Mast size/material for little boat

Discussion in 'Sailboats' started by hospadar, Aug 1, 2011.

  1. hospadar
    Joined: Apr 2011
    Posts: 62
    Likes: 3, Points: 8, Legacy Rep: 30
    Location: Michigan

    hospadar Junior Member

    The little boat that I'm building is getting ready for launching (pictures coming soon) and I'm wondering about building the mast for it.

    It's a 12-footer (a 'summer breeze'), and will probably carry between 65-75 sq. feet of sail (probably a loose-footed spritsail). The mast will probably be some manner of spruce/pine/fir. I'm just wondering if anyone has any recommended dimensions for how big (around) it should be, preferably in nominal lumber sizes, as I'd like to use finish-quality pine lumber from the lumber yard. It's fairly cheap and is straight-grained and knot-free.

    My thoughts:
    I'd like the mast to be square - it will be non-rotating and I don't particularly want to round it. I may cut it into an octagon at most.

    If the mast only needs to be 1.5" x 1.5" I can make it with a pair of laminated 1x2's, if it needs to be bigger, I'll probably laminate it from 1 or 2 x 3's and rip it to size.

    Are there any common rules for what kind of mast bend is acceptable? any thoughts on this or rules of thumb I should know about?
     
  2. lewisboats
    Joined: Oct 2002
    Posts: 2,329
    Likes: 126, Points: 0, Legacy Rep: 1603
    Location: Iowa

    lewisboats Obsessed Member

    There are specs for the mast on the site where you got the plans. 1.5x1.5 sounds right but a sprit rig really should be able to rotate as the sail is pretty bound to the mast by the sprit and it will not draw well unless it can angle itself to the wind properly. I used a fir stair rail for my sprit rig and it worked quite well.
     
  3. gggGuest
    Joined: Feb 2005
    Posts: 828
    Likes: 24, Points: 18, Legacy Rep: 76
    Location: UK

    gggGuest ...

    THis could be relevant

    http://www.intcanoe.org/iclife/hist/acabook/aca_p41.html

    Think you'll regret a mast with corners: it will get bashed to hell in no time. A round or oval one will
    - set the sail better
    - look better
    - last better
    - need less maintenance
    - weigh less
    Obviously you wouldn't need the track in the above, but easy enough to leave that off.
    Big influence on construction is whether you wish to have stays or not: obviously an unstayed mast needs to be a deal more solid.
     
    1 person likes this.
  4. lewisboats
    Joined: Oct 2002
    Posts: 2,329
    Likes: 126, Points: 0, Legacy Rep: 1603
    Location: Iowa

    lewisboats Obsessed Member

    I'm sorry...I should have said 2.5x2.5... which is what mine is for a 75 sf sail. The stair rail was for a 60 footer.
     

  5. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    A 12' mast for a sprit rig of usual proportions, will want a 2.75" base with a continuous, straight taper to 1 5/8" at it's head. This will be moderately flexible, but not overly so and good for an inshore cruiser. This mast will weight just a tad over 9 pounds as a solid spar of Sitka spruce and about 11.5 pounds if Douglas fir. This is pretty darn heavy for such a little spar.

    If it was me, I'd build a birdsmouth spar and change the dimensions slightly to 2.5" at the base to 1 9/16" at the head. A Douglas fir birdsmouth spar would weigh about 6.2 pounds and Sitka spruce will be about 5 pounds. The pine you have in mind will likely be near the Douglas fir weight (just guessing at the actual species you'll use). This spar will have a 20% wall thickness and be just as stiff as the solid one at half the weight.

    The birdsmouth construction method is covered in many places on line, including some YouTube videos of larger ones being built. The process is the same for all and it's an easy way to make a strong, self aligning during assembly, spar.

    The mast doesn't have to rotate and this much area also doesn't need stays or shrouds, though again I'm assuming it's not flying a jib.

    A "composite" mast is something I (and others) often call for in small boat plans. I have a small cat boat that carries a 78 sq. ft. sprit boomed rig and the mast is a two piece assembly. The lower section is 2.5", 6061, T-6 aluminum tubing, .083 wall, with a birdsmouth upper section of spruce. The wooden upper section is glued into the lower aluminum section and also carries all of the taper. This is about as easy as it gets to have a light, strong and stiff stick.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.