knockdown, how did it happen?
30 October 2011
I mentioned in an earlier blog entry I would elaborate a little more on the knockdown we had on October 20st, while in a force 8 (35 knots wind, gusting 40) gale between Mississippi outlet and Florida South coast. A knockdown is nothing more than a breaking wave action that hits the boat on the side (abeam) and is of such size that it pushes the boat on its side. Larger breaking waves can push boats over. Knockdowns are not normal and should always be prevented. However knock downs are an inherent risk of many significant storms so any boat should be able to handle a knock down. Our boat is fully capable of handling a knockdown and not any moment we felt insecure or concerned. Why did it happen? Long story short because we kept up to much sail for the sea condition. So this could have been prevented very well. We looked regularly at the measured wind speed (measured at top of mast), which was steady in the 34 to 38 range, which was slightly higher than forecasted (30 knots) but of no concern to us. We have sailed before in 34 knots winds and that time the boat did very well with a triple reefed mainsail and the staysail set and the winds from behind on a corner with the stern (this is typically a direction you had planned to go anyway). As she did so well under triple reefed main that time, we felt she was ok now with similar strength winds. The seas however were much different this time. They were steep and irregular. A short steep swell from the direction of the wind and more importantly regularly breakers appeared from under a 45 angle with the wind. First small ones, perhaps a few feet in length steadily increasing to a larger length of perhaps 10 to 12 feet at length. I had noticed these breakers early on to the point I had told myself and my father to be tethered on at all times while outside sitting in the cockpit. I am aware of the fact that in case of knockdown it is easy to be thrown outside the cockpit straight over the side.
As they came in under a 45 degree angle with the ship, they did not pose too much of a threat really. However very occasionally when the wind was gusting to 38+ winds, the boat would have a tendency to turn up into the wind. This had happened two or three times already in the past 16 hours. This is a clear sign you are over canvassed and should have alerted us to lower the triple reefed main and perhaps continue on the stay sail only or raise the double reefed mizzen sail instead of the main. Instead we continued and 12 hours further in the night (those things always happen at night...) a wind gust turned the boat towards the wind, bring the seas abeam. Just at that time a breaker of sufficient length hit us on the side and pushed us over on one side. This happened very fast, and immediately she right ended herself. I was sleeping in the main cabin at the time and as I felt her going over I quickly realized what was happening and made a move to get out of my bunk. I had to dug for a heavy binocular which came flying from port to the starboard side and hit the bulkhead a foot above my head. When I checked on my father, who was outside in the small cockpit at the time, I found him happy as a wet cat in his bad weather gear. As the Starboard rail came under water, a dorade air scoop on the starboard outer side scooped up a large quantity of seawater. We have blinds for every dorade, but naturally they were still in the drawer. You can say it is easy to place them early however you also want to keep fresh air coming into the boat, also in bad weather where you have to close the hatches as the living environment quickly detoriates without fresh air. In order the remain in good condition which allows you to make the right decisions the importance of good living conditions inside the boat while in a gale cannot be underestimated, as is the necessity to continue eating. In our situation inside the main cabin it was a relative oasis of rest during the gale. Allowing the get a proper rest. As there was still oil and gas activities (deepwater platforms) around and shipping related to that, we maintained a look out outside during the gale. We changed our normal 6 hours shifts to 3 hours shifts in order to make it bearable sitting outside in the small cockpit.
It was a good lesson and now I will pay more attention to the sea state versus the actual wind speed. Again a normal non-breaking wave cannot push a ship over. This has been proven in several wind marine test centers. There is some good literature available (Heavy Weather Sailing, Adlard Coles is a good example). Breaking seas however can push a small boat over, on its side or even completely upside down. Marine test centers with wave basin have shown in controlled tests that any breaking wave with a length larger than the largest width of the boat (in our case 4 meters (16ft) does have the energy to push a boat over when hit abeam and hit the boat with the full length of the breaking wave. So there are quite some conditions that need to exist in order to have the situation that allows a knockdown, however you cannot gamble you will never encounter all these condition to come together. It is my opinion that your boat must be fully prepared to handle that situation if it occurs, if you decide to sail offshore.
I am still trying to figure out why those breakers occurred in the Gulf, and we have the idea they were caused by winds and current working against each other causing these breakers at 45 degree angle to the main high steep swell. All in all a good learning experience and a good prove the boat is well set up to handle these events. Inside there was hardly anything not fixated properly. The binocular that went flying was not stored in his right place (by me, oops) plus several items located in the galley, only stored on a rubbery mat went flying. The laptop I use for communication via the sat phone was located on the chart table on Portside, on a rubbery mat and went flying, ending up in the dishes in the galley on the Starboard side, together with other loose items from the chart table such as camera, (died in the ordeal). The rest remained solid in its place, including the batteries, items often overlooked and in our case stored under a heavy wooden bar on our boat. I will certainly keep a better eye at the sea state going forward and not so much on the actual wind speed. Enjoy the movie.
02 September 2011
While travelling, Heloisa wants me to make some videos of our live on board. Not the actual sailing or the actual places we will visit, but really about the life on board. Doing the laundry on a boat, sleeping while under way, preparing meals at sea and at anchor and so on. So we have bought this little camera and I am doing this self-learning crash course in making movies. I already struggle with shooting a still picture so making a movie will most likely be an "interesting" experience.
I went out to sail a few hours yesterday afternoon, as I had made some changes to the running rigging (lines that control the sails) that I wanted to test. The weather was calm so I decided to shoot some movie minutes at the same time. In the evening I played around editing those movie minutes. Well that was an interesting experience and I became quickly aware that shooting a movie is not easy. I am fairly convinced that even with those good cameras nowadays available and free editing software available, there will always be a market for professional movie makers. They certainly will not have me as competition I found out yesterday.
I am sure by the time we have sailed around the globe in two years, I perhaps have it down to a science this movie making stuff...
(ps, right in the begin on the left behind the boat you see a dolphin jumping. Dolphins were around the whole afternoon, till they saw the camera, that's typical.)