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Old 06-12-2019, 12:09   #46
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by skipmac View Post
That's how i read the post and I think that figure is grossly inflated.

It's worse than that. ICE power ratings aren't based on INPUT power, but on OUTPUT power. Beyond an engineering curiosity, or perhaps a global warming consideration (both are useful discussions), the efficiency of the engine is irrelevant. A 30hp engine puts out 30hp, regardless of internal efficiency. After that, it's drive train efficiency (which is rather high), and electric motors and ICE motors both have to deal with that. Electric motors don't have different shafts, struts, seals, or propellers. Yes, they perhaps can avoid the transmission -- but those run around 90% (https://www.machinedesign.com/archiv...x-efficiencies)
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Old 06-12-2019, 12:18   #47
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by harlem24 View Post
Hm, Silent Yachts use a cat, Engergy Observer which is completely run by solar is a cat. So there seems not to be such a big issue with two hulls...
Even the premiere vessel for the launch of Volvo Pentas electric propulsion system is a freakin' Fountain Pajot!
Why is that? Did they all miss something?
I think the obvious factor in the examples you gave is the additional space for solar cells.
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Old 06-12-2019, 13:01   #48
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Re: Gemini 105mc conversion Diesel to EV?

So, you can place about 1kW of Solar on a Gemini if you build an arch.
With that you would be able to produce about 6,4kWh of electricity over a normal day, with good weather even more.
For sure you would need a not too small battery, but even 14-20kW should be enough.
This should give you more then enough energy to go places.
And even a Gemini is still a sailing vessel, so it's just auxillary power.
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Old 06-12-2019, 13:18   #49
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by harlem24 View Post
So, you can place about 1kW of Solar on a Gemini if you build an arch.
With that you would be able to produce about 6,4kWh of electricity over a normal day, with good weather even more.
For sure you would need a not too small battery, but even 14-20kW should be enough.
This should give you more then enough energy to go places.
And even a Gemini is still a sailing vessel, so it's just auxillary power.

Questions:
* Are you saying a 1kW solar panel will give 6.4kWh a day? Full power for 6 hours? That seems very high -- like double.
* How much power are you assuming for house loads? I use 2kWh a day for house loads on my 43' monohull. That takes away from the solar budget to propulsion power.
* Batteries are not normally rated in kW (well, yes, they are, as in CCA, but amps are rarely the issue). Normally they are in kWh (or Ah). 20kW will give two hours of motoring with a 10kW motor. For a day sailor, going from anchor to sails up, and from sails down to anchor, yes, agreed, that's plenty. But not for motoring 20 miles home on a windless Sunday.
* It's just auxiliary power for all sailboats. But many cruising sailors motor far more than an hour a day, at least on some days. We did a 9 day cruise of the Chesapeake Bay this summer. Probably covered close to 300 miles, with the first 7 days almost 100% sail. But the last two days were 30 miles each under power. You can't just look at the first 7 days (where electric would have been awesome) -- you need to account for the last 2 days too.
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Old 06-12-2019, 13:25   #50
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by sailingharry View Post


Or you start home and it's blowing 30 knts from the direction you are heading (my 34 monohull with a 27hp engine makes 3 knts with a wide open throttle in those conditions). Your choices are motor (figure out how big THAT battery needs to be!), sail (upwind in a Gemini in 30 knts?), or stay at anchor and call out of work Monday.

Honestly my experience sailing my cousins 1980 era Prout cat 37 foot ,8 ton craft with 35 HP Myanmar central leg with large prop is in 30 knot head wind forward speed at full tilt was less than two knots with fuel figures of less than 1 mile to the uk gallon .


Noise and thumping and spray one hour is all any human can take of that futile excersize
Sailing close hauled was faster , 8 knots but going nowhere lucky to make 1 miles a hour against the wind with leeward drift.
Engine assist not very useful as the prop was maxxed out at 5 knots so was acting more like s drag if the speeds exceeded 5 knots and still used gobs of fuel

Larger waves keep prop often out of the water except if you motored down wind

Low wind 5 knots cat don't move against head wind but if water is calm the engine at 2000 rpm returns ~4 knots and uses about 5 liters per hour so about 4 nautical mpg

Faster than this like 5 knots often doubled the fuel consumption so was only useful if entering ports for extra steerage control

When head wind is about 12 knots going against the wind tacking might gain 1 mile per hour with large sidewards drift and forward speeds of about 4 knots.

motoring against 12 knot wind with engine probably 2.5 miles per hour with engine at 2000 rpm some 5 to 6 liters per hour closer to 2.5 N mpg . The prop often exits the water with hobby horsing on three to five foot waves .

Did 300 miles of this so know the results started with 80 gallons and sod all left after few days of calm and mostly headwinds on a 1000 mile journey

Across the wind engine assist with 12 knot wind moves speeds from sail of 4 knots up to 5 knots and uses about 4 liters per hour or tad over 4 N mpg .

The cat showed it used more fuel than the fudge number ,0.4 liters per ton even in calm wind to push 2 hulls.
Windage and hobby horsing doubled fuel figures easy .

Twin 30 engines would probably make a better job with deeper props and return better speeds even if it used more fuel in head wind story .

For me the idea a light cat with electric can work well with stiff head wind or worse with waves thrown in wont compute .

Light cats going against head winds need serious power compared to mono hulls due to huge windage factors .

Just my two cents
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Old 06-12-2019, 14:13   #51
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Re: Gemini 105mc conversion Diesel to EV?

Quote:
Originally Posted by sailingharry View Post
Questions:
* Are you saying a 1kW solar panel will give 6.4kWh a day? Full power for 6 hours? That seems very high -- like double.
* How much power are you assuming for house loads? I use 2kWh a day for house loads on my 43' monohull. That takes away from the solar budget to propulsion power.
* Batteries are not normally rated in kW (well, yes, they are, as in CCA, but amps are rarely the issue). Normally they are in kWh (or Ah). 20kW will give two hours of motoring with a 10kW motor. For a day sailor, going from anchor to sails up, and from sails down to anchor, yes, agreed, that's plenty. But not for motoring 20 miles home on a windless Sunday.
* It's just auxiliary power for all sailboats. But many cruising sailors motor far more than an hour a day, at least on some days. We did a 9 day cruise of the Chesapeake Bay this summer. Probably covered close to 300 miles, with the first 7 days almost 100% sail. But the last two days were 30 miles each under power. You can't just look at the first 7 days (where electric would have been awesome) -- you need to account for the last 2 days too.
Sorry, forgot the h...
0,7-0,8kW for 8h. In the summer you should get enough sun from 8 a.m. to 4 p.m. Especially when you are somewhere in the southerly degrees.
You don't go full power, usually. So with about 5kW usage for propulsion, you can go 3h which should amount in about about 12-15 sm. And still have enough power left to run your house load for a day or longer...
But you want to sail, don't you?
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Old 06-12-2019, 14:42   #52
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by sailingharry View Post
Resale value is a concern too. If you decide you have no interest in motoring much, and you are OK with the limitations of electric -- it is good for you. The next buyer may want to motor down the ICW one year -- impossible on electric. Or want to cover ground on a week long cruise on the Chesapeake, where winds may or may not agree. He'll be looking at that electric and think "boat has no motor." But if you plan on keeping the boat 10 or 20 years, that's less of a concern.
Why is resale of the boat any more a consideration then resale of a shoe or a vegetable? You buy a boat to use/consume not as some kind of weird failing investment.

Quote:
Originally Posted by capn_billl View Post
I wouldn't want to be stuck in the doldrums mid Atlantic in a Gemini. It all depends on what you want to use the boat for.
Why not? If you're in the doldrums that means nice calm flat seas. I would have thought a Gemini is perfect for that, especially considering it is easily sailed in light winds.

Quote:
Originally Posted by bouncycastle View Post

Light cats going against head winds need serious power compared to mono hulls due to huge windage factors .

Just my two cents
A Gemini, or an 80s Prout as you referenced probably has less windage than a modern mono. A freeboard of about 1m compared to 1.5-2 on modern monos. Smaller mast and sails to less windage there, lower or similar heigh coachroof than modern monos etc.. I suppose the problem is between the hulls.
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Old 06-12-2019, 16:53   #53
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Re: Gemini 105mc conversion Diesel to EV?

Cats do not do conservation of momentum
Cats without deep dagger boards don't do sailing in straight line with wind side on to them they are moving sidewards sometimes as fast as they go forwards as they have no grip on the water

Going into head winds even without waves the speed drops rapidly when wind gusts hit then head on as they have no momentum like heavy boats do unless you have invested in gobs of extra power

Going about cats can easily stop and get stuck in irons and take off sailing backwards easy .

With waves going into head winds the waves can stop the cat dead in its tracks. There are two hulls to hit on the bows and stop the boat.

I also owned a 33 ft cat with 35 HP outboard and weight 3 tons very hard to go into strong head winds of 30 knots with waves accept at full power .
The speed would be two knots and drop to zero in split second
Then the boat could lose all steering and be side onto the wind sometimes and even pushed backwards .

The boat came with the 35 HP and MPG was at best in calm ~3 mpg at ~60% power ~4 knots and a lot less going against any strong headwinds.

I tried out a 15 HP but any headwind above ~20 knots the boat virtualy stopped dead .

Sailed ireland to Uk to Portugal and Spain and with 5 gallon tank at 3 mpg so I often had to sit in doldrums for days drifting at 1/2 knot using the 1/2 knot Portugal current to go south .

After that you learn northern climates have wind and south of that invest in inboards as you will tend to use them five days out of seven due to lack of winds in mid latitude regions and places like the mediterain sea in summer time .

Yes as solar cells improve and batteries improve electric will be king but I don't see it arriving just now

Cats are great machine for long haul ocean travel as long as you only go downwind and keep them light .

Modern tec 2 stroke outboards return much better mpg than the older 1980 era things do and are not so heavy as inboards and are so ideal for short range uses on smaller cats and trimerans .

Solar power driving a electric engine prop direct drive with no heavy battery can give some speed in day time one knot or so giving a cat a few extra miles a day in the doldrums

This for me would be where it is with a cat to keep the enemy weight for cats as weight kills cats speeds .




If you want to go upwind long hauls then buy a mono hull and big inboard engine .

Mono hull's ability to carry weight can more easily allow a solar power battery combination to electric motor that can drive the boat for a few hours.

Just my two cents on this
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Old 07-12-2019, 02:07   #54
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Re: Gemini 105mc conversion Diesel to EV?

Talking weight, a 3-cylinder Diesel engine weights about 300lb, the 36 gal diesel on the Gemini is about 240lb. So all together we are talking 500lb for coventional propulsion.
1 12kWh 48V LiFePo4 battery weights about 160lb, you would like to put in two, so we are at 320lb. A 10kW Tourqueedo longshaft outboard is about 120lb.
So in the end it's a little less, but no big change.
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Old 07-12-2019, 02:52   #55
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by bouncycastle View Post
I also owned a 33 ft cat with 35 HP outboard and weight 3 tons very hard to go into strong head winds of 30 knots with waves accept at full power .
The speed would be two knots and drop to zero in split second
Then the boat could lose all steering and be side onto the wind sometimes and even pushed backwards .

The boat came with the 35 HP and MPG was at best in calm ~3 mpg at ~60% power ~4 knots and a lot less going against any strong headwinds.
My cat is 4.500kg fully loaded so similar to Gemini. I have a 29hp Yanmar and a 16/14 prop. In 30knts on the nose the boat will do about 3.5-4 knts. In lesser winds 5knts isn't a problem. The issue is more the waves. Even as low as 16knt winds can produce waves the boat crashes into and drops from over 5 knts to 2.8knts speed, then accelerates, then hits the next one hard enough to try to rip fixtures off the walls.

Excluding those events, fuel economy is roughly 2.5l per hour. The tank is 125l but you can only get 100l in there, giving a range of 200nm miles.

If went electric, I would want a minimum of two 15kw motors, for rougher weather, and would want to run them at close to full speed. At that rate I'd need 10 times the LFP bank I already have to run the motors for an hour.

That would weigh 200kg plus cables. My current engine weighs 141kg and the fuel 60kg.
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Old 07-12-2019, 05:56   #56
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by harlem24 View Post
Talking weight, a 3-cylinder Diesel engine weights about 300lb, the 36 gal diesel on the Gemini is about 240lb. So all together we are talking 500lb for coventional propulsion.
1 12kWh 48V LiFePo4 battery weights about 160lb, you would like to put in two, so we are at 320lb. A 10kW Tourqueedo longshaft outboard is about 120lb.
So in the end it's a little less, but no big change.

Any price on those two by 12 kilowatt 48 packs ??

Anyway 36 USA gallons converted to kilos to KWatts energy and estimate 5% of that power makes some 55 KWatts useful power to the boat
2x12 KW electric packs makes 24 kilowatts and with energy conversion estimate 10% makes 2 .5 kw useful, power to the boat .

Best case with deep prop under one of the hulls in calm condition getting estimate 20% return of the electric power using low speeds like 2 knots in calm condition make 5 kilowatts of useful power suggests range will be reduced by a factor of 10 times
Topping up recharging the battery with solar cells can extend range but that but comes at cost and weight
Diesel generator can extend that range but also comes at cost and weight

Using Tesla battery types can extend range due to better power density than LiFe type but comes at much greater cost
Also charging a 24 Kilowatt pack from a marina wall outlet will take many days

Recharging the pack from solar will take many days


I luv the electric solution for the future when mere mortals can do it affordably
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Old 07-12-2019, 06:29   #57
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Re: Gemini 105mc conversion Diesel to EV?

The funny thing about all of these electric conversion threads, is they all look the same. lots of people talking about how great it will be, lots of people talking about how they're designing their project, lots of people talking about how they're doing it, and of course lots of people talking about how bad it will work. What's missing is after years of hearing about people doing it, we never hear the people who have done it. Where are the Fanboys? Where are the people who live it everyday and love it? Has no one actually done it? Or have they never gotten it working well? The only person that I personally know who has experienced it, ripped out her hybrid system, sailed across the Gulf of Mexico without an engine, and installed a conventional diesel at the end of the trip.
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Old 07-12-2019, 07:36   #58
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by bouncycastle View Post
Any price on those two by 12 kilowatt 48 packs ??

Anyway 36 USA gallons converted to kilos to KWatts energy and estimate 5% of that power makes some 55 KWatts useful power to the boat
2x12 KW electric packs makes 24 kilowatts and with energy conversion estimate 10% makes 2 .5 kw useful, power to the boat .

Best case with deep prop under one of the hulls in calm condition getting estimate 20% return of the electric power using low speeds like 2 knots in calm condition make 5 kilowatts of useful power suggests range will be reduced by a factor of 10 times
Topping up recharging the battery with solar cells can extend range but that but comes at cost and weight
Diesel generator can extend that range but also comes at cost and weight

Using Tesla battery types can extend range due to better power density than LiFe type but comes at much greater cost
Also charging a 24 Kilowatt pack from a marina wall outlet will take many days

Recharging the pack from solar will take many days


I luv the electric solution for the future when mere mortals can do it affordably
Under 5k per 12kWh pack. At a marina you should get 240V/16A, so it would take about 4h to charge the battery from zero to full. Even if it's 100V/16A it's possible to do a full charge over night.

I am aware, that it's not optimal atm, but for some people it could work. Not for someone on a tight schedule for shure. That will take some years of development.

What I don't get is, what are you talking about engergy conversion? An electric motor has an efficency of over 95%. If you lose 5% in transmission, then there is 90% usable power at the prop. Compared to about 25-30% you get out of an ICE...
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Old 07-12-2019, 07:40   #59
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Re: Gemini 105mc conversion Diesel to EV?

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Originally Posted by sailingharry View Post
The funny thing about all of these electric conversion threads, is they all look the same. lots of people talking about how great it will be, lots of people talking about how they're designing their project, lots of people talking about how they're doing it, and of course lots of people talking about how bad it will work. What's missing is after years of hearing about people doing it, we never hear the people who have done it. Where are the Fanboys? Where are the people who live it everyday and love it? Has no one actually done it? Or have they never gotten it working well? The only person that I personally know who has experienced it, ripped out her hybrid system, sailed across the Gulf of Mexico without an engine, and installed a conventional diesel at the end of the trip.
Posted some YT channel who are 100% electric, but all monos.
Sailing Uma, rigging doctor, Beau and Brandy sailing.
Uma and rigging doctor both crossed the atlantic without problems.
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Old 07-12-2019, 08:06   #60
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Re: Gemini 105mc conversion Diesel to EV?

Yes indeed. But they are outliers. Their sailing style does not match the vast majority of the sailing public. Many boats race across the ocean without using the engine at all -- that's sort of the point of a race. Hell, the Pardeys don't even have electric propulsion! But even people in events like the ARC, use the engine for a significant percentage of the trip. I'm not looking for outliers who are comfortable sitting for days on end waiting for the next wind, I'm looking for the people who use their battery system for active sailing schedules during typical coastal cruising -- in other words, typical sailors.
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