Join Date: Mar 2007
Location: New England
Thanked 7 Times in 7 Posts
Rep Power: 13
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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