The New Scows

Discussion in 'Sailboats' started by Doug Lord, Mar 15, 2012.

  1. goodwilltoall
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    goodwilltoall Senior Member

    Maybe the rounded bow comes into it own after a certain speed and has the rain drop effect. Its great that after decades of calling scows slow because of hull form it the exact opposite now.
     
  2. daiquiri
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    daiquiri Engineering and Design

  3. sharpii2
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    sharpii2 Senior Member

    Probably because the near vertical rounded bow transom. A bow transom raked 45 degrees or more would have been better, but that would have robbed waterline length, and, with the tall rig mandated in that class, that might have heightened the boat's tendency to pitch poll.

    As it is designed, I can imagine the bluff bow slamming into the back of a wave, acting like a brake on the front wheel of a bicycle, which has no rear one.

    The stern might want to slew around past it, creating another kind of broach. The wide stern might heighten this tendency, but be worth it in the extra sail carrying ability it provides.

    With racing, there are few concessions to comfort.
     
  4. ancient kayaker
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    ancient kayaker aka Terry Haines

    As far as I know the use of bluff bows on racing sailboats is a fairly recent innovation (or perhaps a revisit of an old idea) so it's likely that a period of experimentation and optimization will be needed to get out all the bugs.
     
  5. CT 249
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    CT 249 Senior Member

    Scows have been in racing boats since the first or second international small-boat race (Seawanhaka Cup of 1895). Three of the ten most popular classes in the USA and the second most most popular class in the UK (as measured by national title attendance) are scows, and of course there's also the enormously popular pram dinghies with square bows such as the Opti, Mirror, Sabot, Int Cadet, etc. So racing sailors have been fully alive to the scow shape for well over 100 years and to be honest I don't think anyone has called them "slow".

    On the other hand, years of experience in the top dinghy development classes has shown that the scow is generally not as quick as a fine bowed boat, partly because they present major issues in wave penetration and pounding upwind and can also create major problems with nosediving downwind. Almost all fast boats have been moving steadily towards wave-piercing bows to differing degrees, where the idea is not to generate lift to prevent nosediving (because that lift is generally created by drag, which slows the boat and therefore increases apparent wind which causes major control issues) but to drive through the wave without increasing drag.

    Scows have been subject to many years and many hundreds of design iterations across various rule sets (from As to Moths to Fireballs, 18 Foot Skiffs, etc) so the problems and strengths in general are pretty well known. Personally I'd like to see more of them, because they can provide a great combination of user-friendliness, sensation and performance. They also have inherent problems, so IMHO it's also cool if restrictions are introduced to keep them out of classes that don't want those problems (I grew up on scows, but if banning scows was good enough for Herreshoff....)

    Raison's boat is interesting, but it could just be another demonstration of the fact that development class boats are often creatures of the proportions allowed by their specific rule and the course and conditions of the main events in which they compete, rather than being an example of a type that is optimum for other areas of the sport.
     
  6. Dirteater
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    Dirteater Senior Member

    any pictures sharpii2?
    just curious to see how she looked. :)

     
  7. MalSmith
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    MalSmith Ignorant boat designer

    I agree. In my experience, and not with scows necessarily, a fuller bowed boat will tend to decelerate rapidly when the nose goes down, leading to a pitchpole. Furthermore, with more volume in the bow, the stern will lift further, the rudder comes further out of the water and control is lost earlier.

    With a finer bowed boat will the nose will be pressed more easily, but it will not decelerate as rapidly and is able to drive through the back of the wave before it comes to grief. The stern will not rise as far and the rudder stays immersed. On a finer bowed boat the LCG may also be further aft to begin with, which further helps the situation.

    I would expect that in general a scow would be faster upwind due to it's greater stability and more favourable heeled waterlines, and a conventional bowed boat would be faster downwind in conditions where you can press it harder.
     
  8. MalSmith
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    MalSmith Ignorant boat designer

    I think the situation for a ballasted yacht is a lot different that that of a dinghy. The advantage of the scow is its greater stability upwind when heeled. Dinghys tend to be sailed flat so all you are doing with a scow, sailed without heel, is dragging around more wetted surface. Also, in relative terms a yacht is travelling slower than a dinghy, hence why chines which work for dinghy scows may not necessarily be better for a scow yacht.
     
  9. sharpii2
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    sharpii2 Senior Member

    Sorry to say I don't.

    It was 10 ft long, 4ft wide and about 7.5 inches thick.

    It was totally enclosed, so if water got in (which it did all the time), you had to stand it on end, so the water could drain out a corked hole in the transom.

    On the water, it looked like a backwards sloop rig on a floating piece of plywood.

    If i had it to do over again, I would have cut a 1.0 ft wide by 2.0 ft hole in the deck for a foot well. then I could have bailed it out when it took on water and I could have kept it dry inside so it wouldn't have rotted away.

    Despite her faults, she had some virtues. She was fast and her huge balanced jib didn't need any sheeting.

    One of my favorite boats was a Super Snark (r) I once owned.

    I have since designed a boat to combine Delila's virtues with that of the Super Snark and came up with this: (see attachments)

    I hope to build it next spring.

    It won't be as fast as Delila, but will be able to carry more and be a dryer ride.
     

    Attached Files:

  10. Dirteater
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    Dirteater Senior Member

    Thanks Sharpii,
    I have a thing for these smaller and unique designs :D
    I tip my hat to you and your efforts, and certainly look forward to your build!
    I'd give up speed to stay dry too :D, (I kinda of went that route as well).
    Its no easy task to say the least ..., there just soooo much one has to consider.
    and you have experience on your side...
    she looks good!

    DE
     
  11. sharpii2
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    sharpii2 Senior Member


    Thanks, DE.

    I recently sketched up the cut layouts and discovered it's going to take five sheets of plywood.

    If made of 1/4 inch, she will weigh about 140 lbs for just the hull.

    The layouts have been an interesting part of the project themselves. Here I've had to make decisions on just where the butt joints are going to go. I have discovered that by using them, I can take advantage of the extra strength (across the butt) they provide. I can also orient the outer grains of the plywood for maximum strength.

    The bottom at the bow is going to have several but joints, to maximize use of the plywood (cut down on waste) and to provide some additional athwart ship strength there.
     
  12. Dirteater
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    Dirteater Senior Member

    Hey Sharpii,

    sorry late getting back to you.
    5 sheets sounds about right, my little rig took 8 sheets.
    I have 1 butt joint on my hull, and sides as well. (not sure why you mention several). 140 lbs sounds about right (still need a dolly :). again I tip my hat to you, I have no drawing engineering skills. still I agree that the pre lofting is quite enjoyable as well. I felt pretty good once she was completed.
    It takes he** of a lot of work/time and dedication.

    thanks and
    keep us up to date, :D
     
  13. CT 249
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    CT 249 Senior Member

    Why so much weight and rocker on the Coal Car 12, Sharpii?

    Many hundreds of people were involved in the evolution of the scow Moths. While perhaps somewhat different in purpose to your boat, an enormous amount of effort, trials, testing and ingenuity went into the scow Moths andn surely those lessons could be applied to a boat like the Coal Car?
     
  14. Dirteater
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    Dirteater Senior Member

    Fair question :) CT 249,
    I was thinking 5 sheet @ approx 20lbs. (ish)

    perhaps 3/8 may be an option.

    at 13.5 feet and a 4 foot beam, (dory)
    I wieghted in around 130 lbs.

    sharpii?
     

  15. Stephen Ditmore
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    Stephen Ditmore Senior Member

    It looks like I may have posted this to the wrong thread. I'm posting it here, now, to remedy the error:
     

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