David,
I ran some quick numbers to see if 20 miles at 6kts is reasonable from that battery bank.
214Ah @ 72V = 15.4kWh
80% depth of discharge = 12.3kWh usable
Using a Peukerts exponent of 1.15 for AGM to compensate for high amp draws, I backed into the constant load that would let the batteries last 3.3 hours (6kts x 3.3 hrs = 20nm)
The 3.3 hours rate to 80% depth of discharge is 42A @ 72V or 3024W. So the question becomes whether or not the Hunter 27e can cruise at 6kts while only using 3kW (4hp) of power. Given the observed data from similar boats, that might be optimistic. A Catalina 30 (longer waterline) conversion that is pretty well documented uses 3.2kW (4.2hp) to hit 5kts and 6 kts takes about 6kW (8hp).
So lets slow it down, just a little. The 4 hour rate (5kts x 4 hrs = 20nm) for this battery pack to 80% DoD is 36A @ 72V or 2592W. That looks like were getting closer with 2.6kW (3.4hp) to run at 5kts.
One step down, lets look at 4.5kts. The 4.45 hour rate (4.5kts x 4.45 hrs = 20nm) to 80% DoD is 32.5A @ 72V or 2340W. Now we're looking at 2.3kW (3.1hp) to drive the boat at 4.5kts and that rate sounds a lot like the numbers that various owners have reported in this group.
So I would believe 20nm @ 4.5kts from specific info that you posted from Hunter. That is very good performance from an electric conversion of this size.
If we use the rule of thumb that doubling the power will increase boat speed by 1.5kts, then 6 kts will take 4.7kW (6.2hp) and the batteries will be 80% discharged in 2 hours or 12nm. Again, this sounds a little optimistic to me, but somewhat believable). Hull speed on this boat works out to be between 6 and 6.5kts.
Of course, these are all estimates based on experience collected here and with other electric conversions. Hunter's results may vary, the only effective way to find out is to put one of their 27e's through its paces. Let's hope that someone here buys one and gives a detailed performance and efficiency report.
Fair winds,
Eric
Marina del Rey, CA
I personally haven't found quick reviews in the glossy sail magazines to be the most technically reliable sources. This might be one of those marketing things, saying the boat can hit 6kts and has a range of 20nm doesn't necessarily mean that it can go 20nm at 6kts. :)
--- In electricboats@yahoogroups.com, David Goldsmith <suntreader@...> wrote:
>
> I don't have any more info than is available from Hunter or from a brief
> article in Sail:
>
> http://sailmagazine.com/boat-reviews/best-boats/hunter_27e/
>
> I know I gave that last boat a hard time, so let me make it up by saying
> this is a pretty sweet little set up. Elco is a very good name in electric
> boats, I'd love to have their systems and expertise designing my set up. The
> batteries are six 210amp/hr AGMs (4d?), which is a good compromise on cost
> and easy of maintenance. This is just the right sized boat to have a system
> like this, small enough that the motor and battery requirements are
> reasonable, but big enough it can handle the weight and room. Their claimed
> 20 miles at 6 knots sounds reasonable and not like an 'ideal conditions at 2
> knots' type of situation....
>
>
> Very cool, thumbs up!
>
> David
>
No comments:
Post a Comment