Aluminum mast for Flicka 20?

  • 05 Sep 2023 18:30
    Reply # 13250334 on 13159620

    This vendor appears to have significantly lower prices. 

    Last modified: 05 Sep 2023 20:45 | Anonymous member (Administrator)
  • 04 May 2023 23:54
    Reply # 13191638 on 13159620
    Deleted user

    Gentlemen thank you for your replies. Arne I appreciate your analysis and info on your boat. 

    Ingeborg displaces 2150 kg and carried 34m with 15 cm wide mast 5mm thick wall.

    Roger Taylor's Ming Ming 2 mast was a lamp post with 3.5 mm thickness and carried 25 m sail. Although Achilles 24 is much lighter boat.

    My 6.09 m boat displaces about 2700 kg and the mast will be carrying 25 m sail. I hope I can make assumption that 7 inch (17.78 cm) wide mast with 4.775 thick wall made of 6063-T6 aluminum should be safe/strong  enough.

    Last modified: 04 May 2023 23:55 | Deleted user
  • 15 Apr 2023 11:37
    Reply # 13168841 on 13159620
    Anonymous member (Administrator)

    Another way of calculating the load on the mast

    Deciding on the right dimension on a freestanding mast  (or any sort of mast) appears to be a bit of a black art.

    In the early days of commercial junks in Britain, the masts (from Needlespar) appeared to be terribly slim. Several photos show Sunbird 27 and 32 sailing along with a lot of bend in their masts. Some of these appear to have ended up with fatigue problems and eventually snapped.
    (..the photo below shows a Sunbird 27 with the mast bending quite a bit in moderate conditions....)

    At the other end of the scale are the scantlings specified for wooden masts in Practical Junk Rig. Their formulas needed to be adjusted for lighter craft with the generous sail areas that I use, or the resulting masts would end up much stronger than needed  -  and much heavier than could be tolerated.

    Nowadays I have tried to base my calculations of aluminium masts on the calculated ultimate righting moment of the vessel. See Chapter 6b of TCPJR.

    There is another way to roughly find the load on a mast, based on the calculated wind pressure at maximum wind strength before reefing.
    About the wind pressure, we know that it varies with the square of the wind velocity.
    A place to start is to find the wind pressure at wind speed 10m/s. This turns out to be 6.1kp/sqm

    Case Ingeborg:
    SA = 35sqm and CE is sitting 4.4m above the partners. At a wind strength of 10m/s (about 20 knots), the bending moment should be around (roughly)...

    Mb35 = 6.1kp/m2 x 35m2 x 4.4m = 939kpm

    However, I know that at this wind strength, my Ingeborg will be down at 5 panels ( 25sqm) and the CE will now only sit only 3.4m above the partners, so the bending moment should come out at

    Mb25 = 6.1kp/m2 x 25m2 x 3.4m = 519kpm.

    This is about a quarter of the designed strength of Ingeborg’s lower mast section (Ø150 x 5mm). Practical sailing has shown that there hardly is any discernible mast bend at all, much unlike on the shown photo.

    My conclusion is that my way of calculating mast scantlings based on the boat’s ultimate righting moment, probably results in slightly over-strong masts. Still, I will rather be there than sailing under very flimsy under-size masts.


    PS: For weekend sailing, I guess I could safely use masts that are only 2/3 as strong as the strength I calculate while using the righting moment method.

    Last modified: 16 Apr 2023 20:58 | Anonymous member (Administrator)
  • 15 Apr 2023 01:21
    Reply # 13168627 on 13159620

    It looks like the flagpole you are considering is 6063-T6 alloy. I have been using a mast made from this alloy for a couple seasons now. I have not had any issues. I determined that I would need a 7-in diameter mast using this alloy. I was not able to find a flagpole vendor that could provide such a flagpole.I purchased my mast from a lamp post manufacturer.

    If I had the time and money I would like to try a 6-in diameter mast on my boat to see how well it works. It would be nice to have less weight. Right now I am very confident that something else will fail before the mast itself becomes damaged.

    My boat is 22 feet long and, according to sailboatdata, displaces 2200lbs.

    If i understand correctly (it could happen!) the yield strength of 6063 is much less than other 606x alloys.

    Last modified: 15 Apr 2023 01:22 | Anonymous member
  • 14 Apr 2023 08:36
    Reply # 13167617 on 13159620

    Weaverbird, that I used to own, was a bit longer but not so heavy as your Flicka, and carried a 7in mast with a 0.128in wall. This was right, in terms of strength and stiffness, for her 22 sqm sail. So I think that 7in x 0.188 should be fine to carry 25 sqm.

  • 13 Apr 2023 23:36
    Reply # 13167267 on 13159620
    Deleted user

    I found this post on wooden boat forum:

    Still I wouls appreciate any guidance in this area. I lean toward 7 inch diameter pole with 0.188 inch thick wall. 

    I've had two boats on which I used aluminum flagpoles for masts, unstayed. On the 42 foot steel schooner I had two 8 inch diameter poles that tapered to about 3 1/2 inches at the top. The taper started around the midpoint--straight section half-way up and then tapered to the top. One pole was 44 feet long, the other 39. Both carried 400 sf junk sails. Wall thickness at the base was .187 inches.

    Any comments highly appreciated!

  • 06 Apr 2023 23:02
    Reply # 13159622 on 13159620
    Deleted user

    link to Specs info from the supplier of the flag poles

    Last modified: 07 Apr 2023 01:33 | Deleted user
  • 06 Apr 2023 23:01
    Message # 13159620
    Deleted user

    Hello Everybody.

    I wanted to build 27 to 29 ft wooden mast for my boat but it is impossible to buy decent wood in Florida. I called numerous suppliers with no luck on quality lumber. So I think that my only option is aluminum flag pole/lamp post. 

    I found some suppliers online. They offer 33 foot flag pole with 0.156 or 0.188 inch wall. Diameter of the pole is 5 inch or 6 inch at the bottom and it tapers to 3 or 3.5 for heavier mast. What do you recommend? 

    My boat displaces almost 6000 lbs. Total planned sail area is 25 m for main and 5 m for mizzen. I still want to build wooden mast for mizzen. I may be lucky to get some smaller local pine lumber. Also I would like to build tabernacle for main mast.

    Thanks, Kristof

    Last modified: 07 Apr 2023 01:40 | Deleted user
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