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Re: Grampus Jr.

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  • Gary
    Thanks Alan, I was thinking that over these many years Grampus might have become public. You are right, taking another look at Heron I do see the similarities
    Message 1 of 6 , Dec 4, 2011
      Thanks Alan, I was thinking that over these many years Grampus
      might have become public.
      You are right, taking another look at Heron I do see the similarities
      though to topsides are quite different.
      I mainly wanted to see the changes in the tunnel that eliminated the squat.


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    • Alan Boman
      Gary, I was thinking a bit more about the apparent difference between Heron and Rescue Minor in terms of squat when underway. Given that the Station
      Message 2 of 6 , Dec 5, 2011

        Gary,

         

        I was thinking a bit more about the apparent difference between “Heron” and “Rescue Minor” in terms of “squat” when underway.

         

        Given that the Station spacings are about the same, you can directly compare the Offset measurements for the Tunnels from the two hulls.  Working aft from Station 7 you get the following:

         

        Heron:-   3.25”, 4.75”, 6.75”,      9”, 11”,      10.75”

        Rescue:- 3.25”, 4.5”,    6.875”, 10”, 11.75”, 10.5”

         

        In front of the propeller, the tunnel on Rescue Minor is a little more pronounced than Heron, but the killer is the downward curve after the propeller at Station 11.  The difference between the tunnel’s highest point and the height when it leaves the transom on Heron is only 0.25”, whilst Rescue Minor is 1.25”.  So, the wash leaving the tunnel in Rescue Minor is being pointed downward at a much greater angle than Heron, which presumably accounts for the extra lift.

         

        Alan

      • Gary
        Alan you have answered my questions and confirmed my thoughts sounds like you ve done a lot of research along these lines many thanks Gary
        Message 3 of 6 , Dec 5, 2011
          Alan you have answered my questions and confirmed my thoughts
          sounds like you've done a lot of research along these lines
          many thanks Gary
        • Alan Boman
          Hi Gary, Atkin did publish another Tunnel Stern design after Rescue Minor . In 1947 came Nibble , (Ideal Series, Volume 38). Nibble is 17 long, but
          Message 4 of 6 , Dec 6, 2011

            Hi Gary,

             

            Atkin did publish another Tunnel Stern design after “Rescue Minor”.  In 1947 came “Nibble”, (Ideal Series, Volume 38).  “Nibble” is 17’ long, but surprisingly draws 13.5” compared with “Rescue Minor” at 6”, which seems a backward step if you’re trying to design for very shallow water.  I wonder if perhaps there were stability issues with “Rescue Minor”; not that I’ve read a bad word about it anywhere. 

             

            Do any of the members “out there” have any ideas ?

             

            I don’t have the Offsets for “Nibble”; if anyone has access to them, I’d be very keen to have a look!!

             

            Alan

             

            ps

             

            I’m building a “River Belle”, so I’m very interested in Tunnel Sterns.  It’s not in the water yet, but I’m really keen to see if it performs as well as Atkins suggests.  Check www.RhapsodyInGlue.com if you’re interested.

             

            A

             

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