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post #1 of 19 Old 05-16-2012 Thread Starter
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Mast height question

I am buying a boat and near my house there is a bridge height I am concerned about. When looking I see "mast height" listed in the specs. Is the mast height the max height measured from the waterline to the top of the mast (which seems right) or is it the height of the mast from where it is stepped causing me to do math.
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post #2 of 19 Old 05-16-2012
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Re: Mast height question

I'm no more sure then you are, but it seems it *should* be from the waterline. What type of boat, and what specs are you looking at? If you find the sail specs and the forestay goes all the way to the masthead, then the "I" dimension in the rig dimensions should be the height from the bow to the top of the mast, which could give you a clue. If that is substantially less then the listed mast height, then I would say the mast height is from the waterline. Of course,if its not a masthead rig, then a little more figuring will be in order...

EDIT: I guess that would also depend on if its deck stepped or keel stepped.

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post #3 of 19 Old 05-16-2012
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Re: Mast height question

Sailboat Rig Dimensions at Mauri Pro SailingHere's a link to measurements. You can look up your boat.

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post #4 of 19 Old 05-16-2012
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It's from the waterline; hence the term "clearance".
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post #5 of 19 Old 05-16-2012
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Re: Mast height question

you could just hike a tape measure up the halyard. Wouldnt be exact but you could over estimate.
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Re: Mast height question

and add on for the extras - vhf antenna, wind.
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post #7 of 19 Old 05-16-2012
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Re: Mast height question

Also remember that bridge clearance on charts is at high tide, which means that you can get a little more clearance (or a lot, depending on the tides in your area) at low tide.
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post #8 of 19 Old 05-16-2012
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Air Draft

Mast height is almost always measured from the water. But to be sure you know the how high the top of your mast is from the water, measure the actual height of the mast from the deck to the top of the halyard (tape measure) and then add a foot to account for the sheeve typically being below the actual top of the mast. Then measure the height of the deck off the water. You should be pretty close to the height to the top of the mast. Add height for antennas. I then add another foot for "safety" for bridge clearances.

As far as bridge clearance, yes the chart data is typically reported as clearance at high tide, but high tide typically changes so I'm pretty sure it as bridge clearance/height is reported at Mean High High Water. If you have an unusally high tide, the clearance is less.

My mast height is a little under 53 feet with antennas and such. We have to go under a bridge for winter storage that is 49 feet. The tides here are about 9 feet, so we have to wait until after mid tide on a falling to tide to go the 3 miles down stream to fit under the bridge when we start the season and go upstream for haul out at the end of the season during low slack tide on the flood side of the cycle.

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post #9 of 19 Old 05-16-2012
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Re: Mast height question

If you look at your "I" dimension it is usually taklen as a mast height from the sheer at the mast base. But for a lot of cruising boats the "I" dimension is from the top of the cabin top at the mast. I think Otter has it right. Don't trust printed dimensions. Haul a tape measure up to the masthead on a halyard and add some fudge factor for instruments and error, then add another 12" just to be safe.
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post #10 of 19 Old 05-16-2012
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Re: Mast height question

And if you have a VHF antennae/windvane on top, you must account for that too.

Brian
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