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Re: [AtkinBoats] Did Atkin mean BHP or SHP?

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  • Ronald Fossum
    Having worked the SHP for various props that Atkin recommended for his boats and comparing those with the engines he mentions, my results indicate SHP -
    Message 1 of 5 , Jul 19, 2007
      Having worked the SHP for various props that Atkin recommended for his boats and comparing those with the engines he mentions, my results indicate SHP - usually.


      ----- Original Message -----
      From: adharvey2
      To: AtkinBoats@yahoogroups.com
      Sent: Thursday, July 19, 2007 6:42 PM
      Subject: [AtkinBoats] Did Atkin mean BHP or SHP?


      I'm wondering if when Wm. Atkin wrote about those older small gas
      inboard engines like the Grays, Scripps, Universals, etc., should the
      HP ratings he quotes be thought of as BHP or SHP? I'm thinking that
      since they were marketed as marine engines, often with gear included,
      that maybe the HP figures were meant to be taken as SHP, but I"m just
      quessing.





      [Non-text portions of this message have been removed]
    • John Kohnen
      The ratings of older engines were a bit conservative, more like contiuous or maybe medium duty for the high speed engines, rather than the peak
      Message 2 of 5 , Jul 23, 2007
        The ratings of older engines were a bit conservative, more like
        "contiuous" or maybe "medium duty" for the "high speed" engines, rather
        than the "peak" horsepower most modern engines are advertised at. An old
        engine rated at 2000 rpm is designed to run at 2000 rpm all the time. So
        my guess is that the ratings are BHP, but conservative. Most of the Atkin
        designs don't use a power robbing reduction gear either, though you'll
        usually need to use one with modern engines in the same designs.

        But. I've run across a curious thing in the listings of marine engines in
        old Rudder magazines I've been looking at, some manufacturers give the
        rpm. of their engines at the output shaft if there's a reduction gear.
        Thus an engine that is rated at 2000 rpm with a straight through reverse
        gear is rated at 1000 rpm. if it has a 2:1 reduction gear! That points to
        the possibility that hp. is rated at the output shaft too, except that the
        hp. figures are the same for the same model engine whether it ahs a
        reduction gear or not... <shrug>

        On Thu, 19 Jul 2007 18:42:27 -0700, adharvey2 wrote:

        > I'm wondering if when Wm. Atkin wrote about those older small gas
        > inboard engines like the Grays, Scripps, Universals, etc., should the
        > HP ratings he quotes be thought of as BHP or SHP? I'm thinking that
        > since they were marketed as marine engines, often with gear included,
        > that maybe the HP figures were meant to be taken as SHP, but I"m just
        > quessing.

        --
        John <jkohnen@...>
        People say that life is the thing, but I prefer reading. <Logan
        Pearsall Smith>
      • alankornhauser
        Gears are very efficient. According to Mark s Handbook, the efficiency of single reduction spur gears is 93-96%. Since most marine gearboxes are
        Message 3 of 5 , Jul 24, 2007
          Gears are very efficient. According to Mark's Handbook, the efficiency
          of single reduction spur gears is 93-96%. Since most marine gearboxes
          are single-reduction, this means that SHP is almost identical to BHP.

          If you think anything on a boat is designed to better than 7% accuracy,
          think again!
        • adharvey2
          That is welcome news. I read in some remote corner of the Glen-L website that to get SHP from BHP multiply by 87%. That is quite a loss.
          Message 4 of 5 , Jul 24, 2007
            That is welcome news. I read in some remote corner of the Glen-L
            website that to get SHP from BHP multiply by 87%. That is quite a loss.



            --- In AtkinBoats@yahoogroups.com, "alankornhauser" <alkorn@...> wrote:
            >
            > Gears are very efficient. According to Mark's Handbook, the efficiency
            > of single reduction spur gears is 93-96%. Since most marine gearboxes
            > are single-reduction, this means that SHP is almost identical to BHP.
            >
            > If you think anything on a boat is designed to better than 7% accuracy,
            > think again!
            >
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