Loading ...
Sorry, an error occurred while loading the content.

Re: [bolger] Re: Isometric of Bolger's 1 Man live-aboard concept.

Expand Messages
  • Fred Schumacher
    ... Yes, I have seen this, and it s what originally got me to thinking about the benefits of a box keel. If a box keel has the same profile as a salient keel,
    Message 1 of 13 , Sep 2, 2010
    • 0 Attachment
      On Wed, Sep 1, 2010 at 1:25 PM, prairiedog2332 <arvent@...> wrote:
       

      Fred,

      Have you seen this?

      http://groups.yahoo.com/group/bolger_study_plans_only/files/Small%20Moto\
      rsailer/


      Sort of a scaled down version of the Alaskan Motor Sailor. I think the
      box keel creates too much wetted surface to make for good sailing
      performance in a hull this short, but is an ideal location for a tiny
      diesel engine. This cartoon also points out another disadvantage - lack
      of storage space - mainly due to the deadrise in the hull shape.
      Anything stored in the box keel - you lose standing headroom there.

      Nels

      Yes, I have seen this, and it's what originally got me to thinking about the benefits of a box keel.

      If a box keel has the same profile as a salient keel, it has virtually the same wetted area, especially if its on a box boat. The two sides of the box keel are the same as the two sides of the salient keel; the bottom of the keel replaces the bottom of the main hull. The added area comes from curvature and, when following Bolger's pressure equalizing "Sea of Peas" formula, more area toward the bow of the boat, since it would not have the "drag" (cut away forefoot) of the salient keel.

      As you note, several problems enter because of the deadrise hull. There is less lateral plane (only 9") because of the deadrise coming down to meet the box keel, and the dead rise hull has nearly the same inefficiency of space utilization as a complex curved boat. It would pound less than a box boat, especially in a chop or at anchor.

      The box form provides so much usable space that a much smaller boat becomes functional. There  is also more lateral plane, since the box keel extends lower below the main hull. A narrower box keel would also provide more lateral resistance. On Bolger's boat, it's 2.5 feet; on my sketch I kept it at 2 feet. A box keel is a totally submerged body and would act somewhat like a submarine. It would not create the same wave making resistance as a surface body of equal displacement. I wonder if a bulbous bow would be useful.

      A center cockpit boat can use a box keel to great advantage. Tankage can be placed under the cockpit. As for placing the engine in the box keel, I like the direction Phil and Susanne have gone with the use of lightweight air cooled diesels placed above the water line with sail outdrives. They used Deutz engines. I think for smaller boats, another German manufacturer, Hatz, makes a nice line of small, lightweight industrial diesels that would work. Their vertical shaft models could be mated to an outboard's lower unit.

      The box keel allows for reduction of top hamper and replacement of lead ballast with cheap steel plate that also protects the bottom and lowers the center of gravity. Over the past few years, Phil and Susanne moved away from the full length box keel, only retaining the cutwater portion. Perhaps they discovered some serious problems with it. However, I'm thinking of knocking together a quick and dirty 5/8 scale test boat (10.5' x 4' x 1.2', 700# estimated displacement) just to see how a box keel Micro would act.

      fred s.





    • Bruce Hallman
      ... One of the benefits I get from modeling a whole bunch of Bolger boats, is that I sometimes get glimpses into the thought process of PCB and PB&F as
      Message 2 of 13 , Sep 2, 2010
      • 0 Attachment
        > Yes, I have seen this, and it's what originally got me to thinking about the benefits of a box keel.

        One of the benefits I get from modeling a whole bunch of Bolger
        boats, is that I sometimes get glimpses into the thought process of
        PCB and PB&F as he/they worked out trade-offs that go into the
        development of their design ideas. To me, the biggest issue that
        comes up with box keels is the effect on hull displacement and mass.

        Fundamentally, the AS-29 is an extreme case of box keel. And, the
        AS-29 needs lots of ballast to make her settle down into her
        waterline. If the AS-29 was reconfigured where the hull bottom was
        to be stepped with a box keel, the biggest thing that would change
        would be the amount of ballast.
      • Fred Schumacher
        ... Bruce, I want you to know how much I look forward to every new model you post. They re fascinating, and I think all of us here appreciate what you are
        Message 3 of 13 , Sep 2, 2010
        • 0 Attachment
          On Thu, Sep 2, 2010 at 10:05 AM, Bruce Hallman <hallman@...> wrote:

          One of the benefits I get from modeling a whole bunch of Bolger
          boats, is that I sometimes get glimpses into the thought process of
          PCB and PB&F

          Bruce,

          I want you to know how much I look forward to every new model you post. They're fascinating, and I think all of us here appreciate what you are doing.

          If the AS-29 was reconfigured where the hull bottom was
          to be stepped with a box keel, the biggest thing that would change
          would be the amount of ballast.

          That's exactly right. A box keel is a submerged body, and even a narrow one displaces a lot of water. Total displacement goes up, even with the main hull floating higher, and more ballast would need to be added. The benefit of the box keel is that that ballast can be inexpensive steel plate which also protects the bottom and is located at the lowest possible point on the boat, lowering the center of gravity.

          fred s.

        Your message has been successfully submitted and would be delivered to recipients shortly.