Sail boat engine choice - electric or diesel

[Dave_S]

Originally Posted by seandepagnier

Current yacht propellers are around 20-25% efficient at best speed.

So where are the improvements?

1) much larger propellers needed
2) contra-rotating propellers
3) kort nozzles.
4) variable pitch, variable camber propellers

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[/URL]

These are all things you can apply to a diesel as well as electric. No benifit of one over the other, both technologies will benefit equally.

Don't get me wrong, I'd love electric to surge ahead and for some applications it might be ok but for most uses I don't think it is the right decision.

[Dockhead]

Originally Posted by seandepagnier

again and again this is repeated but it's wrong. It's because everyone is doing regen wrong. You can regen on any boat and even at slow speeds, but you _cannot_ use a propeller to do it efficient. You must have a purpose built repeller which is not a propeller flipped around (unless you can reach through the 4th dimension and convert left shoes into right ones) So once you have a repeller, it must be sufficient size for the speed, and then you will produce that much power, and it can be hundreds of watts at 2 knots if your repeller is 6ft diameter.

If you try to regen using a tiny undersized inboard propeller it won't do much below 5 knots and even then the efficiency (power/drag) is terrible.

No argument here -- IF you have a purpose built regen propeller, then that's a different ballgame altogether. But that is not what people do and not what the OP was proposing.

Originally Posted by seandepagnier

In bad weather the sails are very powerful, and I clawed off many lee shores using storm jib beating in 40 knots. Counting on an engine to do this is poor seamanship and often boats are lost and talked about at length on this forum doing just this, rather than using sails!!

You simply do not need to power against weather and this way of thinking needs a shift.. . .

In bad weather and in all kinds of situations, Plan A for me is to always use the sails and not the engine. For many reasons -- boat is more stable, sails are more powerful, engine vulnerable to fuel problems in really bad sea states, etc. etc.


HOWEVER, as I think all really experienced sailors know, there ARE dangerous situations where you really need power to get out. If you are badly embayed for example -- not just a lee shore, but an indented one. In very close quarters -- getting through a narrow opening directly against the wind. Some situations with strong currents. It's a minority of what you encounter -- normally in my book the sails are primary in bad weather -- but powering out of a bad situation is one of those things which -- when you DO need it, you REALLY need it.

[Mirage35]

Originally Posted by seandepagnier

only because they don't use stupidly undersized propellers like 99.9% of cruising boats do.



Your prop diameter must be more than half the beam of the vessel. If this is not true, you are doing propulsion wrong.

I've been half-following this discussion to see what I might learn, and would really like to see if I understood this properly.

A prop diameter equal to half the beam would mean that my prop would have the same draft as my keel. This would make me nervous in shallow waters.

Did I read it right?

[oldgoat]

Woww ~~~ lots of electric grumpy nonbelievers here, lol

As anyone considering chopping off his mast, covering his entire monohull with high density cells on an awning, and adding small propellers mounted dynamo under the hull by the dozen?

[MichaelPrichard]

Originally Posted by Dockhead

No argument here -- IF you have a purpose built regen propeller, then that's a different ballgame altogether. But that is not what people do and not what the OP was proposing.

As someone who has done what the OP is proposing (to a degree), I can at least validate that regen is possible below 5knots, even with "propellors" as opposed to specialized "repellors" (sp?). I've replaced twin 18hp Yanmar 2GM20F engine/saildrives with twin retractable 7.1kW POD drives and 15" propellors. At 5 knots, I'll usually see around 150W, but there's still 75-125W coming in at 4 knots. I top out at about 900W at 10 knots in our 38 foot FP Athena catamaran, and we're definitely under-propped as we hit max RPM (under power) with the motors at only 60% load, so one would assume that larger, better tuned props should yield more. The motor dealer claimed they'd seen 1.2kW regen per motor for the 7.1kW POD. I agree that electric drive offers the opportunity to use larger props with peak torque at stall and lower RPMs without using a transmission (my POD drives top out at 1050rpm, perfect for slow props).

Originally Posted by Dockhead

In bad weather and in all kinds of situations, Plan A for me is to always use the sails and not the engine. For many reasons -- boat is more stable, sails are more powerful, engine vulnerable to fuel problems in really bad sea states, etc. etc.

HOWEVER, as I think all really experienced sailors know, there ARE dangerous situations where you really need power to get out. If you are badly embayed for example -- not just a lee shore, but an indented one. In very close quarters -- getting through a narrow opening directly against the wind. Some situations with strong currents. It's a minority of what you encounter -- normally in my book the sails are primary in bad weather -- but powering out of a bad situation is one of those things which -- when you DO need it, you REALLY need it.

I think, as stated elsewhere in this thread, the above statement applies at least as well for electric drives, and I'd argue that the simplicity and lack of required maintenance makes them significantly safer in exactly these types of emergency situations. Sure, a perfectly maintained diesel "should" start right up when called upon, but assuming mine were at least partially indicative of the state of many older boats out there (the vast majority), there is a great deal that can go wrong and usually does at the very worst moment; clogged or air locked water pump">raw water pump, water in tank shaken by rough seas makes it into fuel pickup, transmission shift cable linkage pops loose as operator pushes it a bit too hard.... these aren't theoretical, they've all happened with the 3 diesels I've owned, admittedly older and possibly abused (former charter), but nonetheless all-too possible.

Compare this to my POD drives which have a single moving part (ignoring the balls in the bearings). As long as they get power (and the controller functions) they provide instant power with no maintenance. I never sail with less than about 40% in my pack and on my boat, with 21.2kWh of battery, and 5kW required for 5 knots of speed that amounts to 1.7hrs of operation or 8.5 miles. If I can afford to dial that down to 4 knots, I only consume 1.7kW which raises my range to ~20miles. That should get me out of any lee bay, I'd guess.

It's been mentioned many times on many threads here, but it keeps getting missed or ignored; any electric drive boat can extend its limited battery range with the addition of a generator, as the OP himself has stated. This option is easily added/removed as needed depending on cruising plans and gives the best of both worlds; day sailing, leave the generator at home (we haven't even bought one yet); going on a long cruise and want the luxury of long range motoring, pop it in. My motor dealer had a client that installed an 8 or 12kW (can't remember exactly) generator to keep his twin 7.1kW POD drive driven cat motoring so that he could do the Great Loop. But for those of us who mostly day sail or do short coastal cruises (like the OP), a generator isn't even necessary.

Some folks may want/prefer/need diesel if they plan to motor a lot or simply want the comfort of guaranteed long range, but just like many folks are discovering that a Nissan Leaf, Chevy Bolt or a Tesla has enough range for their needs, so, too can electric drive boats be the best option for many of us, and the OP appears to be one of us. We sail our boat at least 3 times more (almost every weekend) now than we ever did with the diesels, mostly because I was the only diesel "mechanic" available to nurse those beasts and they were a source of ongoing anxiety that limited our enjoyment. Now we don't waste any time dithering; we just drop the lines and go when the mood hits us.

[carstendenmark]

MichaelPrichard, thanks for your view and experiences !

I wish that the latest readers would read all posts before replying :-)


I see it as a HYBRID sailboat. CAN go alone, and CAN go hybrid.

Popular with cars, so why not boats...
People with electric cars seems to do more planning when making longer trips than those with gas cars.
Same as for sailing.

[Fore and Aft]

Michael Prichard that's a great bit of information. May I ad that I think it depends on your cruising ground when it comes to range. Here in the Sandy Straits Fraser Island area 4 knots for 20 miles is just not going to work on a bad day. We have been caught on a number of times pushing the tides and 20+ knots head winds for 20 miles+ just to get home. The sea state is not the issue, it's relatively sheltered but we needed every bit of our Yanmar diesel to push us through. As for diesel engines being unreliable I would say you have had some bad luck. None of these issues have happened on the 5 yachts l have owned. Maybe we have different idea's of maintenance?
Cheers

[Pete7]

Originally Posted by carstendenmark

People with electric cars seems to do more planning when making longer trips than those with gas cars.
Same as for sailing.

I think this is the key, planning to avoid bad weather for example. You are correct you can't go to windward in 40 knots. Nor 35 knots for that matter, we tried and failed, went home and set off again the next day with much better conditions. Lets be honest NW Europe is blessed with pretty accurate weather forecasts 5 days out. You might get a variation of one BF scale up or down locally, but storms are well forecast. The sudden squalls seen in the US mid-west or Chesapeake bay very rare this side of the pond.

Careful planning around tidal gates which for us means The Needles, Portland and Start Point etc, need some thought. However, tides work both ways, get them right and you are on a conveyor belt eating up the miles.

The Baltic won't be much of a problem, other than the wind that picks up after lunch and dies down at sunset. Across to Norway again just plan carefully.

If you are not on a tight timetable and can afford to take your time or choose when to make a passage in the best conditions, EP could really work.

We did meet one old Danish guy sailing a electric yacht about 26ft a couple of years ago. He said he was leaving and good bye, then cast of the mooring lines without starting the engine. I was up like a flash going for the boat hook less it all went pear shaped. He flicked a switch in the cockpit, pressed a small lever and silently moved away. He looked back with a smile. That summer he had traveled from Denmark to the Scillies and was now on his way home for the winter.

I think you should go for it, you only live once.

Plus more Europeans may be following in your foot steps in years to come. One way to encourage the use of EV will be to slowly increase the fuel duty on carbon fuels until EV becomes financially beneficial to the masses. No new petrol or diesel cars planned for the UK beyond 2035.

Pete

[carstendenmark]

Thanks, Pete7 !

Another aspect of "going electric", not mentioning the element of feeling environmentally well, is the pricing of diesel and power.
You will not need any more diesel, for sure.

So, to go almost completely "for free", a small investment in solar (flexible ?) panels may be very beneficial in certain countries, please see below. For leisure cruising, put up one or two panels facing the mid day sun, when you leave your boat at the berth.
If you're in a hurry, just plug your charger to shore power.

Diesel/Liter prices Sep. 7. 2020, https://www.globalpetrolprices.com/diesel_prices/ :
USA : 0.64 Denmark : 1.40 UK : 1.55
Power/KWh prices June 2020, https://www.globalpetrolprices.com/electricity_prices/ :
USA : 0.14 Denmark : 0.36 UK : 0.27

Of course, all this "saving money in the long run" doesn't mean much at all, if you just use your sails :-)

Environment :
I filled up my MD6A diesel in the marina by a jerrycan, and spilled just an oz of diesel in the water. It was a bit shameful for me to see that two days after, there were still a visible oil film on the water, up to 10 berths away.

[newhaul]

Originally Posted by carstendenmark

Thanks, Pete7 !

Another aspect of "going electric", not mentioning the element of feeling environmentally well, is the pricing of diesel and power.
You will not need any more diesel, for sure.

So, to go almost completely "for free", a small investment in solar (flexible ?) panels may be very beneficial in certain countries, please see below. For leisure cruising, put up one or two panels facing the mid day sun, when you leave your boat at the berth.
If you're in a hurry, just plug your charger to shore power.

Diesel/Liter prices Sep. 7. 2020, https://www.globalpetrolprices.com/diesel_prices/ :
USA : 0.64 Denmark : 1.40 UK : 1.55
Power/KWh prices June 2020, https://www.globalpetrolprices.com/electricity_prices/ :
USA : 0.14 Denmark : 0.36 UK : 0.27

Of course, all this "saving money in the long run" doesn't mean much at all, if you just use your sails :-)

Environment :
I filled up my MD6A diesel in the marina by a jerrycan, and spilled just an oz of diesel in the water. It was a bit shameful for me to see that two days after, there were still a visible oil film on the water, up to 10 berths away.

Then there are those of us that sail year round so also have diesel heat.
If you spilled any fuel into the water the best option is a small squirt of Dawn dish soap.
Use of sorbent pads when fueling are a real good idea .

Most sailors abhore using the diesel mains to charge batteries .
The price of electric means nothing if you are using solar or wind to recharge .

[valhalla360]

Originally Posted by Adelie

The Uma folks have posted that 1.2kW with their old motor got them 3kt boat speed in flat conditions. That 1.6hp.

Would a 1.6hp gas motor get that boat to 3kt?

Assuming the same prop and a reasonable reduction gear to effect the same torque a the prop shaft.

By definition, yes. HP = Torque * RPM

Or to state it differently: RPM = HP / Torque. Turn the same prop at the same RPM, I would expect the same speed.

[valhalla360]

Originally Posted by carstendenmark

Thanks, Pete7 !

Another aspect of "going electric", not mentioning the element of feeling environmentally well, is the pricing of diesel and power.
You will not need any more diesel, for sure.

So, to go almost completely "for free", a small investment in solar (flexible ?) panels may be very beneficial in certain countries, please see below. For leisure cruising, put up one or two panels facing the mid day sun, when you leave your boat at the berth.
If you're in a hurry, just plug your charger to shore power.

Diesel/Liter prices Sep. 7. 2020, https://www.globalpetrolprices.com/diesel_prices/ :
USA : 0.64 Denmark : 1.40 UK : 1.55
Power/KWh prices June 2020, https://www.globalpetrolprices.com/electricity_prices/ :
USA : 0.14 Denmark : 0.36 UK : 0.27

Of course, all this "saving money in the long run" doesn't mean much at all, if you just use your sails :-)

Environment :
I filled up my MD6A diesel in the marina by a jerrycan, and spilled just an oz of diesel in the water. It was a bit shameful for me to see that two days after, there were still a visible oil film on the water, up to 10 berths away.

The item in red is the real elephant in the room regarding electric conversions.
- If you really are a purist sailor, you will use a negligible amount of diesel anyway, so the cost per liter is really irrelevant and has to be balanced against the higher up front cost of an electric system (system not just the motor).
- If you actually motor regularly, electric can't provide the speed and range and becomes a major limitation.

I do appreciate that you used "feeling" when discussing the eco aspect.

PS: There really is no excuse for spilling fuel into the water. I suggest getting a good siphon. Never had an issue with spillage using a simple siphon to transfer from a jerry can. Also, if the fuel fill is in an awkward location, consider moving it.

[skipmac]

Originally Posted by oldgoat

Woww ~~~ lots of electric grumpy nonbelievers here, lol

As anyone considering chopping off his mast, covering his entire monohull with high density cells on an awning, and adding small propellers mounted dynamo under the hull by the dozen?

Grumpy? Nonbelievers?

Belief has nothing to do with the science and the facts. I am an electrical engineer and for many reasons would love to convert my boat to electric but I have done the math and it is not practical.

With the current state of technology you have just a couple of options if you want to switch to electric drive.

1. Reasonable cost system but with extremely limited range. Basically just enough battery to get from the dock out the channel to sail and to get back again.

2. Longer cruising range two very expensive options:

- Very large battery system that would be very expensive, add weight and require some very large system to recharge all the batteries. Unless you have a large catamaran there is not enough room to install enough panels so you have to add some other method which will be a large, diesel generator so you are just back to another diesel engine.

I looked at the costs for both options and it would be more than double possibly more than triple the cost of a complete new engine, transmission and the cost of professional installation.

If you have data or personal experience that shows otherwise I would sincerely like to hear it.

[Dockhead]

Originally Posted by MichaelPrichard

As someone who has done what the OP is proposing (to a degree), I can at least validate that regen is possible below 5knots, even with "propellors" as opposed to specialized "repellors" (sp?). I've replaced twin 18hp Yanmar 2GM20F engine/saildrives with twin retractable 7.1kW POD drives and 15" propellors. At 5 knots, I'll usually see around 150W, but there's still 75-125W coming in at 4 knots. I top out at about 900W at 10 knots in our 38 foot FP Athena catamaran, and we're definitely under-propped as we hit max RPM (under power) with the motors at only 60% load, so one would assume that larger, better tuned props should yield more. The motor dealer claimed they'd seen 1.2kW regen per motor for the 7.1kW POD. I agree that electric drive offers the opportunity to use larger props with peak torque at stall and lower RPMs without using a transmission (my POD drives top out at 1050rpm, perfect for slow props).

Not to be a wet blanket, but this really confirms what a lot of people have been saying about the relative usefulness of regeneration.


150W -- is that per POD? So 300W total? If so, then an hour of regen gives you -- two minutes of full power. Even an hour at full chat at 10kn will only give you enough power for 12 minutes at full power. This is not going to be a major power source.

Originally Posted by MichaelPrichard

. . .I think, as stated elsewhere in this thread, the above statement applies at least as well for electric drives, and I'd argue that the simplicity and lack of required maintenance makes them significantly safer in exactly these types of emergency situations. Sure, a perfectly maintained diesel "should" start right up when called upon, but assuming mine were at least partially indicative of the state of many older boats out there (the vast majority), there is a great deal that can go wrong and usually does at the very worst moment . . .

No argument here. Electric is certainly better in this situation, and significantly so, BUT ONLY if you have enough stored power.


AND if you have enough power in the first place -- 14kW is what, 20hp? Isn't that significantly less than a cat your size would normally have? Is it enough to power off the rocks in a storm?

Originally Posted by MichaelPrichard

. . . Compare this to my POD drives which have a single moving part (ignoring the balls in the bearings). As long as they get power (and the controller functions) they provide instant power with no maintenance. I never sail with less than about 40% in my pack and on my boat, with 21.2kWh of battery, and 5kW required for 5 knots of speed that amounts to 1.7hrs of operation or 8.5 miles. If I can afford to dial that down to 4 knots, I only consume 1.7kW which raises my range to ~20miles. That should get me out of any lee bay, I'd guess.

In an emergency you are likely needing full power, so forget the flat calm motoring calculations. But if you really keep minimum of 40% available, that's more than half an hour of full power -- I guess most emergencies could be solved with that amount of stored power. IF, as I said, 20hp is adequate at all.

Originally Posted by MichaelPrichard

It's been mentioned many times on many threads here, but it keeps getting missed or ignored; any electric drive boat can extend its limited battery range with the addition of a generator, as the OP himself has stated. This option is easily added/removed as needed depending on cruising plans and gives the best of both worlds; day sailing, leave the generator at home (we haven't even bought one yet); going on a long cruise and want the luxury of long range motoring, pop it in. My motor dealer had a client that installed an 8 or 12kW (can't remember exactly) generator to keep his twin 7.1kW POD drive driven cat motoring so that he could do the Great Loop. But for those of us who mostly day sail or do short coastal cruises (like the OP), a generator isn't even necessary. . . . .

Proof of the pudding is in the eating, and if you are happy with it, that's all that matters.


I've said it before -- if you are day sailing a lot and with cheap (or unmetered) shore power available every night, electric power is fantastic.


Other use cases might or might not work OK.

[seandepagnier]

Originally Posted by Dave_S

These are all things you can apply to a diesel as well as electric. No benifit of one over the other, both technologies will benefit equally.

This is true, but why do boats with diesel power not do these? My theory is because they can already do hull speed for prolonged periods with very inefficient drive systems so they don't bother optimizing prop efficiency, instead prefer the other advantages of smaller propellers. People who use diesel power obviously don't care about efficiency very much, since the engines themselves aren't very efficient.


If you optimized efficiency like this, you could have an engine with 1/3rd the power and run on vegetable oil you buy at a grocery store price and it would still cost you less. coconut oil is also proven a lot better for engines as well as the emissions are not un-healthy.


The problem is when you try to adapt an existing drive system to electric where you really start to care a lot about efficiency, and the false assumption that the drive system was engineered with efficiency in mind: it wasn't


A single person pedal powered boat needs a 16 inch propeller to be really efficient. How does that scale to powering your vessel?

HOWEVER, as I think all really experienced sailors know, there ARE dangerous situations where you really need power to get out. If you are badly embayed for example -- not just a lee shore, but an indented one. In very close quarters -- getting through a narrow opening directly against the wind. Some situations with strong currents. It's a minority of what you encounter -- normally in my book the sails are primary in bad weather -- but powering out of a bad situation is one of those things which -- when you DO need it, you REALLY need it.

These situations you described:


1) likely you can wait it out if the opening is narrow, it's probably protected inside
2) it is not a very far distance to cover so electric power will do
3) really experienced sailors can tack their boats in 2-3 boat lengths. So it's really an impossible scenario that you would need prolonged maximum power for more than a few minutes anyway.

Originally Posted by AnglaisInHull

I've been half-following this discussion to see what I might learn, and would really like to see if I understood this properly.

A prop diameter equal to half the beam would mean that my prop would have the same draft as my keel. This would make me nervous in shallow waters.

Did I read it right?

Yes. My electric outboard is on an elevator so it can adjust to any depth. So at best efficiency, the lowest point is the propeller, but it can raise up to any level even with the propeller partially out of the water so this is not a limitation in shallow water.

Originally Posted by Fore and Aft

Michael Prichard that's a great bit of information. May I ad that I think it depends on your cruising ground when it comes to range. Here in the Sandy Straits Fraser Island area 4 knots for 20 miles is just not going to work on a bad day. We have been caught on a number of times pushing the tides and 20+ knots head winds for 20 miles+ just to get home.
Cheers

This is a perfect example of what I suggest no one ever should bother trying to do: motor against a strong tide. It is much better to wait for tide change, either way the boat is waiting before or after it gets there, so it doesn't waste any time.

Originally Posted by carstendenmark

Environment :
I filled up my MD6A diesel in the marina by a jerrycan, and spilled just an oz of diesel in the water. It was a bit shameful for me to see that two days after, there were still a visible oil film on the water, up to 10 berths away.

This probably was not the diesel you spilled: people spill all the time.

Originally Posted by skipmac

Grumpy? Nonbelievers?

Belief has nothing to do with the science and the facts. I am an electrical engineer and for many reasons would love to convert my boat to electric but I have done the math and it is not practical.



- Very large battery system that would be very expensive, add weight and require

I am also an electrical engineer and have built hundreds of autopilots for cruising boats. I have built my own MPPT that today harvested more power into the battery than the panel was rated.

I think your math is wrong.

I got 320 watt hour lithium battery for $54 (free shipping) and bms for $12. This ends up being $660 for a 3.2kwh battery (and weight only 16kg) for those who want larger capacity. The prices are lower than ever.

Originally Posted by newhaul

Wrong and lets not play the bs climate change card shall we .

the climate change "card" is not bs, but stating so is denying science and certainly invalidates many of your other false assumptions.