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Old 18-03-2016, 10:02   #61
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Re: Electric motor for sail boat

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Originally Posted by valhalla360 View Post
Example: I typically run at 6.0-6.5kts and figure 6mpg. I've played with dropping back to around 4.5kts and figure it jumps up to 10-12mpg. If I never wanted to exceed 4.5kts, I could drop back to a 10-15hp engine...very similar to the folks claiming you need less HP with electric motors. But in a few situations, I've needed the full 7-7.5kt hull speed for 15-30minutes and the engine provided it without a fuss (other than being noisy at WOT). An underpowered electric motor would have left me scratching my head how to get upriver against a 5kt current.
No it wouldn't, just like your internal combustion motor you can run an electric drive at partial power for peak efficiency, but full throttle when you need it.
15 t0 30 min you could do on battery, much longer would need a generator to provide enough current in my opinion, and in those cases of course your being powered by an internal combustion engine, but there are other times when you wouldn't have to be, those other times you could go on electric drive.
Be nice to be able to sneak out of an anchorage early in the morning for example, you concern being quiet raising the anchor, lots of time I'd like to be noiseless if I could.
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Old 18-03-2016, 10:17   #62
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Re: Electric motor for sail boat

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No it wouldn't, just like your internal combustion motor you can run an electric drive at partial power for peak efficiency, but full throttle when you need it.
15 t0 30 min you could do on battery, much longer would need a generator to provide enough current in my opinion, and in those cases of course your being powered by an internal combustion engine, but there are other times when you wouldn't have to be, those other times you could go on electric drive.
Be nice to be able to sneak out of an anchorage early in the morning for example, you concern being quiet raising the anchor, lots of time I'd like to be noiseless if I could.
Just pay your dockage fee. I guess you would be appreciated at 3AM. For God's sake don't get a Yanmar diesel outboard, I might wake the dead?
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Old 18-03-2016, 12:09   #63
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Re: Electric motor for sail boat

As always the problem with trying to use a generator to provide propulsion power is what do you do with it th rest of the time? The typical AC generator in a 50' sailboat is going to range around 10kw while the propulsion engine is going to be around 80kw. If you install an 80kw generator to handle propulsion needs it would be massively oversized for house loads so you also need a small generator for house loads.

The only reasonable solution I have seen for this is two smaller generators paired with a very large battery bank. Say a 20kw generator to charge the batteries and a 60kw generator to drive propulsion when you need it. The problem here is that it doesn't get you much, you still have two large engines and need a really large battery bank to store the power.

The real solution is a battery bank with enough usable capacity to drive the boat at full speed for say 4-5 hours and a moderately sized generator and battery bank. But these batteries simply don't exist right now, and likely won't for years to come.
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Old 18-03-2016, 15:37   #64
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Re: Electric motor for sail boat

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Now I said form the beginning I believe that the near term future for electric drive is for a non cruising boat, which I believe is the majority of sailboats, an electric drive ought to appeal to the masses, cruisers are I believe a minority of boat owners, and I believe are less likely to buy a new boat than the average buyer, but I have no data to back that up, just observation is all.

All I'm saying is it's feasible is all, and may well be the best thing for the average sailor who will never really leave the bay and returns to work on Mon. morning and may one day find itself in cruising boats.
I would tend to agree that the vast majority of 30-50' cruising boats are not purchased by long term/long distance cruisers (many dream of it but few do it)

They tend to be bought by cruisers who take weekend trips and maybe 1 or 2 trips per year of a week or two. They don't burn a lot of fuel per year, so fuel savings are negligible. Particularly if you can afford a new boat that costs 6 figures, it's just not an issue. But if that weekend trip is to a destination 30 miles away and the electric boat only has a 20 mile range at 4.5kts, it's a non-starter because the most of these buyers need to be home Sunday night to get to work Monday morning and counting on an unreliable wind is not acceptable.

While it sounds great to use a diesel generator, it's a sizing issue. A generator sized for house loads is unlikely to manage even the 4.5kts feeding the propulsion system once the batteries are dead. A larger generator will be very inefficient running house loads. And the overall system would be more expensive than a standard propulsion system.

Cruising boats are not akin to the prius in terms of use case. As previously shown, a conventional drivetrain can match or beat the prius highway driving. It's city driving where the prius can dominate efficiency. Typical cruising boat operation is not akin to a city driving use case.

Also, the prius was designed and refined based on selling tens of thousands of units per year. As such they can justify massive efforts to refine and squeeze out every last little bit of efficiency. Many of those efforts have little or nothing to do with a hybrid drivetrain.

Your average cruising boat sells less than 50 units per year. A model with more than 1000 units sold over the life of the model is rare. If efficiency was critical, there are many ways you could boost efficiency without changing from conventional diesel to hybrid or pure electric.

If you are willing to accept the limitations, you can have a pure electric or a hybrid boat now but other than to feed the eco-market, it just doesn't make sense from a business perspective. Hybrid cars on the other hand have viable business case.
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Old 18-03-2016, 15:52   #65
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Re: Electric motor for sail boat

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No it wouldn't, just like your internal combustion motor you can run an electric drive at partial power for peak efficiency, but full throttle when you need it.
15 t0 30 min you could do on battery, much longer would need a generator to provide enough current in my opinion, and in those cases of course your being powered by an internal combustion engine, but there are other times when you wouldn't have to be, those other times you could go on electric drive.
Be nice to be able to sneak out of an anchorage early in the morning for example, you concern being quiet raising the anchor, lots of time I'd like to be noiseless if I could.
You missed the point. There are advocates claiming a 10hp electric motor will provide the same power as a 20hp ICE. That is patently false. What is pretty much always comes down to is accepting reduced capabilities.

If you buy the idea that a 10hp and reduced capability are acceptable, you can drop back to a 10hp ICE and call I good while achieving huge advantages.

PS: I don't understand the quite claims for electric motor enthusiasts. When I'm on the bow directing the helmsman with hand signals...I can't hear the motor running and I can't recall hearing others. Then again I've been startled by 1 ton diesel trucks (newer models) sneaking up on me they are so quiet.
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Old 18-03-2016, 15:57   #66
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Re: Electric motor for sail boat

I see 40 to 80 kw being thrown around. Do these people have any idea of the size of these unites.
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Old 18-03-2016, 18:57   #67
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Electric motor for sail boat

Yeah I don't miss the point, a 25 hp or so generator would drive my boat at or close to hull speed, cause my Yanmar making about 25 HP will.
That's roughly about a 24KVA generator, which as you guys say is large for house loads, but the point is you have a large Life-PO battery bank that could be charged at least 10KVA, bank gets close to full, gen off until bank gets low, gen back on. Point is to not run the generator unless there is room in the bank for it.
But if you accept say 70% of hull speed as being all you need straight off the generator, then you get down to probably close to a 10 KVA generator, and that's not all that large really.

It feasible, but probably not economically viable, except for a few that will pay a premium for being green, but I believe
a pure electric drive boat with even only a 20 mile range is viable as a day sailer, It is after all the auxiliary motor, a few have even cruised with no motor and a few even do so with small outboards.


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Old 18-03-2016, 19:07   #68
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Re: Electric motor for sail boat

Sounds adequate for exiting and entering a marina, and little else. Glad it works for you.
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Old 19-03-2016, 00:46   #69
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Re: Electric motor for sail boat

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I see 40 to 80 kw being thrown around. Do these people have any idea of the size of these unites.
Go take a look at the engine size on the average 40' boat. You would expect to see about 2kw/1,000lbs. The 80kw number was from our old 54' with a 120hp engine. It's probably a little large for this discussion admittedly.

But if we assume a 40' boat with a 40hp (30kw) motor, that's the size of generator you need to equal the same propulsive power. Assuming parasitic loads of the engine roughly equal the peak/vs continuious output of the generator. Since it is incredibly difficult to sync two or more AC generators the option really is one large or two small DC generators as well as a massive inverter to run house AC loads.

The problem of course is that you rarely need this much power, most of the time something like 1/2 power is all that's really needed. But those times when you need every bit of power you can get, you really need it. Clawing off a lee shore for instance, or motoring into hurricane force winds to reset a dragging anchor. Even motoring up a strong current, being able to maintain hull speed for a few hours can be critical.

So for our hypothetical 40' with 40hp, operating a 48v DC electric motor, a realistic generator profile would be what a 10kw and 20kw. By the time you price these out plus the electric motor you really haven't saved anything.


A64,
When did you pull the 44hp out of your IP?
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Old 19-03-2016, 01:55   #70
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Re: Electric motor for sail boat

"We may too get one further down the track but we will need a small genset too for the longer hauls. I am considering a small Honda then."

Nope, the genny's ac you need a big dc alternator driven by ? or straight dc genset, they do exist

Not trying to be a dick here but clearly understanding of electricity (& other things) is all over the map on here, a whole lot way past any factual area as well in some instances.

Also antimatters great stuff for energy density but a little hard to get and contain, Antimatter is NOT darkmatter however. antimatter is the fully observable mirror image of normal matter and is regularly created ( and clearly observed) in particle accelerators currently. Darkmatter is predicted by current models of the universe, but unobservable, thus far.

for the true ultimate power source micron diameter wormhole to the expansion phase of the universe.... Now thats the stuff with range!!
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Old 19-03-2016, 02:19   #71
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Re: Electric motor for sail boat

take out the Yanmar and put in a Prius drive train...?
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Old 19-03-2016, 03:17   #72
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Re: Electric motor for sail boat

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Actually in point of fact, all gensets are DC off the coil, which is then rectified to AC so if you know anybody who works on electronics you might try getting them to put a tap in before the power is rectified to AC (with a switch) that might suffice for DC power to charge/run the motor..
Umm... Zeph, you might want to rethink and edit that post...

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Old 19-03-2016, 03:21   #73
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Re: Electric motor for sail boat

OK here goes, look at diesel submarine's drive/charging systems. The really tough part of duplicating these are the various clutch transmission systems that vary the way power is produced for either or both Propulsion and power production/ battery charging.
The poster who was pondering the 80kw ? Was searching for this solution, although in some ways the same as Prius in others a little different the premise is I believe sound. That is borrowing a Prius drive. If it were me though I'd look for a diesel powerplant for the internal combustion part..

I'm sure someone somewhere is doing this, I'd be real interested in hearing about how that works out
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Old 19-03-2016, 03:40   #74
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Re: Electric motor for sail boat

Yeah Jim you're right I was thinking of these honking mil surplus deals I've been dealing with, it wouldn't let me clarify so I just deleted the post to look less idiotic 😀
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Old 19-03-2016, 07:06   #75
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Re: Electric motor for sail boat

If our engine needs to be replaced in a few years I will seriously consider going electric. Battery technology is rapidly changing and sole phelps are getting more efficient. A few years ago I vaguely remember reading about an example of going electric, the weight saved on the electric motor was negated by the weight of the added batteries and generator. There is a federal tax credit (expiring this year) for adding energy efficient stuff to a first and second home. Hopefully the credit will get renewed and allow for the purchase of fuel cells and electric motors.
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