Upside-down hybrid mast

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  • 22 May 2020 18:35
    Reply # 8987037 on 8982609

    Arne.

    Nailed it! That's a strong joint there. I wonder if it would be beneficial to tie it into the upper partner in some way? Also what about routing out a bit of the wood to sleeve the aluminum into. This could work as the bottom spacer for the aluminum. I would think with a tight fit, the sleeve could act as a flashing or ferrule.

    Oscar.

    Your so sexual.

    David.

    You are right. It looks like I am building a Tabernacle. I would do just that if I were planning on keeping the boat on the trailer. Contessa 26 would make for a very beefy trailer sailer. But I got big plans for this one and want to make as strong on a mast as I can get away with. That being said. I can buy a pole, straight or tapered at 50 ft in length if I needed. With the cost of lumber around me, unfortunately I don't think I will be making this design. It has got me thinking of new ideas though. Like having a two part aluminum mast. Maybe a straight pole that sleeves into a heavier one below the boom. Anyway i thought it would be a fun thing to talk about, even if it doesn't come to fruition. 


    Jeff

  • 22 May 2020 08:20
    Reply # 8985934 on 8982609

    Jeffrey,

    Structurally, this is quite similar to putting an aluminum mast into a wooden tabernacle, so we know it can be done strongly enough. A tabernacle that ends at boom height brings no problems of tapering to be solved. The question then is, can you get a long enough aluminum tube to go the rest of the way? 20ft tubes are available in N America, and sometimes 24ft, I seem to remember - is that enough? If not, since your skills are in woodworking, it would seem that you're into building a short wooden topmast in any case. So a good practical solution might be a wooden tabernacle, which brings advantages with it, in being free from renting cranes to step the mast, and you get your pleasanter wooden section inside the boat>>>straight aluminum tube, as long as you can get>>>short wooden topmast.

  • 21 May 2020 23:33
    Reply # 8985274 on 8982609
    Jeffrey wrote:

    Wood inside the boat looks nice, and I can hang a picture of Mom on it.

    It's also warmer to the touch and not subject to condensation. Like your mom. ;)

    The wood could taper as it moved up the joint to decrease the hard spot that would form. (Where the wood bit ends and the aluminum is exposed)

    Yeah, I don't see a problem if you create a taper so that any batten parrels run smoothly over the joint when lowering the sail.


  • 21 May 2020 23:26
    Reply # 8985266 on 8982609
    Anonymous member (Administrator)

    Jeffrey,

    I have never thought of that one before, but I think it is doable. 
    I would use a sleeve from aluminium to avoid that the joint ends up as a weak spot.

    Se diagram below.

    Arne


    Last modified: 22 May 2020 08:47 | Anonymous member (Administrator)
  • 21 May 2020 20:55
    Reply # 8985015 on 8982609

    Len

    You are correct. I was referring to the "boom" 

    I agree with setting the aluminum to be the male end of the joint. This would make it into a "neadlespar" looking thing. It would probably be easier to box in the aluminum then to hollow out a solid piece of lumber. One could also align the grain orientation to acomidate. 

    The wood could taper as it moved up the joint to decrease the hard spot that would form. (Where the wood bit ends and the aluminum is exposed)

    I understand that the wood section will be quite girthy. But what's the down side of that? The aluminum could be made thinner and the wood section would offer a larger serface area to meet the mast partner. 

    I also understand that none of this is practical from a construction standpoint. I never was afraid of a bit of work though.

  • 21 May 2020 19:28
    Reply # 8984758 on 8983485
    Anonymous wrote:

     I could try and tackle the weekest point in the mast with what wood working skills I have, (I don't have any aluminum skills). I imagine a shorter wood section to get past the majority of the area of maximum force. I would guess that the joint above that would be the strongest section on the whole mast. By the start of the joint I could be at the first batton.

    First batten? Do you mean the batten that is also sometimes called the boom or the batten at the top of the first sail panel? If you truly mean the batten at the bottom of the first panel (which is how your drawing looks to me), then perhaps a wooden tabernacle would fit.

    No need to taper the wood to meet the aluminum,( shy of aesthetics.) Just plane the wood down to meet the ID of a straight pole. Then carve a dragon just below the joint so it looks like it is eating your mast. Or whatever... 

    Rather than having the wooden part slide into the aluminum pole, I would suggest that boring out the wooden part would make more sense strength wise. This keeps the wooden part at full diameter rather than weakening it to less than the aluminum pole. Boring out the centre of the wood may not be that practical either as you would be looking at a bore length of a meter or so. It may be easier to build the lower part of slats or at least split it vertically to make removal of the centre portion possible. As others have mentioned, the wood would have to be much bigger for the same strength.

    The other method, not seen on a junk I would think, is to do the tall ship style of join of lapping the two mast portions together. This works on a tall ship because they have no rings, parrels, etc. that have to slide up and down the mast.

  • 21 May 2020 19:01
    Reply # 8984685 on 8982609

    Attached a scetch

    I would think I could use a smaller piece of aluminum tube as the force of the sail is spreading out over the battons.

    Correct me if I'm wrong, but I am under the impression that the sail works as a total force that is applied to the partners. The partners are acting as a fulcrum for our big cantilever. So when you build a mast from a single piece of material you would detumin the maximum area of force and build it around that number. If you are building out of multiple materials, you could divide up the jobs that the mast has to do.

    It seems like an opportunity divide the work into two sections. The materials seem to be best suited in this orintation to utilize the best qualities of both. 

    There is definitely a week spot in my design. I have put a note on the sketch. I wonder if I could reinforce that part of the "socket joint" with some fiberglass our reversing the joint so the aluminum is the male end of the joint? 

    Again, I am probably going to go with a tapered aluminum mast. I wanted to explore this idea though as I think it could be a good bit of conversation.

    Jeff

    1 file
  • 21 May 2020 10:24
    Reply # 8983814 on 8982609

    Hi Jeffrey.  The usual reason for a hybrid mast is the inability to find a suitable tapered alloy section.  I can see a serious problem with your idea to make the bottom from timber and join it to a tapered alloy tube around the first batten.  The highest stresses on the mast are at the partners, from my understanding.  The timber lower mast section will need to be substantially bigger at the partners than an alloy section would be.  To join it to an alloy section at the first batten would therefore require a much bigger alloy section than you normally would use.  The only way it would work, in my opinion, is if the timber section is about 60% of the overall length of the mast, at a minimum.  And if you are going to do that then maybe it would be just as easy to build a complete timber mast?  Usually, if one cannot find a suitable tapered alloy spar, and one does not want to built a complete timber mast, then buying a straight alloy tube, usually coming in 6-6.5m lengths, and adding a tapered timber topmast makes sense.

    Your ideas sound like fun, especially the carved dragon, but I am not sure if it is practical unless you go for a timber mast.  But an interesting thought!

  • 21 May 2020 05:48
    Reply # 8983485 on 8982609

    Hi Graham.

    What I was thinking of what the perfect mast might look like. 

    A mast with thickness in all the right places, that taper to meet with every working section... It would be glorious!!! Hahahaha 

     I could try and tackle the weekest point in the mast with what wood working skills I have, (I don't have any aluminum skills). I imagine a shorter wood section to get past the majority of the area of maximum force. I would guess that the joint above that would be the strongest section on the whole mast. By the start of the joint I could be at the first batton. No need to taper the wood to meet the aluminum,( shy of aesthetics.) Just plane the wood down to meet the ID of a straight pole. Then carve a dragon just below the joint so it looks like it is eating your mast. Or whatever... 


    Scott.

    The aluminum mast is what I will most likely end up with. (I might need a little help picking out what size and color I should get). I would be very happy to use your guy. Please feel free to email me! Would like a good chat.

    I really think there is something to this upside-down hybrid mast though. Maybe I just am being a sucker for aesthetics.

  • 21 May 2020 02:41
    Reply # 8983242 on 8982609

    Hi Jeff,

    Welcome aboard!

    From your profile I gather that you will be sailing on Lake Michigan. I am over on the other side of the lake. The Contessa 26 is one of the boats burned into my memory from reading John Vigor's Twenty Small Sailboats to Take You Anywhere over and over again before buying my first keel boat. It would be amazing to visit Navy Pier and see your junk rigged Contessa 26 underway from the top of the ferris wheel! 

    I just recently purchased a pole that I hope will be a mast some day. The company that provided the 6063 alloy tube is even closer to you, assuming you are in Chicago. If you are interested I can send you the contact information in a private message.

    I expect you will find many businesses willing to sell you a straight tube of stronger 6061 alloy. I think it might be less costly to build a hybrid mast, square or round, right side up or upside-down, with a straight tube. I may be wrong, but I also expect it will be more time consuming to build a hybrid mast compared to buying a tapered pole.

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