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Go Back   SailNet Community > On Board > Boat Review and Purchase Forum > Sailboat Design and Construction
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  #11  
Old 03-10-2012
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Re: Mast tabernacle project

Forward dropping will likely make the balance point even further off the end of the boat. As a cheap backup, here is an idea you might consider if you are on land. Take three poles and lash them together in a tripod which you would stand on the ground to help hold up the overhanging mast end when inserting and removing the hinge pin. The tripod could be way out near the end, where it would only carry half the weight of the mast, or in closer to relieve more weight at the hinge. It would avoid a crushing weight at the bow pulpit.

I use tripods all the time, for support or lifting (like a well cover). There is a tripod holding up the ridge over one of my tarped in sailboats right now. I cut the size poles I need in the woods, and only buy some rope. Here is how I lash the tripod, it never slips (This actually is "an old Indian trick"!):


Lay two poles on the ground, side by side, touching. Take the third pole and make a large inverted "V" with the top end of the third pole crossing over the top ends of the two side by side poles. The top single pole has it's base to the right side, the double poles have their bases to the left side, when standing between them looking at the top of the inverted "V". Leave a bit of the poles sticking up beyond the crossing point. Tie the poles tightly together with a short, smallish diameter rope at the crossing point. Then take a long rope and tie that over the small rope, also binding the poles together, leaving a long end free (two half hitches).

Now stand the inverted "V" up, using the free end of the long rope to help pull it up, and swing the outermost pole of the two away from you. This opens the tripod, tightens the lashing, and interlocks the poles.


You can hang on the long rope for lifting, or rest the mast on the intersection of the poles at the top. By bringing the pole bases in or out, you can fine tune the height of the intersection. For major adjustment just re-lash the poles higher or lower.

If you are on pavement (I never am) you might need to tie the bases of the poles together at the correct spread, so they don't slip.

I can't visualize your "capture device" at the tabernacle, could you explain it a bit more? Thanks!

Last edited by skygazer; 03-10-2012 at 10:49 AM.
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Old 03-10-2012
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Re: Mast tabernacle project

Sky,

I have given some thought to how to manage the mast but that system is still "on the drawing board". I expect to mount a crutch at the bow. It will be braced to the bow rail and perhaps the chain plate. It will have a nylon roller to support the mast. How high it will extend is still a question. It could easily be adjustable. There will be an upward moment at the tabernacle and the mast will want to roll on its side. I can probably prevent the roll at the bow crutch but will need to be able to lift the mast to clear the steaming light so roll control would be good to have at the tabernacle end at least at the "capture". The mast will get rolled to the stern where it will be supported by a stern crutch. This stern "crutch" will be able to keep the mast from rolling on its side while it is riding above the deck. The sketches I have of a "device" at the tabernacle are simply two pieces of 1/4" x 2 aluminum bar, their actual length is yet to be determined, with 3/8" bolts connecting them at each end. One end of this pair is bolted together through the slot in the tabernacle under the mast after the mast is resting on the bow crutch but before the mast bolt is released. The other end of the pair is bolted together with a nylon roller between them. This roller is above the mast. I might use 2 pair of bars and two rollers to form a sort of triangle with the rollers above the mast. When the mast bolt is released the mast base would rise and be "captured" by the rollers above it. The aluminum bar / rollers would store easily.

It is more complicated than that. Being able to adjust the bow crutch might help when moving the mast aft?

Tinker, tinker.

What do you think?

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Old 03-10-2012
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Re: Mast tabernacle project

Of course, I haven't seen the DVD I think you mentioned at the start of this thread. I'm just going by the "pictures in my head". But what those pictures show me is that the pressure on the hinge pin will jam it in place. If you could remove the pressure it would just slide right out. If you drive it out the mast will fly up and add momentum to the already crushing weight at the bow pulpit. You know how leverage works, pipe over the wrench handle, or even a nut cracker. With the length of your mast if a bird landed on the end it could raise a human on the short end. I'd prefer you to be in total control at all times, able to stop and clear lines or just pause and think.

If you think the tripod sounds too complicated (it's really quite easy when you are doing it, harder to explain or understand than do) you might at least consider a vertical support from the ground lifting the weight of the mast. The tripod can't tip over, but the vertical pole might work if the bow support is rigid.

On my (other) boat I am using the mast for a ridge for the large tarp, set up high enough to work under. I just took a piece of cardboard and cut and scribed and fit 'till I got a good fit around the mast (sail track down). I then transfered this curve to a piece of wood, and hacked it out. This cut out is on top of the vertical wooden support (2x6 or 2x8 I think) and holds the mast from rotating. Fit a cut out on the vertical support I'm saying is not as good as the tripod, and you can support the mast without it twisting on you.

Nothing much to lose, even if it's just a back up. But that leverage is a killer, so be safe. I used to do lots of ladder work in Portland, I can tell you that if you are short of the balance point there is no limit to the apparent weight.

Remember Murphy, just at the critical moment a bird will land on the end, a big gust of wind will come up, and you will slip on a banana peel.

Edit: Maybe you can figure the amount of weight it would take to balance the short end. And maybe your bow support will be substantial. And maybe you are a big heavy guy. In that case, you can just sit on the mast to unbind the hinge pin, and let it slowly up.

Last edited by skygazer; 03-10-2012 at 07:51 PM.
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Re: Mast tabernacle project

Sky's absolutely correct.. the leverage exerted by the mast will be huge, but it's sneaky.. straight up it may be/seem manageable, but if the stick gets out of plumb in either direction you'll have a hell of a time keeping it from going on its own.. esp if it gets out of line with your tackle.. I reckon out of control it may well do your tabernacle in on the way down.

There are systems and methods.. I think they all provide some means of limiting lateral wander as the mast is lowered.. Lowering forward leaves you the minimum advantage and working area.. lowering aft would seem a better idea.. wider platform and longer distance for reduced leverage of the overhang.

Best of luck and work safely!! Anyone trying to be a hero and 'catch' a toppling mast is going to be in for a fair bit of hurt...
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Re: Mast tabernacle project

I also strongly prefer the lowering the mast towards the stern. I would not do it forward unless some major structure made it impossible to go aft. I'm working at lowering a skylight base and making the light removable so that I can lower mine to the rear - well, actually raise it since I've never had it up. I brought a snow shovel to dig out the boat when I picked it up, and the snow is only now melting away from it.
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Re: Mast tabernacle project

There is no doubt that lateral movement must be restricted as the mast comes forward. The video I mentioned earlier does a very through job of showing how to rig fixed lines to control it. My weight will be sufficient to counter the upward moment of the base of the mast when it comes to rest on the bow crutch. Having the height of that crutch adjustable is another way of adjusting that force a little. We will see.

Ed Zacko's story of building his rig in a boat yard while being watched and having the yard express amazement when it worked, gives me hope. His video is what it took for me to fully understand how it is done.

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Re: Mast tabernacle project

Here are a couple of screen captures from Ed Zacko's video that might help you understand the rig I am building.



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Old 03-11-2012
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Re: Mast tabernacle project

The screen shots were great, thanks. The tabernacles I've seen have without exception had the hinge pin on one end or the other of the base. The mast has a flat base bolted to it with the matching hinge on one end. When the mast is raised it sits squarely on the base, the hinge only keeps it form skidding around, the heavy weight is borne on the bottom plate and transferred down through the compression post.

A single centered pin will carry the full weight of mast, stays, and wind. An enormous load. Not saying it won't work, but it simply cannot be even remotely as strong, and I see no point in doing it that way.

Just curious, how did you figure that your weight will be adequate? I'd think you would need to know the actual weight of the mast, plus the distribution of that weight (spreaders, lights, mast head, etc.), and then figure the effect of leverage by measuring from hinge to support at the bow.

Maybe I'm overly cautious, but when dealing with heavy stuff it pays to be cautious. I've raised buildings and large beams and etc., I've seen that things can go wrong and careful thought prevents problems, damage, and injury.

When I purchased my 24 ft. Seafarer it was on stands. I drove to the boat with a plan, lumber I'd sawed out from pine trees or had laying about, jacks and levers etc. plus the almighty chainsaw. I too had people watching as I proceeded to cut the timbers and shape by eye (and cardboard template) and finally moved the 4000 lb. boat onto my equipment trailer, entirely by myself a long ways from home. They were calling me McGyver (spelling? I've heard it a lot but don't watch TV) and were amazed. I had no problems or scary moments, it went smoothly because I visualized it in my mind and planned for every problem I could "see". I didn't want to waste money paying someone else to move it, and like independance.

I'm merely trying to offer insights, what you choose is fine with me, no pressure. And I hope all goes well.




Edit: Perhaps your hinge pin can move in a slot and allow the mast base to settle onto the bottom plate? I'd look into buying a commercial tabernacle and bolting it on. Proven performance on a huge number of boats. Phone call just when I hit submit kept me from looking over my post right away.

Last edited by skygazer; 03-11-2012 at 12:31 PM.
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Re: Mast tabernacle project

In the case of those screen shots, the cabin profile pretty much negated an 'aft' drop without a hugely cumbersome tabernacle. The advantage I can see, though, is that the boom is a longer lever and more robust connection than any gin pole or spinn pole might be used to support an aft drop.

The other complication to this (and any system relying on athwartship support) is that ideally the center of rotation for both the mast pin and the supporting rigging ("A" in the diagram above) should be in line. Does he have shrouds attached to rigid 'tall' chainplates? or is he using the stanchion as a temporary one? it's not clear on the sketch.

Anyhow mechanically it should work... I just like the idea of being able to catch the rig in the cockpit rather than forward... Hope it all goes well, can certainly see the desire to avoid annual crane rentals and delays.
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Re: Mast tabernacle project

Faster,

"The other complication to this (and any system relying on athwartship support) is that ideally the center of rotation for both the mast pin and the supporting rigging ("A" in the diagram above) should be in line. Does he have shrouds attached to rigid 'tall' chainplates? or is he using the stanchion as a temporary one? it's not clear on the sketch."

You are correct. The most important consideration when locating the mast pin and the swivel point in the upper is that they be as close to perfectly in line as possible. He uses a clever set of nesting shackles on a tall jaw / jaw turnbuckle. It allows the shackles to remain as permanent parts of the rig and it only requires connecting the two A lines which also have turnbuckle ends for adjustment. If you look very closely at the A lines you will see a triangle plate connecting it to the upper and the chain plate. That is another way to hook them up.

Getting it close enough to finalize vertical alignment with the turnbuckle won't be hard. That will be a function of the turnbuckle's length, the fittings and where I cut the upper. I have located the line between the two upper chain plates across the deck and with a model of the base of my mast on the deck have the fore and aft measurement on the side of the mast for the pin. Now I just have to pick a height off the base of the tabernacle for the hole. I am thinking it will be centered at a height equal to the width of the mast which is 3 3/4". I will have a couple of 1/4" cheek plates welded onto the outside of the base of the mast, transfer the measurements and drill a couple of holes. That will take a bit of care but I have a portable drill press I can use. I will install a compression tube that will carry a 1/2" pin. Cutting the leading edge of the base away will decrease the vertical travel as the mast rotates through 90 degrees and reduce the effort required a bit. I hope to step the mast onto the tabernacle with a boom truck this next launch. The rigging mods happen after the mast is up. It will be interesting.

I can certainly attach a line over the mast's base to manage any upward moment. I don't have the bow pulpit the Nord'Sea enjoys.

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