Sail boat engine choice - electric or diesel

[valhalla360]

Originally Posted by Adelie

Propulsive effect per horsepower is significantly higher for electric motors than for ICE.

No HP is HP. There is no such thing as magic electric HP.

Where electric has an advantage is it can generate more HP from lower RPM since it can generate max torque from zero RPM.

So if you are doing 0 to 6kt drag races, yes, the electric powered boat has an advantage.

But cruising monohulls get up to speed and run at constant speed from then on...HP = HP.

[valhalla360]

Originally Posted by carstendenmark

I use the main engine (the sails) as much as possible.
By saying "bad conditions" I didn't mean motoring when unnecessary. I mean BAD.

At 5.5 knots for two hours I can get to calm waters at any time and drop an anchor, even in rough conditions.

My "two hours" is simply a safety issue, not meant for daily constant motoring.

So what's your assumed power draw at 5.5kt against a 40kt headwind and steep 2m waves?

[valhalla360]

Originally Posted by Mauruuru

maybe you would be surprised to know that the US Navy use diesel gen sets driven at constant rpm to drive generators and motors .... is to power ship board ac/dc power and PROPULSION MOTORS! Why, the answer is simple maximum efficiency. A Carnot cycle engine has a max theoretical efficiency around 30%-driven by extreme differences in inlet and exhaust temperatures. So give it 30% then realize max torque from a diesel occurs around 60-70% of full rpm whereas a high (90+%) motor delivers 100% of torque from 1 to top rpm. If you bothered to do the research and ask the questions you might actually come to a different conclusion! Oh yes then you opinions might take some woirk to develop.

Large ships are drastically different animals and not comparable to a small cruising boat.

The real reason they use diesel-electric (as do train locomotives) is because a transmission that can accommodate thousands of HP would be massive and hugely complicated. Also at the sizes involved, they can minimize the losses in power conversion in ways that a small cruising boat can't come close to.

[valhalla360]

Originally Posted by carstendenmark

I live in Denmark, and most people do coastal sailing.
My setup is not meant for world cruising.
However, please watch Youtube "Sailing Uma", a pure electric live-aboard 36' sailboat who criss-crossed the Caribbean and now also crossed the Atlantic.
The electric motor can recharge when sailing by sails.

People buy a sailboat for sailing, not motoring, in my mind :-)

Coastal sailing is where motoring is more critical.

Very few ocean crossings are done under power. If you lose wind or are in storm conditions, you can wait it out typically without risk of hitting anything solid.

Coastal cruising, you often need to make tides or pass thru channels where sailing is difficult to impossible.

Without a generator backup...which defeats the purpose, I would not want a less capable boat for cruising.

As others have mentioned, if you just day sail, it could be quite viable but even though it's a common usage pattern, most buyers have dreams of at least week long trips where they may need to cover miles when the wind isn't cooperating.

As mentioned, solar on a small 29ft monohull is simply not going to work. 500w to fill say 40kwh of battery bank assuming 100% efficiency and no other power draws, will take 80 days.

[newhaul]

Originally Posted by SailMoonShadow

I don't see that a diesel would be any better than electric in that scenario.



That's interesting, I hadn't heard that, thanks for the tip.

On the other hand, what I have heard about the Panama is that yachts are generally rafted in threes with the middle boat providing the propulsion so I would have thought that there's nothing to stop an electric powered boat being on the outside in that configuration. I'll have to investigate!

Has to dow with minimum speeds through the passage/ region
In the Panama it's passage time and lockage timing.
In some others it's about safety from piracy.

[carstendenmark]

valhalla360 (As a dane, I like your name :-), I will not go against the waves in such conditions. With 3 ropes in the main, I can go 270 degrees directions, but not directly to the wind. Riding WITH the waves (smooth sailing), and seek sheltered waters. Please see the map I attached in a previous post, plenty of sheltered waters.
Planning the trip, including the weather forecast, is also about avoiding such conditions. I am not ocean sailing, and if I was, motoring against the wind would be useless anyway. The sails are the main propulsion.
If I want to cross the Baltic, I would bring a sufficient portable generator - I am not religoius to only use the batteries at all times. Then it's a hybrid system, and that's fine with me ! Safety first.
For the "weekenders", a diesel is for sure the best option, if there is any time limit to a passage.
Then they should consider a motor or motorsailer, not a sailboat.
A sailboat is for sailing !

[valhalla360]

Originally Posted by carstendenmark

valhalla360 (As a dane, I like your name :-), I will not go against the waves in such conditions. With 3 ropes in the main, I can go 270 degrees directions, but not directly to the wind. Riding WITH the waves (smooth sailing), and seek sheltered waters. Please see the map I attached in a previous post, plenty of sheltered waters.
Planning the trip, including the weather forecast, is also about avoiding such conditions. I am not ocean sailing, and if I was, motoring against the wind would be useless anyway. The sails are the main propulsion.
If I want to cross the Baltic, I would bring a sufficient portable generator - I am not religoius to only use the batteries at all times. Then it's a hybrid system, and that's fine with me ! Safety first.
For the "weekenders", a diesel is for sure the best option, if there is any time limit to a passage.
Then they should consider a motor or motorsailer, not a sailboat.
A sailboat is for sailing !

Great plan...until it's not.

It's not often but yes, there are times when it's a major problem not to be able to apply power and you can't always just turn and run before the wind and the forecast isn't always right.

[Dockhead]

Originally Posted by carstendenmark

I live in Denmark, and most people do coastal sailing.
My setup is not meant for world cruising.
However, please watch Youtube "Sailing Uma", a pure electric live-aboard 36' sailboat who criss-crossed the Caribbean and now also crossed the Atlantic.
The electric motor can recharge when sailing by sails.

People buy a sailboat for sailing, not motoring, in my mind :-)

Recharging by regeneration works pretty well on larger faster boats, but doesn't work well on smaller slower ones. You should get an exact factual estimate before you count on getting any usable power from regeneration. I doubt that you would on a boat that size.


I would second what A64 said -- if you are day sailing in weather you choose every time (so avoid going out in dead calms), and can charge every night from shore power, this will be great.



Otherwise, the drastically reduced range could be a problem. Would be like having a 2 liter fuel tank -- could you live with that? Think about it.


Diesel propulsion has only one advantage, but it's an advantage that most can't live with out -- power density. There is a lot of energy in a tank full of diesel fuel, and most of us need that energy. I personally have motored for days at a time, on occasion. For any kind of longer distance cruising, it's really good to have that option.


Power can also be needed to get off a lee shore in bad weather, or similar situations in bad weather. Don't fall into the magical thinking trap of counting on x hours of motoring at y speed, when those parameters are chosen according to ideal conditions. How long can you motor at full power? Even for a day sailer, you will want to have a certain amount of endurance at full power, to deal with that kind of situation.

[Dockhead]

Originally Posted by valhalla360

Coastal sailing is where motoring is more critical.

Very few ocean crossings are done under power. If you lose wind or are in storm conditions, you can wait it out typically without risk of hitting anything solid.

Coastal cruising, you often need to make tides or pass thru channels where sailing is difficult to impossible.

Without a generator backup...which defeats the purpose, I would not want a less capable boat for cruising.

As others have mentioned, if you just day sail, it could be quite viable but even though it's a common usage pattern, most buyers have dreams of at least week long trips where they may need to cover miles when the wind isn't cooperating.

As mentioned, solar on a small 29ft monohull is simply not going to work. 500w to fill say 40kwh of battery bank assuming 100% efficiency and no other power draws, will take 80 days.

I recently sailed from one end of the Baltic to the other, nonstop, and without starting the main engine. We were in a race, so it wasn't allowed. It took a week.



It's probably more realistic than most cruisers realize, provided you have light air sails on board and the crew to use them. We had a large A2 assy.



It can sure be tedious in very calm weather, of which we had a few days. And dangerous, crossing heavy traffic areas at very low speed under sail in calm weather.



For cruising I think for the overwhelming majority of people the option to make a bunch of miles under power would be very hard to give up. Do you always have an unlimited amount of time to wait for wind? You never need to get somewhere? But maybe someone could be happy with it.

[chrisr]

something i mentioned earlier, and wish to stress again, is that most (all ?) diesel installations will produce free hot water via waste heat / exhaust

if we are going to compare apples with apples, how will an electric motor produce this hot water ? i suppose via the already over-burdened solar / battery set up ? have you factored this into the power equation ?

what is the comparative efficiency of the the electrical system if you also expect 30l of hot water when you get to your anchorage ?

apples & apples...or apples & lemons ?

cheers,

[Dockhead]

Originally Posted by Mauruuru

maybe you would be surprised to know that the US Navy use diesel gen sets driven at constant rpm to drive generators and motors .... is to power ship board ac/dc power and PROPULSION MOTORS! Why, the answer is simple maximum efficiency. A Carnot cycle engine has a max theoretical efficiency around 30%-driven by extreme differences in inlet and exhaust temperatures. So give it 30% then realize max torque from a diesel occurs around 60-70% of full rpm whereas a high (90+%) motor delivers 100% of torque from 1 to top rpm. If you bothered to do the research and ask the questions you might actually come to a different conclusion! Oh yes then you opinions might take some woirk to develop.

Have you actually done the math? I have.

Take a fuel map for real life gensets and take real life electric motors and calculate the total efficiency. Then take a fuel map for any given real life diesel propulsion motor.

You'll find that even in ideal conditions, the diesel-electric is at least 15% less efficient than the direct drive diesel. Do it; and post your results. I posted mine; they are in one of these threads (we repeat this discussion periodically and for years).

Might be different in big ships, but I kind of doubt that too.

[DeValency]

Funny how some responses ignore completely the OP case - mainly the sailing pattern and specific area.
Based on his situation, a Diesel engine is a total waste if he is now forced to repower at any case.

[valhalla360]

Originally Posted by Dockhead

I recently sailed from one end of the Baltic to the other, nonstop, and without starting the main engine. We were in a race, so it wasn't allowed. It took a week.

Open water passage making, I already said, it's usually not an issue as you can heave to or run because you have space to work with.

It's when you start messing about near land (ie: coastal cruising) where having the ability to power out of a situation is a huge advantage.

Of course, even coastal cruising, it's not once a week that you need that ability. I may only be once every year or two where you run into a situation where it's really nice just to be able to pour on the power and get out of a sticky situation.

Now, is it possible...sure people sail engineless boats but it's way outside the mainstream and any potential future buyer is likely going to look at a marginal system as a big negative.

[Dockhead]

Originally Posted by valhalla360

Open water passage making, I already said, it's usually not an issue as you can heave to or run because you have space to work with.

It's when you start messing about near land (ie: coastal cruising) where having the ability to power out of a situation is a huge advantage.

Of course, even coastal cruising, it's not once a week that you need that ability. I may only be once every year or two where you run into a situation where it's really nice just to be able to pour on the power and get out of a sticky situation.

Now, is it possible...sure people sail engineless boats but it's way outside the mainstream and any potential future buyer is likely going to look at a marginal system as a big negative.

Certainly powering out of a sticky situation is crucially important; I agree. The OP is very smart to be considering electric power with the same horsepower as his old diesel -- not falling into the "magic horsepower" trap of those who foolishly think that an electric motor with 1/3 the power is equivalent.

Can he run that motor at 100% for 30 minutes? I would think that's enough for any given "power out of trouble" situation.

The OP has to decide for himself whether it will work for him or not -- I think it can work in some cases. Like A64 said -- if you're day sailing and recharge every night in a marina, and can always pick your weather -- I think electric power is pretty good.

If you're out for long periods of time coastal cruising -- then I think it's much worse. Carrying a 3kW portable generator kind of defeats the purpose, and would have to be run for long periods of time, if he doesn't have constant access to shore power. Carrying the generator might be tolerable if it's just an occasional thing.

[Adelie]

Originally Posted by waterman46

....
Has anyone mentioned the short battery life and environmental cost that will result from constantly running batteries down every time an electric powered boat goes out even for a daysail?

I use electric propulsion for daysailing. I’ve never run my batteries all the way down.