Air drag and turbulence of a wind generator

[jfoster]

Have any of you compared boat speed a)with the wind generator blades locked, b) free wheeling and c) spinning under load?

My guess is that the effects are more serious on the smaller boats.

Is there any published information on the effects of air drag and wind turbulence on boats in a downwind race such as the SHTP?

 

[tiger beetle]

Have any of you compared boat speed a)with the wind generator blades locked, b) free wheeling and c) spinning under load?

My guess is that the effects are more serious on the smaller boats.

Is there any published information on the effects of air drag and wind turbulence on boats in a downwind race such as the SHTP?

The only data point I have to contribute is that the AirX wind generator produces 80 pounds of horizontal load when spinning in 100 knot winds. Hopefully no one will be sailinging in that kind of breeze.

- rob/beetle

 

[Alchera]

Have any of you compared boat speed a)with the wind generator blades locked, b) free wheeling and c) spinning under load?

My guess is that the effects are more serious on the smaller boats.

Is there any published information on the effects of air drag and wind turbulence on boats in a downwind race such as the SHTP?

Downwind it's not going to be a problem, since since the drag is helping to push you along. But in most any winds under 20 knots, I've found that downwind it's not much use since once you subtract the boat speed you don't have much apparent wind left to generate much power. Last STP I left the wind generator at home to save the weight. Perhaps Tiger Beetle can say more about how much power he was able to generate on the downhill stretch.

- Mark

 

[tiger beetle]

Perhaps Tiger Beetle can say more about how much power he was able to generate on the downhill stretch.
- Mark

Hi Mark -

Short answer - very few amps from the Airx wind generator once we cleared the High and got into the run. The Airx needs about 12 knots of wind apparent to produce 2 amps. Beyond 12 knots it will produce prodigous amounts of power, most I've seen is 25 amps coming in through the battery monitor.

Longer answer - the wind generator forms an interesting symbiotic relationship with the autopilot: when it's blowing hard and the autopilot is working hard and the wind generator is also whizzing around producing more than enough power to pay for the electricity used by the pilot. When the wind goes light the pilot isn't working as hard, uses fewer electrons, and the wind generator ceases to produce.

In the 2004 race we spent the first 3 days close reaching in gale conditions and I didn't have to do anything on the boat as regards power 'cause the Airx was kicking out power like nobody's business. When we hit the ridge 500 miles down the course the generator stopped and didn't do anything useful again until anchored in Hanalei Bay. In 2006 we didn't have the gale conditions, and on occasion (squally nights) the generator would kick in for a while and help out with putting some juice back in to the battery bank - but not a heck of a lot.

For battery charging I think it is most useful for the skipper to wire up the boat to play to its strengths. If you have an inboard engine, put a hi-output alternator on it. If you don't have a motor and are small, go with solar. If you have the time and want to spend the money, go for all three: engine-driven alternator, solar, and wind power.

- rob