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Old 08-11-2006, 16:50   #1
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What is the Advantage of a Keel Stepped Mast?

I have looked into this just a little, and I have to say I can't find any REAL advantage - one that I believe in anyway.
Most of the proponents of keel stepping say that it could save your rig in the event of a rigging failure, but I really find that hard to believe.
Unless you happen to snap a stay on a day when there is virtually no wind, I can't see how supporting the mast so far from the centre of effort would hold it up - either the mast would bend or break off at deck level, or more likely in a glass boat, the mast would tear out a huge portion of the deck as it fell over. (From memory this happened to "Stand Aside" on the 1998 Syd - Hobart)

What are the real advantages?
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Old 08-11-2006, 17:05   #2
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A deck stepped mast is cheaper. Advantage to the builder. If you're quick you can prevent a catastrophe if you have a rigging failure on a keel stepped mast by dumping the sails. Happened to a friend of mine. Forestay went at the stemhead fitting, luckily he was sailing downwind and the genny blew out and up and spilled the wind. He was singlehanding home from Atigua. Undid the Profurl section by section and didn't lose anything.

I prefer keel stepped as it's a lot easier when unstepping a mast.
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Old 08-11-2006, 19:01   #3
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Very little

Actually, it's more of a disadvantage. I have one and the only advantages I can even think of is if you have a mast jack but that can still be installed with a deck stepped mast, it's just more complicated.
And if you want to pull shrouds/stays for maintenance reasons the mast will stand on it's own as long as the boat is steady.

The compression post does the same thing as going all the way to the keel. Plus, it can be made if some fine looking wood, or it can be a bulhead.

If you want to hear the complaints that'll take another half hour but it came with the boat so it stays until replacement............................_/)
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Old 08-11-2006, 19:33   #4
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Thing's like water pissing in through deck collars that never seem to seal?
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Old 08-11-2006, 20:09   #5
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I believe it's stronger. You are not relying on a compression post and the deck to cary the load. If you button up the partner correctly you really do not have any leaking to speak of.

We use a rubber boot followed by neoprene followed by boot tape. No leaks but it will take a couple hours to do correctly.
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Old 08-11-2006, 21:11   #6
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When you have a compression post does the deck carry any load? And isn't the compression post usually at least as strong as the mast?
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Old 08-11-2006, 23:44   #7
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Hi ...,In the boat that l am building the compression post is many times stronger than the mast. The compression post sits right down onto the keel. Further l have set the mast up as a "tabernacle" mounted mast which means that l can lower the whole lot down by putting the boom on the front of the mast and using it as a gin pole. Then undoing a few bits and using the anchor winch, drop the whole lot on the deck. For more information see previous article l wrote for the metal boat society journal. (sorry cant remember the issue no.) Unless the boat is very strong a collapsed keel mounted mast may take some of the coach roof with it. This could be as much of a problem as no rig. l have a feeling that the original origin of the keel stepped mast was to allow for the changing of stays or shrouds without the nessesity of a crane or similar.cheersMartin
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Old 08-11-2006, 23:50   #8
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All in all,a chain is only as strong as it's weakest link.And I would imagine where the mast joined the compression post would be it's weakest point.Just a thought.Mudnut.
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Old 09-11-2006, 00:00   #9
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Compression posts are right under the mast between the keel and the underside of the deck, at least they are suppose to be. At that point the deck should be solid fiberglass or cored with solid wood.

One of the problems with the old wooden boats is that area under the mast would rot out and compromise the rigging. Todays boats are built so that area should be one of the strongest parts of the boat.

One of the problems with keel stepped masts is that the deck around the mast will start to bow upward when heeling over.The shrouds start squeezing the hull together bulging the deck. So, to compensate, a draw bar (brain fart-can't remember the name) is attached between the keel and a deck plate, keeping the deck from rising up when the shrouds are pulling on the chain plates.

Some boats have a bulkhead fairly close to the mast, which helps to support the deck and to keep the hull from squeezing together. My bulkhead is 18" + or - but I still have the draw bar as extra strength. But when she's heeled over 35 degrees I can see the deck around the mast moving. I can see the boot working up/down. If I take this boat offshore I'm cutt'n the mast and steping it over a mahogany post. One hand carved like from the Philippines.............................._/)

BTW the base of a deck stepped mast should be trapped by a casting made to fit the mast and bolted to the deck.
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Old 09-11-2006, 05:01   #10
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Quote:
Originally Posted by 44'cruisingcat
What are the real advantages of a keel stepped mast?
more than a little bit of a problem for a catamaran!
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Old 09-11-2006, 05:30   #11
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I spent the last 2 years looking at both thru deck and tabernacle installations and both have drawbacks. Keel stepped leak at the deck, maybe not after re-stepping but eventually and usually before your ready to service the mast. The base of the mast when keel stepped is more prone to corrosion. With deckstepped installation any loss of integrety of core or compression post could create pumping of the rig and failure. A keel stepped boat makes routing of wiring easier and the need to make holes to mount a base or tabernacle which leak and cause core damage are not needed. Look closely at an older boat with a deck stepped mast for any sign of deformation in the deck, water that is slow to drain away is more reliable that eyeballing the profiles of the deck.
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Old 09-11-2006, 05:49   #12
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Quote:
Originally Posted by Joli
We use a rubber boot followed by neoprene followed by boot tape. No leaks but it will take a couple hours to do correctly.
Same here. No leaks. I use the rubber boot, but load it up with silicone sealant like you'd use on ports and use 2 large hose clamps. Took me 20 mins, tops. Hasn't leaked since I did this last year.

Del's mast must be quite close to the deck where it passes through for it to be pushing the deck around while sailing. I have a 1" gap all around the mast, which makes sure it doesn't touch the deck's fiberglass if/when it flexes. Different designs, probably.
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Old 09-11-2006, 13:12   #13
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There is a thick rubber strap wrapped around my mast where it goes thru. The deck is slightly rising due to the stress of the shrouds being pulled, which happens on all boats. I can see mine because my mast boot only goes over the water guard and not sealed to it. It moves up/down about 1/2" when I really heel her over...........................~~~~~~~~~_/)
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Old 09-11-2006, 13:22   #14
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The principle advantage of a keel stepped mast is not really "strength" but rather stiffness. A keel stepped mast is stiffer than the same size (diameter and wall thickness) mast stepped on deck. This lets the rigging designer make a number of changes to the standing rigging that reduce weight and cost. Maybe a smaller mast section, maybe a single spreader instead of a double spreader rig, etc.

In the book "The Rigger's Apprentice" Brion Toss devotes most of a chapter to explaining the variables involved.

Without consultation with an experienced and professional rigger, switching a design from keel stepped to deck stepped without making other changes would be a very risky project.

Bill
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Old 09-11-2006, 19:13   #15
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Deck stepped masts

Generally, the advice I ahve read is that keel stepped is better than deck stepped, especially for bluewater boats.

As to pros/cons of deck stepped vs. keel stepped masts, can anyone explain why Hallberg-Rassey - one of the most respected blue water sailboat manufacturers - uses deck stepped masts?

Is it more a matter of the execution of the particular design rather than the simple choice of deck stepped vs keel stepped.
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