Hi
Anyone on the list have power/speed comparison figures for sailing
catamarans in the 8 to 10m (28 to 35 ft) range. Displacement around 4000 to
6000lbs (2 to 3 metric tons).
-----Original Message-----
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
On Behalf Of Eric
Sent: Wednesday, 3 August 2011 6:05 a.m.
To: electricboats@yahoogroups.com
Subject: [Electric Boats] Re: converting big boats
Hi Pitt,
No worries. If you don't have good consistent data, then posting your
results can cause more confusion than just a subjective "I love it!".
Unfortunately, subjective opinions may not be as useful to someone new that
is considering a conversion. What I consider to be a huge success may be a
bitter disappointment to someone else. Someone posted about a magazine
article a few months ago where the owners of a converted cruising boat that
was converting back to diesel after a few years of going electric. If I
understand correctly, they used the same purchased drive system as many
satisfied electric boaters on this group, and yet they were obviously
unimpressed enough to justify going through another conversion and to write
an article for a mainstream publication. I think that the conversation
focused around the fact that the regen capabilities of their boat did not
meet their expectations. But I believe that what they got was all they
should have expected, it may have been their vendor that mistakenly set
their expectations too high. As you've seen, my position is that regen is
usually "oversold", and the real numbers don't live up to the vague "you'll
be generating electricity everywhere you sail" that you see in some
promotional materials.
I do want to thank the people that have taken the time to measure their
performance and post their results. When I was first considering my
electric conversion, back in 2009, there wasn't much objective data
available concerning electric conversions. The best estimates for a 30'
sailboat that I could come up with were 1500W for 3 kts and 4000W for 5 kts.
Since then, my conversion has delivered 500W for 3kts, 1100W for 4kts and
2500W for 5kts. Almost all of the data published in this group by other
29'-30' conversions have been within 10-15% of those numbers. So now we
know what to expect from my size boat and the more data that we can collect
from different size conversions, the better that we can set the expectations
of people that are thinking about taking the plunge.
Since I've become a local proponent for electric drive, I've had a number of
people with bigger boats (40'-50'+) discuss converting to electric too.
Since I don't have access to much real world data for large electric boats,
it's difficult to quantify what kind of tradeoffs that they should expect.
Most of these boats displace between 30,000 and 40,000 lbs so they have
power requirements that are much greater than my little 5 ton ketch. I can
fall back to my EV roots and spec out a much more powerful system than what
is typically available from our regular electric boating vendors, but
without realistic performance targets, I can't recommend that someone to
commit their money and their boat to this size experiment. But the bottom
line is that any boat can be converted to electric, it's just a matter of
putting together a drive system that is well matched to the boat's demand.
Quantified demand is the missing link right now.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, Pitt Bolinate <boombolinate@...>
wrote:
>
> Hi Eric ,
> Don't take offense, I did do trials write up numbers one day with just the
motor and no sails. There was somewhere near 1.7 kts of current that day and
that's water current. The numbers are all over the place and there fore not
accurate or relevant. Perhaps when I am next on flat still water I will do
the numbers but till then you will have to accept my WoW factor as being a
valid expression. I diddn't want to sound like I have the biggest or best,
just observing that it's bigger than average on this site, but not bigger
than many boats on my finger at the marina. Perhaps it's about the size that
the average person might think twice about converting?
>
> Pitt
>
> Sent from my iPad
>
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