The Windsurf Loop: Gusty Pleasure Bay

Sunday, February 26, 2012

Gusty Pleasure Bay

Yesterday, we sailed for the first time in Pleasure Bay in South Boston. It was a rather interesting day. For the second time in two months, I rigged my 5.8 KA Koncept while winds were around 30 mph, only to be greeted by 58 mph gusts as soon as I hit the water. 58 mph is a 10 on the Beaufort scale, described as "storm" or "whole gale". There's no chance that I could control a 5.8 m sail in that much wind!

A big part of the problem was that the wind was westerly, coming from the land across South Boston. That made it very gusty - within a few minutes, both Nina and I experienced being totally underpowered and totally overpowered. Here's a wind graph:

I think the wind sensor is at a pretty exposed location. Were we started, we definitely had some wind shadow from nearly buildings, and the lulls were definitely lower than the 20 mph the graph shows for 12 pm. But I'm pretty sure we got the full force of the gusts - at some point, I had a hard time even walking upwind, with the board getting blown out of the (rather flat) water several times.

After derigging my 5.8, I went for a run on Nina's 3.7. I was nicely powered on the way out, but had to schlog the entire way back - not exactly my idea of fun when air and water temperatures are just above 40 F (6 C). I saw quite a few other good windsurfers have problems, too. Scott was totally overpowered on a 4.7, and Martin ended up falling in several jibes - something I had rarely seen him do before. But shortly before we left, Gary went out and seemed to be doing fine; so did Jay, who went out again, after a very short initial set of runs.

What I saw did not really make sense to me - good windsurfers sailing without problems, while better sailors like Martin had a hard time. So I went and looked a bit more closely at the wind data. The graph below shows how gusty is was while we were there (measured as the increase in wind strength in the strongest gust, relative to the lowest lull, in a 30-minute period):

Nina and I sailed between 12 and 1 pm. During that time, the wind speed in gusts increased by about 200%. I am reasonably efficient, and not too bad at holding an overpowered sail; for example, I can stay planing on my favorite 7.0 in 17 mph winds, and keep it in control until about 35 mph. That a 2-fold range, or a 100% increase in wind speed in the gusts. With the actual increases of up to 250%, no sail would have worked...

Martin sailed until at least 1:30, during the time of the lowest lulls (15 mph) and the strongest gusts (58.5 mph). No surprise he had a few problems! By the time Gary went out, the wind had become a bit steadier - one could say it was only half as gusty as a bit earlier. I guess we just went out too early once again.

For comparison, the graph above includes the data for Point Judith in Rhode Island. Point Judith has a much better fetch in WSW-W winds, so the wind is a lot steadier. With increases mostly below 100%, planing the entire time with a single sail would have been possible. The only issue is that the averages were above 40 mph most of the time. We have sailed in 40+ mph gusts a number of times, but never in 40 mph averages. If it had been a bit warmer, we might have given it a try... perhaps we should have, anyway, since we still got the gusts in the high 50s, and the lower averages only made things harder.