Effects of racing rules on boats

Discussion in 'Boat Design' started by rugludallur, Sep 17, 2010.

  1. dskira

    dskira Previous Member

    Sorry Paul, I can't resist the last one. I had fun. :D
    I am going away on this one. You are absolutely right.

    Daniel
     
  2. Milan
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    Milan Senior Member

    Plumb bows are much older then racing rules. Many traditional working boats had no overhangs, British pilot cutters for example.

    Aside from advantages in racing classes measured by the over all length, vertical bows are also simply most efficient, in terms of material usage. (The reason they were used by working boats and why they could be interesting for modern cruising boats).Waterline length is good.

    Comparing plumb bow versus overhang makes sense only when we first agree do we compare on the basis of waterline length or length on the deck.
     
  3. rugludallur
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    rugludallur Rugludallur

    I think a good way to discuss this is if we put it in the form of a question, given the choice of two boats, one with a plumb stern, the other with an overhang assuming same waterline length, same weight, sail area and cost which would you choose and why?
     
  4. Paul Kotzebue

    Paul Kotzebue Previous Member

    I believe the plumb bow on British pilot cutters was to minimize measured tonnage under the Thames Measurement, which was also used to handicap racing yachts.
     
  5. MikeJohns
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    MikeJohns Senior Member

    Certain materials suit certain styles better. The old workboats with a plunging vertical stem also had very full ends (high Cp) and consequently a robust longitudinal stability.

    Reserve buoyancy from a raked stem is effective and practical and you’ll see it all small special service, rescue and patrol vessels that need to cope with rough seas. The form already evolved from plumb stems from the earlier 1900’s

    For performance in a seaway the wave resistance is far more important than any theoretical speed based on waterline. The entry angle of the stem is just as important in this as the angle at the static waterline.

    The theoretical static waterline speed is a bit of a red herring for small vessels in anything other than sheltered water. Also wetted surface area can be more important in a light wind scenarios. The old long overhang boats had the best of both worlds and were surprisingly efficient comfortable sailors. You can find good boats in all sorts of genres and it’s not sensible to tackle anything in isolation.
     
  6. troy2000
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    troy2000 Senior Member

    Lest anyone forget: the old oystering sharpies had plumb bows and long overhangs aft, for reasons that had nothing at all to do with racing or rating.
     
  7. Paul B

    Paul B Previous Member

    Why would you use WL length as a constraint? If you do then you are pretty much mandating a non-plumb bow. This is what all the old racing rules did to cause the long overhangs.

    So for a given WL lenght of 25 feet you might have a 30 footer with a raked bow or a 27 footer with a plumb bow. If you are going to build the 30 footer, why wouldn't you just build it with a plumb bow as well?
     
  8. Cheesy
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    Cheesy Senior Member

    On the other hand there have been significant advances that are not allowed in some clases, for instance the metal matrix composites that some of the honda cylinder heads are made of....
     
  9. Cheesy
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    Cheesy Senior Member

    Back to boats.... have a look at some of the 70s-80s NZ local designs, The Y88 would be a reasonably good example of a boat that wasnt built to a rating rule
     
  10. jimbo2010
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    jimbo2010 Junior Member

    How about this example?

    [​IMG]
     
  11. MikeJohns
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    MikeJohns Senior Member

    That's certainly illustrates that a raked stem has many advantages as PaulB said you'd immediately go for an overhang if LWL was fixed and the rest was open. In fact there's no advantage in not doing so.

    But outside of racing a vessel is designed to different criteria so the dire necessity of squeezing the last fraction of a knot out of the hull can be happily ignored for other factors. Like seakeeping.
     
  12. MikeJohns
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    MikeJohns Senior Member

    Well it's an extreme design, I'm not sure extremes are helpful here.
    They are wet boats to windward. They exhibit considerable trim with heel and rely on strong modern expensive lightweight materials.

    Strictly a professional racing crew to operate such a vessel. They also fair better in adverse conditions when they are large. For example the open 60's had a much better record than the open 50's in the Southern ocean.
     
  13. TwoByFour
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    TwoByFour Junior Member

    Hello Cheesy,

    If I understand you correctly you are saying that the MMC has been implemented in everyday road cars, while it's not allowed in at least some racing classes. I don't know this particular case but you are probably right.

    From what I can find on the web, the MMC (Metal Matrix Composite) first saw use in aerospace applications in the early 80's. I can't find any information on it's use in racing but I'm guessing some have tried it.

    A lot of technology and materials that were first seen in aerospace get used in race (cars, boats, etc.) applications once they become available at a reasonable enough price. If they ever happen to become cheap enough , they become common in mass-manufactured things such as cars.

    Carl
     
  14. troy2000
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    troy2000 Senior Member

    You appear to be somewhat fixated on the idea that the only reason for a raked bow is to increase length on deck for a given waterline. There are more reasons than that: like reserve buoyancy forward, a drier ride, and more foredeck space.

    Overhang, especially at the bow, is not simply about looks. Rather, as Robert Perry pointed out (in Robert Badham and Robby Robertson, Sailor's Secrets, International Marine, Camden Maine, 1999 at p. 193:

    "Some things, though, begin to look better the heavier the weather gets. Plumb stems are a modern trend. They obviously maximize waterline length, but in a cruising boat do you want to give up a foredeck and make your boat into a submarine for an extra little boost in top end speed? Traditional elements like overhang are traditional because they work. Overhang keeps people dry and provides space to do what foredeck work you have to do."

    To this I would add the importance of front overhang in anchoring - have any of you tried to retrieve an anchor in a boat with a plumb bow? It is virtually impossible, in most conditions, to avoid banging the anchor into the topsides - even with an anchor roller that extends a short distance past the bow.


    http://www.cruisersforum.com/forums/f47/benefit-of-long-overhang-15340.html
     

  15. Paul B

    Paul B Previous Member

    If you do not artificially constrain the design by limiting WL (as if we are back to using an old measurement rule like IOR or Universal Rule) the modern plumb bow has MORE reserve bouyancy forward, the same foredeck space, and just as dry a ride. See my jpeg of the Pendragon modification earlier in the thread.

    A plumb bow should not be considered "chopping off" the bow overhang, it should be considered "filling in" the bow overhang.
     
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