Sail boat engine choice - electric or diesel

[carstendenmark]

@ Pete7 : I actually have a spinnaker, unused by the former owner :-)
But so far, it's just me sailing her. My wife is not of much help (yet).

By courtesy to DMI, I attach a today map of the currents outside my "back door", showing 3.5 knots. Quite normal, and more than your estimated half knot.
Waves can get rough, when a current from N and the waves from SW (built up from Germany to here) meets.
So, because of the current, it often needs some planning to cross the Langeland Belt in a sailboat if you are going to be where you intend to go. Timing is the keyword - run with the current, or wait.

When crossing the DWR running N-S in the same area (main route to the Baltic), I feel that it is good to be able to get the heck out of there when the wind suddenly dies, and the fog comes sneaking. My weak horn honking will never be heard by a drunken russian coaster captain. I don't believe much in any passive radar reflector, and I don't have an active.
A big motor with a big prop will have the "rabbit out of hole effect" = a steady hull speed at 6.8 knots, I think.

- And maybe more economic when cruising at normal speed, because of the big prop ?? Anyone with actual experience, not theory ?

[TrentePieds]

Uhm... Near as I can recollect in the Langelandsbelt which is the only place near your homeport where you might have any reason to worry about the strength of current, the tides are "mixed tides" i.e. two unequal peaks and troughs each day. In consequence the direction of current also changes four times a day. Which means that you'll never have a long wait before things turn in your favour if they are not at the moment. And it's cruising and sailing for pleasure, we are, is it not?.

This morning, Sept 10, you'd have had a low just after midninght, the following high would have occurred as your alarm clock woke you, a low at noon-ish and a high at suppertime, which is just about now as I write.

I have a hunch, but DMI (Danish Meteorological Institute) could prove me wrong, the rises and falls would be in the order of 6 inches or so. Langelandsbæltet is narrow and not very deep, all right, and the Kattegat and the Baltic are both big waters (by Danish standards), but I doubt that a 3.5 knot current would be the result of a 6" change in water level.

I would guess that as I write your wind is westerly with just a touch of north in it, at about 12 or 15 knots. In other words: Just PERFECT sailing conditions for your boat.

Anyway, planning is the major part of the fun. We all have to do it, don't we? Near me there is a place called Dodd Narrows maybe 300 yards wide, and just over half a mile long. The current often runs 8 knots, and the slack water lasts maybe 15 minutes. It is not possible, when you enter the narrows to see what is coming into the narrows at the other end due to an outcrop about halfway along. In the days before we had VHF, going into the narrows could pucker you a bit because you never knew what was coming the other way. These days you just get on the blower with a 'Securité" and agree with "affected" traffic on who should do what and to whom. That way there is only one boat in the narrows at a time.

In the days when I taught on these shores I sometimes took a 65 footer through there on a following tide, but turning around, stemming the current, slowing down and letting the set take me through the narrows backwards.

Anyway, all that aside, while the weather is good, pop over to "Sydhavsøerne". I doubt that the "Silver Rudder" (Fyn rundt) was held this year due to the pandemic. I would love to have been able to do that, just once. Your little boat would be just perfect for it.

TP

[seandepagnier]

Originally Posted by carstendenmark

@ seandepagnier :
Much respect for the efficiency of a prop system put on the transom. But deplacement boat owners wants a prop that stays submerged, even in rough weather with high waves.
That means an inboard engine.

inboards are never going to be very efficient. There are all kinds of things people "want" but are not always aligned with logic.

If there is rough weather there is really no reason to be using a propeller. dragging a prop sideways and up and down kills efficiency. You would need the individual blades to constantly be changing their pitch with force feedback to a brain to get any sort of decent efficiency. In rough weather you can count on the wind, and exceptions to this are short-lasting.

The bancas in the Phil's is not efficient in rough weather, because the bamboo outrigger system drags heavily whenever hit by a rough wave (and there are plenty).
The efficiency comes because of the narrow shaped hull. The outriggers are just for keeping the hull upright.

The british banned them in past because they could sail faster than their steam boats going more than 20 knots under sail. The bancas are efficient in the philippines, and they would be more efficient in the sounds here too, but people are stuborrn and prefer powerboats that create significant wakes and the waves aren't that big. I think the same logic applies to inboards: people are set in their ways.

All the around the world races are won by trimarans. It's clear trimarans are the most efficient sailing boat and multihulls are also more efficient under power.

Of course, it's all a moot point in terms of comparing diesel to electric as you can apply any size prop you like to either and for a similar HP it will generate the same thrust and propeller efficiency.

It would be interesting to see a cruising boat with diesel engine go more than 50 miles (2-3 knots) in a dead calm on a single gallon of fuel because it would set a new standard and not be a cost concern to run on vegetable oil. It is possible to do this but no one even tries, but instead claim "HP is HP" when what they really mean is, "I want to have lots of HP and use it inefficiently".

diesel junkies don't care about efficiency. So we should ignore what they do when we use electric power and abandon inboards and undersized propellers.

The human powered boat people know what they are doing, and it's not hard to scale this up to larger vessels. In the race to alaska no one even considers inboards.

If I put a larger prop on my boat (with inboard), would you suggest me to use a submarine prop, a tugboat prop or an airplane prop style ? I can 3D print any shape.

For inboards the prop is too close to the hull and the diameter limited. There are also stuffing box losses which I do not have.

It is much better you use an outboard, but if you do anyway, then it really depends on the speed you want to optimize because you have limited diameter. If you want the best efficiency at low speeds (most sensible) use a high aspect ratio airplane style propeller with low pitch and biggest diameter possible, but there are rules regarding hull clearance that limit this more than physical space unfortunately. Maybe you can built a kort nozzel.

How do you 3d print the prop? I 3d printed my repeller and glassed over it. Do you make a mold or glass over a print as a form? I also need to 3d print a left-hand propeller so I can have dual counter rotating props.

Could you please provide information of your higher efficient mppt ?
Every Watt counts when sucking up energy from the sun !

I got high output for a brief moment because it had just rained and the panels were cool then full sun with reflections. This explains the higher than rated output. I don't claim higher output than other mppt, but it cost $12 to build the mppt I use. I get up to 18% increase in power over a non-mppt, and it can buck or boost the voltage.

https://github.com/seandepagnier/mppt

Originally Posted by skipmac

Actually you just proved my math. 3.2 kwh battery bank on moderate sized cruising sailboat motoring even in a dead calm would last maybe half an hour. To motor for just 3-4 hours you would need ten times the battery capacity so almost $7,000 and nd kg, assuming your weight spec is correct though it sounds a bit light to me.

at 3.2kwh I can motor for 26 hours. So the $65 battery I have 0.32kwh is enough to motor for 2-3 hours and I think this is what you meant to say is long enough and proved my math is right or you are using the wrong figures for actual power consumption. This $45 motor is also a good one, but now it cost a little more so I got a deal:

https://www.ebay.com/itm/C6374-effic...gAAOSwc39bh2AF

There's your problem. Thrust and power are different things.

It is thrust that you need to control the boat in the "difficult situations" mentioned.



Regardless, most inboard propellers are less than 40% efficient because they are too small in diameter. This is just a physical fact. Fish, whales, dolphins, all have tails optimal size to their body, and nature is efficient. It's not hard to see a 16 inch prop is not anywhere near enough on a boat with 9ft beam.

It's possible to have propellers that are 90% efficient and this is really a huge difference in energy and really important for electric boats but historically not very important for diesel powered ones. The same is true with cars: their wheels are too small and they weigh a lot for what they carry. No one cares because fuel is too cheap, and the speed limitation isn't energy but it's just unsafe to go faster than they do. It's the electric bicycles that can go hundreds of miles a day on just the solar panels on the trailer: not cars.

[newhaul]

Originally Posted by seandepagnier

The human powered boat people know what they are doing, and it's not hard to scale this up to larger vessels. In the race to alaska no one even considers inboards.


.

There is a reason they don't use inboard engines on the R2AK race they are banned in all forms including electric .
.

[wingssail]

seandepagnier, I'm sorry, and respectfully, I think you have some loose screws somewhere. You are actually suggesting a propeller which is 50% the size of the beam of your boat?

Originally Posted by seandepagnier

"All the around the world races are won by trimarans. It's clear trimarans are the most efficient sailing boat", Wrong! Maybe in terms of speed alone. But in boats there are a few more measures of useful efficiency. Ability to carry a useful load, for example. Few racing trimarans can do that, and the ones that can are immense in size. Show me a 40' trimaran which is as efficient as, for example, an Island Packet 38, in any measure other than speed.

"On Bancas the efficiency comes because of the narrow shaped hull. The outriggers are just for keeping the hull upright." Irrelevant! But the difference in racing tri's is that the amas are big enough to support the boat, so the rest of the vessel is out of the water when fully powered up. Bancas do not have that capability, it is a matter of what materials they have available, and the purpose of the vessels, which is to carry a few people and a small payload for the least amount of energy (petrol, BTW).

"It would be interesting to see a cruising boat with diesel engine go more than 50 miles (2-3 knots) in a dead calm on a single gallon of fuel because it would set a new standard and not be a trimaran which is cost concern to run on vegetable oil" I would be interesting to me to see a battery powered boat which could go more than 50 miles (2-3)knots in a dead calm on a single charge of one battery the size of a gallon of diesel fuel. It would be more interesting to see a battery powered boat which could go ANYWHERE in a strong breeze under power.

"the $65 battery I have 0.32kwh is enough to motor for 2-3 hours" You are bragging about this? At 3-4 knots you are going to get about 7.5 miles down the track. Very impressive! My yacht, at 3.4 kts, uses .26 gal/hr, and one gallon will get me 13 miles, and that is bringing my house along with me.

"This is just a physical fact. Fish, whales, dolphins, all have tails optimal size to their body, and nature is efficient. It's not hard to see a 16 inch prop is not anywhere near enough on a boat with 9ft beam." Wrong! The fastest fish have very small tails, look at a tuna.

Bottom lines seandepagnier:

For going slow under power a big propeller is more efficient. For normal speeds, and for many other reasons, a smaller propeller is better.

For regen, even the most efficient repeller is simply a drag device which slows the boat MORE than the amount of power it produces.

HP is HP. No electric engine is going to propel a boat, using the same propeller, any faster than a diesel (or gasoline, or any fuel source, of the same horse power. The propeller does not know how the shaft is being turned. To think otherwise is ignoring physics.

And MOST OF ALL, regardless of how nice and quiet and clean and simple an electric purports to be, the fact that you cannot carry a fuel source to go 500 miles means they are a non-starter for the vast majority of cruising vessels. When they can, come back to us.

[skipmac]

Originally Posted by seandepagnier

at 3.2kwh I can motor for 26 hours. So the $65 battery I have 0.32kwh is enough to motor for 2-3 hours and I think this is what you meant to say is long enough and proved my math is right or you are using the wrong figures for actual power consumption. This $45 motor is also a good one, but now it cost a little more so I got a deal:

https://www.ebay.com/itm/C6374-effic...gAAOSwc39bh2AF

So you use 0.12-0.16 kw when you're motoring? Maybe I forgot basic math but wouldn't that approximately equal 0.2 HP? That seems incredibly low to me. Maybe with no current and a good tail wind. Even a 5 hp motor could barely move a large cruising boat at full throttle. As a rough estimate it takes 10-15 HP to move a moderate sized 35-45' cruiser at a few kts, roughly 8-10 kW.

The link you posted shows this: C6374 efficience sensored brushless motor 170KV for electric skateboard US SHIP. The motor shaft is 10 mm, less than 1/2". Not sure what they mean by 170KV but I'm pretty sure that isn't a 170,000 V motor. Unless you're powering a canoe I don't see how you could ever get more than a knot or so in a flat, dead calm, with a motor this small.

And no, 2-3 hours total run time is not enough for 99% of the boaters and cruisers I know. Again, that is just enough to motor from the dock to the ocean and back. For long distance cruising it is only slightly different than sailing without an engine at all. That's fine for some people but not most.

[carstendenmark]

@ seandepagnier :

Once I had a sailboat with an outboard. In rough waves, it rpm'ed high and low. NOT useful.
Have you tried your own outboard in rough waves yet ?

For optimum performance we should simply copy nature and install a horisontal and flexible whale tailfin (a monofin) between the keel and the rudder. It can even be as wide as the beam if you like, and not going any deeper than the keel.
It will need the up-down movement provided by some mechanic gear.
For reversing, the fin needs to be rotated 180 deg., as the propulsion of the fin is only one way. That will limit the size of the fin.
Here's one to watch :

https://www.youtube.com/watch?v=VR9bIVwjUmQ

His patent : https://www.patentauction.com/patent.php?nb=13043
It might take a while, before this becomes mainstream on a sailboat...

A trimaran is very efficient, no doubt !
But a philippine banca is basically a large outrigger canoe. It's NOT a trimaran. And most of them has huge guzzling gas engines, all leftovers from the US. Manouvering a banca is in best case a mess, when coming to a port.

Use ABS or ASA for 3D-printing. You can even make it hollow inside to save material.
Reinforcement by using a carbon fiber filament is possible.
ABS is not resistant to UV light, so cover up the surface with epoxy.
ASA is UV resistant.

"Fuel is too cheap", you say.
Well, the fuel itself IS very cheap, but taxes are certainly not cheap where I come from !

**********
"Feeling environmental correct" : Use a fuel that does not make our common air toxic.
CO2 is not a toxic - the plants love it !!

[seandepagnier]

Originally Posted by newhaul

There is a reason they don't use inboard engines on the R2AK race they are banned in all forms including electric .
.

They don't use pedal powered inboards because inboards are not efficient. This is nothing to do with engines or motors, but drive systems.

Originally Posted by wingssail

seandepagnier, I'm sorry, and respectfully, I think you have some loose screws somewhere._ You are actually suggesting a propeller which is 50% the size of the beam of your boat?

yes. I have screws loose for suggesting something different from what you are used to? I also suggest cars should have 4-5ft diameter wheels and they should drive slower and the fuel consumption would be less than half.

Bottom lines seandepagnier:

For going slow under power a big propeller is more efficient. For normal speeds, and for many other reasons, a smaller propeller is better.

speeds under 35 knots without planing, a bigger propeller is _always_ more efficient. Even at 6 knots or 8 knots. An even bigger propeller is even more efficient. smaller propellers are only more efficient at speeds above 35 knots and/or planning.

smaller propellers may be cheaper or more convenient maybe this is what you mean by "better" ?

HP is HP. No electric engine is going to propel a boat, using the same propeller, any faster than a diesel (or gasoline, or any fuel source, of the same horse power. The propeller does not know how the shaft is being turned. To think otherwise is ignoring physics.

Electric motors don't weigh as much. I can't mount a diesel engine on an elevator and turn a high aspect ratio prop in the way that I do. So electric motors are easier to adapt to use in more efficient ways.

diesel engines are very heavy compared to electric so they need to be mounted lower down and this leads to inboards with all the compromises or other losses.

And MOST OF ALL, regardless of how nice and quiet and clean and simple an electric purports to be, the fact that you cannot carry a fuel source to go 500 miles means they are a non-starter for the vast majority of cruising vessels. When they can, come back to us.

why 500 miles? I cruised everywhere without any propellers motors or engines. Why is this a non-starter? How do you get this 500 number? I think a better number is 5 miles.

Originally Posted by skipmac

So you use 0.12-0.16 kw when you're motoring? Maybe I forgot basic math but wouldn't that approximately equal 0.2 HP?

Yes. Actually only 0.16HP. Did you see my video? I am motoring 2 knots using 120 watts. 1 knot is 70 watts. Once I improve this a bit I expect 3 knots to be 200-240 watts.

I was going against a slight wind not with the wind. If you used a ICE to power this propeller instead of electric, it would go more than 100 miles on a gallon. It seems people who use engines aren't interested in this type of thing since about 100 years ago.

That seems incredibly low to me. Maybe with no current and a good tail wind. Even a 5 hp motor could barely move a large cruising boat at find.ull throttle. As a rough estimate it takes 10-15 HP to move a moderate sized 35-45' cruiser at a few kts, roughly 8-10 kW.

check your numbers again.

sailing uma went 3 knots using 1.2kw and their system was terribly inefficient. It does not take 8-10kw: this is not in line with even the inefficient electric conversions that use inboards.

Despite this, the sails should always be up. I know this from sculling everywhere in canals and harbors etc.... The motor then is just to enhance control and the power used is in short infrequent bursts and to keep the sails full if the air is really light.

The link you posted shows this: C6374 efficience sensored brushless motor 170KV for electric skateboard US SHIP. The motor shaft is 10 mm, less than 1/2". Not sure what they mean by 170KV but I'm pretty sure that isn't a 170,000 V motor. Unless you're powering a canoe I don't see how you could ever get more than a knot or so in a flat, dead calm, with a motor this small.

I'm surprised as an "electrical engineer" you don't know what 170kv means in this context. it is rpm per volt. Anyway, you should post some schematics of interesting things you design.

This motor is capable of 3.2kw, but at only 120 watts I am already going 2 knots.

Originally Posted by carstendenmark

@ seandepagnier :
Once I had a sailboat with an outboard. In rough waves, it rpm'ed high and low. NOT useful.
Have you tried your own outboard in rough waves yet ?

again, I would never do this, I use the sails in rough waves. no propeller is efficient in rough waves unless the blades are individually dynamically re-pitching all of the time, and I have never even heard of someone implementing this.

For optimum performance we should simply copy nature and install a horisontal and flexible whale tailfin (a monofin) between the keel and the rudder. It can even be as wide as the beam if you like, and not going any deeper than the keel.
It will need the up-down movement provided by some mechanic gear.
For reversing, the fin needs to be rotated 180 deg., as the propulsion of the fin is only one way. That will limit the size of the fin.
It might take a while, before this becomes mainstream on a sailboat...

You are correct. This is more efficient than a propeller as well, but as far as I know it's difficult to efficiently actuate it without room temperature superconductors.

I also consider making the sculling oar power assist. This would be really interesting, and with a high-efficiency ball screw it could rival my electric outboard in efficiency as the blade is much larger.

A trimaran is very efficient, no doubt !
But a philippine banca is basically a large outrigger canoe. It's NOT a trimaran. And most of them has huge guzzling gas engines, all leftovers from the US. Manouvering a banca is in best case a mess, when coming to a port.

all trade offs for different boats. A 40ft banca with 8 phillipinos and 1 american can go 7 knots using a 150cc engine and 10 knots using two engines. The outriggers lift out of the water when they are going fast for very little drag. This would save a ton of fuel around here where the waves are no bigger than the philippines, but the local rednecks use boats with significantly larger engines and go only marginally faster while making large wakes.

Use ABS or ASA for 3D-printing. You can even make it hollow inside to save material.
Reinforcement by using a carbon fiber filament is possible..
ABS is not resistant to UV light, so cover up the surface with epoxy.
ASA is UV resistant.

I need to enclose the printer, but I had to print the repeller in 2 pieces because it is 18 inch diameter and I could not print it in a single piece. This limits strength and I feel like at high speeds it will just break apart. I do make it hollow inside of course. I covered it with fiberglass and it seems very strong.

"Fuel is too cheap", you say.
Well, the fuel itself IS very cheap, but taxes are certainly not cheap where I come from !

Right now it's $2 per gallon, or about 50 cents a liter: this is way too cheap and encourages wasting it.

I think they should tax it until the price is the same as vegetable oil or better yet, just not allow it, and you can just use vegetable oil instead.

*********
"Feeling environmental correct" : Use a fuel that does not make our common air toxic.
CO2 is not a toxic - the plants love it !!

vegetable oil exhaust isn't very bad, but diesel fumes are. I'm not talking about co2 making the air toxic, but the slick I see in the harbor and the black smoke coming out of exhaust.

Plants in the wild land are not benefiting much from extra co2 in most cases because the limitation is lack of water or nitrogen and other nutrients, not co2.

[newhaul]

Originally Posted by seandepagnier

They don't use pedal powered inboards because inboards are not efficient. This is nothing to do with engines or motors, but drive systems.


yes. I have screws loose for suggesting something different from what you are used to? I also suggest cars should have 4-5ft diameter wheels and they should drive slower and the fuel consumption would be less than half.

speeds under 35 knots without planing, a bigger propeller is _always_ more efficient. Even at 6 knots or 8 knots. An even bigger propeller is even more efficient. smaller propellers are only more efficient at speeds above 35 knots and/or planning.

smaller propellers may be cheaper or more convenient maybe this is what you mean by "better" ?
Electric motors don't weigh as much. I can't mount a diesel engine on an elevator and turn a high aspect ratio prop in the way that I do. So electric motors are easier to adapt to use in more efficient ways.

diesel engines are very heavy compared to electric so they need to be mounted lower down and this leads to inboards with all the compromises or other losses.
why 500 miles? I cruised everywhere without any propellers motors or engines. Why is this a non-starter? How do you get this 500 number? I think a better number is 5 miles.

Yes. Actually only 0.16HP. Did you see my video? I am motoring 2 knots using 120 watts. 1 knot is 70 watts. Once I improve this a bit I expect 3 knots to be 200-240 watts.

I was going against a slight wind not with the wind. If you used a ICE to power this propeller instead of electric, it would go more than 100 miles on a gallon. It seems people who use engines aren't interested in this type of thing since about 100 years ago.
check your numbers again.

sailing uma went 3 knots using 1.2kw and their system was terribly inefficient. It does not take 8-10kw: this is not in line with even the inefficient electric conversions that use inboards.

Despite this, the sails should always be up. I know this from sculling everywhere in canals and harbors etc.... The motor then is just to enhance control and the power used is in short infrequent bursts and to keep the sails full if the air is really light.
I'm surprised as an "electrical engineer" you don't know what 170kv means in this context. it is rpm per volt. Anyway, you should post some schematics of interesting things you design.

This motor is capable of 3.2kw, but at only 120 watts I am already going 2 knots.

again, I would never do this, I use the sails in rough waves. no propeller is efficient in rough waves unless the blades are individually dynamically re-pitching all of the time, and I have never even heard of someone implementing this.
You are correct. This is more efficient than a propeller as well, but as far as I know it's difficult to efficiently actuate it without room temperature superconductors.

I also consider making the sculling oar power assist. This would be really interesting, and with a high-efficiency ball screw it could rival my electric outboard in efficiency as the blade is much larger.
all trade offs for different boats. A 40ft banca with 8 phillipinos and 1 american can go 7 knots using a 150cc engine and 10 knots using two engines. The outriggers lift out of the water when they are going fast for very little drag. This would save a ton of fuel around here where the waves are no bigger than the philippines, but the local rednecks use boats with significantly larger engines and go only marginally faster while making large wakes.
I need to enclose the printer, but I had to print the repeller in 2 pieces because it is 18 inch diameter and I could not print it in a single piece. This limits strength and I feel like at high speeds it will just break apart. I do make it hollow inside of course. I covered it with fiberglass and it seems very strong.
Right now it's $2 per gallon, or about 50 cents a liter: this is way too cheap and encourages wasting it.

I think they should tax it until the price is the same as vegetable oil or better yet, just not allow it, and you can just use vegetable oil instead.
vegetable oil exhaust isn't very bad, but diesel fumes are. I'm not talking about co2 making the air toxic, but the slick I see in the harbor and the black smoke coming out of exhaust.

Plants in the wild land are not benefiting much from extra co2 in most cases because the limitation is lack of water or nitrogen and other nutrients, not co2.

Just so much wrong in this post . Also I'm still waiting on the specs of your battery iaw the questions I asked about it.

Btw yes there are always a couple pedal power boats in the R2AK.

[Jim Cate]

Sean, could you elaborate upon your large diameter props as applied to larger, say 40-50 foot, typical cruising yachts? I find it hard to conceive how one could drive a perhaps 6 foot diameter prop, mounted astern of the boat, nor how one could then raise it above the water somehow to avoid the obviously large drag from such a prop when sailing? And then support it adequately in severe weather whilst raised

I'm not denying the efficiency benefits of the large prop, just having a hard time seeing a practical method of doin' the job as described.

Jim

[chrisr]

Originally Posted by Jim Cate

Sean, could you elaborate upon your large diameter props as applied to larger, say 40-50 foot, typical cruising yachts? I find it hard to conceive how one could drive a perhaps 6 foot diameter prop, mounted astern of the boat, nor how one could then raise it above the water somehow to avoid the obviously large drag from such a prop when sailing? And then support it adequately in severe weather whilst raised

I'm not denying the efficiency benefits of the large prop, just having a hard time seeing a practical method of doin' the job as described.

Jim

jim,

i think what we are seeing here is an example of theory meeting reality

cheers,

[newhaul]

Gougeon 32 Refit in 2015: Pedal drives on 2018 R2AK boats

[seandepagnier]

Originally Posted by newhaul

Gougeon 32 Refit in 2015: Pedal drives on 2018 R2AK boats

Pictures of outboard style propellers far away from the hull with high-aspect ratio large diameter propellers.

Originally Posted by Jim Cate

Sean, could you elaborate upon your large diameter props as applied to larger, say 40-50 foot, typical cruising yachts? I find it hard to conceive how one could drive a perhaps 6 foot diameter prop, mounted astern of the boat, nor how one could then raise it above the water somehow to avoid the obviously large drag from such a prop when sailing? And then support it adequately in severe weather whilst raised

I'mt not denying the efficiency benefits of the large prop, just having a hard time seeing a practical method of doin' the job as described.

Jim

It's a great question, and the ultimate answer remains unclear but it is up to us to explore the possibilities and find new solutions.

It's a lot easier to engineer an inboard with small fast turning propeller, and with fossil fuels the compromise almost makes sense because of the heavy engine needing to be located where it is, and difficulty and expensive in gearing it down and being able to handle such high torque on the shaft as well as no where for a larger propeller to be located. When fuel is so cheap and it can already go hull speed for long distances with significant prop slip no one questions it. Once something is working in a useful way, most people tend to just copy it which explains the proliferation of inboards we have today.


When dealing with electric conversions efficiency is very important especially using solar power. I have a few ideas I think can work on any size boat.



1) use multiple motors/propellers. This allows you to use smaller propellers as the swept area is the same. This may be more manageble on larger boats the same as multiple masts and sails while also offering redundancy. The propellers can be counter rotating to improve efficiency.
2) a towing submarine: This could have a large propeller on a submarine kept on deck. It can be deployed/retrieved much like an anchor. The submarine would dive below the surface under waves and tow the main boat. It offers superior maneuverability and efficiency. The power can be supplied along the tow cable.
3) use 2 bladed high-aspect ratio propeller. This makes the large propeller less awkward because when aligned vertical it really isn't that wide or difficult to deal with, and 2 blades is the highest efficiency.
4) use variable pitch propellers to maintain high efficiency over a wider range of conditions.
5) use elevator on the back of boat to raise lower the propeller to allow it to operate in shallow water, or deeper when possible. This eliminates drag under sail, and makes it easy to unfoul from lines as well as work on the motor.
6) use large shrouded propeller (kort nozzel) with belt going around the outside of the propeller. This makes it possible to reduce the motor speed with a single stage reduction giving higher efficiency as well.

Any other ideas for electric propulsion with high-efficiency greatly appreciated. I really like the dolphin flipper idea but I am skeptical about actual efficiency vs a propeller with current technology.

@newhaul and @skipmac

You seem to just want to justify diesel power because it's what you are doing already. This is basic human behavior: typical for people without much imagination. It's also clear you are not really very good sailors or engineers, not knowing the first thing about electric motors insisting that you need to motor 500 miles which everyone knows is a nonsense requirement, despite this, electric boats have a longer range as they generate power underway. I have nothing more to reply to your statements, I will ignore your biased perspective from here on.

[TrentePieds]

Quote: :"4) use variable pitch propellers to maintain high efficiency over a wider range of conditions."

Antique technology. Was is fairly widespread use in Scowegian fishing boats a hundred years ago. Here is a link to a factory that still makes them. I think their smallest is about 30"D. Given Sean's comments about the desirability of large props, this should be grist for his mill. Smaller VP props are made by others, and some are indeed reversible props so as to save the hassles of a reversing gear box.

TrentePieds

[wingssail]

seandepagnier, I think it was me that proposed 500 miles as a meaningful target for motoring capability, not newhaul or skipmac, so I am the one you should dismiss as unimaginative and a bad engineer, not them.

Originally Posted by seandepagnier

...You seem to just want to justify diesel power because it's what you are doing already. This is basic human behavior: typical for people without much imagination. It's also clear you are not really very good sailors or engineers, not knowing the first thing about electric motors insisting that you need to motor 500 miles which everyone knows is a nonsense requirement..., despite this, electric boats have a longer range as they generate power underway. I have nothing more to reply to your statements, I will ignore your biased perspective from here on.

Not everyone "knows" that 500 miles is a nonsense requirement. We each have our own requirements and it is not up to others to ridicule that which someone else thinks is important.

I cross oceans, under sail, but that 500 nm under power for me is a requirement. I have other requirements which the devices you demonstrate don't yet meet, like the ability to hold up in storm conditions, whether in use or not. Gliding slowly across a glassy calm lake with a home built contraption is useful for demonstrating a concept but it is nowhere near useful for demonstrating its practicality.

You are obviously on to something with your large diameter high aspect ratio and slow turning propellers. Lets see some development of the concept. It's obvious the R2AK crowd had gotten father along than you have.

But we need some inventors with outlandish ideas to explore and lead the way toward something better for the future. Maybe you are one of them. So we should encourage you, and I do, but we need to see a prototype which can truly demonstrate actual possibilities not a delicate home made contraption which doesn't convince me of much (nor does it need to, I am nobody).

For you to go ahead you need refine this to a practical level. If you don't have the funds for that, and if you are confident, then a well documented proposal might help you acquire some funding to build a useful prototype.

But your mis-characterization of the motivations of those who are skeptical, claiming that we just want to justify diesel power because it's what we are doing already, and that we are without much imagination and not really very good sailors or engineers shows an arrogance which is probably going to be limiting of your success.

You need to understand that people besides yourself have valid requirements of their own and also brains.