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Old 08-08-2007, 19:28   #1
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Mast

I am new to boating. Have notice one thread about (keel stepped/deck stepped) mast. From what I have read seems most boats with a cabin have some type of support for the mast. I understand the compression post concept but not sure how the keel stepped system works. Sounds like it sits in a tube.

Please KIS. I am sure there are lots of tech about loads and lift etc.
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Old 08-08-2007, 20:03   #2
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The mast penetrates the deck and is supported on the keel.

The compression post in a deck stepped is like a line of columns in a two story building... the loads all end up at the foundation or in this case the keel where is the strongest part of the hull.

Keel stepped can be leaky, but they don't need rigging to stand. A deck stepped is more like a guyed radio tower. Cut the stays and the tower falls down.

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Old 08-08-2007, 20:27   #3
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Quote:
Keel stepped can be leaky, but they don't need rigging to stand.
Not quite that simple. They come they way they are so you don't usually get a choice. It is easier to take down a deck stepped mast but it's not much less effort. I can't see either being much better. the leaky part isn't hard to deal with unless you let it go too long. Keel stepped masts still have water coming down the center of the mast.

Keel stepped masts sit on top of the keel. Deck stepped masts sit on top of a post attached to the keel. They ALL need shrouds a whole lot.
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Old 08-08-2007, 20:47   #4
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Originally Posted by defjef
Keel stepped can be leaky, but they don't need rigging to stand. A deck stepped is more like a guyed radio tower. Cut the stays and the tower falls down.
Everything Jef says, except many larger keel stepped masts will collapse under their own weight without rigging holding them "in column" (straight up and down). They do that by bending and breaking, not just falling over!

If everything else was identical, the keel stepped mast is stiffer. To compensate for this, the deck stepped mast has to have more stiffness "built in" with diameter or metal thinkness or else it has to have more fancy rigging.

For an offshore cruising boat, given two boats that were identical in all other respects, I'd chose the keel stepped mast, but wouldn't make it a real big reason for selection of one boat over another. If you are cruising canals with low bridges, keel-stepped might not even be a useful option to consider.

Bill
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Old 08-08-2007, 21:19   #5
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Quote:
Originally Posted by defjef
Keel stepped can be leaky, but they don't need rigging to stand.
jef
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Maybe in a marina on a still day. I've seen photo's of a Sydney-Hobart boat (wish I could find them again) which broke some of it's rigging - the mast fell over, but unlike what would happen on a deck-stepped boat, (the mast would simply fall down) the mast took half of the coachouse with it, which eventually resulted in the boat sinking.
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Old 17-08-2007, 23:05   #6
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Maybe in a marina on a still day. I've seen photo's of a Sydney-Hobart boat (wish I could find them again) which broke some of it's rigging - the mast fell over, but unlike what would happen on a deck-stepped boat, (the mast would simply fall down) the mast took half of the coachouse with it, which eventually resulted in the boat sinking.
Definitely a concern with the lighter, tapered spars on bigger boats. Average keel stepped mast on a 30 footer will hold up to a moderate wind.

The keel-stepped masts do allow a certain amount of rain to come in through the (internal) halyard sheaves, and sometimes around the mast boot, but there is a product called Spartite that seals this quite well. It also replaces mast wedges and serves to lessen the likelihood of the mast breaking at the partners, as there are no 'hard points' of compressive force on the side of the mast.
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