# Find the height and time of tide for a secondary port

STANDARD PORT : MAINHAVEN-ON-SEA | |||||||
---|---|---|---|---|---|---|---|

TIMES |
HEIGHTS (metres) |
||||||

HW |
LW |
MHWS |
MHWN |
MLWN |
MLWS |
||

0000 | 0600 | 0500 | 1100 | ||||

and | and | and | and | 4.2 | 3.4 | 1.1 | 0.4 |

1200 | 1800 | 1700 | 2300 | ||||

DIFFERENCES: LITTLEPORT |
|||||||

+0035 | +0023 | +0047 | +0004 | +1.1 | +0.8 | +0.2 | +0.1 |

Question: If the time and height of high tide at Mainhaven-on-Sea is 0638 GMT and 4.2m, when and what is the high tide at Littleport?

Work out your answers on paper and, when you are ready click "Reveal the answer" to show the computed results below.

## Explanation

First of all, secondary port data is given for GMT so, if the date you are calculating for is in BST, subtract 1 hour (and remember to add it back on at the very end).

If the time lies (as likely) somewhere between the times for the standard point, you need to interpolate (eg. if the high water is at 0300, that time is halfway between 0000 and 0600 so the difference is also halfway: +0029 minutes).

The height is calculated in a similar way. If it is not an exact match (eg. 4.2 or 3.4), you need to interpolate between the values. (Note: the answer when interpolated is given to 2 decimal places for testing purposes although you would normally give it to one, the same as the question.)