[Public-List] Alberg 30 Sail Plan

Wed Mar 17 14:39:25 PDT 2021

I added 4 group 31s, each weighing in at about 70lb. 2 of them went
under the aft ends of the v-berth, and since I switched to a compoating
toilet at the end of '09, I removed the top from the integral holding
tank (Candy Cane being a liner boat), and put the other two in there
(actually, because the tank has a sloping shape, only the aftmost
battery in the former holding tank is a group 31; I moved the group 27
from the house bank to the forward position in the holding tank, and put
the last propulsion battery in the battery bilge -- either way, all the
batteries that aren't under the aft end of the v-berth are under the
cabin sole in the saloon).

If I really want some additional cruising range under power, there's
plenty of freed up space in the engine compartment for me to be able to
stow a Honda 2000 or equivalent, and still be able to leave it ashore
while racing. Alternately, I've browsed around and seen marine diesel
generators (for a fixed installation) in the 10kW range, that would fit
quite comfortably in the vacant space in the engine compartment, but I
don't want to spend that kind of money or add that kind of weight.

If I were sticking something like that in, I'd probably upgrade the
motor to 10kW, even though I have yet to run it harder than 4kW -- and
even that was just to test current draw vs. speed on an initial install
(the testing from which I got my estimate on how much power you'd want
to go how fast, and which was done in early 2018, with 2 years of
uncleaned growth on the bottom). I haven't run the motor higher than 4kW
(and rarely even go above 2kW, which gets me 3-3.5kts) because even
without Peukert's Law reducing capacity, higher speeds give lower range,
and I want to conserve that power for when I might need it.

Lithium seems like a nice alternative because it's lighter, can be fully
discharged without damage, and doesn't see significant capacity
reduction at higher draw. Outside of being expensive though (about 4x
the cost of a flooded cell lead-acid, last I checked), it also takes up
a lot of space. Sure a 105Ah lithium battery is 1/3 the weight of a
105Ah lead-acid -- but they're still roughly the same size.

The way I see it, increasing range under battery (or getting some sort
of generator going) is a future problem. I'm pretty sure it won't be
terribly long before the appropriate technologies exist and are
affordable, because the world needs to get to carbon-neutral by 2050.
Candy Cane's already 46 years old and still going strong, and I don't
think it's unreasonable to expect that she'll still be sailing then. The
electric motor itself (along with the controller that drives it) already
has an efficiency rating of 97 or 98% (I don't have the spec sheet
handy), so that's a pretty stable technology to move to. Meanwhile,
lead-acid batteries are kind of a consumable anyway, so it was really a
decision when the old engine needed a rebuild, of doing a bit to
future-proof the boat, or continuing to throw piles of money at a
technology that has an expiry date within my lifetime -- because I'm
significnatly younger than the people suggesting that it's almost
heretical to go electric. They'll probably have died of old age by 2050,
while I'll be about as old then as they are now. (And on that note, I
don't see any need to convince them that electric is good, or even ok; I
think that Max Planck's famous remark on scientific progress applies
quite adequately to this topic.)

Cheers,
Kris

On Wed, Mar 17, 2021 at 03:53:17PM +0000, R Kirk wrote:
> Nice analysis, Kris. You show that youneed 5-7 KW to power the A30. And also:
> 
> “Ofcourse none of this addresses range: batteries, generators, howmuch
> theyweigh, or where you'd put them -- and that's really thetricky
> businesswith repowering an A30 to electric.”theyweigh, or where you'd put them -- and that's really thetrickybusinesswith repowering an A30 to electric.”
> 
> I’mguessing that to replace an Atomic 4 and keep the boat’s weight thesame you could add about 6 lead acid 12v batteries. (More, of course,if you used lighterLithiums,but where would you put them?) Those6 plus the 2 existing batteries could be wired to give you a nice 48Vsupply for the electric motor and wouldgive you about 10Kwh storagecapacity.
> So,in broad terms, you have an hour or two of power from fully charged batteries to use if you’rein a hurry or fighting strong currents. More - but how much - if you only need acouple of knots in calm water. Remindsme of the WW2 submarines that could stay underwater at 2Kts for acouple of days but only had ½ hour at full speed in battle.
> Any thoughts?
> 
> -----Original Message-----
> From: Kris Coward via Public-List <public-list at lists.alberg30.org>
> To: Mike Meinhold via Public-List <public-list at lists.alberg30.org>
> Cc: Kris Coward <kris at melon.org>
> Sent: Wed, Mar 17, 2021 12:38 am
> Subject: Re: [Public-List] Alberg 30 Sail Plan
> 
> On Tue, Mar 16, 2021 at 02:18:33PM -0400, Mike Meinhold via Public-List wrote:
> > Diesel electric is a good technology for ships when it serves the
> > arrangements well.  If you are forced into compromises such as a very long
> > shaft, or increasing section beam aft to accommodate an engine, then it can
> > pay off.  It works well for vessels that use as much electricity for house
> > or for weapons as for propulsion. In these cases physically separating the
> > energy conversion from the propulsion motor can work well.  In an A30 , you
> > simply add weight and complexity to go diesel-electric, unless you
> > significantly reduce the requirements for speed and range.  The gains in
> > propulsive efficiency will be small - we already have a good match with
> > small diesel and gas engines - so for matching peformance, your diesel
> > generator will have to generate 16 or so horsepower, and you will need a 16
> > hp motor.  You could use a smaller engine combined with batteries , and run
> > it longer , but that will get heavy quickly.
> 
> Except that a 16hp electric motor doesn't match the performance of a
> 16hp gas or diesel. Hell, even gas and diesel don't match each other's
> performance on the same horsepower, but at least they're a lot closer to
> each other than either is to electric. The torque curves are completely
> different between electric and internal combustion, and on the internal
> combustion side, the shape of the curve means that the engine is only
> really putting out its rated power when it's spinning the prop somewhere
> around 2-3x as fast as is needed to get the boat to hull speed (hence
> the existence of reduction gears as an option on a lot of models of boat
> engine -- of course it's just an option because, as anyone who's ever
> dropped their car into a lower gear for better acceleration while
> passing knows, the best engine speed for power is not the best engine
> speed for fuel economy or wear).
> 
> Now considering that power is torque * revs, and ICEs hit peak torque at
> higher revs, as you dial back those revs to something that's actually
> useful to the boat, you're also dialing back the torque, so the rated
> power of an ICE tends to run about 3-5x the actual useful power you can
> get out of it in the applications we're talking about. On an electric
> however, the torque curve tends to be a very close approximation of
> input voltage * input current * efficiency rating = torque * revs.
> On a well-controlled brushless DC, efficiency ratings of 95% or higher
> are not uncommon.
> 
> So you don't want to match the electric to the ICE horses to horses;
> there's no efficiency band to worry about on the electric, and you don't
> have a torque curve working against you. You just want to put in a big
> enough electric to be able to spin the prop fast enough to push the boat
> through the water as fast as you think you'll ever need to go. If you
> anticipate being in enough of a hurry or fighting against strong enough
> currents that you want that to be hull speed, you're probably looking at
> around 7kW which is roughly 10hp. If you're happy topping out around
> 4.5-5kts, 5kW (roughly 7hp) is plenty.
> 
> The difference in torque curves is the big reason you see so much diesel
> electric, not just on ships, but on trains, earth-movers and other
> mining equipment, etc. -- all applications where low-end torque is
> really important, often in the band of engine speeds where an ICE not
> only fails to deliver much torque, it straight-up stalls, even when
> unloaded. Of course this doesn't apply to our boats; we accomplish
> approximately nothing by spinning our props at 10rpm -- even 100rpm --
> but the point remains that on a boat, electric horsepower to ICE
> horsepower is an apples to oranges comparison.
> 
> 
> Of course none of this addresses range: batteries, generators, how much
> they weigh, or where you'd put them -- and that's really the tricky
> business with repowering an A30 to electric.
> 
> Cheers,
> Kris
> 
> -- 
> Kris Coward                    http://unripe.melon.org/
> GPG Fingerprint: 2BF3 957D 310A FEEC 4733  830E 21A4 05C7 1FEB 12B3
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-- 
Kris Coward					http://unripe.melon.org/
GPG Fingerprint: 2BF3 957D 310A FEEC 4733  830E 21A4 05C7 1FEB 12B3