Well, there you go!

I've read that some ships are built specially to stay in the St. Lawrence Seaway. They are called lakers and they sail in this fresh waer system which stretches all the way from the East Coast of Canada, to the Port of Thunder Bay at the top of Lake Superior. These Lakers are shaped differently from the Salties which also sail the oceans.

What we have to look at is the front or bow of the ship. It provides some clues. Lakers have verticle bows, while ocean going ships have angled bows. Some of these have a big bulb or or sphere just at or below the water level.

Another clue is the position of the wheel house : on most of the lakers it is located at the front of the ship. Profiles of two ships shown below may help us to identify any ship we see.

If we see a ship up close, we can look for special markings and other interesting features.

First, I look to see if the ship is flying a flag of a country. Then, I look or its name, which is painted on the front (bow) and the back (stern).

I look for clues to see if the ship is carrying a cargo. There are two clues. The first one is a depth indicator on the bow at water level.

How does the depth of the ship below water tell me whether it is carrying a cargo or is empty?

Remember the places along the highways where trucks must stop to be weighed? They are weighted because each truc is built to carry a maximum load - it can be dangerous if they exceed that load. It's the same for ships : each is also built to safely carry a maximum load; but they can't drove off and be weighed. However, as a ships takes on more and more cargo it sinks deeper and deeper into the water. When we get back home I must show you how a floating cup slowly sinks as stones are placed into it.

Where is the second clue?

It is midship (halfway across the length of the ship) and close to the water. We'll find one of two types of markings, one for ocean-going ships and the other for lakers. They look something like this.

I wonder why they have different levels for summer and winter? Also, why are there different levels for fresh and sea water?

It's just a matter of density. A cup will float deeper in water than in syrup or honey, which are both denser than water. We'll be able to continue our previous wxperiment by marking how deep the cup floats in the water. The cup should float higher in the salt water. So the salt water mark is lower than the fresh water mark. Think about it.