Prop for Electric Motor

[coldfish]

Originally Posted by TrentePieds

Seems to me that few of us are in rigorous pursuit of maximum efficiency in the manner Sean seems to be. Surely the majority of us - condemned though we may stand in the eyes of some - are in leisurely pursuit of adequacy?

On a 32 foot Choi Lee doing weekend duty for a family is San Francisco Bay it seems to me that a 30 horse diesel with a garden variety prop dimensioned as calculated by VicProp's on line calculator is quite adequate.

I also fail to get agitated about poor old TP's consumption of dino-juice. TP with her 1/2 gallon an hour consumption is surely not what enables such splendidly free ennerprize organizations as SunCor to destroy the Canadian environment through their tar sands mining.

So coming back to the question of efficiencies, I, like many others, think we can individually be much more efficient in solving the problems for which converting yachts from diesel to electric drive purports to be a solution by putting our individual efforts, and financial resources, to use in other ways.

So I'm back to the point I made in my first post in this thread: Pick a prop that suits the Choi Lee for its intended use. THEN pick the power plant. If it amuses you to go electric, then by all means do so. No reason whatever you shouldn't. But if you want to sell the notion of electric drive to me, you will have to do it on grounds other than efficiency and elimination of dino-juice as a fuel for yachts :-)

Cheers

TP

The reason for electric is actually unrelated to efficiency or dino-juice. That old diesel was LOUD. I mean, even with lots of insulation and trying my best to block it out, it was simply impossible to have a conversation. Since we're in SF Bay, quite often we'd be coming back against a very heavy tide and we'd need a bit of power-assist for 30 min or so. Moreover, It gets cold as it gets dark here, so the kids, wife, friends, etc.. end up going inside. It's a big pilot-house model, so the kids go down and watch a movie, the adults play cards and I can steer from the galley right there. However, it is LOUD.

What's worse: The diesel really permeates the boat. It doesn't bother me, but the wife said it made her sick, so everyone would be inside and she'd be sitting on the back deck with a blanket.

So: Electric = Quiet and no smell.

Did that sell you on the notion of electric drive.

[RaymondR]

One of the characteristics of DC motors is that they draw a lot of amps at low speeds.

Another characteristic is that their maximum efficiency from a power output viewpoint tends to occur at about 50% of the free running speed.

Then there's battery life/discharge rate both short and long term to be considered.

A 32' sail boat would not generally require a 70hp engine to achieve hull speed I'd say 30hp would be more than adequate.

From a design viewpoint this project looks a bit shaky and I'd be inclined to put the prop you already have on and try it out to see what happens before going to the expense of buying another one.

[coldfish]

Originally Posted by Adelie

A big prop outboard would not be great for getting in and out of marinas or the rest of it, except for extending your range at low speed. If you dropped your speed to somewhere around 2.8kt, demand would be around 400-600W and range would be about 60nm for a 300hr bank discharged to 75%DoD and somewhere around 80-90nm at 2.5kt.

Personally I would install the Thunderstruck motor in place of the inboard using a feathering or folding prop for use in maneuvering and higher load uses and also the outboard for distance efficiency.

I pulled the inboard volvo and put in a thunderstruck motor with a 72v 100ah lithium battery. It's still in the shipyard, so I haven't tested it, but I think I may just stick with the prop I've got for now. It is am 18LH12
https://ds.morrisdev.com/mo/sharing/t4bGWgfu7

[coldfish]

Originally Posted by RaymondR

One of the characteristics of DC motors is that they draw a lot of amps at low speeds.

Another characteristic is that their maximum efficiency from a power output viewpoint tends to occur at about 50% of the free running speed.

Then there's battery life/discharge rate both short and long term to be considered.

A 32' sail boat would not generally require a 70hp engine to achieve hull speed I'd say 30hp would be more than adequate.

From a design viewpoint this project looks a bit shaky and I'd be inclined to put the prop you already have on and try it out to see what happens before going to the expense of buying another one.

Well, I think next week we're going to see. I'm going to stick with the current prop. In the past, I've never motored for more than about 30 minutes the entire time I've been out. There's almost always a lot of wind here, so it's mostly maneuvering in the marina or when the tide is going faster than I can sail.

[coldfish]

I just wanted to mention one thing about that old diesel that has brought me to this point.

Shifting Gears.

The old engine really didn't have much power on the start. So, from neutral to motion, there was a pretty good pause, but that diesel was very powerful, so once it DID go, it REALLY pushed. When trying to get around Pier39 in SF, where there's sudden gusting winds and crazy tides, you have to be ready for some chaos. So there are a lot of times where you need to backup or move forward *right-now*. And the powercurve of a diesel just doesn't work like that. At least mine didn't. With Electric, it's got torque out the wazoo. Shifting from forward to reverse is instantaneous.

But... we'll see. I'll keep people here updated.

[PineyWoodsPete]

Originally Posted by Adelie

A big prop outboard would not be great for getting in and out of marinas or the rest of it, except for extending your range at low speed. If you dropped your speed to somewhere around 2.8kt, demand would be around 400-600W and range would be about 60nm for a 300hr bank discharged to 75%DoD and somewhere around 80-90nm at 2.5kt.

Personally I would install the Thunderstruck motor in place of the inboard using a feathering or folding prop for use in maneuvering and higher load uses and also the outboard for distance efficiency.

I'm afraid these figures are totally unrealistic for the OP's heavy, short waterline 32'er with 7.2kWh lithium bank, giving about 5.4 kWh @ 75% DoD.


A point of comparison is my 12,000# semi-displacement hull 33' Greenline Hybrid (32' WL) w/ 165 HP diesel in-line with a 7/5kW motor/gen and an 11.6 kWh lithium bank (8.7 kW @ 75%).



Under electric, it takes about 1.5kW for 2.5kt, and max range of only 15nm. Max speed @ 7kw is about 5.5kt @ 1250 RPM which can be sustained for only a few min. before dropping to 6 kW output and 5kt, for a range of less than 10nm. This with turning the diesel's 17x14 5-bladed scimitar prop w/ 2:1 red. gear



With its winds, tides and currents SF Bay's challenges beat any place we've found sailing the length of both coasts, and I hope the OP's sailing skills are up to the challenges he'll face.



Because if not, he may well be greatly compromised by his limited powering range with the 72V/18 kW motor giving less than 30 min. full power. And his claim that this motor is equivalent to the 52kW/70HP diesel is sheer fantasy.

[coldfish]

Originally Posted by PineyWoodsPete

I'm afraid these figures are totally unrealistic for the OP's heavy, short waterline 32'er with 7.2kWh lithium bank, giving about 5.4 kWh @ 75% DoD.


A point of comparison is my 12,000# semi-displacement hull 33' Greenline Hybrid (32' WL) w/ 165 HP diesel in-line with a 7/5kW motor/gen and an 11.6 kWh lithium bank (8.7 kW @ 75%).



Under electric, it takes about 1.5kW for 2.5kt, and max range of only 15nm. Max speed @ 7kw is about 5.5kt @ 1250 RPM which can be sustained for only a few min. before dropping to 6 kW output and 5kt, for a range of less than 10nm. This with turning the diesel's 17x14 5-bladed scimitar prop w/ 2:1 red. gear



With its winds, tides and currents SF Bay's challenges beat any place we've found sailing the length of both coasts, and I hope the OP's sailing skills are up to the challenges he'll face.



Because if not, he may well be greatly compromised by his limited powering range with the 72V/18 kW motor giving less than 30 min. full power. And his claim that this motor is equivalent to the 52kW/70HP diesel is sheer fantasy.

We'll, we're gonna find out. Folks at thunderstruck seemed convinced that it was the proper setup for the boat, and the numbers come from their own calculations, so I wasn't gonna argue

Luckily, I have been sailing since I was a kid, worked everything from river boats to Alaskan long liners in the past 40yrs, so I'm not exactly a beginner. However, I have enough experience to know that things are unpredictable and I'm gonna have a towboat follow me while I test this out.

[Bullshooter]

Good luck, coldfish. Please report back on how it works out. I think you are right to try it first with the prop you have, at least as a starting point. When you have time, you may want to look at a few of Sailing Uma's videos where he tests out his regen output and gets some rough numbers, if that is of interest. Or check out the CF member Growley Monster, who has some experience in the electric motor (on his sailboat) area.

[PineyWoodsPete]

Originally Posted by coldfish

We'll, we're gonna find out. Folks at thunderstruck seemed convinced that it was the proper setup for the boat, and the numbers come from their own calculations, so I wasn't gonna argue

Luckily, I have been sailing since I was a kid, worked everything from river boats to Alaskan long liners in the past 40yrs, so I'm not exactly a beginner. However, I have enough experience to know that things are unpredictable and I'm gonna have a towboat follow me while I test this out.

All great to hear! I imagine the TS folks felt it was an appropriate auxiliary motor for your boat. That original 70HP Volvo sure put the boat deep in motor-sailor land! Way back in the 70's we had a heavy Endeavour 32 sail with a 22HP Yanmar aux., which did just fine, reaching about 6.5kn under power.

Best of luck to you!

[Adelie]

Originally Posted by PineyWoodsPete

I'm afraid these figures are totally unrealistic for the OP's heavy, short waterline 32'er with 7.2kWh lithium bank, giving about 5.4 kWh @ 75% DoD.

A point of comparison is my 12,000# semi-displacement hull 33' Greenline Hybrid (32' WL) w/ 165 HP diesel in-line with a 7/5kW motor/gen and an 11.6 kWh lithium bank (8.7 kW @ 75%).

Under electric, it takes about 1.5kW for 2.5kt, and max range of only 15nm. Max speed @ 7kw is about 5.5kt @ 1250 RPM which can be sustained for only a few min. before dropping to 6 kW output and 5kt, for a range of less than 10nm. This with turning the diesel's 17x14 5-bladed scimitar prop w/ 2:1 red. gear

With its winds, tides and currents SF Bay's challenges beat any place we've found sailing the length of both coasts, and I hope the OP's sailing skills are up to the challenges he'll face.

Because if not, he may well be greatly compromised by his limited powering range with the 72V/18 kW motor giving less than 30 min. full power. And his claim that this motor is equivalent to the 52kW/70HP diesel is sheer fantasy.

PWP:

Your vessel is not a good basis of comparison to the OP's vessel. As you indicate your vessel has a semi-displacement hull which means that it is optimized for minimum drag near S/L-2.0. That means that it will tend to have very high drag at low speeds compared to displacement vessels, especially displacement sailing vessels which are optimized for low drag at very moderate speeds (near S/L-1.0).

This is the tradeoff power vessels make, they trade higher power requirements and higher fuel consumption compared to length and displacement in exchange for larger interior volume and accommodations and generally higher speeds.

I have been collecting data regarding measured energy demand for various speed for various sailboats.
For sailboats near 35' and 13,000lb displacement, demand is about 950W-1.2kW at 3.0kt. The peak reported demand at 3.0kt was 1350W by a Morgan-45. Demand at 2.5kt is observed to be about 1/2 that of 3.0kt but varies a little from boat to boat and fewer boats report demand at that speed.

[Cynara]

What does the instructions from the kit tell you

[PineyWoodsPete]

Originally Posted by Adelie

PWP:

Your vessel is not a good basis of comparison to the OP's vessel. As you indicate your vessel has a semi-displacement hull which means that it is optimized for minimum drag near S/L-2.0. That means that it will tend to have very high drag at low speeds compared to displacement vessels, especially displacement sailing vessels which are optimized for low drag at very moderate speeds (near S/L-1.0).

This is the tradeoff power vessels make, they trade higher power requirements and higher fuel consumption compared to length and displacement in exchange for larger interior volume and accommodations and generally higher speeds.

I have been collecting data regarding measured energy demand for various speed for various sailboats.
For sailboats near 35' and 13,000lb displacement, demand is about 950W-1.2kW at 3.0kt. The peak reported demand at 3.0kt was 1350W by a Morgan-45. Demand at 2.5kt is observed to be about 1/2 that of 3.0kt but varies a little from boat to boat and fewer boats report demand at that speed.

Agreed, the Greenline folks call it a "super-displacement" hull with an interesting underbody as below, but what I was contesting were your range numbers:


"A big prop outboard would not be great for getting in and out of marinas or the rest of it, except for extending your range at low speed. If you dropped your speed to somewhere around 2.8kt, demand would be around 400-600W and range would be about 60nm for a 300hr bank discharged to 75%DoD and somewhere around 80-90nm at 2.5kt."

It appears that you weren't using the OP's figures for his battery bank size - a 7.2kWh lithium bank, giving about 5.4 kWh @ 75% DoD, and a ~30nm range @ 2.8kn with your 0.5 kW draw. What is a 300hr bank?!

[TrentePieds]

Coldfish asked: "Did that sell you on the notion of electric drive? "

Well, no, it doesn't actually - but chacun son goût :-)!

Here in the Gulf Islands in the Salish Sea (and in the American SanJuans, too) we have tidal currents that are, as I have been told, quite the equals of those in SF Bay, and that, of course, speaks in favour of having auxiliary power, though it sez nothing about what should generate that power. So you cannot convince me on that score :-)!

TP calls itself a "pilot house" sloop, but it isn't really, having no "inside" steering station. So let's call 'er what she is: a "raised deck saloon" sloop. You'll know that in the Salish Sea its get darker (earlier in the winter, though later in the summer) than it does in SFB, and as for cold...! Oof! But having had the great good fortune to be born a Norseman, I simply put on another sweather under my foulies. And pull my foulie hood up over my cap. Seaboots, of course.

But I agree with you, a 70-horse had no place in your boat, and if you and those with more tender ears spend a lot of time below, the racket woulda been a tad overwhelming. And as for the stink - hmm. TP's little 20-horse doesn't stink, but that may be the result of better installation. Or of my declining olfactory capacity, perhaps, but MyBeloved whose nose is as good as it ever was, has not complained :-) The noise is far from unbearable. What does get my goat at times is the harmonic vibrations that can sometimes rattle the hatch covers. A slight change in RPM usually cures that.

Though you haven't convinced my that Electric is superior I look forward to your performance reports. You never know. Hope is evergreen :-)!

All the best

TrentePieds

[Adelie]

Originally Posted by PineyWoodsPete

Agreed, the Greenline folks call it a "super-displacement" hull with an interesting underbody as below, but what I was contesting were your range numbers:


"A big prop outboard would not be great for getting in and out of marinas or the rest of it, except for extending your range at low speed. If you dropped your speed to somewhere around 2.8kt, demand would be around 400-600W and range would be about 60nm for a 300hr bank discharged to 75%DoD and somewhere around 80-90nm at 2.5kt."

It appears that you weren't using the OP's figures for his battery bank size - a 7.2kWh lithium bank, giving about 5.4 kWh @ 75% DoD, and a ~30nm range @ 2.8kn with your 0.5 kW draw. What is a 300hr bank?!

Super-displacement, marketing speak.

Since I was discussing an outboard that is not in production and isn't on the OP's boat, I also decided to use the bank size and voltage that is typical for EP. 300hr should be 300Ahr, I did not specify voltage, 48v which is typical for EP. That works out to about 14.4kWhr, which is 10.8kWhr effective.

[RaymondR]

Sounds like an ideal application for one of those variable pitch props with the pitch control rod down through the centre of the prop shaft. You could vary both motor speed and prop pitch to most suit the propulsion requirements in a range of circumstances.

The down side of them on a diesel powered boat was that they were constantly engaged and you could not just throw them into neutral if picking up a line threatened. Not as severe a problem with electric drive.

Although they a considerably more expensive than a fixed pitch prop it might be possible to do away with the reduction gearbox thereby reducing the overall cost. A similar scheme works well with prop driven aircraft.