advice on bowsrit size

Discussion in 'Boatbuilding' started by martincn35, May 21, 2010.

  1. martincn35
    Joined: Oct 2008
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    Location: montreal

    martincn35 martincn35

    Hi,
    I would need an advice on what size to use for a bowsprit that I want to install on my 37 ft steel classic. It should be around 7ft long in front of the bow(outside the boat) and 4ft on deck on the inside of the boat.

    I was thinking of 4in or 5in steel tube with 1/8 in wall. Would it be sufficiant or too much and too heavy?

    Martin.
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Depends on what loads you will be putting on it and what kind of rigging it will have
     
  3. martincn35
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    martincn35 martincn35

    I want to go gaff rig, but have not made any rig plans yet.
     
  4. Stumble
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    Stumble Senior Member

    Martin you really need to speak with a Naval Archetect about this project. The force calculations for a bowsprit like this can be enourmous, and improper design can lead to massive failure aelving a big hole in the front of the boat.

    It won't cost nearly what you might think, to have the calculations done, and compared to either letting your boat sit up for months fixing it, or other dangers involved it is cheap insurance...
     
  5. alan white
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    alan white Senior Member

    The sprit is in compression. Most important is that the rigging angles (bobstay, whisker stays, jibstay) are adaquate (10 degrees or better is considered a minimum). Four inches by 1/8" would be pretty beefy as the sprit isn't very long. Even 3" x 1/8" would be satisfactory I think.
    As with a mast, the rigging is designed to carry 100% of the lateral loads (meaning the sprit could be attached by a universal joint rather than bolts and if properly rigged, it would still do its job). The sectional configuration of the sprit need only keep the spar in column and transmit the compression load to the deck/structure.

    It's easier to step out on a square sprit and easier to weld fittings to a square section too, though it's not as attractive as a round section.
     
  6. martincn35
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    martincn35 martincn35

    alan,

    If I install a square bowsprit, should I stay within the same sizes, around 4 in.
     
  7. martincn35
    Joined: Oct 2008
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    martincn35 martincn35

    Stumble,

    I agree with you, it would be preferable that I consult a naval architect.
    Before I do so, I want to get a picture of what I want to instal on my boat and what it would look like.
     
  8. M&M Ovenden
    Joined: Jan 2006
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    M&M Ovenden Senior Member

    Martin,
    An interesting contact for you would be Andy Soaper in Kingston, Ontario (Kingston Sail loft). When it come to gaff rigs, Andy will help with passion. He is also the best around for traditional sails and rigs. If you end up heading towards Kingston, we are half way between there and Montreal, and you're welcome for a chat.

    You should also get Elements of yacht design by Skenes to get a grasp of gaff rig sail plans, spars and rigs.

    Should post a picture of your boat.

    Murielle
     
  9. martincn35
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    martincn35 martincn35

    Here are pictures of my boat.
     

    Attached Files:

  10. M&M Ovenden
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    M&M Ovenden Senior Member

    Sweet boat!
    Looks like you have a well for an outboard, has the inboard engine been taken out? I sort of like that idea for auxiliary power of smaller sailboats.

    The fore foot of the keel is fairly cut away, be careful not to spread your sail plan to far forward.
     
  11. martincn35
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    martincn35 martincn35

    I have already closed the well for the outboard with a plate and started to install an inboard (marinized VW)
     
  12. alan white
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    alan white Senior Member

    You could go a half inch smaller. Square is stiffer.
     

  13. daveyw
    Joined: May 2011
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    daveyw New Member

    Martin, were you modifying your keel on the boat?
     
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