Quarter Beam buttock line

Discussion in 'Boat Design' started by Sipoka, Jan 26, 2015.

  1. Hampus
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    Hampus Junior Member

    That I don't argue against :)
  2. Easy Rider
    Joined: Oct 2009
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    Easy Rider Senior Member

    Good reads all

    Hampus that's the 36' Willard. The "Vega" series of boats include the 30 (greatest in numbers) 36 and 40. The 36 was designed by Garden but the others were designed by Rod Swift I believe. I suspect Mr. Swift designed mostly sailboats as the Vega boats have some similairities to sailboats.

    I love the 36 hull and almost bought one. The 36 was the first of the series built about 1966. Most of the 30' boats were built in the mid-70s.

    I've seen that "Clam" drawing before. Would like to put it on a wall as wallpaper. It looks like the hook is mostly above the WL whereas the hook is lower and more pronounced in the W30. PAR the "hook" I'm talking about (previously described) is convex .. not concave as the traditional "hook" is configured as in some Texas Dories. Both of course create drag.

    I guess I'm say'in I'd rather have a stern more like the 42' Krogen.

    Hampus I'm having trouble w your " Now imagine a diagonal run perpendicular to the surface (all the stations) from bow to stern. It would probably be a curve with fairly large radius up until station 3, then decrase in radius until the midship section only to increase again as it continues aft." .. especially the perpendicular part. I think I understand the "jist" of it though (I think). I see that the flow is quite different than the QBBL and much more important .. and much more complicated. It looks like the flow direction on my W30 isn't profoundly inward right under the center of the stern as I think there would be a hump on the wake if so. And the angle should IMO come closer to the QBBL or longitudinal at higher speeds. I also think the W30 is more efficient at slower speeds like 5 to 5.5 knots. And when there's boats like PAR's Yellow Cedar it seems silly talk'in about the efficiency of a Willard. But I have the Willard.

    I'm not a NA or even close. Just an observant boater that's been interested in design since I built a Kayak in 1950. Spent years heavily browsing boat design books by Atkin and others in the Seattle Public Library in my early teens. I still browse the Atkin boats on the computer.

    And I have no intention of modifying my Willard. Just wanted to talk about what I considered to be an interesting observation and wondered what others thought about it. I probably wouldn't change my stern even if I had a magic wand to do so. Both the Rod Swift and William Garden Willards are masterful designs and I fell a bit guilty talking about modifing the W30 … but it's just a mind exercise.
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    There isn't much I'd change about that design, simply because it answers most of the boat's needs. I would stretch out the stern post rake a bit to soften up the quick turn in aft end of the WL's and buttocks, if only to easy helm effort in a heavy following sea or if being sailed and well heeled. Bill and Rod knew enough to make the quickness of the most aft quarters, as far above the LWL as practical, but a more steeply raked stern post would help and the boat would be easier to plank (if wood) too.
  4. Easy Rider
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    Easy Rider Senior Member

    Hha not much I'd change either. It's a wonderful boat.

    When you say "I would stretch out the stern post rake a bit to soften up the quick turn in aft end of the WL's and buttocks," do you mean to go w a bit of negative rake like so many Dutch vessels? I like the look. And that would allow one to stand closer to or at the aft rail and I would indeed like that.
    Yes that's basically what I had in mind. A little more WLL and easing of the lines right at the stern. I like the expression "quick turn" as it applies so well.
    She does following seas very well and has a relatively light helm always. Any heaviness of helm on my boat is the product of an overly large hydraulic system that obviously has large seals in the cylinder and pump. It's a Capilano variable ratio system suitable for a 40' boat .. I think.
  5. manishindian979
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    manishindian979 Junior Member

    Ok. regarding the planing or displacement hull question of yours, even a boat with chine and flat bottom may run in displacement mode or vice versa. The difference is made by the speed to length ratio or more precisely what we call as a DISPLACEMENT FROUDE NUMBER (Just search over the net). If it holds a value less than 1 then we call it displacement mode, near to 1 it's semi planing and above around 2 it becomes planing. However the term planing refers to lifting of bow due to the speed. If more than half of the weight of the boat is balanced by the upward lift generated by water onto the hull, it is said to be planing. Just remember all boats, at slow speeds will be under displacement mode i.e. whole of the weight will be balanced by the buoyant forces only. But as the speed increases, the lift force starts coming into the play and that's what decides whether the bow will lift or not. There are various approaches which can tell you about this topic. Another one is regarding the bow wave system generated by the boat and due to high speed the boat is not able to overcome the lift and it planes. Just refer to some texts like principles of naval architecture (SNAME) and all.

    Manish Verma

  6. Easy Rider
    Joined: Oct 2009
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    Easy Rider Senior Member

    Thanks for the excellent words on a tricky subject.
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