Saturday, 3 July 2010

Not going to St John

It's official, I am the queen of procrastination! When I have work to do I will do laundry, hoover, cook large and time consuming meals, clean the bathroom, re-do the silicone seal around the bath, buy stuff I shouldn't on the internet, blog, edit the photos I've been meaning to get around to editing for two years.... anything but the thing in hand! And so, in that spirit....

Before we didn't go to St John, we went to Halifax, my nav work book starts to get a little more technical here, with tide print outs and lists of instructions on the use and set up of radar and echo sounders and steering and propulsion tests; I was getting a bit more comfortable in my surroundings on the bridge by then. I got ashore in Halifax too, we didn't go far, just down the wooden boardwalk to the first decent looking restaurant we saw, where I recall eating a very good lobster sandwich.

Next day we were due to go to St John, which we had actually been to before as a 3 day cruise from New York, but I failed to mention it when I was writing about early September (my excuse is that my brain was fried at the time of writing, having only recently got home. It wasn't a big event anyway; I did get ashore, but only as far as the nearest restaurant where I devoured as much lobster as I could!) Anyway, I was rather looking forward to getting to see a bit more of it, as we were due to spend a longer time than normal there, due to the tides and depth of water at the entrance to the harbour.

The weather wasn't good, and there had been much discussion on the bridge over the days preceding as to whether we would be able to make it in, but the final decision was only made when we were a few miles off the pilot station. We would have been able to get in, but the forecast for when we were due to be leaving was simply too bad and it would have been too dangerous to try it, which left us with the chance of getting in but not getting out and thereby screwing up a lot of people's holidays by making them late back to NYC, or not going in. That's it in a nutshell, but for the more technically minded I thought I'd put in what I wrote in my nav workbook here, I'm afraid you'll have to do without the charts and diagrams that should accompany it, but I hope it's vaguely interesting (If it's not, just skip to where the italics end!)

The ship was due to call into the port of St John today, arriving on the flood at high tide and departing on the flood of the next hight tide. The ship is only able to get into St John at high tide and has a very narrow window of opportunity to get up and down the channel. The port authority will only allow ships to enter or leave between 2hrs before High water and 2hrs after high water, and they must have at least 5meters clearance over the bank at the entrance. Chart datum at the bar is 8.8m, QM2 has a draft of 10.3m and also has to take squat into account. Squat occurs in shallow waters when a ship is travelling at speed, water is displaced more than normal and so the depth of water is reduced (though the ship's draft stays the same). For the channel at St John squat is estimated at 1.5m, the ship therefore has a clearance of 0mover the bar at datum [datum being the height of water the lowest astronomical tide] and so needs a Height of Tide of at least 5m to be allowed into the harbour.

Looking at the tidal graph for St John that day it was apparent that the ship could make it from the pilot station to the berth by slack water (when the tide turns) but there was not much margin for error or contingency, even without the bad weather that was developing. The forecast for our due time of departure showed a large depression right over St John, bringing winds of 35-40kts. As a depression passes over, the cold front comes first, as this happens the wind tends to alter direction suddenly, first veering slightly and then backing dramatically. If this was to happen when the ship was in the narrow channel the ship could be pushed off course and grounded very easily.

The forecast showed that this bad weather would be likely to happen when the ship was leaving the port, so while we would have been able to get in to St John, we could have been stuck there for much longer than the itinerary allowed and therefore all the passengers who had to catch flights from New York would have missed them, so the Commodore took the decision not to to in. It was not a lighthearted decision, and was only taken at the last moment, when the most up-to-date information was at hand and much advice from shoreside support had been listened to. At the end of the day, it's the master's responsibility to keep the ship safe first, and being on schedule comes after, and we could not have done both.

To fill the time we should have spent in St John, we took a slow scenic cruise down the Grand Manan Channel, heading for New York. However, it wasn't quite as simple as that and the navigator had to work out some extra legs for the ship to sail so that she could go fast enough to be able to keep the water making plant working. The ship uses approximately 1000 tonnes of water a day, and there's no way she could store that much! She has three evaporators, which, when making a speed of 26kts can produce 1500 tonnes of water a day. To be able to run one evaporator the ship needs to be going at a minimum of 13kts so the navigator had to extend our passage to enable the ship to travel at that speed and not reach New York too early.

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