"Easy" mast stepping - alternatives for a tabernacle?

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  • 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.

  • 16 Feb 2017 20:08
    Reply # 4613021 on 4611808

    This is one of those issues that has been looked at a million ways for a few thousand years.  The tabernacle seems to be the conclusion for nearly all of those designs.

     

    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.

    For your scale, I'd lean toward in a simple u-shaped tabernacle, that becomes a closed box below decks.  Scantlings need research, or a smart guy like Arne or David to chime in.

     

  • 16 Feb 2017 19:41
    Reply # 4612978 on 4611808
    Anonymous member (Administrator)

    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


    Last modified: 16 Feb 2017 22:36 | Anonymous member (Administrator)
  • 16 Feb 2017 13:50
    Reply # 4612209 on 4611808

    Jami,

    Having watched Robin slotting in his mast on a similar  sized boat, I would say on anything bigger than a dinghy, not easy. 

    A timber tabernacle, as Pete Hill's should not be unduly heavy,  though they are bulky and may not look good on your pretty wee boat.

    How about using a heavy gauge ali tube, say 140 x 9.5mm, even when cut in half may be strong enough?  (1.5m about £180). Shape the top such that the sides extend up to hold the horizontal mast.  The half cut is not the full depth of the bury, so it as the mast is lifted vertical it drop down the last part.  Always use temporary stays when lifting.  Once in wrap around the mast and tabernacle together with rope or webbing (no holes in mast).  Below deck, extend with a nice timber insert.

  • 16 Feb 2017 12:03
    Reply # 4612088 on 4612080
    Arne Kverneland wrote:

    Before I start, do you have access to a shop where  some aluminium welding can be done for you?

    Arne

    I might have, yes. The aluminium way has been on my mind, too - but hasn't turned out as a plan of any sort.


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