by GreenLake » Mon Sep 29, 2014 10:06 pm
I believe steepness, which is height relative to wave length, is an important factor. For the same height, I would expect more problems from short, sharp waves (or longer, but breaking waves) than from wider, gently rolling ones.
I gave my experience with a ship wake on purpose. Because the speed of those things, the wavelengths are relatively long to begin with. Because of the distance, the longer wavelength part of the wake has had a chance to run away from any shorter waves, making the wave train smoother. I was in (very) deep water at the time, so no shallow-water effects. Because at its source the bow wave was 6-8 feet high (that's probably a low-ball estimate) there was substantial wave height left when it reached us. Powerboat wakes cannot compete.
My experience before that was from powerboat wakes in a confined channel, with reflections. Talk about criss-crossing waves. Not a pattern like you observed, but just random peaks rising at double the average height and troughs opening at double the average depths. The area has a speed limit, but for some boats that makes the height of the wakes worse. However, the lower speed makes the waves shorter, and therefore steeper, than when the same boats rush by on the open lake.
From that experience, where wakes slam into the hull and I regularly take small amounts of water, I had feared the worst when we first saw that ship's wake following us. When the first wave crest didn't slam into the transom, but lifted us I was beginning to be relieved, until we tipped down in the first trough, which made the second crest look even taller. I was sure that the DS would "dig in" but, as I wrote, it "just fit" into the trough and rose over the next crest as easily as over the first.
In that way this was very different also from wind-driven chop, which, for some angles, does slam into the hull (it's harder to sail backwards into chop, even if on some occasions I have surfed it on a downwind run, so slamming happens when you sail into it). And unlike chop, this did not come in direction that was related to the wind.
So, my question with respect to your swells, Talbot - did you have any issues with the waves being steep to the point that they were slamming into the boat? Or that you were actually taking water? Or were they smooth enough that you were "bobbing" over them like a cork. I think those cases may make for different strategies.
Non-breaking waves have an interior circulation that is based on a circular motion of the water (each tiny volume of water proscribes a circle as the wave passes). Because of that you get a surface current that goes with the wave when you are on the crest, and one that goes against the wave in the troughs. If you sail with the waves, steering can be affected as the wave crests under you, in some conditions, the flow over your foil might even reverse direction. (That's how really big, especially breaking waves, will broach boats). If you hit the wave at an angle, the cresting wave will set you leewards. And in the troughs, you may experience less wind.
Those are the basics and your strategies for sailing would be expected to be making use of that. So, for one, I would expect that if you tack like a skier on a mogul, you would have both the wave circulation and the (extra) wind to contend with. Whether that helps or hurt you would appear depend on what angle to the swells you were sailing. (Having to deal with multiple crossing wave trains is no fun). I think that crossing the bar was the most gutsy move you made...
A boat like the DS behaves differently from a keel boat in one important aspect. On a keelboat, especially a more traditional hull with narrow beam, you would expect that boat to stay closer to the vertical, because the pendulum effect of the keel counteracts the effect of the "tilted" water. On a DS, with no ballast and wide beam, you would expect the boat to tilt immediately to conform to the wave surface (if you sail more or less parallel to the crests).
~ green ~ lake ~ ~