Whaleboat sail

Discussion in 'Boat Design' started by fish53, Feb 4, 2020.

  1. fish53
    Joined: Apr 2018
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    fish53 Junior Member

    I guess a Maine winter and boredom have taken a toll on my ability to make decisions. I've spent quite a bit of time toying with ideas for how to complete my boat project. As many will be able to identify with money is a driving factor, my impending divorce has done serious damage to my coffers. Anyway back a cheerful subject, boats. As I've striven to define my goal I realized I'm attempting to stuff a tremendous amount of demands into a 26' hull. This started as a small time one man commercial fishing boat with very low fuel demand, that soon morphed into also including some cruising. I've always wanted to transit the New York State Barge Canal as I grew up on it in Spencerport, NY. Then I became interested in adding a sail for even better fuel efficiency and now you can see where this is going. On top of that my fiscal constraints make utilizing my sizable collection of boat "junk" to save cash. A little background on the boat, it's a 1976 Webbers Cove USCG motor whaleboat hull in which I've installed an 18hp Lister diesel, Capilano Hydraulic steering and a sizable cuddy with head forward. I've recently (last week) traded some of my boat swag for an aluminum pilothouse that will fit aft quite well leaving quite a bit of free open deck from which to fish or lounge depending on the object of the day. I have lying around a 24' mast with 8' boom and though I originally intended simply a steadying sail now I'm imagining a sail for downwind propulsion ala Tad's Timbercoast 26. I don't want to add ballast or any more to the keel so downwind is all I expect. I'm planning a tabernacle for the mast although the mast is quite manageable by one person though a bit cumbersome. My latest Idea is a riding sail on an unstayed mast at the stern and a roller furling foresail from the main mast, the pilothouse with the attendant radar and other antennas precludes the possibility of a main sail. I've calculated approximately 100 square feet in the foresail and I'm wondering if this is reasonable area for a desired effect, which is either 3-4 kts sail alone or at least a meaningful fuel savings motorsailing. I've estimated with engine alone cruising at 5kts and using .3 gallons per hour. I have a fuel capacity of 40 gallons and more range would be nice. Thanks for allowing me to bore you on a cold February morning. I posted this originally in "stability" but assumed it was more appropriate here.
     
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    For reference, here is a link to Fish's previous thread -
    Steadying sail https://www.boatdesign.net/threads/steadying-sail.63336/

    And a link to Tad's Northcoast 26 -
    Northcoast 26. Double-ended Wooden Cruiser, Schooner Rig or Flyingbridge. ~ Small Boat Designs by Tad Roberts https://www.tadroberts.ca/services/small-boats/displacement/northcoast26

    I think that your estimated speed of 3 - 4 knots with 100 square feet of sail is probably rather optimistic unless you have a good Force 5 -6 on a beam to broad reach.
     
  3. fish53
    Joined: Apr 2018
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    fish53 Junior Member

    Yeah I thought that was quite optimistic but as I said it was a desire and as we all know "you can't always get what you want". I assume the most benefit would be motorsailing. Somewhere I once read a rule of thumb that 100 square feet of sail in a 15kt breeze generates 1hp, as my boat will require 4.5hp to attain 4.5kts at an SL ratio of 1 that single horsepower appears to do something. I don't believe it would be 25% as the wind is apparent but the assumption some benefit could be derived makes it enticing, unless of course I'm grossly mistaken.
     
  4. fish53
    Joined: Apr 2018
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    fish53 Junior Member

    I have to modify that a bit. In Dave Gerr's book "The Nature of Boats" he states that 50 sq. ft. of sail will generate 1hp at Beaufort force 4 (11-16kts) so if indeed that works it would appear that perhaps 2-3kts is feasible under sail alone based on the 1hp per 500 pounds of displacement for an SL ratio of 1.34. This of course would be on a day where time was no constraint or in an emergency get home situation. I understand the pitfalls of attempting to evaluate sail power using engine power but that's the limit of my engineering ability. Also this is undoubtedly highly variable and ballpark at best but I'm still optimistic of a decent benefit when motorsailing. As I have the majority of components it seems worthy of some effort and experimentation.
     
  5. bajansailor
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    bajansailor Marine Surveyor

    I am sure that you will be pleasantly surprised by the effect that motor sailing will have - very often it can appear to be a 2 + 2 = 5 scenario, where you are getting a bit extra as a result of combining the two.
     
  6. fish53
    Joined: Apr 2018
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    fish53 Junior Member

    I imagine the turning prop would replace the drag a stationary prop would present with some added thrust. I believe this'll be fun to play with, at least it gets me on the water and occupies my brain.
     
  7. JSL
    Joined: Nov 2012
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    JSL Senior Member

    re the stationary vs turning prop matter.
    if you are under sail alone (you are not motorsailing) it is better that you lock the prop/shaft so there is no free-wheeling (auto-rotation). This will reduce drag slightly & lessen the chance of fouling in the event a sheet or line goes overboard. Also, some marine gears don't like free-wheeling (some call it back driving.)
     
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  8. fish53
    Joined: Apr 2018
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    fish53 Junior Member

    I have a hydraulic gearbox so I can't allow it to turn while there's no oil pressure (engine not running). Thank you for pointing that out however.
     
  9. ziper1221
    Joined: May 2018
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    ziper1221 Junior Member

    Disagree. Assuming you have a fixed pitch prop, it is more efficient to freewheel. Locking rotation is only preferable if you have a feathering prop.
     
  10. bajansailor
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    bajansailor Marine Surveyor

  11. fish53
    Joined: Apr 2018
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    fish53 Junior Member

    While I see where this issue is a concern for some it isn't really applicable on my particular project.
     

  12. JSL
    Joined: Nov 2012
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    JSL Senior Member

    Years ago we did some freewheel/locked prop tests on a 40' racing sailboat fitted with a 18" 2 blade fixed pitch prop. At about 6 knots and after 10 'tests' there was about a 1/4 knot loss of speed with a free wheel prop. In some cases you could liken it to an auto-gyro aircraft... the rotating free wheeling blades generate lift.
     
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