Dutchmans

Timing how long a piece of wood or scrap of paper takes to travel from bow to stern to find speed through the water works well in gentle weather but, as winds and seas increase, it becomes nonsensical.

If the chip travels 9 metres (30 feet) in five seconds then you are travelling at 2 metres (6 feet) per second (see Figure 11.2). Multiply this by 0.592. If you have no

calculator call it 0.6 and you have a speed of 3.6 knots. For those using a 10-metre distance, 2 metres per second becomes 3.9 knots when multiplied by 1.944.

You can skip the maths. If you are travelling at one knot you cover 0.5 metres (1.6878 feet) per second. Put marks along the toe rail at intervals of 1.7 feet and divide the number of marks the chip passes by the time it takes to pass them. You then

11.2 Speed, Time, Distance Triangle

have your speed in knots. If your log passes nine marks in 2 seconds then you are making 4.5 knots.

If you choose a Dutchman's log it is best to:

1. Mark bow and stern to give a known accurately measured distance.

2. Have someone standing in the bows to throw the chip into the water ahead of the mark and shout, 'Now' when the chip passes the mark at the bow.

3. Have another crew member by the stern mark who starts timing on the cry of 'Now' and stops when the chip passes the stern mark.

0 0

Post a comment