Boot Key Harbor
"Marathon- the Heart of the Florida Keys"

An On-Line Cruising Guide for the Florida Keys & Cuba
Best viewed at 1024x768 or higher

TIDES

USE YOUR BROWSER BACK BUTTON TO RETURN TO THE PREVIOUS PAGE

Do you want to go aground, lop off the top of your boat on a bridge, or maybe even worse yet get a $175,000 fine from NOAA for going aground in some sand and grass? I think not. Most of our year-round boaters here know tides intuitively, but some of our seasonal boaters might want a quick refresher. OK, so tides 101: Here in the Keys we get a couple of low and couple of high tides each day, roughly 6 hours apart for each. Each day the peak of the tides will shift by about 50 minutes. They’re usually not very big – maybe a foot or two, more on new & full moons. When you’re “pushing the envelope” even this can be quite a bit. When we go in to the anchorage at Newfound Harbor I can cut directly across the flats during high tide, but will go aground at other times (Shhhh! I didn’t actually SAY I went aground). The 7 mile bridge over Knight’s Key channel, like most of the bridge clearances here in the Keys, is 19 feet at high tide (Remember bridge clearances on charts are at high tide, and depths at low tide). This is close to our own vertical clearance so we watch the tide level carefully for this – if a passing boat throws a wake when we cross under at high tide it can crunch our superstructure. The hard part here is in knowing what the tide level is, and more importantly whether it’s going up or down. Everyone that’s had our boating classes has learned to use the tide charts to interpolate tides from various reporting points – in our case Key West. But how many of you actually go to all that trouble to keep those charts at the helm and interpolate them? None of you. I know I don’t. It’s more trouble than it’s worth in most routine situations, even though it affects safety. What’s changed all this is the advent of the tide calculators in many of the GPS units, which most people use. At the touch of a button you can see a graph of tides at your current position to know its level and direction of change. This becomes enormously useful because it’s so easy to do this before cutting over that shoal, or under the bridge. If you’re heading into “skinny” water you can afford to be more adventuresome on a rising tide because it will save you if you bump & stick. This does not address the question of tidal current however, and we’ll do that later.

P/C Gregory Absten