You Asked: How close to the wind can a conventional sailboat sail? Is there a theoretical limit to the angle to the TRUE wind that a boat can achieve (including lateral drift)? I was taught (many years ago) that the limit is 45%. Is this considered correct today?
Good question. I don’t think there’s a fundamental limit that is the result of some physical law. I think the 45 degree rule is about **efficiency** – if you sail any closer than this, then you’re not taking maximum advantage of the wind. But in our little home sailboat, I think you can get closer than 45 degrees – albeit with a lot of loss. In particular, you notice at smaller angles that the sail flops back and forth close to the mast – what sailors call ‘luffing’.
Dr. Kenneth Ragan
Professor of Physics at McGill University