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"Easy" mast stepping - alternatives for a tabernacle?

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  • 17 Feb 2017 08:58
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    Reply # 4614186 on 4612978
    Anonymous member
    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
    Quote
    Reply # 4613174 on 4611808
    Anonymous member

    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
    Quote
    Reply # 4613039 on 4613021
    Anonymous member


    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
    Quote
    Reply # 4613023 on 4611808
    Anonymous member

    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
    Quote
    Reply # 4613021 on 4611808
    Deleted user

    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
    Quote
    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
    Quote
    Reply # 4612209 on 4611808
    Anonymous member

    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
    Quote
    Reply # 4612088 on 4612080
    Anonymous member
    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.
  • 16 Feb 2017 11:43
    Quote
    Reply # 4612080 on 4611808
    Anonymous member (Administrator)

    Jami,

    your letter put my mind in "on".

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

    Arne
  • 16 Feb 2017 06:05
    Quote
    Message # 4611808
    Anonymous member

    Hello again, an sorry for putting up a new thread - but I thought I might get a better response this way, because the question at hand might be relevant to other boats as well as mine.

    I seem to start getting frustrated with my plans of converting my Joe 17 trailer sailer.

    I've been trying to find out the best way of having an easy way of stepping and lowering the mast on every sail. I keep the boat on the trailer, and never leave it in the water after sailing.

    My current sailplan has a mast height of 6300mm above deck level. Most probably I will have a hybrid mast with 5000mm of 100mm aluminium tube and a wooden top.

    I've been adviced to build a tabernacle from wood. I seem to find it hard to accept the thought that this would be strong and light enough at the same time, considering the sloppy seas I often go to. I'm afraid a strong tabernacle will weigh too much together with the moved (compared to the bermudan rig) mast.

    The 6300+ mast weighs perhaps 25kg. I think would be possible to lift it through the deck and step it in a normal JR way every time. But then again there would be a need for temporary stays or some other nuisance in order to keep the mast stable enough when lifting it alone.

    Have you come up with solutions to this? Should I just stick with the tabernacle plan and deal with the weight issue?
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