Sail boat engine choice - electric or diesel

[seandepagnier]

Originally Posted by MichaelPrichard

It's probably easier on a catamaran than other hull types, but here are my POD drives partially retracted; I can stop them at any point and you can see that I have ample clearance for very large props, something I'm hoping to experiment with on one side to do direct A/B comparisons with a "standard" 15" prop. My primary limitation will be depth as my max shaft centerline depth is only around 20" which limits me to a 2-2.5ft prop diameter before the tips get too close to the surface and likely start cavitating. But as they'll likely be spinning a lot slower, hopefully I can afford closer surface proximity before cavitation compared to a faster spinning standard prop.

Yeah, you don't want the prop too close to the surface. It's smart your props are between the hulls and not behind them at least to keep them in a cleaner flow. Also really cool how you can retract them under sail.

Maybe it's possible to make these lock in a position where the prop is half out of the water for shallow navigation? Also any way to make the arms longer so they can go a bit deeper?

Another thing to watch out for is, a larger prop will need much less speed and much more torque so the gears will have to be able to handle this.

[Chotu]

Originally Posted by newhaul

Here is something worth keeping an eye on
https://www.designboom.com/technolog...is-09-30-2020/
now as soon as battery tech catches up it may be worth considering for use on outboard capable craft.

Are there any real efficiency gains here as compared to a traditional prop?

The parallel I see here is comparing a propeller aircraft to a gas turbine engine in some ways. At least in the nozzle way.

If there are gains from this prop, they might be enough to help electrical shortcomings

[TrentePieds]

Seems unlikely that there could be efficiency gains. "Ducted fans" are old hat and are, to the best of my knowledge deemed LESS efficient that conventional "free" props.

That the notion of the "outrunner" electric motor (the shaft is stationary, the casing spins) should confer advantages when applied to the design of a "propulsion device" for yachts (rather than to their motors) is not obvious to me.

It also seems to me that the induced drag of the nozzle itself would more than negate the avoidance of the drag induced by the "axis" (Probably a mistranslation of the French "l'axe"), the bit we call the propeller shaft.

Kortz nozzles are common enuff in tugboats. They are advantageous insomuch as they reduce the "tip losses" of "free" propellers, but the essence of translating engine/motor power to thrust is still found in the design of the propeller blades.

Making due allowance for an inept translation into English of the original French of the publicity material, I am skeptical that this is more than yet another exercise of some "marketing department" in "selling into a market of ignorance"

I'll be pleased to be proved wrong in my opinion, but for my kind of cruising the conceivable advantages are far, far too small for me to go chasing the science in any serious way.

TrentePieds

[carstendenmark]

@ seandepagnier :

Quote
- this changes with an electric motor, because you can now use an extremely small amount of energy the last few seconds (less than a minute in most cases) to accomplish this and also not have to worry about wind shifts tacking in extremely narrow areas
Unquote

Sean, thank you SO much for the tip about tacking, using electric motor bursts !!

An electric motor is always available, and needs no startup to deliver full torque right on.

I'm always having trouble making fast tacks singlehanded in my boat.
Such a burst will really help to keep up the speed when passing through the head wind, no need to accelerate again after the sail is set in the opposite side !
I'm ALL in for changing my old Penta to electric now !!

[MichaelPrichard]

Originally Posted by seandepagnier

Yeah, you don't want the prop too close to the surface. It's smart your props are between the hulls and not behind them at least to keep them in a cleaner flow. Also really cool how you can retract them under sail.

Maybe it's possible to make these lock in a position where the prop is half out of the water for shallow navigation? Also any way to make the arms longer so they can go a bit deeper?

Another thing to watch out for is, a larger prop will need much less speed and much more torque so the gears will have to be able to handle this.

The draft of the boat with mini-keels is a little over 3ft on this boat, so a 24" prop could be located 6" below surface and still be 6" above mini-keel bottoms, but running the props half out of the water would probably work slowly if the prop were larger; doing that with these props does make a racket, but would probably still generate some usable thrust.

I designed these arms with the 15" props in mind to be as long as possible without overlap when fully retracted. Extending might be possible, but would require offsetting the PODs front/back or ensuring that one always retracted before the other so that they could stack vertically when retracted, something that would require some additional logic/control. But I think I can put large 2-blade props on them in their current positions as those could stack next to each other (overlapping swept area) without hitting.

Regarding motor speed, I'm already way under-propped with these little propellors as I hit max. RPM on the motors (1100rpm) while only consuming ~63% of the available power from them (4.5kW for each 7.1kW POD). I'm thinking that even if I'm "over-propped" with too large a propellor to reach max. RPM, the high torque characteristics of electric drive will still allow plenty of thrust at much lower RPM and will allow me to use more of the available power of the POD, even at only 30-60% max. RPM. Obviously, the motors would have to be carefully monitored so that they don't overheat (passively cooled only through casing into water).

That said, I'm coveting the very cool Hy-Generation nozzle thrusters that newhaul posted recently; those look to generate more thrust/swept area while apparently optimizing blade angle at all RPMs, passively.

[valhalla360]

Originally Posted by MichaelPrichard

The draft of the boat with mini-keels is a little over 3ft on this boat, so a 24" prop could be located 6" below surface and still be 6" above mini-keel bottoms, but running the props half out of the water would probably work slowly if the prop were larger; doing that with these props does make a racket, but would probably still generate some usable thrust.

With a giant slow turning prop, you will get a lot of prop walk with the prop fully submerged. Lift it half out of the water and it will act like a sideways paddle steamer...the bulk of the thrust will be to the side with very little forward or reverse thrust.

[valhalla360]

Originally Posted by TrentePieds

Seems unlikely that there could be efficiency gains. "Ducted fans" are old hat and are, to the best of my knowledge deemed LESS efficient that conventional "free" props.

That the notion of the "outrunner" electric motor (the shaft is stationary, the casing spins) should confer advantages when applied to the design of a "propulsion device" for yachts (rather than to their motors) is not obvious to me.

It also seems to me that the induced drag of the nozzle itself would more than negate the avoidance of the drag induced by the "axis" (Probably a mistranslation of the French "l'axe"), the bit we call the propeller shaft.

Kortz nozzles are common enuff in tugboats. They are advantageous insomuch as they reduce the "tip losses" of "free" propellers, but the essence of translating engine/motor power to thrust is still found in the design of the propeller blades.

Making due allowance for an inept translation into English of the original French of the publicity material, I am skeptical that this is more than yet another exercise of some "marketing department" in "selling into a market of ignorance"

I'll be pleased to be proved wrong in my opinion, but for my kind of cruising the conceivable advantages are far, far too small for me to go chasing the science in any serious way.

TrentePieds

Tugs are more about thrust than HP. Kort Nozzels help with thrust by ensuring the power generated doesn't get wasted pushing water radially out from the prop but mostly directly to the stern (could also be called tip losses). Also it minimizes prop walk effects.

Thrust is useful when trying to push a 1000ft ship that doesn't want to move.

Also until you get that ship moving, the prop is spinning in place and keeps generating prop walk until the 1000ft ship is moving, so eliminating prop walk avoids having to use a lot of rudder to compensate which wastes forward thrust directing water to the side.

On our low power sailboats, we rarely need much thrust and prop walk effects become negligible once the boat is moving forward.

If there really was substantial efficiency benefits without any major negatives by going with oversized props or fancy bolt on gear, you can bet, they would already be incorporated into diesel powered boats.

[MichaelPrichard]

Originally Posted by valhalla360

With a giant slow turning prop, you will get a lot of prop walk with the prop fully submerged. Lift it half out of the water and it will act like a sideways paddle steamer...the bulk of the thrust will be to the side with very little forward or reverse thrust.

Interesting. Fully submerged shouldn't cause any prop walk since I've got dual counter-rotating props, but running with any portion of the props out of the water sounds like a non-starter given that sideways thrust which hadn't occurred to me; sort of like a sailboat with no keel which is effectively only half a "prop"...

[seandepagnier]

Originally Posted by valhalla360

With a giant slow turning prop, you will get a lot of prop walk with the prop fully submerged. Lift it half out of the water and it will act like a sideways paddle steamer...the bulk of the thrust will be to the side with very little forward or reverse thrust.

The bulk of the thrust is still forward at least with lower pitched props. My prop is 32 inch diameter 10 inch pitch and it works half out of the water. My prop diameter is currently the same as my draft, so I don't actually need to run it partially out, but when it is deeper it works a little better, but then it could hit bottom before the boat does.

Originally Posted by MichaelPrichard

Interesting. Fully submerged shouldn't cause any prop walk since I've got dual counter-rotating props,...

With twin counter rotating props I think the prop walk would cancel and they could both be half submerged. Surface piercing propellers have been used before, and this is only needed in very shallow water anyway.

Originally Posted by valhalla360

If there really was substantial efficiency benefits without any major negatives by going with oversized props or fancy bolt on gear, you can bet, they would already be incorporated into diesel powered boats.

I have compared 12 inch typical propeller on trolling motor to 32 inch carbon propeller on homemade outboard. The small propeller uses 250 watts to do the same speed as the large propeller at 120 watts.

I have also tried to row my boat using a kayak paddle go 1 knot vs a sculling oar which is 6ft long at more than 4x the surface area and also cambered producing lift where I can go almost 2 knots with the same physical effort.

According to physics, there are substantial benefits possible, on the order of doubling efficiency over what most cruisers have. It's just not easily possible to do with diesel power because the engine is very heavy compared to electric so it must sit where it is, and then there is no way to transmit the power to such a large prop because it can no longer be located where most inboard props are.

diesel is already very inefficient (most of the energy going to heating water) so why would ultimate energy efficiency be a priority? It already can push the boat fast for a long time and so it explains the compromises taken by the industry to greatly simplify things.

carbon fiber propellers are cheaper and always outperform bronze ones, but bronze propellers are still very common.


It's also well known that variable pitch greatly improves efficiency across speeds but this is rarely seen. Since you can burn a bit more diesel which has huge energy potential to compensate since it is extremely cheap ( it's subsidized as debt onto future generations) it's cheaper than getting a variable pitch one.



dyneema or galvanized wire are both superior to stainless steel for standing rigging yet most people still use stainless. the windows operating system is a joke compared to alternatives yet still very popular. The list goes on, but the reason changes are not made is because not enough people are making them and most people just copy what the majority is doing.

Originally Posted by TrentePieds

Seems unlikely that there could be efficiency gains. "Ducted fans" are old hat and are, to the best of my knowledge deemed LESS efficient that conventional "free" props.

That is only true at speeds above about 10 knots. At lower speeds they make more sense.

That the notion of the "outrunner" electric motor (the shaft is stationary, the casing spins) should confer advantages when applied to the design of a "propulsion device" for yachts (rather than to their motors) is not obvious to me.

I'm skeptical of the hy-generation. In the video you can clearly see they are missing a lot because of all the turbulence created behind the boat. My propeller barely disturbs the water at all. I also wonder what kind of bearings they are using and how they prevent iron in the water from building up around the magnets in the motor if it uses magnetic bearings (no friction). I'm not so sure such a small pod could be as efficient with so many blades, and it looks vulnerable to breaking them if something hard got sucked through.



Some actual numbers on power consumption comparing to some other drives would be interesting.

[wingssail]

Sean, you already know that i think most of your ideas are so far extreme that they land in fruitcake zone. But that is OK since we need the extreme view in order to sense where the middle is, (who ever wants the middle, not me)

But among all your fruitcake views, this large diameter, slowly turning propeller intrigues me. No matter what power source we have, if we can increase the efficiency with a large, slow turning prop, that's got some real potential.

Originally Posted by seandepagnier

...My prop diameter is currently the same as my draft, so I don't actually need to run it partially out, but when it is deeper it works a little better, but then it could hit bottom before the boat does...

But NO, if we really are going to rely on "sailing" instead of motoring, we need a good sailboat, and that means more draft then a 33ft toy tri with little keels. My boat has 8' We could install quite a large propeller on boats like this. (Even normal cruisng boats have 6' draft. This goes back to my suggestion that you come up with a "real" prototype for a cruising sailboat, 40', good sailing, suitable for a family of four, with a, oh, say 100mile range)

...It's just not easily possible to do with diesel power because the engine is very heavy compared to electric so it must sit where it is, and then there is no way to transmit the power to such a large prop because it can no longer be located where most inboard props are...

I can't believe that you have such a limited imagination when you have already come up with all these other ideas. How about put the diesel in the middle, down low, turn it around so the shaft comes out pointing forward, then put a v-drive up front and an exit out the side of the hull, and a LONG shaft to the back of the boat, with a mechanism to raise the prop up out of the water for sailing. A R2AK competitor already did this.

.

[Singularity]

Originally Posted by seandepagnier

...According to physics, there are substantial benefits possible, on the order of doubling efficiency over what most cruisers have.

The laws of physics include bumble bees and bird wings. Bumble bees ought not fly and, to date, it's impossible to build a propeller that can change cord, camber, and span/diameter on the fly (outside of small models). Modulating these variables is not what a variable pitch prop does.

It's just not easily possible to do with diesel power because the engine is very heavy compared to electric so it must sit where it is, and then there is no way to transmit the power to such a large prop because it can no longer be located where most inboard props are.

Think of a hydraulic windlass. It's really no big deal to mount a hydraulic drive unit on a pylon below a boat to swing a large prop driven by a diesel engine located anywhere on the boat. So why isn't this done more often, or to swing massive diameter propellers?

diesel is already very inefficient (most of the energy going to heating water) so why would ultimate energy efficiency be a priority? It already can push the boat fast for a long time and so it explains the compromises taken by the industry to greatly simplify things.

Big oil people move a lot of oil. They have a lot of money, always want more, and have the means to pay for technology to move oil more cheaply, but to date they haven't figured out how to swing a 100 foot prop beneath an oil tanker. Could real-world engineering challenges be the answer, and not some devious plot to hide fuel-saving technology?

carbon fiber propellers are cheaper and always outperform bronze ones, but bronze propellers are still very common.

I've got a 26" prop. Are you telling me that I can get a carbon fiber replacement for less money than a bronze replacement? From where?

It's also well known that variable pitch greatly improves efficiency across speeds but this is rarely seen.

This is simply not correct, while the idea seems to underpin much of your analysis. A fixed-pitch prop will always be more efficient precisely in the performance window for which it was designed. In other words, a fixed-pitch prop designed to turn XXXrpm at hull speed XX.X will always outperform a variable pitch propeller at the same rpm and hull speed. You can haggle over diesel vs electric torque curves, but if I (probably like most) run my engine I only run it in a small window for maximum efficiency in the first place. So why should I want a variable pitch contraption?

Since you can burn a bit more diesel which has huge energy potential to compensate since it is extremely cheap ( it's subsidized as debt onto future generations) it's cheaper than getting a variable pitch one.

Again, this sentiment is like a great eraser that allows ignoring the real-world engineering difficulties that real-world engineers with funding have yet to sort out....while intermixing the ecologic aspect of things. It's quite easy to engineer and build mock-ups and partial-scale models where loads are small...quite another to engineer in larger structures. Frankly your application is, effectively, a scale model. You can suggest that everyone conform to a scale no larger than your own, but this is an unrealistic supposition.

[seandepagnier]

Originally Posted by Singularity

The laws of physics include bumble bees and bird wings. Bumble bees ought not fly and, to date, it's impossible to build a propeller that can change cord, camber, and span/diameter on the fly (outside of small models). Modulating these variables is not what a variable pitch prop does.

A variable pitch and variable camber prop would be very interesting. Changing the span as well? I'm not sure this is useful, why would it be?

Does anyone know about a variable camber prop? Fish, dolphins, whales all have this already.

My sculling oar is variable pitch. I notice I intuitively have a lower pitch when the boat is first being blown backwards by the wind after just pulling the anchor and I gradually increase the pitch (by changing the pressure or hand placement along the handle which must be mounted at an angle to the shaft) as the boat starts moving faster into the wind.


I wonder how feasible it would be to use electric power on a sculling oar as it's essentially a single blade counter rotating propeller with variable pitch and very large surface area and is a good emergency rudder. It also gives maneuverability similar to an outboard that can hinge.

Think of a hydraulic windlass. It's really no big deal to mount a hydraulic drive unit on a pylon below a boat to swing a large prop driven by a diesel engine located anywhere on the boat. So why isn't this done more often, or to swing massive diameter propellers?

Because of hydraulic losses which are substantial. They waste about half the power which would basically negate the benefit. For a windlass the duration is short and it doesn't matter. Hydraulic autopilots use about twice as much power as fully electro mechanical ones.

Big oil people move a lot of oil. They have a lot of money, always want more, and have the means to pay for technology to move oil more cheaply, but to date they haven't figured out how to swing a 100 foot prop beneath an oil tanker. Could real-world engineering challenges be the answer, and not some devious plot to hide fuel-saving technology?

The latest I've seen is twin props which cost a million each and are basically as big as they could make them on the ship. Also have a look at the titanic propellers, they are similarly fairly large.

I've got a 26" prop. Are you telling me that I can get a carbon fiber replacement for less money than a bronze replacement? From where?

I got a 32" carbon prop from hobbyking for $60. I'm don't think this prop could work for you, but it gives an indication of cost. You could certainly make a carbon prop yourself, and consider it can be thinner it will be more efficient. How much does carbon and epoxy cost and what would it cost for the materials to make this prop. What does your bronze replacement cost?

This is simply not correct, while the idea seems to underpin much of your analysis. A fixed-pitch prop will always be more efficient precisely in the performance window for which it was designed. In other words, a fixed-pitch prop designed to turn XXXrpm at hull speed XX.X will always outperform a variable pitch propeller at the same rpm and hull speed.

By how much does the fixed pitch outperform the variable pitch? How did you determine this?

A "performance window" is easy to engineer specifically for, but maybe not a realistic usage because I constantly see the same boats going at different speeds, dragging things like trawling nets behind them, or with different levels of windage also changing with with potential if there are sails. The window changes so a variable pitch is useful and I have seen them on a few boats and they are also a lot better in reverse which is not really important, but there is that.

[seandepagnier]

Originally Posted by wingssail

Sean, you already know that i think most of your ideas are so far extreme that they land in fruitcake zone. But that is OK since we need the extreme view in order to sense where the middle is, (who ever wants the middle, not me)

But among all your fruitcake views, this large diameter, slowly turning propeller intrigues me. No matter what power source we have, if we can increase the efficiency with a large, slow turning prop, that's got some real potential


But NO, if we really are going to rely on "sailing" instead of motoring, we need a good sailboat, and that means more draft then a 33ft toy tri with little keels. My boat has 8' We could install quite a large propeller on boats like this. (Even normal cruisng boats have 6' draft. This goes back to my suggestion that you come up with a "real" prototype for a cruising sailboat, 40', good sailing, suitable for a family of four, with a, oh, say 100mile range)



.

A toy tri? It's big enough to live one for one person. It can sail 20 knots on a reach, can your boat sail 20 knots? Will my boat without a diesel engine make most passages faster or slower than a typical cruising boat? Which boat is more likely to avoid the center of a storm?

For a family of 4, they make 60ft trimarans, and they can sail even faster.

Maybe I consider success already being able to motor 5 miles on $50 worth of lithium batteries without sun. I use 120 watts motoring and I have 600 watts of solar panels so this is basically unlimited motoring. If it's winter I would rather scull to stay warm, but realistically the sailing efficiency is what is most important and similarly lacking from most cruising boats but outside the scope of this thread.

If you want a 100 mile range, fine, but maybe you should come up with the prototype not me, because I don't need such a range and never will, but you can be sure it's possible to do it for a reasonable cost.

[newhaul]

I will stick with diesel . Just love burning anchient plant life .

[Pete7]

Interesting set up, got any photos, of the boat and the engine bay?

Pete

Originally Posted by misfits

Logged in twice in one day, omg.

I've had an electric boat for 4 seasons now. It spends the summer swinging on a mooring or at an anchorage up on Penobscot Bay in Maine.
Yes there are limitations but I have no plans on being a world cruiser. I have a Honda generator in addition to 260 watts of 24 volt panels that are wired in series.
This spring I motored 24 NM in 5 hours from it's winter home to my mooring using the generator to drive a 25 amp charger. I arrived at my destination with the battery bank at 65% SOC. My propulsion bank is 150 AH, 48 volt, FLA. I also have a separate 12 volt house bank that powers a 2000 watt inverter for a microwave, plus refrigeration in addition to the other normal stuff.

I realized my propulsion bank just sits most of the time so I installed a 48 volt DC water heater element. I came up with that approach after a thread here on this forum 5 years ago about heating hot water.

95% of the time the solar system provides all the energy to run this boat .

For me the way I use my boat, electric works. Are there times I wish she had diesel, abso****inlutely. But I don't miss the maintenance or smell.