Hi, Eric and everyone,
Part of my problem in figuring all this out is that I am in fact NOT a
sailor.
I have only sailed twice, I think, about 40 years ago, in a 12 foot
dinghy, I think it was, maybe 15, with a friend and my first wife, a
boat hater and boat ownership restrictor. (pls check the first 3 letters
of the word 'boat').
My boat is something over 6000 pounds, 3/4 long keel.
I will actually be on a mooring buoy, in about 50 feet of water, so will
have some room. So that is the 'docking' that I will be doing, at least
to start with. I am hoping to be able to eventually moor without any
propellor use. Eventually.
I also, for safety reasons, will have ICE power available.
An easy to figure electric setup would no doubt be as big a motor and
batteries as I can find useful, although I am not expecting to need long
range 'under power' travel, but like to expect the unexpected.
The ideal, for me, includes price, and with no shore power, independence
in recharging.
My first real boating experience (after getting a couple of dinghy
sailing lessons as soon as the dinghy trainers have opened up summer
shop at my club this season) will be with the 15 foot dinghy that I
intend to be my tender. And I intend to electrify that, mainly to gain
some knowledge.
I will not have time to get electrified in the main boat this summer,
there are too many other things to fix. It has an Atomic 4 that may, or
not, run. I have an outboard that is 'Plan B'. It is a 2 stroke, and
therefore stowable on its side.
Once I am able to sail, I can better judge what I need, of course.
But right now, I suspect that I will need an ICE for long range if I
need it for safety, or to correct my mistakes. And I will need something
less powerful (and less smelly and noisy) for maneuvering or gunkholing
I believe it is called, with the centreboard up, into shallow places.
The best way if ignoring cost might be a big electric motor, and a
generator for long range, this makes really good sense, but that idea
fails when the cost is considered - if I have to run an ICE, I can get
it cheaper, and gain motor redundancy/backup by having it as an
independent engine such as the existing Atomic 4, (and an electric
outboard) or, as I intend, the outboard I bought for $100 (I live in
Nova Scotia - we fix stuff!) and the inboard changed to electric.
Your 3 knot(ish) figure I believe it was, using 500 watts or so, seems
just right. With that kind of battery load, I can use solar or/and wind
to recharge, and with just a couple of batteries, have enough power for
quite a few minutes use.
The previous owner, who used the boat with no running engine, said that
if I tied some buckets to a line, that would be enough brakes for an
emergency! But, he knows how to sail, and I don't yet.
So, I believe that I can get away from the 'lots of power' mindset as
far as electric goes, because if I need that, God forbid, I have some
kind of stink engine as backup. If the wind is at ten knots, and if that
represents a problem, then I would hopefully have the ICE running.
So, back to topic,
" When you say 'pushing the motor hard' are you say by high volts, or by
slowing it with a large load, such as too large or pitched prop?
Looking at the speed Eric gives for a 500 watt load, (10% of what he
uses to go only twice the speed) does this indicate that if I had his
boat I could use, say, a 1 HP motor, and have 200 watts to spare, as far
as heating goes? This assumes that I gear/prop it to run at a reasonable
speed, say, only as low as maybe 80% of no load speed?
What I am trying to say is, what would be a good guesstimate of good
starting points as far as motor HP spec to end up with a system that
draws about 500 to 700 watts continuous and does not waste resources by
making heat? "
I can now edit the above by adding the word 'excessive' in front of
'heat' at the end.
Once I have the running figured out, I can then look at maybe having it
set up for bursts of over-power by using 'too many' volts for a few
seconds. But that is for another thread.......
So, if a load slows down a motor, how much (best guess) can it be
allowed to slow it down before excessive heat is created?
Thanks,
John
4d. Re: power requirements
Posted by: "Eric" ewdysar@yahoo.com ewdysar
Date: Tue Apr 5, 2011 4:27 pm ((PDT))
I've noticed that with fin keel boats, I can usually sail into or out of
my slip. However, with my heavy full-keel ketch at slow speeds, I often
have to hit a quick blast of forward thrust to kick the stern around.
With an upwind slip, I don't use much reverse while docking. When
everything goes well, I don't need hardly any power at all. But the
motor is just in case. The worst scenario is coming in slow and the bow
starts to get pushed off by the wind. It's those situations where more
power is helpful in keeping my boat off of my neighbors directly
downwind while I back out to the main channel and set up for another
try.
But this points to one of the advantages of electric drive. You can be
sailing in with no motor on and if things start to get difficult, you've
got full power available in about 1 second. No starting, no warm up, no
panic. But my earlier point was that full power needs to be enough to
handle the situation.
Eric
--- In electricboats@yahoogroups.com, Matthew Geier <matthew@...> wrote:
>
> On 06/04/11 05:16, Eric wrote:
> > John,
> >
> > As a sailor, I'm sure that you've tried coming into a dock with even mild (10kt) wind. On my boat, as I'm approaching the dock at speeds of less than 2kts, I occasionally need bursts of 2500W or more to stop or steer the boat.
> Interesting about how much people rely on reverse thrust as a brake - my
> boat, back when it was powered by a 2 cylinder two stoke engine, had no
> gearbox. The only way to get reverse power was to start the engine
> backwards (being two stroke it would run either way subject to spark
> timing). There was no way you could get the engine restarted in reverse
> in the short time frame required for using it as a docking aid.
>
> Thus I learned quite young, to dock the boat with out reverse thrust.
> My boat is only 5m long and 750kg which probably helps things some what.
>
> Now I'm lazy and give it a burst of reverse thrust to slow to a stop.
>
>
> I've watched people in rental boats trying to 'park' them like they
> would park a car. I was watching some one once who I was certain were
> going to blow the gearbox.....
>
--
http://www.fastmail.fm - Does exactly what it says on the tin
No comments:
Post a Comment