We have been under that RR bridge. In preparation I measured the
mast height by tying a 'tomato stake' in two places to the main
halyard tied in a circle and raised stake until my wife at the far end ot the
dock with a pair of binoculars said that projected end of the stake was even with the tip of the
VHF antenna. I knew the length of the stake. I had tied a 100 ft tape measure to the the bottom of the stake. Doing my sums (stake+tape to
boat hook laid across the deck+boat hook to water), I then knew the height of the
VHF antenna above the
water. A quick look at the
internet sites previously mentioned, and I held my breath and motored under the bridge.
Bill