Dropping from 5kts to 4kts halves the power demand. With sun overhead 2kW of panels will push you at 4kts without battery drain in no wind without burning diesel.
You would target a minimum speed of say 4kts. Motor sailing up to about 6kts then lift the drives and sail at speeds over 6kts.
In my experience calm overcast days are rare although there are some locations where fog will last for most of the morning. Those days usually have calm sunny afternoons.
A large solar array can lift average speed significantly over an extended range. The energy is delivered to the boat in the same many as wind. Any fuel carried will tend to be kept as reserve for extended cruising.
On 20/03/2015, at 8:32 AM, "mateo002@yahoo.ca [harryproa]" <harryproa@yahoogroups.com.au> wrote:
>Well let's run the numbers
Ok i prefer to keep it metric... so if 4kW makes 5kts, a 12 hour day electro-motoring will consume 48kWh. If we had sunshine that day perhaps we could capture 12kWH with 2kW of panels, so the remaining 36kWh could be recharged with less then 2 hours of 20kW genset run time.
At 300g / kWh we'd use 10.8kg or about 13 litres of diesel. So about 3 gallons to cover 60 nautical miles in 12 hours.
But to me the real value is measured in 10 hours of silence vs 12 hours of noise.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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