When your phone is dead or the tide app is out of reach, you can still work out roughly where the tide is and where it is heading. A simple mental rule gives you a usable backup, and it needs no equipment at all.
Treat everything below as a rough sketch rather than a forecast. It will point you in the right direction, but the official numbers still come from a proper tide table.
The first thing to memorise is this: the tide shifts roughly 50 minutes later each day. If high tide was at six today, tomorrow it lands near ten to seven, and the pattern keeps sliding.
The moon drives it. Each day the moon rises about 50 minutes later, and the water follows, so after two weeks the times come back close to where they started.
From high tide to low tide takes about six hours, and six more hours bring the next high. So if you know one time, you can sketch the rest of the day.
The full high-low-high-low cycle takes about 12 hours and 25 minutes, and that extra 25 minutes is exactly why the times drift a little every day.
To estimate how high the water sits at a given hour, use the rule of twelfths. Take the total range between low and high and split it into twelve parts. In the first hour the water rises one part, the second hour two parts, the third three parts, the fourth three, the fifth two, and the sixth one.
Half the water arrives in the first three hours and the other half in the last three. It is a rough curve, not a measurement, but it beats guessing blindly.
Batteries die, signal drops, and sometimes you are simply in a hurry. A quick mental estimate tells you whether the water is pushing in or draining out, and whether a channel is worth entering right now.
Keep tide state separate from wind. A strong northwest wind can push the level down and a southerly can raise it, so the real high may arrive lower or higher than the rule suggests.
Never let a rough calculation replace an official tide table, especially in shallow water. The channels of Kuwait Bay are unforgiving, and half a metre of error is enough to put you aground.
the B7R app is free on Google Play and gives tide times for Shuwaikh and Shuaiba ports alongside sea state and weather, so you can check real numbers before you launch and keep the mental rule for emergencies.
Use the rule when you have nothing else, and use the B7R app for the numbers you actually trust. Download the B7R app free on Google Play.