Engine size for Farmers' Piute

Discussion in 'Boat Design' started by Green65, Jan 22, 2021.

  1. Green65
    Joined: Sep 2011
    Posts: 3
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    Location: Whitehall, MI, USA

    Green65 New Member

    Most things I can figure out. Once in a while it helps to ask for help. To call in a Professional as it were...and while I could assume the answer, that does not always end well.

    Weston Farmer designed the Piute and in a very colorful way (he always seems to) described his choice of powerplant. If I am to build this beauty someday, I will need a powerplant, and I do not have, nor want anything weighting 650 lbs. ...and who wouldn't want to instantly subtract 500 lbs.

    If I am correct, he is calling for an engine large enough to turn a 16 inch prop that when idled down to 1000rpm, still makes at least 20 hp. It also looks like the 16 inch prop is mostly preference and not really necessary.

    So, my question is: could a 20 hp engine be used to turn a 9, 10, or even 12 inch propeller and if gearing is correct, still provide adequate power to drive this hull to 18 or 20 mph, or would a larger engine be recommended?

    BTW, as someone else mentioned, I think Semi displacement hulls should be more popular. I also really like the looks of this design because it looks just like a small PT boat to me

    "The hull is of semi-planing type. She will lope along all day at 18 to 20 miles, will not be insufferably wet when checked down in the harder chances, and is premised on weight, length, brawn, and slow turning prop—about 16-inch diameter at 1,000 rpm.

    Now this is fortunate. You can use the modern and utterly reliable -40 to 50 horsepower runabout fours with a reduction gear and net the prop kick you need. Without a reduction gear on today's motors in this boat you won't have that Cadillac ride. Modern motors without reduction do not have prop diameter enough to give a real horse kick to the business end.

    Fig 2
    So, to get this kick on a direct drive, we can revert to type in motors, too, and use the kind shown Fig 2- an older type such as the Red Wing AA, or Kermath Vanadium 20. This kind of motor never seems to wear out in normal use.

    Motor makers are always well-stocked with such engines they have taken in trade, reconditioned good as new, and can sell for $200 to $300. Gray model Z, Kermath, Palmer, Red Wing— all are available today. They will swing the wheel area wanted, and they have Percheron horses in their cylinders—not hysterical Shetland ponies.

    Any motor of about 4-inch bore by 4-inch stroke delivering 20 to 25 hp at 1000 to 1200 rpm and weighing in the neighborhood of 650 pounds will be ideal.

    I mention power at some length, with highlights, because you won't get the feel designed into Piute if you substitute a lightweight, high output direct drive mill. Large diameter props of low pitch, wound up at 3,000 or so, won't give you the lope and ease and range you need. So much for feel."
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