Why a Yawl or Ketch instead of a sloop

Discussion in 'Boat Design' started by saltydog123, Apr 29, 2009.

  1. Paul B

    Paul B Previous Member

    Headsails do have the max camber closer to 30-35% than 40%.

    This latest iteration of your foils would still be luffing.

    I don't think I will ever understand what you are trying to show.
     
  2. Paul B

    Paul B Previous Member


    Next you will mention Mari Cha?

    Specialty boats. In the 15 years since EM was launched, how many have followed?

    Let's see how this boat would stack up against a TP52. Upwind there would be no contest.
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    Paul

    Then perhaps ive missed the question/point you're asking?
    sorry!
     
  4. Guest625101138

    Guest625101138 Previous Member

    The apparent wind as experienced on the boat will be different to the true apparent wind as you experience aligned to the hull. These are caused by the leeway of the hull and the change in airflow around the sails.

    To get the true angle of the wind you need to be removed from the infuence of the sails

    Attached shows a foil of 1% thickness, with 10% camber located at 30% chord and an AR of 4. It is aligned to the position of maximum lift. You can see from the streamlines that the air has curved quite a lot as it enters the sail. This is not the true apparent wind.

    The second image is the same sail but zoomed out to show that the flow is directly left to right.

    The sheeting angle with respect to the apparent wind is about 15 degrees. The sheeting angle would be much greater for the wind angle approaching the front of the sail.

    So the angles you experience depend on your frame of reference. There is no instrument using wind data around the boat that can give you the far field apparent wind. You would need to be collecting wind data from a fixed point and then adjusting to the actual velocity vectors to determine the far field apparent wind. All the angles I have shown above refer to the far field and this is taking undisturbed airflow directly left to right.

    So sheeting angles with respect to apparent wind need to consider the frame of reference of the observer.

    Rick W
     

    Attached Files:

  5. Boatpride
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    Boatpride Boatpride

    Yawl Enthusiast!

    Last week I sailed on board http://www.sailingnetworks.com/boats/view/2 in the photo she has four sails up. But we also used the Mizzen Stay Sail as well.

    The sloop designs were quicker in light air. They are lighter and have longer keels. On the light air days we came in around the middle of the finishing order.

    But on the two days when the winds were over twenty knots constantly we lead the field, being able to put up five sails and avoid broaching!

    My money is on yawls!
     
  6. brian eiland
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    brian eiland Senior Member

    Rivival

    I was just reviewing a few subject threads, and ran through all of this one real quick. There was much really good conversation here. I thought it desired reviving.
     
  7. brian eiland
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    brian eiland Senior Member

    Deketchification....what a concept !

    Just found a great new word....invented by Eric Sponberg

    Naturally I was interested in anything discussing ketches......

    [​IMG]
     
  8. beau.vrolyk
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    beau.vrolyk Crew

    Brian,

    Despite the author's longing for a split rig, I believe he's wrong about the advantages of a split rig of any kind (Yawl, Ketch or Schooner). The historic motivation for a split rig was not to balance the boat it was to reduce the sail area of any single sail to a number of square feet that the on-deck crew could deal with. The common and highly reliable methods of furling sail that are now in use basically eliminates the need for a split rig.

    In the 1950s a sailor needed to drag a headsail to the deck and tie it down with sail ties. Today, that same sailor sits in the cockpit and rolls the sail up around the jib stay. Back then the sailor had to haul the mainsail down and either reef it or tie it to the boom with sail ties. That same sailor can now either use a LeisureFurl to roll it up in the boom or roll a much less useful mainsail up into the mast. In all these cases a significantly larger sail can be managed by one person.

    The massive improvements in technology have made split rigs obsolete, not some "Western corporate wisdom." Perhaps the author needs to develop a better understanding of how modern cruisers sail sloops with much larger rigs than they could of 40 years ago. The sloop is demonstrably better performing in all conditions, it is less expensive to build and maintain, and it's sole drawback (being able to manage large sails) has been solved with modern technologies. Split rigs solved a problem that sailors no longer have.

    Beau
     
  9. pdwiley
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    pdwiley Senior Member

    I think you're making a claim that you will not be able to substantiate when it comes to cost.

    What is your cost for a sloop rig for a 12m LOD, 7.5 tonne displacement sailboat, in round figures? Include all required deck gear.

    I can rig my schooner with all new sails, standing & running rigging for less than $10K. I doubt you can even buy the spars for yours for that price if they include furling booms etc.

    PDW
     
  10. PAR
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    PAR Yacht Designer/Builder

    Beau, welcome to the forum. I have the same opinion as Eric with a well thought out ketch rig, for the the cruiser. The manufactures are intrinsically interested in just a few things, the most likely racing fad they can incorporate into their designs, for marketing purposes (understandably) and a price point. The winged keels of the mid 80's and water ballasted ridiculousness of the 90's certainly have proven this, as has just about every other "innovation" in production yachts, since the golden days of sail. None of this is applicable to the serious cruiser, though many wannabe's that haven't figured out what they do need, might think they do. Interestingly enough, a significant percentage of small and mid size yacht purchases are by those thinking cruising is what they want and this will be their first foray, into an ocean capable craft, so having all the doodads that the production builder's marketing team suggests, is a sales goal and marketing ploy.

    [​IMG]

    This is an Open 60 design of Eric's that proved fast, possibly too much for the first owner and certainly so for it's second. You don't design vessels like this, lacking "understanding". He's highly accredited and has a design listed, one of the "100 Greatest Sailing Yachts in North America" by Sail magazine. His designs are in production, by the very folks you think he doesn't have sufficient conceptual grasp of.

    Simply put, I'd suggest your understanding might be the one in question, as there's considerably more to the subject, then just sail handling gear. I have a 65' yacht with a 71' mast, which I'm converting to ketch, if for no other reason then to make it a practical craft to live with, not to mention bridges. Balance is and has always been an issue, particularly with modern hull forms and appendages. There are many advantages of a well thought out divided rig and though you may not wish to acknowledge them, this doesn't mean they don't exist. These considerations are considered by serious, experienced cruisers, which typically have a well defined set of goals for their SOR in a custom craft or a new (to them) acquisition. In fact, there's nothing more demanding, then addressing the SOR of this type of client.
     
  11. Eric Sponberg
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    Eric Sponberg Senior Member

    Thank you Brian, PD, and PAR!

    Eric
     
  12. michael pierzga
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    michael pierzga Senior Member

    Any issues with the boom dragging in the back of waves ?
     
  13. Eric Sponberg
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    Eric Sponberg Senior Member

    For Project Amazon? Never.

    Eric
     
  14. PAR
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    PAR Yacht Designer/Builder

    With the RM on Project Amazon, Pleeeeease . . .
     

  15. MikeJohns
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    MikeJohns Senior Member

    B.V.

    Didn't you already say most of that earlier in this thread ? Sailors can have the same problems now, at least I often do :)

    I agree with Eric's article, PAR's and PDW's comments .

    I'd recommend a split rig without hesitation for any medium-heavy cruising boat over 45 feet. The working sails get too big. I'd also recommend hank on foresails for a cruising boat, I find them much easier and safer to handle, providing the boat is not so poorly designed that the foredeck is a dangerous place.
    Roller headsails that are too big to handle short handed are left detrimentally left stowed the furler. Ugh....!

    When reaching the ketch has everything going for it and the mizzen staysail is just about worth adopting a ketch rig alone for it's great virtues and ease of use on a passage. And a light air mizz staysail and a big MPS work together to give a very advantageous light air drive.

    To windward the drag of the mizzen and its rigging is small compared to the advantageous effect of the mizzen on the mainsail. Sure you have to sail further off the wind than a sloop but the mainsail drive is significantly higher in compensation.

    One of the reasons I dumped my VDS 57 (LOD) was it's sloop rig. The size of the gear and the cost of maintenance and sail replacement is staggering, and highly stressed rigging is a real concern to me. It's not worth sparkling performance to windward. I was never comfortable with the rig with all it's powered gizmos furlers and sheer towering loftiness.

    I have a similar sized ketch now and I wouldn't swap it back for the world. The ketch is much a more versatile rig, and it's more fun to sail. In heavy weather I think it's a much easier and safer rig either to run with or to heave too. Especially short handed. Also you don't need motorised winches. I also think I can get more drive out the rig with an array of storm sails than I could with a similar sloop, and balance the boat so the autohelm works. Even in a real blow, and the centre of effort is much lower so the boat stays on it's feet and doesn't spill its wind so much with the gusts.

    I could go on, I'm sure you could too :)
     
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