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Old 12-05-2008, 20:13   #1
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Is it possible to put joints in a Mast ???

Probably a really stupid question... as you have already assessed, I am a novice when it comes to sailing vessels, but the idea was to have a way to bring down a 20 Meter Mast (by the way, does anyone know what the abbrv WLH refers to in the length of a Mast) so that it might be possible to motor up a river where the bridges don' t move...

From an engneering POV, it seems like it would be possible and still maintain the integrety of the Mast when extended... I suppose it's just a matter of money...

Thanks for in advance for any thoughts on the topic..

Cheers
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Old 12-05-2008, 20:38   #2
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suppose it's just a matter of money...
That always is a sure fix. Why do you feel the need to add joints?

Masts are commly built in sections Adding them should not be required. It just brings up a lot of things that while possible may not have benefit. Masts are buit as a unified single structure. The use of joints is part of the constrution or it is not. Adding a joint seems doubtful as a solution to a mast problem.
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Old 12-05-2008, 21:05   #3
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As Paul has stated, it is not uncommon for masts to be built in sections that are spliced together. The splices are usually intended to be permanent. If you were to have a way to separate your mast into two or more sections, you would also need to figure out how to separate your standing rigging into sections as well. If you want to take the top section off the mast, you will likely need a crane anyways. If that's the case, then why not just unstep the whole mast and lay it down on deck? That way you don't have to have any openable splices, nor do you have to worry about joins in your standing rigging.

Also, how high (or low) is the bridge you need to get under? Would it be possible to get under it if the boat were healed over? Not a terribly common manuever, but not unheard of either.

I found a form from SELDEN (a spar manufacturer) where WLH appears to be defined as the height of the deck or cabin rooftop above the waterline at the mast location.
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Old 12-05-2008, 22:15   #4
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If your mast is deck stepped you could make a tabernacle to lower it, at 20m it would be quite a mission but could be done. If keel stepped hire a crane and lift it out, tying it down over the cabin top. when you have done river cruising reverse the proceedure. just remember it will probably over hang the bow or stern or both depending how you store it.
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Old 14-05-2008, 05:18   #5
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Thanks all for the input... it does seem folks are working on a telescopic mast for sailing vessels... a neat idea not only for getting to more places for also for bad weather... here is one patent I found on Google... perhaps one day there will be an affordable solution...

Cheers

Retractable sailboat mast - Patent 4016823
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Old 14-05-2008, 05:43   #6
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Your profile says you are seeking a 50 foot cat. The spar for that boat will be substantial. Why do you want the ability to raise and lower it?
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Old 14-05-2008, 15:35   #7
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The leaders in telescoping mast technology are in the military communications industry where they devise various ways to erect communications masts (antenna masts) from vehicles.

The solutions tend to be damned expensive and much weaker than sailboat masts, so don't hold your breath. The answer to low bridges was found many decades ago: You either dock someplace downstream of the bridge, or you get a powerboat.

Sorry, but that's where it is right now. There are tremendous loads on a sailboat mast, and any solution means weight aloft, which is an incredibly bad thing for a sailboat. If you can find a workable solution you'll be rich and famous.
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Old 14-05-2008, 15:39   #8
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I guess a gaff rig would not work would it?
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Old 14-05-2008, 20:13   #9
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Your profile says you are seeking a 50 foot cat. The spar for that boat will be substantial. Why do you want the ability to raise and lower it?
Actually, the idea was to take it up the Rhine over a summer...

Well, there's always the Dingy...

cheers
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Old 14-05-2008, 20:41   #10
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Maybe hit a marina at the start and pull the rig. Leave it at the marina for the summer and play motorboat. The rig is gonna be close to 80 foot so letting it live on deck is a recipe for expensive repairs.

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Actually, the idea was to take it up the Rhine over a summer...

Well, there's always the Dingy...

cheers
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Old 14-05-2008, 21:57   #11
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You can go to a gaff or maybe a gunter, if you merely want to drop a little off the top. Rob Denney of Haryproa plans to have a telescoping mast for a transpac race. His idea is an external wing mast top section over a heavily built but slightly lower diameter lower section.
Every time you use spreaders, you are effectively saying this sectin is acting like a joint in this direction
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Old 15-05-2008, 01:18   #12
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Originally Posted by capcook View Post
Probably a really stupid question
No, it's a good question but you might not like the answers and it's less likely you will be able to implement them.
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by the way, does anyone know what the abbrv WLH refers to in the length of a Mast
I believe it means height above the waterline. That is a 50' mast on a boat where the bottom is the mast is 4' above the waterline is 54'. Not useful for sail area calculations but really important for bridges.
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From an engineering POV, it seems like it would be possible and still maintain the integrity of the Mast when extended... I suppose it's just a matter of money...
There have been a lot of patents for tilting or telescoping masts. I tried to bring some up but wasn't able. However, that may be a little value anyway as lots of patents never make it to market.

Out of curiosity, what is the navigable width of narrowest section where you are traveling and the lowest bridge height?
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Old 15-05-2008, 02:04   #13
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Outside the square - a smaller boat....

Have you considered a smaller boat? A 38' cat is still a big boat and the mast would be 75% of the height.

The 21' Van De Stadt that I built had plans showing a tubular mast made in sections with internal sleeves. I don't know if the current plans show this.
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Old 15-05-2008, 04:06   #14
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It is an easy thing to have a taberanacle mounted mast. It has been done for years. A sailing boat is the ideal situation. It has fixed angle stays. Plenty of winching power. And to be blunt a very small stick. Even at 50 foot that is an easy thing to deal with. Dont be afraid !!! The forward stays need to be detachable. Pin and split pin is fine. Undo back stay tension by a counted number of turns. This take the tension off the rest of the rig. The loading to lower a mast of that size with a gin pole (use your boom backwards as in on the front of the mast) is way less than the strain that your mast and boom will encounter whilst sailing. The important thing is that the pivot point of your mast is at the same line as your attachments of your stays. Having put up and down towers of significantly more height in gales (wind generator towers with a few hundred killos on top) it is not a problem. Do the geometry. The (if you are lowering aft) the stays should all pivot just slightly aft of the mast pivot. This means that as you lower there is no tightening up of any of the rigging, just a gentle slackening. By just aft I mean a few millimeters. A piece of cotton passed through the whole pivot points will show you. With anchor winchors and all sorts of other gear, ( and common sense) it has huge advantages. Why go up the mast when you can angle the boat to the jetty and drop the mast over it ? Needless to say the boat that I am building has a tabernacle mounted mast step. GEOMETRY. I rude word didnt allow enough height for my companionway hatch. This means that the mast will lower about 7 deg. less than I wanted it too. Dont make the same mistake !! : )
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Old 15-05-2008, 04:36   #15
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Capcock,

If you dig a little deeper you'll find United States Patent 4016823 is about a small mast for kayaks and canoes. The idea is not all that unique. It's much like a boat hook I used to own.

For a trip up the river over the summer it would seem more piratical to pull the mast before the trip and be a power cat for the summer. Joli has the cheaper solution on this one. People do it all the time to transit canals and other low clearance inland routes. Stepping and unstepping a mast is no fun for each bridge but if it is for a trip you'll find it affordable. You don't normally get to sail on these types of trips given the traffic and bridges.
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