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Advice, please: new mast for Seablossom

  • 07 Jan 2012 18:54
    Quote
    Reply # 789451 on 789310
    Anonymous member
    Gary King wrote:



    However, regarding the so called disadvantage of the composite mast. The stress at the partners is independent of the shape of the rest of the mast, tapered or straight. The reason for tapering is for lightness, tapering does not "spread" forces, the bending forces (or bending moment) decrease as you go higher up the mast tapered or not. It does mean less material is needed higher up the mast, so no strength is lost by tapering.

    The composite masts centre of gravity may be higher than a same height 100% wooden mast, but the composite is lighter, so CoG becomes a moot point. I think in this country, where a pair of flag poles (which I need) are around $6000 (if they do, I haven't shop around yet), composites make sense.

    Gary, you are right that all stresses ultimately must be absorbed at the partners. How they get there is another story. You are however wrong when you say CG does not matter. It does and in some cases very much but I digress. I have a boat to build (and so do you :-) )so do not want to get involved in any theory discussions. I just tendered some advise to Jeff as he was asking and thats as far as I wish to take it. The advise was not incorrect even if you do not agree with all of it, Jeff certainly will not come to harm by following it.
  • 07 Jan 2012 15:56
    Quote
    Reply # 789373 on 788093
    Deleted user
    I can get a 35 footer, 6 inch at base, .125 thickness, tapers to 3.5" top diameter, rated for 91 mph "flagged".  I have not yet found one with thicker wall.  Comments?

    Jeff
  • 07 Jan 2012 12:16
    Quote
    Reply # 789310 on 788093
    Deleted user

    Paul, I agree Jeff's best option is probably to buy a flag pole, they are most likely half the price in the US than they are down here.


    However, regarding the so called disadvantage of the composite mast. The stress at the partners is independent of the shape of the rest of the mast, tapered or straight. The reason for tapering is for lightness, tapering does not "spread" forces, the bending forces (or bending moment) decrease as you go higher up the mast tapered or not. It does mean less material is needed higher up the mast, so no strength is lost by tapering.

    The composite masts centre of gravity may be higher than a same height 100% wooden mast, but the composite is lighter, so CoG becomes a moot point. I think in this country, where a pair of flag poles (which I need) are around $6000 (if they do, I haven't shop around yet), composites make sense.
  • 07 Jan 2012 06:23
    Quote
    Reply # 789221 on 788093
    Anonymous member
    Jeff McFadden wrote:Hello, all, and Merry New Year to you.
    I have come across a modest sum of money and will be able to afford a new mast for Seablossom.  I damaged her wooden mast considerably getting it unglued from the deck when I bought her, although I have been pretending otherwise so I could go sailing, but now I have a choice.
    I priced carbon and it's out of the question.  Of the aluminum options, should I go with a flagpole?  Typically flagpoles are tapered.  Or should I go with a straight tube?  I'm not very interested in trying to make up a step-tapered tube.
    Does anyone have pictures of the step they are using for an aluminum mast, or suggestions on that portion of the project?
    Paul recently designed me a new rig, so the specifics of what I'm trying to do with this mast can be found here.
    Jeff, unstayed masts are tapered because taper permits the mast to absorb the loadings from the sail in a uniform manner over it's entire length. When you use a straight untapered section all loads are transfer to the point where the mast bears against the partners. So that point which is always the most highly stressed part of the mast, is even more stressed if you use a straight section. The centre of gravity is also higher being at around the 50% point versus around 30% up from the partners in a tapered mast.

    Since you are in the states, there are many suppliers of aluminium flag poles and light poles so there is little need to consider anything other than a tapered section. Light poles generally have a heavier wall thickness so may be a first choice. You will be looking for something around 7 to 8 inches at the partners and at least a 1/4 inch wall. The top diameter should be about 40% of the partner diameter. Google is your friend here and their are many suppliers in your part of the world.

    I'd also take a good long look at your existing mast. The damaged that you have inflicted upon it may well be repairable. Maybe asking Maddog to take a look at it might be a good idea as the dog is a skilled wood worker.

    I hate to dampen the enthusiasm for the Annie style composite mast but it would be my last choice, one that I'd take only if I could not afford to buy an     aluminium one, repair your current one or cannot build a wooden one.

    The composite mast was a good choice for Annie's circumstances and it is doing a good job but it is far from an ideal choice. The major objections are that it's essentially a straight section mast, so the loadings at the partners are high. Because the top section is also the heaviest part of the mast (if wood), your centre of gravity is also higher than either a tapered mast or a straight mast. The join between the pipe and the tapered wooden section is also potentially a weak point.

    The above being said, there are composite masts in use and Annie's one is working but if you go that route you should be aware of the disadvantages. The advantages are of cause that it's a relatively cheap and easy way of getting a tapered "looking" mast but as with everything in this life, you pay for it. 
    Last modified: 07 Jan 2012 06:31 | Anonymous member
  • 06 Jan 2012 05:45
    Quote
    Reply # 788417 on 788386
    Anonymous member
    Jeff McFadden wrote:
    Annie Hill wrote: I'm chuffed to death with the whole rig...
    Can you translate this into American English for me, please?

    Yes, send me some pics and I'll love them.  Or just post them on your Box folders.
    Jeff

    Translation: I am very happy with my mast.
    Regarding box.com...envisage slapping forehead.:D
  • 06 Jan 2012 04:48
    Quote
    Reply # 788390 on 788386
    Anonymous member
    Jeff McFadden wrote:
    Annie Hill wrote: I'm chuffed to death with the whole rig...
    Can you translate this into American English for me, please?


    I can translate from Liverpudlian into English: "I'm absolutely delighted".
  • 06 Jan 2012 04:37
    Quote
    Reply # 788386 on 788304
    Deleted user
    Annie Hill wrote: I'm chuffed to death with the whole rig...
    Can you translate this into American English for me, please?

    Yes, send me some pics and I'll love them.  Or just post them on your Box folders.
    Jeff
  • 06 Jan 2012 02:05
    Quote
    Reply # 788304 on 788093
    Anonymous member
    I can send you photos of the mast building process, if you are interested.  I'm chuffed to death with the whole rig and the mast seems fine.  i paid just under NZ$700 for the tube.  The dimensions, etc are all in my profile.

    The other nice thing about the wooden topmast is that you can paint it a pretty colour :-)
  • 06 Jan 2012 00:05
    Quote
    Reply # 788230 on 788194
    Deleted user
    Jeff McFadden wrote:That might be an option.  The existing mast is a birdsmouth mast, so it would take some adapting.  I'm thinking Annie's extension is of solid wood.  I'm not sure I would get much advantage for doing it that way.
    Hi Jeff,
    Annie's mast extension is hollow Douglas Fir box section. If you price aluminium, you should find that a 20'x6" stock tube is way cheaper than a whole flag pole, that is the main advantage.
    I'm going the composite mast route too. :)
  • 05 Jan 2012 22:50
    Quote
    Reply # 788194 on 788144
    Deleted user
    Gary Pick wrote:Hi Jeff, box.com requires a login to access files. 
    Yeah, but... you've got a folder in there yourself.  Surely you have a login?
    Just an idea but if the top section of your wooden mast is okay maybe you could do what Annie did. Build a composite mast.
    That might be an option.  The existing mast is a birdsmouth mast, so it would take some adapting.  I'm thinking Annie's extension is of solid wood.  I'm not sure I would get much advantage for doing it that way.
    Last modified: 05 Jan 2012 22:50 | Deleted user
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