raked masts

Discussion in 'Sailboats' started by bean surchwell, Dec 6, 2010.

  1. bean surchwell
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    bean surchwell Junior Member

    Why do some masts lean to the aft of the vessel?
    Is it possible to create a bow lifting force or angle, one mast, two?
     
  2. RHough
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    RHough Retro Dude

    No
    :)

    Not from mast rake unless you heel the boat or cant the rig to weather.

    R
     
  3. michael pierzga
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    michael pierzga Senior Member

    Many Working boats carried their mast forward to create working deckspace amidships. The raked mast also serves as a cargo lifting crane when its mast head is over the working deck. and keeps the boom free of the water surface when the sheet is eased off.
    To keep forces aligned when the mast is forward you must rake its top aft.
     

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  4. gggGuest
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    gggGuest ...

    No its not. Its a widely help misconception among dinghy sailors. But what you've got to figure is that the sails are pushing on the boat from an average point of getting on for halfway up the mast, but the water is pushing on the boat from an average point somewhere below the waterline. With such leverage its impossible to get a downward force on the bow. Its possible for some rig designs to produce an upward force on the boat, but (unless you have a real kite like a kite surfer) the bow will always be pushed down - effectively the stern is lifted.
    Mast rake and angled sail leading edges do have some potential aerodynamic benefits, albeit rather more subtle, but like all these things there are pros and cons.
     
  5. Perm Stress
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    Perm Stress Senior Member

    One of great benefits of raked mast is that rather long boom could be located close to deck in close hauled position and be well up and clear of the waves when let out.

    At some (quite big) rake, the "roll-over vortex" (refer to F. Bethwaite "High performance sailing", fig. 25.1, 25.2, 25.3, pp 366, 367) could be created at large angle of attack, what delay stall and greatly increase power produced.

    To some, mast rake is esthetically pleasing :)

    I have read somewhere in several sources (cant recall exactly where), and heard some anecdotal evidence, that raking mast aft for ~5 degrees do increase upwind performance.
    ___________________

    There is some historical explanation, dating back to early clipper times:

    When all the ships where bluff-body-ed and slow, over the centuries of development optimum location of mast steps was established; when they begun to build increasingly fine-ended and fast clipper ships, the very dynamics of this kind of hull asked to shift sail area more and more aft; as buiders where not brave enough to revise location of mast steps, confirmed by centuries of practice, the solution was to rake masts further and further aft.

    I do not know for sure, how much credibility there is in this explanation.

    Other things, like unloading somewhat the rigging in downwind sailing with too much canvas (raked mast want to fall backwards, while sail is pushing it forward, greater angle between rigging and mast in side view), or already mentioned problem of keeping extremely long boom above the water could have been viable considerations.

    By the way, with highly raked mast, when hoisting the gaff, its pressure to the mast is considerably lower, so friction is less, and work for the crew easier...
     
  6. Scott Carter
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    Scott Carter Senior Member

    A raked mast lessens the load absorbed by the back stay, which can be of great benefit in a rig with a far-raching boom. With both running back-stays eased, the rig insn't inclined to fall forward due to its pre-lean aft.
     
  7. BATAAN
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    BATAAN Senior Member

    A raked mast with a triangular sail keeps its center of effort in about the same fore and aft position as it is reefed. This applies to very big mains as used in the Bahamas.
    The story about conservative builders and mast steps is rather naive I think. A trick researchers use can usually tell the sharpness of early ships in photos, especially schooners, by how far back into the hull the foremast is placed. Sharp ship, foremast well back. Bluff ship, foremast in the bows, no matter what the rake.
    A strongly raked fore and aft rigged mast is easier to stay with hemp rigging which may explain its wide use in Baltimore Clipper schooners.
     
  8. bean surchwell
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    bean surchwell Junior Member

    Thanks for the info, I like the explanation of asthetically pleasing for the reason behind a raked mast.
     
  9. Gary Baigent
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    Gary Baigent Senior Member

    This 18 foot skimmer had unstayed wing masts originally - but the fore mast base section bent in wind against tide seas - so the canter levered sections were cut off, bearings attached to the new bases and conventional rigging attached. The after mast has four stays to allow the foremast boom to operate ... and more rake applied to give better staying angles. The boat is powerful with the two rigs and surprisingly good to windward, off wind in a breeze, the skimmer lives up to her name.
     

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  10. Perm Stress
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    Perm Stress Senior Member

    Story about conservative builders I did found in a book, on proposed range of sailing cargo ships for post-war use in USSR, published ~1940, by famous Russian sailing ship master Д. лухманов (D. Luxmanov. ). He do not refer to any sources of this information, so it is not easy to check or verify it.
     
  11. booster
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    booster Senior Member

    Raked mast

    gggGuest et al!
    Yes, aerodynamical reasons, see for instance the book by Buddy Melges "Sailing Smart". Harold "Mastrake" Cudmore developed this to mastership. Development in sailmaterial influence as well.
    Regards,
    Booster
     
  12. BATAAN
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    BATAAN Senior Member

    Interesting. I've spent many years as a historian and never heard the theory, but as the world is FULL of different nautical traditions and history, could well be locally true.
    One problem with raked mast is that the boom always falls inboard in light airs, very annoying.
     
  13. Perm Stress
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    Perm Stress Senior Member

    Quote:
    Originally Posted by Perm Stress View Post
    Story about conservative builders I did found in a book, on proposed range of sailing cargo ships for post-war use in USSR, published ~1940, by famous Russian sailing ship master Д. лухманов (D. Luxmanov. ). He do not refer to any sources of this information, so it is not easy to check or verify it.
    Interesting. I've spent many years as a historian and never heard the theory, but as the world is FULL of different nautical traditions and history, could well be locally true.
    One problem with raked mast is that the boom always falls inboard in light airs, very annoying.
    Reply With Quote

    Д. лухманов do not base his story on local tradition. At the end of XIX and start of XX century he spent a couple of decades sailing the world on various sailing ships, old and new, and probably this "conservative shipbuilders" story could be the result of personal observation and analysis of what he did see - at that time there was still a number of "old style" ships afloat or out of service, but not yet broken up.

    ________


    Yes, sail falling to CL as wind became lighter is a real nuisance. :)
     
  14. JPL
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    JPL New Member

    It seems to me in fore-and-aft rigs raking the mast allows the you to combine shrouds and the backstay in one, even nearly vertical. This gives a lot of room for the boom/gaff/sprit to go almost all the way out to a run while allowing the aftmost sail to extend past the stern without use of a bumpkin.

    On small boats at least, this seems like a good way to keep the center of effort low and gain some potential sail area.
     

  15. Perm Stress
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    Perm Stress Senior Member

    Completely agree. It is indeed possible.
     
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