where should the widest part of a sailboat be?

Discussion in 'Sailboats' started by BE_, Jul 20, 2021.

  1. BE_
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    BE_ mr. man

    Where should the widest part of a sailboat be? This is for a 17.5 foot v-bottom skiff with a 5 foot beam.

    My current design has the widest part slightly forwards of halfway; is this acceptable? What are the tradeoffs for moving the widest part forward or back?

    (sorry if i am not using proper boat language)
     
  2. hoytedow
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    hoytedow Carbon Based Life Form

    For some reason, most designers have the beam slightly aft. Look at comparative drawings.
     
  3. hoytedow
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    hoytedow Carbon Based Life Form

    That has changed over history.
     
  4. bajansailor
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    bajansailor Marine Surveyor

    Welcome to the Forum BE.

    Can you post a copy of your design on here when you are able to please?
    Alternatively, you would be welcome to email it to me, and I will post it for you, no worries, as it appears that new folk are not allowed to immediately start adding attachments.
     
  5. BE_
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    BE_ mr. man

    here is the very (very) incomplete design. it is based on several Chesapeake bay crabbing skiffs from Howard I. Chapelle's American Small Sailing Craft. the scale is 4 pixels = 1 inch.
     

    Attached Files:

    Last edited: Jul 21, 2021
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  6. bajansailor
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    bajansailor Marine Surveyor

    Thanks for posting this - that is an interesting rig. Is this a typical rig for a crabbing skiff?
    And the relatively deep forefoot reminds me a bit of Yorkshire cobles in Britain.
     
  7. BE_
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    BE_ mr. man

    the rig is called a "stick-up-skiff", and was popular on the eastern shore of Maryland and Virginia, especially around the pokomoke river, on log canoes and crab skiffs in the mid and late 1800s.

    from what i read, the deep forefoot was to keep the bow from wandering around with the centerboard up in shallow water.
     
  8. hoytedow
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    hoytedow Carbon Based Life Form

    This amateur likes it.
    And welcome.
     
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  9. Will Gilmore
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    Will Gilmore Senior Member

    She's a beauty.

    I see nothing wrong with where you have your beam. If you are looking to maximize hull shape, I'm not the one to ask. I'm just an artist with sailing experience. However, I don't believe there are any real rules and the differences will probably not be measurable by the average sailor.
     
  10. BE_
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    BE_ mr. man

    Thanks! I am similar, more of an artist than sailor, and I too don't care much about maximizing hull shape... I am just making sure i am not doing something horribly wrong, haha.
     
  11. rgouette
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    rgouette Junior Member

    I wonder how dependent it is upon what resides on the extreme ends of the boat..?
    rudder weight, ..?
    Just a sub-amateur chiming in..
     
  12. messabout
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    messabout Senior Member

    Location of maximum beam?.................It is useful to examine the area distribution of the wet section areas of the boat. If you are to do a reasonably proper design, you need to find some of the details such as center of buoyancy, center of lateral area, plan views of the waterlines, and a few other things. Consider also the area of the wetted surfaces of the several choices for bottom configurations.

    More recent layouts for small sailboats have the lowest part of the bottom forward of the middle of the LWL. The beam is then shifted somewhat aft of the middle. The reason for this is to have the area distribution curve appear as a smooth transition from entry to the largest section area. The forward location of the deepest part of the bottom is to allow the angle of the quarter bean buttock to be minimized while having the transom clear of the waterline. To keep the area distribution smooth, the beam must be moved aft to compensate. . It takes a bit of fiddling around with the design to avoid distribution curves that have reflex.

    The crabbing skiff as shown might have been appropriate for its intended purpose but it would not make a suitable boat for casual sailing and certainly not for performance sailing. It is a study in nostalgia, not the best of choices for a pleasure boat. All that said, if the crab skiff turns you on, then go for it.
     
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  13. Kayakmarathon
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    Kayakmarathon Junior Member

    First of all, the Sunfish and Force5 sailboats have the beam ahead of geometric midship. The boats are used for teaching people how to sail. Secondly, the crab skiff is a working boat. It will weathervane, which makes controlling the boat easier. Building the panels will be easier with the widest beam and deepest keel on the same cross section because a station enables better visual alignment than aligning the raked midship (that messabout described) over multiple stations.

    You have a good boat design to build and have fun.
     
  14. messabout
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    messabout Senior Member

    I respectfully disagree with KayakMarathon. It is not more difficult to build a boat, as I described, than it is to build one with both the largest dimensions in the middle. If it has a vee bottom there will be two panels that really won't mind whether you move the deepest part fore or aft of the middle. The sides also will not be any more difficult if the max beam is moved fore or aft a modest amount.

    The reason for adjusting the locations has something to do with the way water is displaced. The general idea is to moderate the acceleration rate of the displaced water as best we can. That notion is based on Newtons law which states that force is equivalent to Mass times acceleration. F = Ma..... If you can mitigate acceleration of a mass, then less force is required to move the object, which in this case is a boat.

    BE's, original question was about where to locate maximum beam. I suggest that it would be entirely appropriate to follow Chappels drawings, or Pete Culler or John Gardner's as well.
     
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  15. BE_
    Joined: Jul 2021
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    BE_ mr. man

    while i agree that following Chappel's drawings exactly would result in a better boat, my goal is to make a boat based on his drawings, not an exact copy, as i think that would be more fun.

    i am still working on the design, and i have moved the max beam aft and increased it to 5.5 feet to closer match Chappel's drawings while also still varying enough to be unique. (i have also determined the placement of the frames) crab skiff II.png
     
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