Hi, Josh,
One of the snags of the written word is that the mood of face to face
conversation is missing. This can lead to assumptions.
We are actually in both agreement to some degree at least.
As the originator of the "cash to throw at a project" comment as far as
this thread goes, I need to clarify.
Just as I might smilingly use the same term when my wife is in the mall
buying shoes at the rate of a demented Imelda Marcos, I would also use
it when the local hospital buys a new MRI machine. It has no bearing on
the moral value of the purchase. I think GNHbus has it right as far as
return on investment etc goes. But it goes deeper than just the use one
gets out of the amount spent. Need for reliability or confidence might
be bigger for some than others, position of dock or mooring relative to
where the boat is used has a bearing also, etc etc, as GNHBus seems to
indicate. It will all vary.
I actually never meant to give any impression re vendor developed
systems, other than my opening that they are the way to go, (probably
for most boating people for various 'assumed demographic' reasons,
middle income, time constraints etc).
I agree with the comment you make re cost of buying the parts separately
but it misses the whole main point I was trying to make in my ramblings,
which includes the same as the comment from Sally re being fixated on
hull speed etc.
The vendor designed turnkey units are also an asset to everyone in
furthering the trend towards electric. Electric makes sense. I switch on
lights in the house every day, and find it convenient. I want that
convenience. Electric is probably more suited to boats than to road
vehicles, as the drive has natural slippage.
It is a good point too, that you make here about the controller maker
versus motor maker issue, I grew up in UK during the days of early TV,
when the snowy screen was the TV if you spoke to the antenna guy, or the
antenna if you spoke to the TV guy. I had never thought of that, it
becomes more critical, too, if larger amounts of money are involved. It
will probably never affect me, as any mismatches will be my challenge
and 'interest in gaining understanding' to sort out. (probably by asking
this group!) But my other thinking is that with lower power levels,
maybe that controller is not needed. I have to experiment, wearing
goggles as I throw the blade switch!
I never intended either, to suggest that I can get the same performance
from my own 'car parts' drive, should I ever get it running. (I am now
looking more at scooter or robotics motors I think). Which raises
another point in favour of the turnkey unit - it is more likely to be
actually seen through to completion than my cobbled up rig. (shoe
repairers please note that this is nothing to do with their trade!- also
as a retired machinist, I am hoping that my ultimate efforts will have
some professionalism in design and manufacture despite my use of the
word 'cobbled')
Anyway, put in less words than I am normally notorious for!!! - My
agreement with Eric was regarding thinking of the overall picture, and
not trying to compete with traditional ICE setups that were probably
never well thought out except to ensure that great amounts of more power
than would ever normally be needed was available to push a boat at hull
speed or more while belching fumes. The use of lower speeds for electric
boats means less battery expense and weight, just as for ICE boats it
would mean a lower cost engine, and less fuel storage needs, but they
never seemed to think of that in the past, preferring the overkill route
- even my Atomic 4 gas engine puts out 25HP or more. Perhaps the true
resolution of the range/hours issue would be to set things up so that I
can ignore it as an electric issue. I personally have the advantage of
ignorance, I have little boat knowledge, and therefore no habits or
ideas about a need to use any engine, other than being terrified of not
having one if I need it. As far as I know, the speed I need is any
amount more than the currents and opposing winds that I might encounter.
And the speed I will regularly need is probably slightly above the known
regular currents in my area.
Actually, if I have any criticism of vendor electric units, (and I could
be wrong here like when I married the first wife), it is that they seem
to be following to some degree the ICE ideas of being more powerful than
needed, and with that power comes price. It is another advantage of
electric that if you keep the power lower, you also decrease the battery
needs. This is providing you can get away from needing/wanting to run
for long periods under power. Powerboats are a whole different scenario
of course.
The figures given on this thread re thrust are useful too, as are the
battery discharge life at lower speed ideas.
Now, are there any vendors out there putting together a unit (mounting
plate or chassis, and motor(s) that can be bolted in place, hooked up to
the shaft, put out about maybe 2 HP equivalent from 2 batteries, (12v or
24v) and cost just a few hundred dollars, say 500 bucks tops? Especially
if there is room to add more motors later. If so, it might be all I
need. It might be all that 90% or more of sailboat buyers truly need.
And it might allow the more visionary sailboat makers to cut their price
to compete. "Outboard motor not included."
John
4.4. Re: Thrust to speed numbers
Posted by: "jrmdive" josh@massie.org jrmdive
Date: Fri Mar 11, 2011 6:27 pm ((PST))
"Cash to throw at a project."
Interesting. I think you are implying that those folks who buy a vendor
developed system are throwing money away (not Geo, the OP). I disagree.
And here's why...
1. It isn't that much more expensive than what you can buy the parts
for yourself, if you duplicate the kit. Maybe 10-15%. They're making
their money buying direct and in volume. If you figure all the time you
have invested in hunting down the various pieces, and the individual
shipping and handling charges, it takes a chunk out of even the 15%
"savings."
2. It spreads the R&D cost over multiple folks. Sure, I could have
bought a bunch of untested stuff, and then had the fun of trying to make
it all work, and realize that I bought the wrong thing, and different
parts to match the others. Or I could just get a bunch of stuff I know
works together very well, and let someone else absorb the costs of
figuring it out. My hobby is sailing the boat, not swapping out motors,
controllers, gearboxes, and props.
3. It's supported by a single source. The motor folks can't point the
finger at the controller folks who can't point the finger back. I only
have to call one number should something go amiss.
4. The purchased drive train parts are only a chunk of what is required
for successful conversion. I planned and budgeted my project, then
added a good chunk for slippage, and then padded my slipped numbers.
I'll be very lucky to hit that target, and will probably have to
sacrifice some of my wanted features to do so. I'm still not sure it's
fair to toss stuff like a new cutlass bearing into the conversion
project, but my wife says that since it's happening at the same time,
it's in (same for the bottom job, ouch).
Here is my take on things. A person might think that, for example, the
system from Propulsion Marine is expensive; they want something cheaper.
There's nothing wrong with buying cheap stuff, if that's your bag. But
you really do get what you pay for, and it's all relative. You could
get a free motor and controller from a golf cart, some belts and pulleys
from an old car, tack together some angle stock, and bolt the whole
thing in. It would make your boat go forward and backward. The golf
cart parts guy will look at your self assembled PMAC kit and wonder why
you wasted so much money when all that free stuff works.
What I see is that the vendors tend to have "higher end" offerings.
Double stator motors, Sevcon Gen4 controllers, ClearView displays, etc.
It makes me wonder, if the cheaper stuff was just as reliable, with
similar performance, why it isn't in the vendor units? Perhaps they've
been down that road before (see above comments on R&D)?
Trust me. Even if you buy your primary drive train parts from a vendor,
and have him/her help you install and align them, there's still *plenty*
of work/ experimenting/ head banging to be done. I spent a couple of
hours just this morning creating cardboard templates for the bulkheads I
need to make to create a smaller engine compartment and for the
controller mounting. I still have to fabricate them, then install them,
then glass them. Then the batteries. Then the wiring. Then a bunch
more stuff. Then the sailing!
Josh
--- In electricboats@yahoogroups.com, GNHBus@... wrote:
--
http://www.fastmail.fm - Or how I learned to stop worrying and
love email again
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