The National Weather Service generates marine weather forecasts, including wind and wave conditions. And this data is available everywhere. On the weather radio, on the Internet, even on smartphone apps. Before heading out sailing, I always check the marine forecast. But I have no idea why.
The marine weather forecast actually "predicts" several days out, but these predictions, like most weather forecasts in the Pacific Northwest are so notoriously inaccurate that I am going to skip over complaining about these. No, it the the "day of" predictions that I take issue with. To start to understand the issue, let's take a look at an example of what the forecast actually looks like:
TODAY...S WIND 5 TO 15 KT...BECOMING NW IN THE AFTERNOON. WIND WAVES 2 FT OR LESS. A CHANCE OF SHOWERS.
TONIGHT...N WIND TO 10 KT. WIND WAVES 1 FT OR LESS.
You may think that the question here is one of accuracy, and indeed, I have been out on "WIND 5 TO 15 KT" days, and has it be dead calm. Yet, this isn't the real issue. The real issue is, even if this is accurate, how does it help me?
You don't have to have spent much time sailing to know that there is a huge difference between a 5 knot wind and a 15 knot wind. In fact, it is worse than it looks, because the force the wind exerts on the sails isn't proportional to the wind speed, but rather the wind speed squared. So, at 15 kts, the wind is exerting 9 times the force on the sails that it was at 5 kts! As a side note, the force on the sail is directly proportional to sail area. So, to maintain the same force on the sails, if the wind speed triples, you'd have to reduce sail area to 1/9th of what it was.
For Solitude III, 5 knots of wind means trimming out the sails, leaning back, lounging in the cockpit, sipping iced coffee, as the boat calmly glides over the water. On the other hand, 15 kts means you'd better have a reef in, crew aboard, and desire to thrash about in exciting conditions. I'll go sailing in 5 kts of wind all day, any day. But, honestly, though sailing Solitude in 15kts of wind is a lot of fun, seldom do I want to go out in those conditions singlehanded! So, how does telling me that the wind will be 5 to 15 kts help me?
Likewise, what does WIND WAVES 2FT OR LESS mean? Wind waves of 2 ft make for a pretty bumpy ride on a boat like Solitude. But, according to the forecast, the wave may be less that 2 ft...they may be 1 ft waves, or the sea may be glassy calm. Aside from assuring me that (assuming an accurate forecast) conditions won't be so rough that I'll be risking life and limb if I go out, I again must ask, how does this help me?
I could continue. What exactly do you mean by "AFTERNOON" or "TONIGHT?" "A CHANCE OF SHOWERS." How big of a chance? Give me something, anything.