In a way, our steam ship is very similar to many smaller boats you see every day. On ships as big as ours and even bigger the concept stays the same. Some ships are powered by giant diesel engines and others by gas turbines. Whether they are powered by steam, diesel or gas, each ship has a propeller connected to a shaft leading to the main engine. All propellers range in size and number of blades, but the angle of the blade relative to the shaft determines how far the propeller turns in one revolution. This revolution is what propels the ship forward through the water. The amount of revolutions per minute determines how fast the ship will move. For example, at full speed our shaft turns at 90 RPMs which results in about 19 knots.
There is no gas pedal on the ship for the bridge to use to speed up or slow down. Instead, there is a telegraph machine in which those on the bridge can send a message to the engineers requesting certain speeds. This machine is called the Engine Order Telegraph (E.O.T). Our speed changes every day based upon the sea state, weather and times we need to arrive. When we left Vera Cruz for Mayaguez, Puerto Rico, we moved at a cruising speed of around 16 knots for basically the whole way.
Looking ahead: We are not too far from Barbados now, and we can feel fun times coming our way. It won't be long until we are enjoying the white sandy beaches and tropical culture that Barbados is known for.
Questions:
1) What are the two main types of propellers?
2) Why are more modern ships using diesel engines instead of steam?
3) If our ship turns 15 rpm's for 24 hours how many rotations has the shaft made?
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