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517Easily driven boats

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  • Leo
    Jan 17, 2005
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      Back when internal combustion engines were first becoming available –
      whether gas or diesel – these engines were massive chunks of cast
      iron and had very low HP to weight ratios. Maybe on the order of 1HP
      per 100 pounds. Today's engines might have 10-20 HP output per 100
      pounds of weight. Refer back to the comments about Rescue Minor and
      how the bow acts without the motor weight that Atkin specified for an
      example.

      So back when Atkin was designing, motors were very underpowered and
      the hull really needed to be "slippery" to fully take advantage of
      the low power that was available in those days from IC engines. And
      yes, I know I'm sorta downplaying, for now, the effect that torque
      has on turning a large propeller slowly.

      Based on my reading, early displacement power boat hulls evolved from
      sailboat hulls that were "sorta" efficient. Obviously the science of
      designing efficient displacement power boat hulls progressed rapidly –
      as NA's learned what worked best and what was less desirable.

      It seems to me that as engines become both more powerful and the
      power to weight ratio improved, that the hull shapes started moving
      away from what slipped through the water easiest and began evolving
      into the "fat-ish" hulls of trawlers and cargo boats and that
      evolution has progressed into the modern plastic floating apartments
      that grace (or is that disgrace?) trade magazines and marina's the
      world over.

      Having recently read a history of the Whitehall Rowing boat, I began
      to wonder why this hull form, with its fine entry, generous mid-
      section and wineglass stern wasn't expanded upon for inboard power.
      What's the drawback from scaling this general design up to make it a
      30-40 footer? Perhaps direct 1:1 scaling isn't practical, but why
      couldn't one incorporate the fine entry, general midships section and
      the fine stern sections into a power boat hull? To my very untrained
      eye, it appears that Atkin did use some of these three design
      principles in several of his designs.

      IIRC, from Gerr's books and others, a large diameter, aggressively
      pitched slow turning propeller is more efficient for moving a
      displacement hull than a smaller less pitched propeller turning at
      higher speeds. Or is my memory getting as gray as my hair?

      It seems to be a difficult task in today's world to find folks that
      agree with this philosophy. Almost all modern (inboard diesel) boat
      propulsion systems rely on high speed engines – many with
      turbochargers – to turn a smaller wheel. Gear ratio's in the 2:1 –
      2.5:1 are common. This translates into prop RPM's from the low range
      of 750 RPM to a high of 1800 RPM when the 2:1 geared engine is wound
      to 3600 RPM.

      Yet just a few decades ago we had engines that idled at 300-400 RPM
      (or less) and had an operating RPM range from 700 to 1200. These
      engines ran for literally tens of thousands of hours nearly trouble
      free. Nowadays we often hear of inboard diesels needing replacement
      in as little as 2000 operating hours. Throwaway power. Yuck!

      I believe that we can generally agree that 1) how/where you want to
      go with a boat, 2) how long you want to stay aboard and 3) how
      much `camping' you're willing to tolerate determines what type, size
      and amenities we'll need. And finally, 4) aesthetics. How a boat
      looks to our eye is vital. And as each of us has different needs and
      tastes, I believe all 4 of these considerations are classic cases
      where Your Mileage May Vary. ;-)

      Addressing #1. My wife is a teacher and a decade younger – I want to
      be able to put the boat on a trailer and go for her summer vacation
      to Alaska via the inside passage this summer, The Erie Canal next –
      Maine and Nova Scotia another – Trent-Severn waterway another. When
      we're both retired then on to the Bahamas for the winter and back to
      Alaska for an extended trip. Maybe put it aboard a freighter and
      ship it to France for a couple of years living on the European canal
      system.

      Addressing #2. At first we're only talking about 10-12 weeks at a
      stretch. Later it could be full time for a few years – or at least 8-
      9 months out of 12.

      Addressing #3. At first – we can tolerate a bit more `roughing it'
      for a few weeks, but some of the things that we will not do without –
      (not an all inclusive list) 1) space to get away from each other when
      need to. 2) a great galley with room enough to prepare a full meal
      without contortions of the body or with the pots and pans. 3) full
      length and width berth(s) with comfy mattresses. 4) a separate full
      sized shower – no sopping TP! 5) an all weather pilot station –
      either fully enclosed or enclosable with canvas.

      Addressing #4. I just plain like boats that look like a classic
      boat. None of this plastic fantastic modern European shapes for me.
      Give me the lines of an Elco or a Lake Union Dream Boat or a double
      ended Salmon Troller or the shape of a Whitehall. Give me a nice
      sheer and a plumb bow. How about bronze ports – either oval or
      round – and a rearward sloping windshield instead of that forward
      sloping monstrosity, regardless of how practical it is. Bottom
      line? Spare me the angular constructs that adorn so many marina's
      and boat shows.

      Finally, I think we can all agree that petroleum products – oil, gas,
      natural gas and diesel fuel – are just going to get more and more
      expensive. The days of a buck a gallon diesel are probably long
      gone. So this means that to have a boat that I can afford to
      operate, it must be very efficient. I'd consider 7-10 statute MPG
      the minimum – this should equate to less than 1 gallon per hour of
      running, in other words, 6-8 knots cruising speed at less than 1
      GPH. Better than that is just that, better. I think that this is
      achievable in a 35'-ish boat if we don't load it down with a ton of
      canned goods. Something less than 20,000 pounds – 15,0000 better
      yet - fully ready to cruise would be the goal. My preliminary
      investigations and calculations indicate that given the right hull
      design and using modern epoxy/ply building methods this appears to be
      an achievable goal.

      Finally, utilize a big ol' slow turning engine with either a VPP or a
      big-ish wheel and set it up to cruise at a V/L of about 1 to 1.15 at
      the most efficient fuel consumption RPM for the engine – probably
      less than 1500 RPM - and one should have a boat that one could afford
      to build and run without breaking the 401k and would be worthy of
      being called a Retirement Cruiser.


      Addressing Manfred's comments about River Belle – This would be a
      perfect boat for cruising the ICW and the various canals, waterways
      and rivers. But would this design be suitable for an Alaska trip or
      a trip to the Bahamas or a summer on the Great Lakes or the coast of
      Maine and Nova Scotia and Newfoundland? Perhaps not. So I still
      think to go to all the various places that I'd like to visit before I
      die, I need a boat with some sort of keel and the ability to take
      some rough weather should the unfortunate happen.

      Any other suggestions?

      Best,

      Leo
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