"Easy" mast stepping - alternatives for a tabernacle?

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  • 04 Apr 2017 10:58
    Reply # 4711071 on 4611808
    Anonymous member (Administrator)

    JRA member Lex Hodgkinson in Newsletter 20 described a clever tube-type tabernacle for his 17-footer which would allow the heel of the mast to be well below deck level. 

    Chris

  • 04 Apr 2017 10:42
    Reply # 4711057 on 4611808

    I had same kind of thoughts, but didn't dare to say them "aloud" :)

    Back to the thinking mood, then!

  • 04 Apr 2017 10:40
    Reply # 4711053 on 4611808

    Yes, 10% of the mast should be within the tabernacle, but I see no reason why you can't make Arne's concept in wood, and then the heel could be lower than deck level. In fact, it's probably easier to work in wood, as you can use a large proprietary stainless steel butt hinge.

  • 04 Apr 2017 09:49
    Reply # 4710984 on 4611808

    Just checking: The height of the tabernacle should be at least 10% of the mast length (over the deck), right?

    (As I stated below, it's not possible for me to build Arne's excellent tube tabernacle. Instead it seems that I have to go with the traditional, wooden tabernacle, which puts the boom higher than would be desirable on my low-ballast ratio boat.)

  • 17 Feb 2017 11:37
    Reply # 4614280 on 4611808

    Economically there seems to be one problem at least for me: the aluminium tubes sold here seem to be 6000mm long. That would mean buying a more expensive tube than the mast itself, and only use maybe 1500 mm of it. Ouch.

  • 17 Feb 2017 10:41
    Reply # 4614273 on 4614186
    Anonymous member (Administrator)
    David Tyler wrote:... ...It's not necessary to let the mast go right down to the bottom of the tabernacle, only to the usual 10% bury, so overall, there's probably the minimum increase in sailing weight.

    Yes, I can see your point, David. All one has to do then is to move that bolt shown in the bottom end of the tabernacle, upwards until the bury of the mast gets just right. That would save some mast length and quite some lifting of the mast as well.

    I guess I drew that bolt in the bottom end because I felt that the bending load was lowest there.

    Arne


  • 17 Feb 2017 08:58
    Reply # 4614186 on 4612978
    Arne Kverneland wrote:

    Jami,

    Now I have made a sketch and made some text about it. It's a bit too long for one posting, so I made a little write-up on my page, here

    Lots of lousy English, I am afraid. Still, I think I spot one advantage of the tube tabernacle: Since the mast is inserted all the way down to the tabernacle's step, there need not be much clearance between deck and the boom:

    Arne


    This is an interesting idea. The tabernacle tube is larger and obviously therefore stronger than the mast tube, so that there is more strength at deck level, the point of maximum bending load. It's not necessary to let the mast go right down to the bottom of the tabernacle, only to the usual 10% bury, so overall, there's probably the minimum increase in sailing weight. It will still need a crew with sufficient strength to lift the mast up and hold it while a locking device is activated to hold it lifted, but that will be OK in smaller boats.
  • 16 Feb 2017 22:17
    Reply # 4613174 on 4611808

    I've seen a half-tube tabernacle of the kind that Mark describes, made in GRP, but unfortunately have no photos of it. 

    any kind of tabernacle or hinge must be appreciably heavier than just a keel stepped mast. Whether wood, metal or GRP, it's going to be heavy, but that's a price you have to pay for a mast that can be raised and lowered without a crane or a team of rugby players. With metal or GRP, though , it doesn't have to be bulky as well. 

    I think the Needlespar /Tammie Norie version is probably the neatest and simplest to make and operate, if you have metal working skills. If not, maybe a wooden tabernacle would look neater if it took half of a staved mast as its design concept, so that it would present a semicircular forward or after face to the world? The three sided wooden box is always going to be quicker and easier to make than this, though.

  • 16 Feb 2017 20:35
    Reply # 4613039 on 4613021


    Scott Dufour wrote:

    I've just finished doing the math for my boat; same problem, different scale.  I elicited the input of a couple of marine engineers that I admire, and the same answer came back:  make it out of aluminum or stainless steel.  It'll be lighter, stiffer, and less bulky than a wooden one.  Costs can be reasonably had.  A good engineer can even work in lightening holes if it's designed in from the beginning.  Though with your smaller scale, I don't think you'll need them, nor is there room.

    Yes, but if the cost is a factor and you can work wood, but not metal, then the wooden one is the way to go.  Certainly here, the quotes from most metal workers make me dizzy.  The taberncale that Pete made for the 20ft Missee Lee was far from clumsy looking and much nicer to have next to your bed than a metal one.  There are a couple of photos of it in my photo ablums. 

    Click here to see the full-size photos.

    Unfortunately, I don't have any of the interior (which I sincerely regret) showing the elegant, open lower part of the tabernacle.
  • 16 Feb 2017 20:10
    Reply # 4613023 on 4611808

    Interesting - thank you, Arne, for your effort. I will take my time to understand this and take it in the consideration as well.

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