Ernest needs to get to grips with neap and spring tides, as well as high and low water. But with so much information of charts still swirling around in his head, will he have room to digest all there is to know about tides?
“Are we going to sail now?” asked Ernest.
“Look over the side. What do you see?” asked Ahab.
“And that is never the right thing you want to see before you set sail. It means the tide is out and we have to wait until the tide comes back in. But it gives us chance to talk more about tides,” continued Ahab, stirring the sugar into his tea.
“Can’t imagine there is much more to know, is there? The tide goes out and the water comes back in.” But Ernest was wrong, there was a little more to know yet.
“How much water do we need under this boat to make her float?”
“Well, you need to know because that gives you an idea if it is safe to move your boat or not. Vessels have different drafts. This is the distance from the waterline of your boat and the bottom of the keel and just to make it a little more complicated, it includes the thickness of the hull too,” chuckled Ahab. “This boat’s draft is just under 1 metre or around 3 feet, and so that means we need at least this amount of water under the boat to lift us off the bottom. This is why when you know the water is shallow or the tide is running out fast that you keep an eye on the depth finder.”
“But anyway, I digress. Back to tides. So, we know the water comes in and goes out. But about the depth and shallowness of these tides? What about neap and spring tides? What do they mean for us sailors?” asked Ahab.
“Yes, you are right. The moon, the celestial planet responsible for tide changes also affects how big or how small the tides are. Isn’t it amazing Ernest?!” Ernest wasn’t quite sure, mainly because he thought his head would explode with so much information being pushed into it.
“Right, let me explain: a spring tide happens when the moon and the sun are aligned. It tends to happen just after a new moon or a full moon. Don’t forget the sun has a part to play in tides too and so think about two bulges of water, one caused by the moon, the other by the sun. When a spring tide happens, these two bulges of water meet, so to speak, and so what do you think happens, Ernest?”
“There’s a lot of water in one place if two ponds of water meet!”
“Yes, excellent, that’s right. A spring tide leads to high and fast water too in some places, local knowledge that a sailor needs which is why talking to fellow sailors is always worthwhile. But what about a neap tide then?”
“I think a neap tide would be opposite, “said Ernest.
“And you would be right. Because of where the moon and the sun are in relation to each other, the two bulges are quite far apart and they cancel each other out. But, it can get a bit more complicated than that…” At hearing this, poor Ernest rolled his eyes. “But it’s OK, “continued Ahab, “I have a website thing for you to tap-tap into that phone thing of yours. Take a look at the website for the National Tidal and Sea Level Facility to find out all about tides.
“We’ll talk more, as there are a few more things I want you to know…”