part in order to preserve the efficiency of the rest. Interestingly Mark Drela has also said here that the components of an airfoil are largely irrelevant; what matters is the whole.

    The really interesting thing about what Mikko, Mark and Tom Speer have said on BDF is that what they say tallies with the real world. It actually works, unlike much of what other aerodynamic "experts" claim.
     
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  15. Doug Halsey
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    Doug Halsey Senior Member

    Old theories never die; they just get recycled endlessly.

    It's been nearly 50 years since Arvel Gentry's series of popular articles (& his boss AMO Smith's more technical version) attempted to debunk the "funnel" idea, but I guess you can't unwrite all the old stuff that's been published.
     
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