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Re: Rescue Minor Motor Placement - Forward or Aft as Designed?

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  • Ronald A. Fossum
    ... motors ... were ... clear ... risk ... over ... Robb did not put in any special tweak . Billy Atkin was the grand master of the tunnel stern Seabright
    Message 1 of 2 , Oct 14, 2006
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      --- In AtkinBoats@yahoogroups.com, "windmill4048" <baileyd4048@...>
      > Rescue Minor has the motor placed between station 7 1/2 and sta. 9.
      > The very similar boats Everhope and Shoals Runner have their
      > placed between Sta. 5 and Sta. 6.
      > I asked a Naval Architect to review the plans and make a few small
      > changes to lighten the boat up.
      > He found that the calculated end to end balance was off and the
      > motor needed to be moved to between sta. 5 and sta. 6. He's not
      > aware of the other two boats, I think.
      > Now Robb White's boat clearly has the motor placed as designed (or
      > very close to it).
      > I believe that Rescue Minor will work as designed since the water
      > that flows through the tunnel adds lift and support.
      > The Atkin plan shows RM floating on her lines. If the balance
      > off at rest that would not be so.
      > I'd like to leave the motor aft since the cockpit is clean and
      > forward of the motor box.
      > So, do I relocate the motor or leave it as designed and take a
      > that Robb White put in some special tweak to over come any balance
      > problem.
      > Note: The weight of the material to build the boat as designed is
      > over 1,800 pounds! With reduced scantlings it's still a little
      > 1,000 pounds. Robb White truly was a genius in building light
      > weight boats.
      Robb did not put in any "special tweak". Billy Atkin was the grand
      master of the "tunnel stern Seabright Skiff" and knew exactly what
      he was doing in motor placement. Rescue Minor is very different even
      for his tunnel stern boats - note that the chines just barely "kiss"
      the water. This is not so with with his other hard chine Seabrights.
      This would indicate substantially less displacement. I'm not sure
      where you come up with the figure of 1,800 lbs. I've worked it out
      and I come up with about half that figure including the engine. A
      10" x 12" propeller turning at 2000rpm requires an actual 15HP to
      the shaft to achieve 17.5 mph (from Dave Gerr's Propeller Handbook).
      If Rescue Minor weighed 1,800 lbs. (not including passengers, fuel,
      motor, etc) there is no way that she could achieve 10 mph, let alone
      17.5 mph. There's very little framing in Rescue Minor - a couple
      three bulkheads, some motor mounts and framing in the box keel, and
      the deck and coaming. The plans as depicted in Motor Boating's Ideal
      Series (which my local library has) show minimal framing.
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