Rational for a Hybrid?

[billknny]

Originally Posted by donradcliffe

I saw an ad for a new controllable pitch propellor the other day, but can't find it again. It would change the rationale for a hybrid sailboat, because it would allow you to do some significant battery charging while sailing in stronger breezes. The only drawback is that it adds complexity and maintenance, and is probably sinfully expensive.

Actually, the variable pitch in not needed. Prop shaft driven alternators have been around and successful for a very long time.

[TonyDove]

As usual in threads of this kind, there are a host of opinions all based on different underlying assumptions … so the opinions end up talking past each other and never reach a rational conclusion.

Starting from basics … an electric propulsion system needs batteries and a motor/propeller. Let's assume that the motor/propeller are sized correctly for the boat we are fitting it to. The size of battery bank determines the range/duration of motoring.

Simplest case … If it's sufficient to get you from the dock to the sailing area … and then back from the sailing area to the dock again … it's done it's job and can be recharged from shore-power.

While sailing, there are designs that provide for hydro-generation (for free) … so some/most charging can get done while sailing, leaving less to be done from shore-power (paid for).

That's the fundamental proposition. The longer the sailing … the greater the hydro-generation and the better the proposition. So long range cruising is a better proposition than day-sailing.

Yes … batteries weigh a lot … let's assume we go Lithium to minimise weight and volume … you get quite a few batteries for the same weight of an equivalent diesel with associated, fuel, cooling and exhaust system.

However … we then come up against two scenarios where this ideal breaks down … becalmed and storm. These scenarios are what give rise to the Hybrid solution.

In either case … we could do what sail-boats of yesteryear did … sit it out. After all … it's only been the past 200 years that sailors have had the option of starting up some kind of engine to provide propulsion.

If we get becalmed … sitting it out is a pretty good option unless there is a strong current and some nasty foul ground down stream in the current. So we would like to be able to crank up a donkey and motor out of harm's way before resuming the sit it out option and waiting for the wind to return. This option has the least requirement for power generation … while becalmed there is unlikely to be significant wave action … and of course there will be no head to wind issues. So we need a sufficiently powerful generator to motor for a while … how long? Well, probably only a couple of hours … we are only talking about getting out of harm's way … not crossing an ocean.

If we have storm conditions … we would have to assume we are on a lee shore … or we would do what sail-boats have done in storms for thousands of years and sail out of it or through it. However, this is definitely a worse situation than the becalmed scenario. We will have head to wind and significant wave action to contend with. Of course we would have to question what sort of seamanship got us onto a lee shore in storm conditions in the first place … but **** happens and that's a discussion for another thread. Again … we need a sufficiently powerful generator to motor for a while … in more taxing conditions. How long for? In this case … probably a fair while longer than the becalmed situation. But let's not go too far with this … again, we need to get out of harm's way … far enough off the lee shore to resume what sail-boats have done for thousands of years and sail out of or through the storm. In other words … to give ourselves sailing room. Or room to deploy a series drogue or parachute or whatever other means of coping with a big storm we may prefer, if it comes to a real big-time bad situation. Let's look at the conditions … few people with a diesel would want to batter themselves or their boat by driving into the teeth of the storm at full throttle. We want to make headway … not win a race. And again … we are only giving ourselves sailing room … not crossing an ocean.

All of the above argue for a generator powerful enough to match or exceed the likely drawdown on the batteries from motoring over a relatively short timeframe/distance. I'll leave you to do the detailed math. If we are resorting to motoring instead of sailing, we are either becalmed or in a storm on a lee shore. In either case … we don't want to go full throttle … so we will be happy to plug away at what? ⅔ throttle or thereabouts? Not happy with that assumption? Remember that electric propulsion provides greater torque at lower revs than a diesel … so I'd be pretty confident about ⅔ power. For the sake of easy numbers let's assume we have a 15Kw electric motor … so we will be drawing around 10Kw. so our generator will need to provide around 10Kw of recharge capacity. Add a bit for losses and other power draw (instruments and what have you) and we are probably looking at around a 11Kw to 12Kw generator.

So back to the original question … does it make sense? We aren't spending much on fuel … most of the time we wouldn't be running the generator unless we are becalmed or in a lee shore storm. Most of the time we will be sailing and will be hydro-generating all the power we need over long periods of sailing. Sure the initial capital cost is higher … and the batteries may be heavier if we have a big battery bank … but we probably had a big house battery bank anyway. I'd estimate doubling the weight of the house bank we already have. I've seen some pretty huge estimates of the battery size requirement … but if our assumption is that we mostly sail and rarely motor for more than an hour or so, our battery bank doesn't need to be massive. It's the propulsion batteries that are the significant additional weight. The diesel generator is only slightly heavier than a diesel engine. Assuming a sail drive … the electric sail drive, prop and motor are only slightly heavier than the equivalent sail drive, prop and gearbox. The fuel requirement is probably less … so there is a weight saving there.

I've also seen people estimate battery weight by adding up lots of 12V batteries to give the 48V (probably) equivalent. Check the specs though … a purpose built 24V battery weighs less than 2 x 12V batteries of the same total AHr rating. Sure the difference is small - but it all adds up - or in this case, doesn't add up.

So is it worth it? As a purely economic proposition … probably not, although it may prove to be equivalent or marginally cheaper over the long haul, simply by not using anywhere near as much fuel or needing as much maintenance, despite the significantly higher up-front capital cost. The additional weight is a problem … but not as big a problem as many make it out to be. It really comes down to what value you place on being green(er) and the peace and quiet of silent motoring for the typical motoring duration. As to the long distance cruiser versus day sailer argument … the more time you spend sailing and hydro-generating to charge the batteries … versus occasional generator charging … the more sense it makes.

Happy Sailing

[gmakhs]

Searching for the perfect schenario for my boat , I will share my current opinion ( which been changing the more I study the issue )
My boat have an 8 hp Volvo penta , this is enouph to move the boat efficiently and inexpensive (0.5l per hour )
In case my engine dies a repair cost (if it's repairable) is 400 to 1000 for a rebuild .
A new Volvo penta engine 10 hp (the 8 hp model aren't on the market anymore )
Will cost me 4000euros with the reverse gear .
That being said changing my motor even if it brake down to electric make no sense since the cost will much higher and the running time.much less (my running time is 80 hours with my current tank 50litters)
Now to the hybrid point :
My tohatsu 2.5 outboard died (in the worst place west Africa and I have to paddle through the strong currents )
My options now are to get a new outboard here or repair or replace it in Caribbean , the cost either way will be around 500 euro .
I can remove the motor of the outboard and replace it with an electric motor of the shame output (rpm and hp), this will give me an outboard that can move my boat for one hour (dropping the batteries to 50 % soc) , and when underway I can charge the battery bank with no much drag from its small propeller (something I already have test using .y wind generator as hydro with the shame size of propeller) a solution that fits my needs (my solar is more than enouph but extra power is always welcome ), and I won't have to start the motor .
This comes with cons :
More weight on the transform (which is the base of.my rudder as well )
Won't work well in both taks
Dinghy will need a battery something difficult to achieve , but maybe possible with some Chinese lithium
.
So finally conclusion this option fits the mother ship but not the dinghy .

That's the only hybrid system that makes sense to me any other that includes generator or.motor to power an electric motor doesn't not fit the cruising world.

P.s going only electric with 3 to 5 hours of range is like going without motor at all but on high expense , I can't imagine an electric motor going up river like I had to do in cassamance for 8 hours after miss calculating the tide

[BigBeakie]

TonyDove,

Thank you for such a lucid summary of the viability of cruising using hybrid EP, when necessary.

In addition to your thoughts, we have seen the benefits of using a larger solar array to exploit the superior performance of electric at lower kW levels which still give respectable hull speeds. We will be able to motor on our 4kW solar alone without drawing down on the propulsion bank, for becalmed situations or cruising areas of very low winds such as equatorial regions, the BC inside passage, up rivers etc.

Solar is the best bang for the buck for low wind EP cruising, next to regen when the wind is blowing. Assuming you have a sailboat, of course.


Sent from my iPad using Cruisers Sailing Forum

[rsn48]

I haven't read all the responses, but I am also a rail fan. All those diesels out there pulling long trains are all diesel electrics, have been for a donkeys age. The only recent change over, and still happening, in the train locomotives is they are moving to AC generators to power their electric motors.

Sometimes when technology crosses over, people tend to think this is something new when in reality its something old. So talking propane powered outboards, realize all the forklifts in North America, or almost all have been propane powered for decades.

And in a funny reversal of life imitating hobbies, in model railroading we have been running trains with wireless receivers, using computers, decoders etc for about 20 years now. Some train companies now run smaller road engines for switching (for example, in Vancouver BC, engines switching grain cars) wireless without an engineer in the cabs. They copied the hobby idea. If you see an engine running in your city with a flashing orange light on top of the cab, its being run wireless. Look for a guy walking around with a box in front of him he's carrying, its the wireless throttle.

[Adelie]

Originally Posted by rsn48

I haven't read all the responses, but I am also a rail fan. All those diesels out there pulling long trains are all diesel electrics, have been for a donkeys age. The only recent change over, and still happening, in the train locomotives is they are moving to AC generators to power their electric motors.

. . .

Was there an intent to suggest diesel-electric drive for small cruising boats?

[john61ct]

And surely all the battery powered forklifts out there are a better example than the propane ones.

[Adelie]

Originally Posted by john61ct

And surely all the battery powered forklifts out there are a better example than the propane ones.

Battery vs Propane for forklifts involve an issue no boat has to deal with, namely indoor operation.

Propane gives off a lot less CO than gas engines which is why is even considered for indoor use. Even then propane can only be used in very large spaces (warehouses) or spaces with large ventilation openings (ie open garage doors) and where there are only a moderate number of forklifts being used. The costs of use are similar between gas and electric but the speed to change propane bottles vs recharging a battery is the big advantage of propane forklifts but depends on location of use.

The choice of propane vs battery for forklifts depends on the circumstances of the particular industrial niche they occupy and the relative prevalence of one or the other holds no guide for use on boats.

[john61ct]

I was just responding to

Originally Posted by rsn48

all the forklifts in North America, or almost all have been propane powered for decades

[a64pilot]

Originally Posted by john61ct

And surely all the battery powered forklifts out there are a better example than the propane ones.

Battery powered forklift is actually a good example.
The ones I operated as a kid working in a warehouse, the batteries weighted I think about 2000 lbs, were about 4’ tall and about 3’ thick and maybe 4’ wide.
You could swap them out with another forklift if you had to, but in limited not constant use the battery would last one eight hour shift and be recharged overnight.

The propane lifts were much more powerful and fast, and could just by changing tanks by hand run as many shifts as necessary, even continuously. The tanks were horizontal and I think about 30 lbs.
Propane has I think about half the energy density of gasoline.