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  1. #1
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    Oct 2011
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    Default need help to build a 2 x 4 stayed wooden mast

    There is a lightning sailboat at our marina that looks like it has a single 2 x 4 stayed tapered wooden mast. I think the mast on a lightning is approx. 25 feet in length. I don't see any joints anywhere. I would like to make a 20 foot mast for my sailboat. How do calculate where and how much to taper the mast and where to attach the side stays?

    Thanks in advance for any help,
    choppy

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  3. #2
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    Feb 2008
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    Eustis, FL, USA
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    Default

    What is the total sail area the mast will carry, the jig masthead or fractional, rig type (gaff, Bermudian, etc.), staying configuration, weight of the boat, beam of the boat, LWL, type of sails currently used, J-I-P-E dimensions and make, model and year of the boat?

  4. #3
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    Default

    Thank you for taking the time to reply.

    What is the total sail area the mast will carry? 150 sq ft
    Is the jig masthead or fractional? masthead
    Rig type? Bermudian/sloop
    Staying configuration? fore, aft sides
    Weight of the boat? 350 lbs.
    Beam of the boat? 6 ft
    LWL? 15 ft.
    Type of sails currently used? this is a new design--no sails as of yet
    J-I-P-E dimensions? J=7.5 ft-----I=20ft-----P=20ft-----E=7.5ft
    Make, model and year of the boat? home made design

    Warm regards,
    Choppy

  5. #4
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    Default

    Your description of the staying arrangements are lacking, but assuming a single spreader, masthead and fixed back, a 3" base with a continuous taper to the head at 2 7/16" will do. If eastern white spruce, it'll weight about 16 pounds if 20% wall, birdsmouth built. If Douglas fir it'll weigh about 21 pounds. This is an average cruising mast. You could save some weight with a foot taper, though not a lot.

    A light racing version would still use a 20% wall, birdsmouth, but would have a 2 3/4" base and a 2 3/16" head and would weight about 13.5 pounds if spruce and about 17 pounds if Douglas fir. This is a light stick, but if well stayed, should stand in everything short of a gale.

    If you want a "bendy" rig, this is a different set of variables and requires a lot more information, particularly about sail shape and preformance envelop intentions.

    You can further reduce weight and windage with stave wall thickness. 15% is as low as I'd recommend unless you just like to replace masts. A 15% mast would be 2 7/8" at the base and 2 1/4" at the head and would weigh about 11.5 pounds. If Douglas fir about 15.25 pounds. This size stick saves a fair bit of windage, but would be quite delicate.

  6. #5
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    Default

    Your description of the staying arrangements are lacking, but assuming a single spreader, masthead and fixed back, a 3" base with a continuous taper to the head at 2 7/16" will do.
    Just so I am clear. I take one 20 foot 2 x 4 and mark at 3" on one end and 2 7/16" on the other end and make a straight taper cut? I am not sure what a "fixed back" is but yes the mast will be single spreader and masthead.

    Thank you for taking the time to help me,
    choppy

  7. #6
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    Dimensions offered were for a birdsmouth build, not a solid stick. I wouldn't recommend a solid 20' stick to people I didn't like, let alone those that I did. If it was a solid stick to those dimensions, white spruce would be about 25 pounds and Douglas fir would be about 32.5 pounds, which is a fair big difference, especially if the wind is blowing and you're trying to manhandle it up onto it's step. A solid mast would have different dimensions and forces the question why a solid stick?

    A "fixed back" is a hard mounted, aft stay arrangement, either split, "Y" or standard (single). You can eliminate this stay if you sweep the spreaders and put more engineering into the rig then necessary, but the fore and aft stay with a simple cap and lower shroud arrangement was what I was thinking. If it was a fractional rig, you could probably lose the cap shroud and just go with a swept lower and head stay. If the base is wide enough you could lose the lower shroud on a masthead rig, but you need a minimum of 10 degrees at the masthead fitting.

    Asking these questions makes one wonder what you're designing and the approach you are taking, as these are fairly basic and routine calculations.

  8. #7
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    Default

    Again, that you for taking the time to help me,

    I am a "shade-tree" boat builder and I don't have the capability to build a birdsmouth mast at this time. As my tool collection grows I would like to build one in the future though. I know that a solid 2 x 4 will not be ideal but that is what I will have to go with at this time. On the lightning sailboat that I saw at our marina it looked like they were using a solid 2 x 4 that was tapered and I was hoping to get some help on something similar. My boat is 16' in length were I think the lightning is 19' in length with a 25' mast. I need a 20' mast to get the sail area that I would like to have. I think the fore and aft stay with a simple cap and lower shroud arrangement will work best for me.

    The 10 degrees that you refer to--would that be measured from the mast to the side of the boat and let's say I have the 10 degrees--at what height would I place the spreaders and how do I calculate the length of the spreaders?

    Thank you in advance for any help,
    choppy

  9. #8
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    Eustis, FL, USA
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    Default

    The mast you've seen at the local marina is a "box section", rectangular, hollow mast and a very common way to build a light weight spar. It's not a solid 2x4, trust me. It's just a box, typically with lapped corners. It would be a very rare 16' boat that can tolerate a solid mast, without capsizes being the norm.

    Place the spreaders half way up the luff and the 10 degree rule is for the lower, not the cap.

  10. #9
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    Default

    Thank you for taking the time to share your knowledge.

    I see now that a solid mast would be a huge mistake. I will try to make a rectangular hollow mast. Do I use something like four 1 x 3s or 1 x4s? If you have time could you please share on how to taper the mast and what size to make the taper? I have searched the internet and I cannot find any images on how to do this.

    Thanks,
    choppy

  11. #10
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    Default

    Tapering is as simple as cutting to the line, but honestly I don't know enough about your design to offer tapering recommendations, more then I have. Given the very basic nature of your questions and engineering requests, I wonder about this project. Have you preformed a weight study so you know where it's going to float on launch day? How have you placed the rig over the hull form/appendages? How much CE/CLP lead? A small boat like this can behave quite badly if not well balanced. When making your first attempts at self design, it's very important to base it on well known and understood models (other designs). In this way you will not be terribly surprised with events on launch day. As you gain experience with design, you can venture farther out on the design "limb". Can you post lines and a sail plan, with the appropriate centers noted? This would help a great deal in understanding what you're trying to do and need.

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