Past a certain size, is surfing still a thing? Wouldn’t you be spanning more than one wave?
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Here is what the IMO says
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1.2.3 Broaching and other manoeuvring related phenomena
Ships in following and quartering seas may not be able to keep constant course despite maximum steering efforts which may lead to extreme angles of heel.
5.3.3 Special attention should be paid when a ship is sailing in following, quartering or head seas because dangerous phenomena such as parametric resonance, broaching to, reduction of stability on the wave crest, and excessive rolling may occur singularly, in sequence or simultaneously in a multiple combination, creating a threat of capsize. A ship’s speed and/or course should be altered appropriately to avoid the above-mentioned phenomena.
When the ship velocity reaches to wave velocity the ship is in surf-riding condition. Large following waves acting on the ship can force her to move with the same speed – the ship begins to move with the wave simultaneously. This is known as surf-riding. It is a one wave phenomenon and will not occur if the ship spans two waves. Small ships are more apt to surf-riding then larger ships.
Large ships (i.e. over 200 meters in length) do not surf-ride because waves of this and greater length tend to travel faster then the ship (i.e. 34 plus knots) and these ships have too much mass to allow them to accelerate to the wave speed before the wave passes. Surf-riding can occur with a following and quartering sea when the speed of the ship (in knots) exceeds a certain multiple of the square root of the ship length (in meters). Surf-riding precedes a broach.
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Had to be real careful on the high speed catamarans with a following sea.
Good fun catching the wave and zooming down the front but then you would get stuck trying to climb the back of the wave in front.
Might be 40,000hp but it isn’t going to drive you up hill very far.
When going down the steep front of a wave, which normally is not good practice, the weight of the ship will considerably increase the acceleration and the speed along with it, racing down the slope. A steep drop could cause the bow to dig in the trough and the following wave to push the stern sideways, in turn creating a broach.
In following seas, it’s best to ride on the back of a wave, moderating your speed to stay there. If you can’t maintain position, let the wave break behind you and flow under the boat. Be careful if your boat has a low transom; the following wave might overtake and swamp the boat.
It is important that you can ‘read’ the waves, you have a better chance of navigating them safely.
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It comes down to maneuverability and power ratio. The guys who tow surfers out to the monster waves behind jet skis and ride them back to the beach make it look easy because they excel in both areas. The larger the vessel, the more it is hampered by hull length and inability to match or exceed wave speeds.
8 posts were split to a new topic: 96 metre Incat
The Finnbirch is an example that also a relatively large vessel (length 156 m) can broach quite easily.
This was discussed in an earlier thread. They had no idea what they were doing and ignored the signs that a broach was imminent.
Stunning was that it became evident during the interviews that the ship’s captain was not aware of the ship’s rather special stability characteristics with larger heeling angles under certain cargo conditions nor how the stability curve of the ship should be interpreted. He was not alone among the masters of the shipping company in this respect.
The master of Finnbirch could not remember that the phenomena which can develop with following seas had been presented during his training at the ship officer’s school. According to the minutes of the maritime inquiry following the sinking, he was of the opinion that it was advantageous to proceed at full speed in a following sea and thereby pass the waves and reach a condition which corresponded with meeting a head sea. I rest my case…
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There’s heavy weather and than there’s very heavy weather.
In very heavy weather when hove-to into the weather becomes untenable Knight’s Modern Seamanship says the easiest position for a ship is usually to lie a-hull.
Knight’s goes on to describe running with the seas aft or quartering as an tactic that suitable for situations where laying a-hull does not result in the seas sufficiency aft. In other words running with seas aft is a variation of laying a-hull.
In this case the engines are run just fast enough to maintain steerage and no more.
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From the accident report:
The calculated wave speed at the time of the accident was approximately 10.5 m/s. (20.4 knots).
The 2nd officer of the Dutch cargo ship Marneborg sailing in an opposite direction plotted the Finnbirch and found it to travel at a speed of 18 to 19 knots. At a distance of four miles the Finnbirch came in sight, yawing heavily and soon after, before his eyes, the ship broached.
From the above can be seen that the wave speed and that of the ship were about the same and that they were already surf-riding, a precondition for a broach.
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I can demo this in a Boston Whaler. You have a big boat go by leaving a big wake. If you chase the waves just a tiny bit faster, at first you need to add throttle to slowly climb the first wave. Once you get over the top the boat speeds up. If you hold speed to be just a knot or two faster, you have a point where the bow is just starting to dig into the next wave and the stern is being slowly lifted. It can take some doing not to broach or dig the bow in. Ships obviously can’t do stuff like trim up, move the passengers aft, and goose the throttle and fly on up and over the wave, but it sounds like you can get that slow motion caught with the bow just digging in effect.
- running a breaking inlet with waves about 8 feet in a Whaler once, we did to good effect ride one wave and get ahead of it and hold just short of climbing the next one. When the one ahead had already broke and the one behind was about too we went full power and got out ahead of it into flat water.