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wood mast for my 15 ft albacore

  • 31 Dec 2014 15:44
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    Reply # 3178776 on 3178049
    Deleted user
    Thanks Arne,  I have seen the youtube video but will need to see it again because I was focused on the sail and sheets.  I think I have read all of your articles but as my learning curve catches up I will reread them.  

    Looked at the video again.  Because of no real reference point for size the mast looks thicker to me than 9 cm.  I would have guessed between 13 and 15 cm.  This is good because smaller is even easier to handle when making.

    Last modified: 31 Dec 2014 17:00 | Deleted user
  • 31 Dec 2014 09:58
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    Reply # 3178662 on 3178049
    Anonymous member (Administrator)

    Corey, just a short reply before going back to sailmaking:

    The strength of a wooden mast varies with the cube of the diameter at the partners.

    (9cm/7cm) CUBED =2.13.

    The PJR formulas have proven to give oversize masts unless the SA/disp. is very low, around 14. When we are down on dinghy size boats, it is better to see what others use and scale up or down a little to suit one's boat.

    BTW, you can have a closer look at Broremann from on board if you go to Youtube and search for Broremann.

    Anyway,

    Happy New Year!

    Arne
  • 31 Dec 2014 02:56
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    Reply # 3178601 on 3178049
    Deleted user

    Time to go back to school. On sailboatdata I saw 240 lbs "displacement" for the Albacore and read it as 420. I'm guesing this differnce wouldn't change mast size much or at all as crew weight especially 'hanging out on the rail' could quickly minimize or negate the hull weight difference between the Albacore and Oslo.

    Phil
  • 31 Dec 2014 01:59
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    Reply # 3178568 on 3178049
    Deleted user

    Thanks Arne and Phil,  so mast strength goes up more exponentially with diameter increase.  The albacore is only 240 lbs hull weight.  I thought the oslo was almost twice that.  

    Phil I see you are outside of Belfast.  Im in Harrisburg Pa.  Got a brother in Liberty.  The longer term plan is to have 3 sail plans for this hull to compare.  I am starting with the aerojunk because of the flat sail, less sheet and ability to keep original mast location. Aesthetically I love Arne's cambered panels. 

    I'm a little slow on the uptake today Phil.  Was that an offer to donate the sail for the cost of shipping?  That being said I have an ex sister-in-law in the camden area that is magic with a sewing machine.   Use to work for Moss tent works in the R&D department.   Might be able to help.  

    Last modified: 31 Dec 2014 03:19 | Deleted user
  • 30 Dec 2014 17:49
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    Reply # 3178345 on 3178049
    Anonymous member (Administrator)

    The first (borrowed) spruce mast I used for Broremann was 7cm. This was on the light side, so I reefed more to avoid a mast fracture than capsize. The next mast was 9cm (4.2cm in the top, I think it was), which is over twice as strong. This (solid spruce) mast weighed 10kg and worked very well on Broremann. I think this would hold on an Albacore as well, even if you hang out on the rail a bit.

    Arne 

    Last modified: 30 Dec 2014 17:50 | Anonymous member (Administrator)
  • 30 Dec 2014 15:14
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    Reply # 3178239 on 3178049
    Deleted user

    Corey

    For your boat you won't need a mast nearly that size. Look at Arne's write ups on Broreman an 18 foot dinghy which is similar in weight to the Albacore. I think he went with a diameter of a little over 3 inches with mast shaped from grown spruce. How committed to the project are you? Are you locked into Pauls' design? I have a sail which I started as a mostly scaled up version of Broreman's. It was for a Com-Pac 16 (1100 lbs) but I sold the boat for a Com-pac 19. I planned it to be 135 ft2 but left out the lowest panel when I had problems with weight when building the mast. The 6 panel version comes out 115 ft2. When I decided to go with a taller aluminum mast I removed the webbing along the foot and sewed on the 7th panel, already cut. The foot is back to unfinished. The sail is finished along the luff and leach with 1inch low stretch webbing on stitched both sides of the sail. The chord is 9ft 1inch. The batten pockets use Arnes amateur method 2, are for 1inch aluminum tubing and reinforced with tough fabric at the mast. The material is 3 1/2 oz nylon coated on one side. It is not rip stop but very difficult to tear even when stated with scissors. The sewing is amateur learn as I go with coaching from my wife. I've  wracked my brain (doesn't take much) to find a way to enlarge the sail for the new boat but haven't come up with anything. I'm in the U.S. but if you are interested shipping should not be too costly as the sail is light.

    Last modified: 30 Dec 2014 15:21 | Deleted user
  • 30 Dec 2014 01:47
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    Message # 3178049
    Deleted user

    I used the PJR formula to determine mast diameter.   Depending on what mast height I decide on the diameter is between 4.8 inch and 5.7 inch.  Wood will be either Sitka spruce or Duglas fur.  I would like to have a hollow enough for wiring.   I have never made a wood mast or delt with an unstayed wood mast on a small boat.  Sail area is to be 120 square feet which is the original stayed mast area.  I will be doing an aerojunk design sail as close to Paul McKay's design i can get.  Can anyone give input on how safe these diameters seem?  If they seem correct should I see much or little bend ?  Thanks folks. 
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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