Steaming Past
Despite the fact the age of steam is long past, it is still common to speak of ships "steaming past". In the same way we refer to an earlier era when we say we are going "sailing" on a ship.
The motion blur on this photograph actually allows us to make a calculation of the speed of the "Spirit of Tasmania I" as it moves past us in the Mersey River. To clarify what I said yesterday, it is important to get everything else in sharp relief so that the only blur we see is the movement of the ship. So I've done some calculations.
The "Spirit of Tasmania I" is 194.33m long (637ft 7in). It is possible to see a single light that appears as a bar representing the distance travelled in the time of exposure. That's the simple formula. The one obvious example is the green light on the top starboard deck. [In the next photograph you will see that this is indeed a single point of green light.] My rough estimate is that this bar represents about 6m. Now given the exposure time here is 0.6 of a second, that equates to 10m per second or 36km/h (19.4 knots). From the river bank it looks even faster, but that speed sounds about right, as the ship slows to make its way into the narrow channel.
Steaming Past
Despite the fact the age of steam is long past, it is still common to speak of ships "steaming past". In the same way we refer to an earlier era when we say we are going "sailing" on a ship.
The motion blur on this photograph actually allows us to make a calculation of the speed of the "Spirit of Tasmania I" as it moves past us in the Mersey River. To clarify what I said yesterday, it is important to get everything else in sharp relief so that the only blur we see is the movement of the ship. So I've done some calculations.
The "Spirit of Tasmania I" is 194.33m long (637ft 7in). It is possible to see a single light that appears as a bar representing the distance travelled in the time of exposure. That's the simple formula. The one obvious example is the green light on the top starboard deck. [In the next photograph you will see that this is indeed a single point of green light.] My rough estimate is that this bar represents about 6m. Now given the exposure time here is 0.6 of a second, that equates to 10m per second or 36km/h (19.4 knots). From the river bank it looks even faster, but that speed sounds about right, as the ship slows to make its way into the narrow channel.