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5191Re: Speed under motoring (4.7 knots at 2.000 rpm)

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  • wispcb
    Jul 5, 2010
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      Tom,
      The original engine in 'Wisp' was a Watermota. From my understanding that was a light Ford truck engine, marinized for diesel useage on boats. I had problems a few years into my ownership and found it was cheaper to replace than rebuild. Old British parts shipped to Florida isn't cheap.
      The new engine (now 15+ years old) is a 3 cyl Perkin's M30 (27hp), a much smaller package than the orig 4 cyl Ford. The trans is the original Hurth v-drive with 2.5 to 1 reduction and original 2 blade prop. Maintenance task's are so much easier with the smaller overall size of the Perkin's.
      The Hurth shaft splines didn't match the new engines damper plate, so I had to have an adapter made. The original engine mounts were of no use at all, so I needed new mounts. I had some real alignment problems between shaft & trans, but I think they're finally resolved. But other than that, no problem mon.
      My normal cruising rpm is about 2300k, for a little better than 5 knots, and a lot less vibration than 2100k. It'll spin up to about 3000k, but that gets a little scary, so I stick to my smooth 2300k.
      Rick CN35 141-Wisp



      --- In campernicholson@yahoogroups.com, "tom1us2001a" <tom1us2001a@...> wrote:
      >
      >
      > JF,
      >
      > Your speed sounds about right for 2K rpm. I usually motor at 2100 rpm and move along at a blistering 5 knots. I used to have a fixed 2 blade and now have a feathering 3 blade. My speeds did not change (while motoring) with the change in props.
      >
      > A little more HP and less reduction in the transmission would help with motoring speeds. Its the 3:1 reduction in forward that limits our speed. Just not getting enough revs on the prop to push you faster. I've thought about changing the transmission to a higher ratio such as 2:1 (which would match the reduction in reverse) but I don't think the motor has enough HP to handle the extra stress and thus could not reach full power if needed. For now I will live with what it is, but if the engine ever needs rebuilding I would consider making some changes. It would be interesting to hear what others have changed (engine, trans) that improved speed and maneuvering power.
      >
      > Regards,
      >
      > Tom
      > CN35-199 Dream
      >
      >
      > --- In campernicholson@yahoogroups.com, "JFR" <jfregnard@> wrote:
      > >
      > > My CN has a 35hp Piranha engine with a two-blade folding propeller. With revs at 2.000 rpm, she sails at 4.7 knots in a flat sea and virtually no-wind. Such a speed seems quite slow to me. Would anyone have figures that I can use as a benchmark ? Should I put in a 3-blade regular propeller ?
      > > Any advice will be welcome,
      > >
      > > JF Regnard
      > > CN35#207
      > >
      >
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