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Old 10-05-2022, 17:01   #76
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Re: Optimal hull and keel shape for electric propulsion

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Originally Posted by valhalla360 View Post
Before someone says electric motors of the same HP have higher torque, since HP = torque * RPM, you can simply add a reduction gear if you need more torque at the prop shaft and other than a couple percentage points for efficiency losses, the HP that reaches the prop shaft will be the same. You can turn the same prop at the same RPM.

YES! This always frustrates me. I can get 10,000ft pounds of torque out of a lawn mower engine -- all I need is enough reduction gear.


The reason we run diesels at high shaft speed and low torque (and EP's at low shaft speed and high torque) is that a small prop (with low drag under sail) works better at high RPMs -- even if it results in lower efficiency. EP solutions put a very high premium on motoring efficiency, so they lower the RPMs, raise the torque, and put big fixed props on -- it certainly hurts sailing speed, but it's the price you pay to get every possible mile out of your battery bank.
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Old 10-05-2022, 20:18   #77
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Re: Optimal hull and keel shape for electric propulsion

I’d like you to take my Tesla for a spin. Touch Ludicrous icon and do some fast math. I have 1100 pounds torque. Tear the keel off a sailboat and de mast it. It’s a genuine hot rod. Cars with more horse power can’t catch me.
A 34’ boat replacement electric drive is $5200. It runs a C&C 34 in one example every bit as fast as the 21Hp that came with it. I think it’s a tiller boat.
Marine motors are really special. I never touched my cats but I did build a beautiful pair of 502 Hawks. It’s a Donavan block all aluminum Corvette cheated one year and raced with them. They never saw second over 4300 rpm. Rev limiters chopped throttles if the blades left the water. This idea torque is rpm might work in gyroscopes but not V8’s with flywheels. It’s valve timing fire trenches Dwell fuel density. Same engine in a car 8500 rpm less torque. 5000 RPM in a boat one of the best big blocks ever built is a grenade. LS3-6 in the water blow up sooner.
454 the crank snaps in half. The Ford 460 stunk. My Tesla Motors product more torque than a 395 turbo cat.
Horsepower Don t mean jack it’s torque which counts, dragstrip or Water.
Japanese motorcycles use rpm and a counter weight on a chain instead of flywheels.
So yes the magic is torque. What cost more fuel or extreme rpm electric does by nature as there is no standoff between pistons firing. The Tesla motor and controller are unique way more efficient
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Old 11-05-2022, 08:00   #78
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Re: Optimal hull and keel shape for electric propulsion

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Originally Posted by Shaneesprit View Post
Quite interested in what your reason is to go electric without a clue about what it means?

Or at least that’s the way the question appeared. Sorry in advance.



Is it environmentally friendly - probably not.

Even in a classic car they say going EV is environmentally damaging. The conversion it’s self does more carbon damage than could ever be repaid, on a boat it’s going to be worse.

300w of solar is about enough for lights chart plotter and a radio.


I don’t know about the OP but if I bought an older boat with an older diesel or an A-4 I would pull it out and sell it Somebody else that prefers an inboard ICE gets one cheap rather than buying new and I would get the EP I want, with a gas outboard backup cuz that’s what I also want. Environmentally it’s probably a wash for some time to come, long term EP is probably ahead environmentally.

My reason for wanting to go EP is mostly the greater self-reliance/independence. I’m happy to trade speed under power to get that.

If there’s sun I’m using it to move the boat or storing it for later. If there’s wind all the power gets stored. I don’t mind trading
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Old 11-05-2022, 08:43   #79
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Re: Optimal hull and keel shape for electric propulsion

What Adelie said. It's for independence and just a little motoring as needed, in and out of marinas, not for any extended motoring, handful of hours at 2-3kts is fine in my current plan.

If you want full environmentally friendly then just go full sail but imo EP would be more friendly than diesel but I'm not analyzing this much.
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Old 11-05-2022, 08:49   #80
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Re: Optimal hull and keel shape for electric propulsion

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A 200A charger (that's a beast!) is about the most you can pull from a 30A shore power cable (it draws close to 25A, so not a lot of room left). 200A @15V, is about 3kW. If you are down 15kWh, that's 5 HOURS at full charge capacity (that's with Lithium, lead acid won't take it and backs way down, taking longer). If you get one of Rum's go fast boats, the banks are a lot larger and the charge is a lot longer (although they probably take 50A 240V, or close to 10kW charge rate). Yes, well configured you can get a full charge overnight -- but it's going to take some engineering to make that happen. Kind of shocked me that it takes that long.
Actually, Drawing 25amps off a 30amp outlet is overloading it. It might work or it might not but 30amps is the short term maximum rating. For longer duration loads, you are limited to 80% or 24amps if you want to stay within the official rating. So there is no room left for house loads.

If you are in a marina and using the air/con and other loads, you might only have 1000-1500w available for charging, so 15kwh might take 10-15hours but 15kwh is not much for propulsion. There's a reason EV cars start around 50kwh (many have 2-3 times that) with the exception of Plug-In-Hybrids because it's simply not practical to go so small.

A 50amp @ 240v outlet is much more viable as 80% of the max rating gives you 9.6kw to work with. But that usually comes with a larger boat with larger loads, so you may be looking at 5kw available to go into the battery bank if you are running 2-3 air/con units and other loads but the battery bank may be 3-4 times larger to propel a much bigger boat, so you are still taking a very long time to charge.

In theory, you can install a 50amp inlet on a small boat but now you may be forced to pay for a larger slip in many cases just to get a 50amp outlet and the owner may not be happy if they catch you using all the available power.

Now if you are just a weekend boater who uses it to get in and out of the slip and then strictly sails, all this becomes much more reasonable but for actual coastal cruising, it becomes problematic very quickly.
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Old 11-05-2022, 10:34   #81
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Re: Optimal hull and keel shape for electric propulsion

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….
Consider a 20HP power (pick any other number and it will work out the same). I'm recalling my Sabre 34, which had a 27 HP diesel but at cruising throttle, probably 20HP, it burned about 1/2 gallon per hour, maybe a touch more -- so at today's prices, about$3/hour or a bit less. 20HP is 15kW, so it burns 15kWh/hour. My electric here at home runs about .012/kWh, so that's $1.80/hour. Not the savings I expected -- I really expected to see numbers better than 50% savings. (yes, you could re-run these numbers with a 2kW motor, but I don't have diesel consumption rates for a 5HP diesel running at 60% load).


.....

Diesels will produce about 18hp/gal/hr operating near optimum RPM. Big engines optimized for economy might hit 20hp/gal/hr.
Turbo diesels don’t affect this significantly, the turbo is used to get more power out of the same sized engine, not increase the efficiency of the engine. They can be used to increase efficiency but they aren’t.
The agriculture folks are a great source of info on this, this is a big sales point in comparing tractors.

Let’s assume that your engine produces 18hp/gal/hr at partial throttle. That means at 1/2 gal/hr consumption it’s probably putting out 9hp, not 20hp.

9hp is 6.714kW. At $0.12 per kW-hr you would be spending $0.805 per hour. Vs $3.00ish per hour using diesel.
If half of your recharging energy comes from solar then price gap is even larger.
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Old 11-05-2022, 11:22   #82
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Re: Optimal hull and keel shape for electric propulsion

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9hp is 6.714kW. At $0.12 per kW-hr you would be spending $0.805 per hour. Vs $3.00ish per hour using diesel.
If half of your recharging energy comes from solar then price gap is even larger.
Us average is $0.15/kwh.
Mid Atlantic is $0.17/kwh
New England is $0.25/kwh (so around $1.60/hr)
California....SanDiego is $0.40/kwh

At the same time you are comparing it to a recent extreme price spike in Diesel. Looking back at more typical prices, diesel is more like $1.00-1.50/hr. If you want to speculate on future prices, we can make up anything we want to justify a position.

But even if we use $3/hr, that's a lot of hours to pay for the swap out. All at significantly reduced performance.

If you are getting half your recharging energy from solar:
- You have to incorporate the price to buy, install and maintain a solar/battery system which is far from insignificant.
- Assuming you actually motor any significant distance, it will have to be a massive system that is very expensive and comes with major limitations.
- If you just use it to get in and out of port, it's a silly discussion as you might use 5-10gal of diesel per year making fuel costs a rounding error in the overall cruising budget. Certainly nothing that would justify replacement of a functional propulsion system and installation of a substantial solar/battery system.
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Old 11-05-2022, 11:24   #83
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Re: Optimal hull and keel shape for electric propulsion

I think a better place to consider is the dingy.
- Many cruisers use a small 2.5hp outboard and don't expect to get on plane so it's not an unusual or extreme use case.
- They may only run 15-30min per day vs cruising boats that often motor 4-10hr per day.
- Coupled with an efficient catamaran hull form, a trolling motor will get you about the same amount of speed as a 2.5hp. Even with an inflatable, it's still quite viable.
- 30min at 1000w requires 500watt-hr per day. A 150w panel can supply that coupled to a 100amp-hr 12v battery (assuming 50% usable).
- With a little preplanning, you could incorporate the solar into a fold down bimini on the dingy or a simple cable to the mothership.
- Lead-Acid would be a simple and cheap solution to test it out or you could go Lithium if you wanted smaller/lighter.

Now you get the advantage of instant on, no mucking about with clogged carbs and a system that has negligible performance loss compared to the ICE option.
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Old 11-05-2022, 11:27   #84
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Re: Optimal hull and keel shape for electric propulsion

$0.12/kW-hr was SH’s cost and I was responding to him so I used his cost.
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Old 11-05-2022, 12:41   #85
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Re: Optimal hull and keel shape for electric propulsion

And that’s what boating is all about it’s low cost right.
I use to love putting my 395 cats to the wall. We were way down the Trent at Viamede and had to get back to port in Georgian Bay in 3 days. 1500$ a day in fuel crossing half of Ontario 36 locks. .
I see a lot of boats never get used in every club. Guess they are saving $$$$
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Old 11-05-2022, 12:47   #86
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Re: Optimal hull and keel shape for electric propulsion

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Originally Posted by valhalla360 View Post
Us average is $0.15/kwh.

Mid Atlantic is $0.17/kwh

New England is $0.25/kwh (so around $1.60/hr)

California....SanDiego is $0.40/kwh



At the same time you are comparing it to a recent extreme price spike in Diesel. Looking back at more typical prices, diesel is more like $1.00-1.50/hr. If you want to speculate on future prices, we can make up anything we want to justify a position.



But even if we use $3/hr, that's a lot of hours to pay for the swap out. All at significantly reduced performance.



If you are getting half your recharging energy from solar:

- You have to incorporate the price to buy, install and maintain a solar/battery system which is far from insignificant.

- Assuming you actually motor any significant distance, it will have to be a massive system that is very expensive and comes with major limitations.

- If you just use it to get in and out of port, it's a silly discussion as you might use 5-10gal of diesel per year making fuel costs a rounding error in the overall cruising budget. Certainly nothing that would justify replacement of a functional propulsion system and installation of a substantial solar/battery system.


SH was discussing operating costs only, not capital costs so I only addressed those.

While peak electric rates in San Diego are near $0.40/kWhr, off peak they can be as low as $0.09/kWhw. And coincidentally off peak would be the time that charging would occurred.

Junking a working diesel with EP is a net loss. If you sell off the ICE then it’s probably a slight loss that will be made up over time.

If the motor doesn’t work when you buy the boat then it becomes a question of whether you buy a new or used ICE vs EP and then short term costs look close to even.

Also, there are non-monetary motivations for some people that are not in addressed in the last several posts.
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Old 12-05-2022, 05:53   #87
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Re: Optimal hull and keel shape for electric propulsion

I'd think you'd have a tough time beating the shape of the Mirage 27 for efficiency. Had one until two years ago when it finally sold. Fairly lightweight but just the right dimensions and sailing characteristics. Exceptional Perry design that left such a small wake that the local fishermen found it almost inconceivable. We upgraded nine years ago but couldn't bring ourselves to sell it until two years ago and still long for it. The 1 cylinder Yanmar was never taxed and hardly used any diesel due to its hull shape.
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Old 12-05-2022, 07:49   #88
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Re: Optimal hull and keel shape for electric propulsion

So true the Mirage 27 were real handsome boats.
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Old 13-05-2022, 12:46   #89
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Re: Optimal hull and keel shape for electric propulsion

Yet another stupid company that can’t do the math.
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Old 13-05-2022, 18:15   #90
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Re: Optimal hull and keel shape for electric propulsion

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Yet another stupid company that can’t do the math.
If your comment is a dig at those of us who are questioning the OP, you aren't reading what we are saying (or chosing not to listen.). The Fantail 27 is an ideal use case for EP. Short motor to sail. Home every night, plugged in. No house loads. Hell, not a single solar panel to be seen! They aren't stupid! But I suspect they aren't offering EP on their 40 foot cruising models...


Oh, to my math on pricing. I was recently (a month or so ago) running some numbers, and my current price including all usage based costs is .122/kWh for BGE (the old Baltimore Gas and Electric). Seems I have cheap rates!
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