Why a Yawl or Ketch instead of a sloop

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

  1. DennisRB
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    DennisRB Senior Member

    I saw a forum member here show the costings of rig and sails when comparing a sloop VS ketch where the ketch worked out cheaper. This was for a larger boat. There may be a crossover point in size where a ketch is cheaper as the cost of large sails, masts/rigging seems to go up exponentially with size. Obviously for smaller boats the sloop will be cheaper. I think this topic deserves some consideration.
     
  2. pdwiley
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    pdwiley Senior Member

    OK, go for it - list the costs.

    I gave you a very specific example to compare to - go back and read what I wrote instead of engaging in 'mis-attributions'.

    My costs are known because I built the boat I'm using as an example. That's why I specified the displacement, LOD etc. If you want to know sail area, it's 850 square feet working sail (no big overlapping headsails).

    I very seriously doubt you can even buy the spars and standing rigging for what you're proposing for the amount of money I spend on my entire rig. If you were limited in dollar terms then your preferred sailboat wouldn't even be able to leave port except under engine.

    So - go for it. List the costs of the rig of your choice.

    PDW
     
  3. DennisRB
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    DennisRB Senior Member

    Twas you then. :) Plus I have seen others come to the same conclusions. At which size boat do you think the crossover point in price might be?
     
  4. MikeJohns
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    MikeJohns Senior Member


    Don’t lose sight of what we are actually trying to do which is to propel a hull through the water by extracting energy from the difference in the velocity of the two fluids air and water. It’s the total drag (Aero and Hydro) and the total drive in equilibrium that we are interested in. It’s not an aircraft where aero drag is the holy grail.

    You should be asking how much extra sail needs to be carried on a split rig to overcome the additional aero drag component and on which relative headings it actually applies ! A sloop will sail faster close hauled, but that’s all .

    The design space is not as simple as many people imagine when looking at a very narrow and quite unrealistic paradigm based on close hauled performance alone. Many factors interact and we’d quickly get into a lot of naval architecture to try and explore their interactions thoroughly within that design space.
    If we were designing a sailing craft we can take everything into account from the starting point of the design. It’s eminently sensible to opt for a second mast to get the sail area for the target ratios for the clients SOR. If so designed it will sail very well to windward. Rig loads will be lower sails will be smaller and more easily handled and the craft is safer to operate.

    As for racing; the Whitbread was won in it’s last 2 years by ketches. Other less high profile races in the past have been dominated by ketches provided they were not rated out of contention. It might come as a surprise to some people to see the polar plots of some of these specifically designed racing ketches. But they need converting to sloop rigs for short haul races as they don’t get the favorable overall wind headings to iron out the average runs.

    There is also weight. If you have a box rule and want to race you must adopt ULDB and necessarily a sloop rig. The drive to ‘weight’ ratio of the rig is of paramount significance to racing design. However …..racing is a very poor design paradigm for a cruising boat. A racing boats design is based on reducing the last 3% of elapsed time over a set course and necessarily keeping everything as light as possible with little or no safety factor.
     
  5. pdwiley
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    pdwiley Senior Member

    I am no expert at all so I really couldn't say.

    Keep in mind my boat is a Tom Colvin design that was designed as a cruising boat and many of then have been built by amateurs. The rig was designed to move the boat efficiently, with two of the efficiency criteria being simplicity of construction/maintenance and cost. Factors that the sloop booster, I suspect, completely ignores.

    PDW
     
  6. brian eiland
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    brian eiland Senior Member

  7. brian eiland
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    brian eiland Senior Member

  8. brian eiland
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    brian eiland Senior Member

  9. brian eiland
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    brian eiland Senior Member

  10. Sailor Alan
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    Sailor Alan Senior Member

    Sloop vs Ketch vs Yawl

    Sloop vs Ketch vs Yawl.

    This subject is very difficult, and very interesting for all that, but there are really no ‘right’ answers, except for the ultimate boat owner/user, to whom the utility or usability is paramount. The ‘plastic’ tubs in the Caribbean, and elsewhere, are successful boats too. They fulfill a purpose, carrying 3 couples in reasonable comfort and privacy, on their ‘trip of a lifetime’ involving some sailing, usually under ideal conditions. Don't knock it. Rather few of these people can sail very well, and wouldn't know if they were doing it ‘wrong’. The companies that realized this first (Morgan, Out Island?) really created a huge market for people who would otherwise have never sailed a boat.

    Please note; It is possible to rig a Ketch cheaper than a sloop. In my case the ‘new’ ketch had only one set of spreaders on the main (instead of two when it was a sloop), and none on the mizzen, they were pole masts, so very cheap. The rigging was all galvanized wire, served and tarred. It had no bowsprit and flying jib now, so the working sail number was the same. No precise costs were recorded that i can recall, it was many years ago in NZ, but the boat sailed rather better after the re-rig. The hull was local, and looked rather like one of George Beuhlers. Perhaps a special case though.

    Though i grew up designing, and building, racing dinghies, by definition sloops, i have since been involved with many Yawls, and Ketches too. In fact i race a 50’s era yawl every weekend. Identical hulls had a 4’ longer mast stepped 18” further aft, and are currently slower (poorer PHRF). This might be because our boat is the only one of the 24 odd boats built that actively races. These days mast position is often dictated by accommodation, and i definitely try to put mast posts where they least intrude.

    As mentioned by “MikeJohns”, we are extracting energy from fluids in motion, not least the different pressures set up on either side of a sail. Leading edge length (height) is of paramount interest in generating forward ‘lift’, the primary vector when sailing to windward. Hence the relatively better performance of the sloop to windward. However, this is merely an artifact of all the sail area being hung from a single mast, and not just that it is a ‘sloop’ or ‘cutter’. Ketches, especially those with high aspect ratio rigs, and widely separated masts, give little away in windward work, and some would argue are actually better if only because their average CP is lower, and their ballast to sail area ratio is better.

    A huge advantage of the Yawl, and perhaps also of the Ketch when beating to windward, is using the mizen to allow the rudder to sit in its ‘neutral’ position. This might be at “0” for a spade rudder, but more likely about 2-4’ to leeward for a long keeled boat. This helps the keel, including the rudder, to take up a more cambered shape, lifting the boat to windward. It also reduces hull (keel) drag on this point of sail. This is a little like a plane (not slotted) wing flap on a airplane. Sailors might call this ‘trim’.

    Modern ocean racers (Steinlarger, Endeavor, Fisher & Paykel, the Kiwi Yachts, and Kialoa 3) used to take advantage of a loophole in the rating rules to use the ketch rig to advantage. By placing the mizzen well aft of the main, enough separation was provided such that the two masts and sail systems could work nearly independently. As soon as sheets could be cracked, mizen staysails etc came into their own. Further off the wind, and though both masts might fly a spinnaker, these ketches did loose a little, hence they avoided going dead down wind, much like a modern multihull.
     
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  11. jazzdog
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    jazzdog New Member

    What do you think fellas?


    [​IMG]
     
  12. PAR
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    PAR Yacht Designer/Builder

    Yeah, jib and jigger, and . . .
     
  13. Sailor Alan
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    Sailor Alan Senior Member

    Cutter to yawl

    In a historical, and possibly humorous, and definitely irrelevant aside. I quote from Dixon Kemp’s, “A Manual on Yacht and Boat Sailing” (1884) pp 18-19. A fantastic book, no wonder the British Royal Navy used it as a text book for many years.

    “We have calculated what the difference in cubical content of the spars of the Kriemhilda (106 tones) would be if she were changed from cutter to yawl, the length of main mast remaining the same. Difference in mast, 20 cubic feet; difference in bowsprit (3 ft shorter), 12 cubic feet; difference in main boom 12 foot shorter), 25 cubic feet; difference in main gaff, 4 cubic feet- making a total difference of 61 cubic feet, or one ton weight.The topmast would remain about the same.
    The bulk and weight of the mizen spars would be as nearly as possible as follows: mast, 16 cubic feet; boom, 4 cubic feet; yard, 8 cubic feet; boom-kin, 2 cubic feet; or a total of 25 cubic feet, making a net reduction of about 12cwt. The difference in the weight of rigging and blocks would be from 4-5cwt, making the total reduction of weight of spars and rigging of about 17cwt."


    Notice how the mainmast gets smaller, and the rigging lighter though still the same height whilst becoming a yawl.
    He then goes on to describe how a yacht so rigged would be faster on passage, have a lower CG, reduce pitching etc. These were huge yachts, with a master, mate, and 6 seamen recommended, so hardly representative of our boats. He also wrote eloquently on moving the mast, placing it properly for a yawl, and moving the mizzen forward so it could be stayed properly. He also wrote disparately about Ketches.
    He includes tables of spar dimensions, rigging wire weights, and recommended stretch factors.

    He gives other examples of similar boats re-rigged, or proposed to re-rigg, including actively racing in various series.

    I was fascinated, but as i said, hardly relevant to this discussion.
     
  14. vagabondman
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    vagabondman New Member

    get rid

    AM thinking of ditching my ketch missen sail . Its so in the way and verses extra power, getting rid of it wins
     

  15. PAR
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    Modern interpretations of these rigs, are changing the preconceived notions of their predecessors. I know a nice schooner a few hours from here, which has a main and fore the same height (within a few inches) and a lot of distance between the sticks. I also have a ketch with the same approach, placing the mizzen as far aft as practical, to provide enough separation to allow the upper portion of the mizzen to be more effective upwind. You can still hoist a mule off wind and the boat still balances well under all combinations.

    Modern sail handling gear has made much of this moot though. Very large sails can be handled with modern reefing and furling gear, which means you can have a 70' sloop. Previously, rigs had their area divided up, so sail handling could be easier.
     
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