This was the last full day of our crossing and un-expectedly we came under the influence of some bad weather all the way to the North. A rather heavy system with lots of wind is moving towards the United Kingdom and that pushed a minor system, near the Gulf of Biscay, a bit further down. As a result the wave field generated by that minor system made it all the way down to our area and thus we had a Prinsendam that moved a little bit more than in the past few days. Still for an ocean crossing, not much movement at all. Later in the day the sun even came out and that was not predicted either.
I have been writing about waves and wave fields during this crossing. So the question should be answered what is a wave is and how do we measure it. On the bridge, for our observations, we eye ball it. A junior navigator has a sample book available with photos that indicate wave heights and that can be used to compare with what is out there. With a little bit of help from a senior officer it is then fairly quickly becoming routine to observe correctly what the wave heights are. Satellites can do the same nowadays with infra red beams which are extremely accurate in measuring the exact height. So are experienced sailors and we do it by just looking out of the window. The height of a wave is measured from its lowest point, the trough, to it highest point, the crest.
Now waves are never the same height. The wind blowing over them changes the height, another wave pattern might interfere and cancel much of the achieved height out etc. etc. Thus for measuring the average wave height we use the significant wave height. That is also the wave height indicated on the chart I attached a few days ago. The definition of the Significant Wave Height: is the average height (trough to crest) of the one-third highest waves valid for the indicated 12 hour period. This means that you can come across waves of double the height, or a nearly smooth patch of sea, where two waves have cancelled each other out. However for the prediction of what the ship will encounter in the near future, the significant wave height on the wave chart suffices.
With the movement of a frontal system, also the wave field (which is basically an area of the same significant waves) can change and thus what is predicted does not happen. Two days ago it looked like it that the bad weather would move directly to the North East of England/Scotland. However it just came a touch more to the south and the waves on our course track changed.
Thus I expect now that during the coming night and next morning, we will see longer and higher waves than this morning. If that will make the ship move more, will depend on how long these waves are, as every ship reacts differently to a certain wave pattern. All depends on draft, width of ship, height of ship, length etc. etc.
For me this is important to know for tomorrow; whether I need to keep the stabilizers going while entering the Rio Tejo to Lisbon harbour. Here long rolling waves can create a ground swell and roll over the shallows and make the ship move even when we are already on the river and nearly under the bridge.
I expect to be nicely on time tomorrow in Lisbon and as it is predicted that the sun will shine, it should be a beautiful arrival.
Leave a Reply
Captain Albert
© 2024 – Captain Albert's Website and Blog –
Theme by Anders Noren — Up ↑
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 9, 2009 at 2:37 pm
Hi Captain — just a question of curiousity —- what, in your career, has been the worst wave field you have encountered, how high, how long a period and where. I understand that transiting the Gulf Stream from the East Coast to Bermuda can be very interesting.
Thanks
May 13, 2009 at 6:30 am
25 meters or 75 feet. The water came over the bridge of the old Rotterdam during a crossing.