Please note the nr 1. differential.
A good prop, will affect the efficiency about 300 % !
Nothing, but nothing, ever, will be nearly as important, ever again.
Typically, you want 1/3 the revs, 3x the size, and 1/3 the rise, of a
typical ICE driveline of same HP.
Or, in truth, more D, less rpm, and less rise, much more efficiency.
A prop of 2x the diameter will have about 1,5 the drive area.
3x D, or 1.5 R about 2.25.
But the efficiencies go up faster than drive area.
Focus all efforts on prop, for now.
Example.
Tugs typically use props of 5x d, and 1/4-1/5 D, for max thrust.
This is what You want.
What happens is that a low-rise prop limits, in ice, acceleration and
top-speed, again in ice, always done at ruinous effciciency.
Nothing wrong with it.
But a low-rise prop, like in subs (most studied props in history, with
biggest budgets), and tugs (where thrust is nr 1), makes a great
result, in one band re: efficient thrust at given speed (low).
A boat is mostly slow, where any prop is cheap in terms of power use at
one single speed.
Optimise for top cruise.
In terms of design, ac servos and or ac motors (aka tesla cars) are by
far the most efficient.
But it does not necessarily matter, at all.
If ...
a Pm motor is 100% efficient, with typical driveline losing 80%, end
result with 1 unit of power is 0.20 units thrust.
With the same system, using efficient prop/driveline, might be 80%
efficient, for 0.8 units thrust. 400% better.
So efficiency of PM/AC/servo is relatively very important in %
range/efficiency terms.
But efficiency of prop system is critical, and all current commercial
systems are 1/3 or so of what they should be.
A prop or windmill is similar.
Efficiencies go up 3 pwr of speed iirc and 2 pwr of D.
The "right" choice" for an efficient cruiser is a prop about 10 M in D,
running about 20-40 rpm. (Impractical. It´s an example, mental exercise.)
A current top-end cruiser is a Nordhavn 60, more or less, using 25-30 kW
/ hr, about 4-8 gallons /hr, or about 16-32 l, 6-7 knots,or == 0.7 - 1.4
gallons/mile.
A really efficient system will be about 1/3 of that, today, no exotic
tech needed.
Windhorse FPB 64 from the Dashews (3.5M$, 64ft, 2x140 hp iirc) and all
studies with data support above numbers, +/-.
Afai, the windhorse is the most efficient system today in "production".
This could be improved about 30%, with bigger props and 3 vs 5 blade
props etc.
They state this themselves, and do these choices for commercial reasons.
All data is public see dashewoffshore.com.
The Dashews data is important for these reasons, imho.
1. They are long-time, 40 years, influential successful yachts
(sailboat) designers with excellent rep
2. They sell to rich-market-segment, but are with Nordhavn the most open
publishers of data
3. I consider anything Steve Dashew states as "real" based on his open,
40 year, track record.
They sell "rich stuff" to "rich people". Fine.
Despite this, the Dashews personally, have done more cruising than 99%
of people with cruising boats.
And 99.9% more than most people with boats.
On 09/08/2016 09:18, hstalker@gmail.com [electricboats] wrote:
>
> Hi John
>
> Thanks for you reply. To be honest this has got all so confusing and
> there seems to be so many options and very very different prices.
>
> I have contacted quite a few different suppliers and i have prices
> from the low thousands with no batteries to the $150,000 - $200,000
> usd from one company recommend by a user here. (i think they just did
> not want the business shame on them).
>
> It also seems to be not clear on which systems to use re- AC vr PMDC
> vr DC etc... so for the layman its super hard to know what to buy.
>
> I have contacted both Torqeedo and Ocean Volt. Both systems are pricy
> but their kits do seem full featured and good systems so not
> complaints there.
>
> Having said this and doing all this research i see there are ways to
> build systems at a fraction of the price. One thing i am very mindful
> of is resale value as this a new yacht and i am not planning on
> selling but you never know the future. If a potential buyer or a
> surveyor thinks the system is a bit mickey mouse then you could
> potentially loose a lot of value.
>
> We have also found walk on solar panels with sun power cells 300w each
> and we measured up the the salon roof and should be able to get 3kw on
> there. Yes i know they will get shaded but we should get at least 50%
> while sailing and more mored.
>
> One thing we have found is locally made LifePO4 batteries that seem to
> meet all the requirements we need at really really low prices. This is
> straight from the factory. The company is contracted by large Japanese
> companies to make there batteries and a fiend of mine who is making
> electric vehicles put us on to them. This is a dream as we can now
> have the battery bank we would normally only dream of.
> They are so cheap even if they do give up i can just replace them.
>
> Here is the kicker tho some of the big systems do not seem so keen to
> sell you there systems without batteries. so i am back to square one
>
> So i would put it to the group a little different. Lets say i wanted
> to run 2x 10-15kw motors and as i stated i can get lifePo4 batteries
> in any config and size i need what would you guys suggest to do in the
> form of motors, controllers to make up a fully working system? lets
> not get into sizing of motors etc. The systems could be either shaft
> drive or sail drive or even pods. We wold prefer shaft though just so
> we can run kick up rudder and this cat has dagger boards so it should
> be possible to beach her is i need to.
>
> This is a 58ft catamaran so space is not to much of a issue either.
>
> Love to hear expertise from people that have done it as we are really
> novices in this area.
>
> Regards
> Hamish
--
-hanermo (cnc designs)
Posted by: Hannu Venermo <gcode.fi@gmail.com>
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