Beam Width and Chine contour

Discussion in 'Boat Design' started by EgliVincent, Sep 1, 2010.

  1. EgliVincent
    Joined: Sep 2010
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    Location: Camas, WA

    EgliVincent Junior Member

    Hi All, I'm a newbie hear at the forum and had a couple of questions for you all. First is in regards to beam width on planing type hulls with hard, measurable chines (90% of the power boats in my area). Why in the heck do they still measure the width at the boats widest point, it really makes comparing hulls in an 'apples-to-apples' sort of fashion nearly impossible. Isn't the max chine width a much more important number (with the exception of a sheriff writing a ticket on an over beam boat)? Or at least give a side flare angle so a person could calculate true wet width of the bottom.
    My other question is with the general sweeping shape of a chine running fore to aft. I've built a couple of boats and basically the rear most 2/3 of the boat is completely straight, muck like it could have been extruded out of a giant extrusion die. The front third of the chine then sweeps upward to the bow and vanishes. While most aluminum boats in the NW are built this way, I was wondering if it is particularly efficient or just a less painful way to build. I've seen some boats where the chines are still relatively straight but keep getting wider towards the transom and max 'Chine Beam' is at the transom. Also have seen sweeping chines that taper in the rear as well as the front, but that might be too hard for me to build in aluminum. Any thoughts would be greatly appreciated.
    I'm itching to build a new aluminum hulled boat about 24-26' long this winter, I want it to be something like a Wally Tender meets a Cabin Dory...very contemporary semi-plumb bow but very classic with a wood and composite top deck. And with modest outboard power 90-150hp.
     
  2. peter radclyffe
    Joined: Mar 2009
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    Location: europe

    peter radclyffe Senior Member

    length

    beam

    draught
     
  3. EgliVincent
    Joined: Sep 2010
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    Location: Camas, WA

    EgliVincent Junior Member

    Hi Peter, Isn't draught the same as draft or how deep it sits in the water and not relating to bottom width? If I look at two boats one with a 7' beam and one with an 8' beam, and yet both have a 78" wide bottom and share the same dead rise , they should perform similar (with the exception that one may be a bit dryer). Although when discussing hulls one might very well jump to the conclusion that the 7' beam boat would be more efficient to push through the water while the wide beam boat more stable. I'm just trying to get my head around this, it just seems like a figure that very often is relatively useless unless the assumption is made that a wider beam will naturally come with a wider bottom.
     

  4. peter radclyffe
    Joined: Mar 2009
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    Location: europe

    peter radclyffe Senior Member

    yes it can be confusing, but its a universal measurement for all boats as you know, for register & transport, well it would help if you can get 3 section shapes for each hull your discussing, it might help you to study ray hunt & other designers, who developed planing hulls, & to study why boats plane, also the world war high speed hulls
     
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