whats the best design for cruising??

Discussion in 'Sailboats' started by rad..., Jun 20, 2009.

  1. Charles Burgess
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    Charles Burgess Naval Architect

    Ketch does rhyme with retch.

    In a ketch or yawl is can be difficult to balance the CE, CG, and CLP when the rig inherently induces yaw in a seaway. Based upon long study and experience, a ketch or yawl are only makeshift attempts to balance (to correct) an unbalanced sail area/helm relationship with the six degrees of freedom. If you want two masts to begin with, and there are many good reasons to do so, then it only makes sense to make it a schooner.
     
  2. peter radclyffe
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    peter radclyffe Senior Member

    how would you describe latifa
     
  3. Charles Burgess
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    Charles Burgess Naval Architect

    There are clients who specify a ketch or yawl rig when commissioning a new yacht design, thus the NA will design the hull/rudder in such a way to make the rig work. A ketch or yawl rigged yacht is only designed because that is what the client desires.

    You can say the same for any rig. On large square rigged ships (tallships) it was common for a single hull to sail under 2, 3, or more different rigs during their lifespan, usually without any drastic impact on performance. But at the size of a yacht, you cannot change the rig without the very real possibility of serious impact on performance.

    Workboats are a different breed...a yawl or ketch rig can make their work at sea safer when heaved to in a seaway under a reefed mizzen - something a yacht wouldn't need to do very often. The difference is that the workboat needs to be safely heaved to for a longer amount of time...a yacht doesn't.
     
  4. john.G
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    john.G Junior Member

    YEAH!!! The popular myth of cruising the South Pacific in a trading schooner.

    Only problem is - IT'S A MYTH!!!

    What we have here is a linguistic anomaly. When the white man first came down here they encountered a stone age people to exploit ... mostly reprovisioning ( mostly done with good grace and good intentions though not always), a bit of blackbirding, a bit of pressing for additional crew or local pilotage. Being a stone age people they didn't speak english... but they learnt enough to get by. In the "old" pidgin, there was recognition of 3 types of boat: Ship - meaning square rigged.
    Schooner - meaning sail propelled and not square rigged.
    Whaleboat - meaning propelled by oars.

    The schooner came from the early yankee trading schooners, mostly sandlewooders from around 1810 or so. From there the name spread across the polynesian language area and then into the south west pacific (melanesia)

    Thing is this.. none of the locally made boats were ever schooner rigged. Oh they might have been called that, but that's the linguistic anomaly coming through. They were almost always double headsail ketches.

    There is a reason for this... schooners don't do so well to windward. In a poorly charted region full of coral reefs... they sink and die.

    Hate to burst your bubble.
     
    Last edited: Jul 7, 2009
  5. Eric Sponberg
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    Eric Sponberg Senior Member

    and

    I take issue with a bunch of old wives' tales and prejudices here! I am a great fan of ketches; they are extremely popular with cruising folks, mostly because they subdivide the sail plan into smaller sails and more manageable sail set options for a wide variety of weather conditions. The two masts are also a great place to put stuff. All of the features that Burgess applies to schooners also apply to ketches. There is nothing inherently wrong with a well-designed and built ketch.

    I do take issue with schooners--the most significant developments came in the 1700s and 1800s on the eastern seaboard of the US. They were more weatherly than square riggers and ideally suited to the reaching conditions necessary to get north and south, port to port. They were not necessarily weatherly beating into the wind, and most schooners these days are not better than sloops and ketches sailing close to weather.

    And where did that come from that wives and kids are always sick in ketches--that is plain falsehood. I've never heard that.

    Finally, fin keels per se were NOT the inherent reasons for the Fastnet Race disaster of 1979. It was a stability problem that involved fin keels, but also took into account the high center of gravity of the boat (internal ballast) and the unusual IOR hull forms that had wide beams and pinched ends. All these factors taken together contributed to the disaster.

    Certainly, the shorter in chord a fin keel is, the more it sails like a car with rack and pinion steering. Fin keel boats require attention to their sailing all the time. But as an example of fin keel boats sailing offshore, just look at the Minis, the open 30s, open 40s, open 50s, open 60s, and the Volvo round the world boats--all deep fin, short chord, keel boats. They get across oceans and around the world, both single handed and fully crewed. I would not advocate such a boat for a family sailing together on a cruise, but you cannot condemn them and fin keel boats as a class.

    On the other hand, a full-length keel boat is not necessarily as weatherly as a fin keel boat. It has to be pretty narrow and deep to compete with fin keelers on the weatherly basis. Certainly they are very directionally stable as a class, and they hold course extremely well. They do make good cruising boats, but they are not the only option. I believe there is a lot to be said in favor of a fin keel boat with a low aspect ratio keel--longer than it is deep, aerofoil shaped and with an end plate type of bulb, and a separate rudder. Such boats are, to my mind, a very good compromise between weatherliness and directional control.

    Eric
     
  6. peter radclyffe
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    peter radclyffe Senior Member

    i cannot believe you dont realise what a joke is,
     
  7. peter radclyffe
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    peter radclyffe Senior Member

    it was in answer to wifes prefer schooners, dont you get it
     
  8. sharpii2
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    sharpii2 Senior Member

    It seems that every time anyone brings up the Fastnet '79 disaster, they blame the boats.

    Ten years later there was a Sydney Hobart disaster.

    Pretty much the same thing happened.

    Boats were caught in wild, breaking seas which often seemed to come from every direction. In the case of the Sydney Hobart, they were equal opertunity destroyers. A long keeled boat was thrashed to the point of sinking and its life raft was pummeled to pieces taking at least three of its crew. I can't imagine the Fastnet '79 would have been much different, had a greater variety of boats been available.

    It seems that in both cases, the boats were in regions of local shoaling, where the effect of storm waves were magnified many times.

    Though it's probably true that the IOR influenced boats of the time might have been more vulnerable, due to their erratic down wind steering manners, I think it is dangerous to imply that better designs would have been able to get through that unscathed.

    Though it is true short, deep, finned keeled boats have routinely sailed around the world, I think it is worth mentioning that was made possible with high tech gear such as advanced auto pilots, often powered by diesel gen sets that ran constantly, and hardened sailor athletes (not necessarily male) who were accustomed to less than ten minutes of sleep at a time and being banged and thrashed every minute of the voyage. I would agree their boats were immensely sea worthy. The results speak for themselves.

    But I don't think they are safe under any kind of budget constraints.

    The less expensive, high tech stuff needed, IMHO, the better. The rich man may have several copies. The poor man may have only one.

    This is where older, lower tech designs come in. They are more likely to be control able with damaged equipment and some can track well, even down wind, with out any self steering gear.

    I think the word "performance" needs a wider scope.
     
  9. jim lee
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    jim lee Senior Member

    This has proved to be true for my boat. Fin keeled spade rudder, goes to weather like a banshee.. Tracks like the common house fly..

    But this is why they invented..

    Monitor wind vanes!

    [​IMG]

    And I'm talking the cat's meow for taming the wandering fin keeler.

    -jim lee
     
  10. Charles Burgess
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    Charles Burgess Naval Architect

    Maybe it was a little too subtle...sort of pun on the six degrees of freedom - it's all about the motion of the ocean :p
     
  11. Milan
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    Milan Senior Member

    I also think that course stability is very important for the cruising boat. Good tracking boat will make living much easier and more pleasurable for the crew, not only because of easier steering. Boat will also jump around a lot less, keeping crew more comfortable. She will also be faster, going in the straight line, not slowed down by the rudder action.

    There are a lot more factors influencing steering control besides the keel length. To name the few – hull balance, interaction between rig, hull and underwater foils, length to beam ratio, curve of area, bow shape, sails shape e.c.t.

    Balanced, symmetrical hulls, relatively narrow for their length, will have much less tendency to change the course when heeled, then short, wide, asymmetrical hull shapes, regardless of length of the keel attached to them.

    I think that you will find that those types of the traditional boats that keep their course well, also have symmetrical, relatively narrow hulls, two characteristics that are probably contributing more to the course stability then their long keels.

    There is one other important point in the steering control –helm versus waves. When boat sails in the chop, course is constantly disrupted by the waves that are slamming a boat from the different directions. To recover from that, boat needs to answer the helm quickly, something that long keeled boats with a rudders attached at the end of the keels just don’t do all too well.

    In the blow, traditional long keel boats are difficult to keep on track, at the risk of the broaching. Modern, light displacement hulls with shallow body, fin and spade rudder are often able to surf the waves under full control in the same cicumstances that would force traditional boat to hove to.
     
  12. john.G
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    john.G Junior Member

    Seems to me that - as per usual - this thread has got off track.

    We have here a gentleman thats chasing input on a CRUISING boat to operate around the coral sea and environs with a crew of man, wife, and two kids.

    And it's become a performance orientated discussion of rigs and keels.

    Now I'm the first to say that a fast cruiser is better then a slow cruiser... but y'all keep designing a performance cruiser and he might as well buy a Beneteau.

    Things to remember are this:
    * KISS is the best principle in cruising yacht design. Keep it simple and its usually cheap, easy to operate, and able to be repaired without too much drama. Hi tech, high stress goes hand in hand with high cost and high failure rates.
    * When ( not if) the power winches die... the reduced sail sizes on a split rig means you can manage them anyway. He's talking about a 40 - 50 footer here... and doing it the old fashioned way on a 50 foot sloop isnt much fun when you can't just duck back into port for repairs.
    * The average cruising boat does not go out in cyclonic conditions. He either stays nice and snug in port or routes around it. Only racers and idiots like me say to hell with it and go straight through.
    * The average cruising boat spends more time at anchor then travelling from A to B. If it takes you an extra day or two at sea to do an 800 mile leg.. who really cares. We're cruising remember, if we were in a hurry we'd be racing.
    * Tracking ability on an 800 mile leg with a watch on/ watch off and no standby crew is important. And the less stress on an autopilot, the lower the failure rate. Long keels or variants thereon are good at that.

    KISS.... KISS.... KISS!!!!

    Just saying:)
     
  13. Charles Burgess
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    Charles Burgess Naval Architect

    Fastnet Race 1979 summary from the investigations:

    Large differences were found in the stability curves for modern fin-keel boats and the traditional V-shaped long keel boats. Two yachts were carefully selected that were of similar size; both raced in Class V; both were selected as being representative of the issues under investigation; one being the Contessa 32 (a cruiser-racer) and the other being the Grimalkin ( a 30 ft LOA extreme racer).

    • Both had the same GM = 0.85m
    • At 1 degree of heel RM 670Nm for Contessa and 550Nm for Grimalkin. Both boats were nearly equal at small angles of heel.
    • Sail Area were nearly equal.
    • Max GZ of Contessa was found to be 40% higher than that of Grimalkin.
    • RM(max) at 80 degrees of heel is 30200Nm for Contessa and only 17900Nm for Grimalkin at 50 degrees of heel.
    • The Contessa was stable up to approx 155 degrees, and zero RM occurs for Grimalkin at 115 degrees of heel.
    • Contessa was stable upside down for a range of 25 degrees, while Grimalkin was stable upside down for a range of 65 degrees; thus the Contessa can be knocked down and even capsized and will right herself almost immediately, while Grimalkin will stay capsized for at least several minutes at a time.
    If you plot the stability curves of both vessels it is clear that the differences in keel design is the main factor.

    It is clear that the traditional full keel is safer than a fin keel. The key factor is the distribution of displacement, the full keel of Contessa having a broader distribution that contributes to RM, and the fin keel distribution of displacement is more narrowly concentrated like in Grimalkin. A broad RM is a whole lot safer than a narrow one. An example is someone walking a tightwire: usually a pole is used to help with balance, the pole has weight; if you hold the pole vertical it will be of little help in helping you keep your balance; if you hold the pole horizontal, it is a huge help in keeping your balance. It is the distribution of the weight that determines the effectiveness of the pole in aiding balance, or not. A fin keel is like holding the pole vertically, while the full keel is like holding the pole horizontally.

    Also, even a full keel, especially a modern one, is an airfoil of a delta wing type. Yes, in earlier years they were rather crude, but today a full keel can be given a more airfoil shape. The full keel has a broader range of speed that induces effective lift, while the fin keel has a narrower range of speed where it can provide effective lift. For a cruising (sailing) yacht, a broader area of lateral plane is safer than a narrow one of the fin-keel type. For a family cruiser, a relatively full length keel is much safer than a fin keel.

    Finally, while ketches and yawls are popular with cruising folks - that means nothing when comparing effectiveness of the rig. Popularity of the ketch and yawl is more a fashion statement and nothing more. My statements come from a pragmatic point of view - I am not criticizing people who specifically choose a ketch or yawl design. I prefer to let the client see the pros and cons of all three types of dual mast rigging and make a choice based upon full disclosure of available information, not on hype.

    Wind tunnel testing, or if you invert the model in a test tank, you will find that the schooner rig is more effective, especially if it has a loose footed foresail that overlaps the main (the mizzen on yawls and ketches tend to back wind the main on certain points of sail). The main factor is that CE's relationship to CG, CB, and CLP shifts around at various angles of heel: the range where the effective sweet spot is much larger for a schooner at different modes of sail, than it is for a ketch or yawl. By sweet spot I am referring to the best point of sail, with various amounts of sail area, in relationship to angle of heel and apparent wind. Also, the individual sails are easier for one person to handle alone than the much larger mainsail of a yawl or ketch large enough for a family to cruise around in, especially in rough waters.

    Basically I rate the following in order of preference for general family cruising dual mast designs:
    1. Schooner Rig
    2. Ketch Rig
    3. Yawl Rig
    The list will shift when specific conditions warrant. So, yes, there are conditions where a yawl will be first in the list, or that the ketch will be first.

    The original question of this thread specified family style cruising, thus the full keel, appropriately shaped, is vastly more suitable for that purpose than a fin keel. If the question was about a racing design, then the fin keel would be on the table too. The first priority of a boat designer is to design with the primary purpose of how it will be used and by whom it will be crewed. All yacht designs are a balance of compromise: in a family cruiser I have for over 30 years given seaworthiness/safety the first priority, with seakindness being second. The qualities of a fin keel that make it perform so well in specific types of racing are the very qualities that oppose the desirable qualities for a family cruiser.

    While designers will have differing opinions on just about anything, I hope we can now concentrate on the original criteria set forth in the original post.
     
  14. Eric Sponberg
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    Eric Sponberg Senior Member

    What you say in principle is all very true. However, the Contessa 32 is NOT a full keel design. See the attachment which is an excerpt from C.A. Marchaj's book, "Seaworthiness--The Forgotten Factor." The Contessa 32 is a fin keel design, although her hull shape, keel design, and weight/CG characteristics give her a very favorable stability curve compared to Grimalkin.

    Be carefull of what you say. A fin keel design per se is not necessarily unsafe. Also, depending on what the client wants for performance, a suitable fin keel design may fit the bill very nicely.

    Eric
     

    Attached Files:


  15. Paul B

    Paul B Previous Member

    You aren't actually a degreed NA, are you? If so, what school presented your diploma?
     
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