Tides & Currents

Is the water coming in
or going out?

Pick your spot, pick your day, read the answer. No working out required.

1 Where are you going?
Or tap one of these
2 Which day?
3 Here's the water

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Reading the tide tables…
Drawing the curve…
How to read this chart
The orange line is the water level through the day. Up means the tide is coming in, down means it's going out. Dark bands are night. The white line is right now. Numbers on the left are how deep the water is above the lowest normal tide, so add them to the depth printed on your chart.
4 High and low water
5 Which way the water is pushing
Looking for the nearest current station…
What is slack water
Slack water is the few minutes when the current stops before it turns around. It's the easiest time to go through a narrow entrance, because nothing is pushing you sideways. Flood means water flowing into the bay. Ebb means water flowing out to sea. An ebb running against an incoming swell is what stands the waves up at the entrance, so an ebb plus a big swell is the combination worth avoiding.
6 Going under a bridge?
Which bridge?
No bridge picked yet.
Where do I find the clearance number
It is printed next to the bridge on the chart, usually in a little box, and it is the height at the middle of the span where the arch is highest. Here is the part that catches people out. That number is not the worst case. It is measured from mean high water, which is the average high tide, not the highest one. On a tide that runs higher than average you get less room than the chart says. This tool does that sum for you using the real tide for the day, so the number you see below is the actual gap, not the chart's average.

Does tide even matter in San Diego?

Mostly no. That is the honest answer. We get about four to six feet between high and low, and the current through most of the bay is under a knot. Nobody here waits on a tide the way they do in the Pacific Northwest or up the East Coast.

But it decides four things, and all four can turn a good day bad.

1 Whether you touch the bottom

The main channel is dredged and deep. The edges are not. Glorietta Bay, the South Bay, the back of Mission Bay and plenty of older berths get thin at low water. A few times a month we get a minus tide, where the water drops below the zero on your chart and you have less than the chart says, not more. That is when boats find the bottom, and it is almost always in a berth or a shortcut, never in the channel.

2 How rough the entrance is

This is the one worth knowing. When the tide is running out of the bay and a swell is running in, the two fight each other. The waves stand up steeper and stack closer together. Same wind, same swell height, completely different ride. An ebb against a solid westerly swell is the difference between a comfortable exit and a wet ugly one with your guests hanging on.

3 How the boat behaves in the first ten minutes

Half a knot sounds like nothing until it is walking you sideways out of your slip. You will feel it near the entrance, around the bridge and by the ferry landing. Knowing which way it is setting before you let go means you plan the departure instead of reacting to it halfway out.

4 Where you end up at anchor

Your scope is measured from the bow roller to the bottom. The bottom does not move but the water does. Drop the hook at low water with what looks like plenty of chain and you have noticeably less scope by high water. Boats here also swing to the current, not just the wind, which is why a group of boats sometimes lies in a direction that makes no sense until you check what the tide is doing.

Where this sits in a passage plan

Tide is not what decides whether you go. Wind and swell decide that. Tide decides when you go and which way you take.

  1. Wind and swell. This is your go or no go. Nothing below this line overrules it.
  2. Daylight. When do you need to be tied up, moored or back inside the breakwater.
  3. Tide and current. Now fit the departure and the arrival into what the water is doing. Check depth where you are shallow, and check the entrance if there is any swell running.
  4. The boat and the crew. Fuel, water, who is doing what, and whether everyone aboard knows the plan.

Most owners do the first two and skip the third. In San Diego that is fine nine times out of ten, which is exactly why the tenth time catches people out.

Tide will rarely stop you leaving here. It will regularly decide how the day feels.
Show more than one day
Handy when you're planning a trip rather than a day out.
Feet or metres
Your boat and your berth
Fill these in once and every tide time below tells you how much water you'll have under the keel. The chart also shades red whenever you'd drop under your margin. Nothing to work out yourself.
What does MLLW mean
Every height here is measured from mean lower low water, which is the average of the lowest tide each day. Zero means the water is as low as it normally gets. Your chart uses the same zero, so the real depth under you is roughly the charted depth plus the tide height. A minus tide means less water than the chart says.
Spring and neap tides
Around new moon and full moon you get spring tides. Higher highs, lower lows, and stronger currents. Halfway between, you get neaps, where everything is gentler. Nothing to do with the season.
Actually heading out?
Run the pre-departure checklist before you slip the lines.
 →

Tide predictions from NOAA, shown in local time at the station.

These are predictions, not measurements. Wind, barometric pressure and swell all push the real water level away from the tables, sometimes by a foot or more. Add your own margin and sound your way in.

First Mate Yacht Club · Confidence through competence.