Optimal hull and keel shape for electric propulsion

[argosail]

Originally Posted by sailingharry

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!

Yup, here are the options (base price new is 97K- expensive)
TORQEEDO CRUISE 2.0 ELECTRIC MOTOR, INCLUDES SP, ONE POWER 26-104 LITHIUM ION BATTERY AND CHARGER
- ADDITIONAL POWER 26-104 LITHIUM ION BATTERY FOR TORQEEDO CRUISE 2.0 +$3,570.00
- TORQEEDO CRUISE 4.0 FP POD DRIVE ELECTRIC MOTOR IN LIEU OF TORQEEDO CRUISE 2.0, INCLUDES SP, POWER 48-5000 BATTERY AND CHARGER AND FOLDING PROPELLER +$5,700.00

[argosail]

Originally Posted by nortonscove

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.

Why'd you sell it???? What did you upgrade to?

There's one not far from me in decent (looking) condition asking 12k! Seems cheap unless there's a lot of wet core and other problems......

[Mauruuru]

This discussion takes more than a post but start here: 1hp = 746 Watts. If you have a 30hp diesel engine you do not need 30hp of electric as a replacement because 1. that diesel is only giving you 30 hp when you have the throttle full bore at 3600 rpm doubt that happens much or for long 2. electric motor is at least 3 x more efficient at converting energy to thrust as a diesel engine (Its thermodynamics folks sorry).

I took out a 30 hp yanmar diesel, replaced it with a three phase Permanent magnet AC motor of 20 kW with a 3:1 reducing gear, Sevcon gen 4 controller with 48v DC AGM 230 AH battery. The sale of the diesel paid for the motor, controller and metering, 48 V DC charger ad some misc parts. Of course the batteries were expensive and extra---I chose Firefly carbon foam AGM technology.

I sail, motor sail or motor a 32 ft Seaward 32RK just fine without smoke or noise.

[argosail]

Originally Posted by Mauruuru

This discussion takes more than a post but start here: 1hp = 746 Watts. If you have a 30hp diesel engine you do not need 30hp of electric as a replacement because 1. that diesel is only giving you 30 hp when you have the throttle full bore at 3600 rpm doubt that happens much or for long 2. electric motor is at least 3 x more efficient at converting energy to thrust as a diesel engine (Its thermodynamics folks sorry).

I took out a 30 hp yanmar diesel, replaced it with a three phase Permanent magnet AC motor of 20 kW with a 3:1 reducing gear, Sevcon gen 4 controller with 48v DC AGM 230 AH battery. The sale of the diesel paid for the motor, controller and metering, 48 V DC charger ad some misc parts. Of course the batteries were expensive and extra---I chose Firefly carbon foam AGM technology.

I sail, motor sail or motor a 32 ft Seaward 32RK just fine without smoke or noise.

I know the Seawards are typically trailer-cruisers and very light displacement, must be a nice set-up! Wondering why you went with AGM batts and not something like Battleborn lifepo batts?

[nortonscove]

Originally Posted by argosail

Why'd you sell it???? What did you upgrade to?

There's one not far from me in decent (looking) condition asking 12k! Seems cheap unless there's a lot of wet core and other problems......

Sorry for the slow response. Been busy at work. We sold it to go bigger. My wife wanted more comfort and a shower. We moved up to a Beneteau 400.

There's very little core to worry about really and they offer great access to every part of the hull and deck.

[valhalla360]

Quote: This discussion takes more than a post but start here: 1hp = 746 Watts. If you have a 30hp diesel engine you do not need 30hp of electric as a replacement because 1. that diesel is only giving you 30 hp when you have the throttle full bore at 3600 rpm doubt that happens much or for long 2. electric motor is at least 3 x more efficient at converting energy to thrust as a diesel engine (Its thermodynamics folks sorry).

1. Sure but if you want to cut the HP to 10hp, you can do that with a 10hp diesel just as easily as a 10hp electric motor.

2. Yes, it's more efficient but energy density of diesel is about 50 times more than lithium batteries, so net effect is around 1/17th the range for the same weight if you convert to battery power.

Of course, this assumes the same boat in the same conditions at the same cruising speeds. To get marginal range in battery boats, the typical solution is to drastically reduce cruise speed and then compare that to a fully capable diesel boat. If you want to assume a 3kt cruise speed, you should resize the diesel powered boat to a lesser HP engine and assuming the 3kt cruise speed, do the comparison.

I know on our 34ft 25hp outboard powered catamaran, at the normal 6.5kt cruise speed, we got around 6mpg. If I cut back to around 5kt, that jumped to around 12mpg...but fuel consumption was so small it was never worth it. Drop back to 4kt and I bet I could do even better but never had the patience to test it out.

[Mauruuru]

Seaward 32 RK fully laden about 12000 #. Used Firefly Carbon Foam technology because I know AGM, its inherently safer than Lithium technology in water and because my design also uses 4kW picco HV, HF generator for extended cruising so range is limited by diesel tank not battery Ah capacity.

[GrowleyMonster]

Originally Posted by valhalla360

Quote: This discussion takes more than a post but start here: 1hp = 746 Watts. If you have a 30hp diesel engine you do not need 30hp of electric as a replacement because 1. that diesel is only giving you 30 hp when you have the throttle full bore at 3600 rpm doubt that happens much or for long 2. electric motor is at least 3 x more efficient at converting energy to thrust as a diesel engine (Its thermodynamics folks sorry).

1. Sure but if you want to cut the HP to 10hp, you can do that with a 10hp diesel just as easily as a 10hp electric motor.

2. Yes, it's more efficient but energy density of diesel is about 50 times more than lithium batteries, so net effect is around 1/17th the range for the same weight if you convert to battery power.

Of course, this assumes the same boat in the same conditions at the same cruising speeds. To get marginal range in battery boats, the typical solution is to drastically reduce cruise speed and then compare that to a fully capable diesel boat. If you want to assume a 3kt cruise speed, you should resize the diesel powered boat to a lesser HP engine and assuming the 3kt cruise speed, do the comparison.

I know on our 34ft 25hp outboard powered catamaran, at the normal 6.5kt cruise speed, we got around 6mpg. If I cut back to around 5kt, that jumped to around 12mpg...but fuel consumption was so small it was never worth it. Drop back to 4kt and I bet I could do even better but never had the patience to test it out.

Of course it must also be remembered that diesels run best within a fairly narrow power band. Sustained operation at very low loads and speeds really isn't good for the engine. Plus there is a minimum idle speed. One advantage of electric is you can run it any speed you like, down to a dozen or a couple dozen RPM, and once you experience docking stern in to your slip with electric, you will never be truly happy bumping a diesel in and out of gear again. There is also no efficiency penalty to speak of, running a high power electric motor at low power. The only reason not to install an electric motor the same power as the usual diesel is cost. You can still run at half or a third of hull speed for extra range, if desired.

The weak point of any EP system is and always will be the batteries: charging efficiency and energy density. The ideal application for EP will always be short range or backup or maneuvering only motoring. Hybrid systems excepted, of course. Oh, and the technical expertise of the owner/operator. Further, there is no reason to replace a running diesel with EP. It is false economy. Replacing a dead and unrepairable diesel or gas engine in a boat mostly used for day sailing is a no brainer. A cruiser needs to think very carefully on EP, before going electric, mostly because of the batteries. And once again, replacing a running diesel with EP is ill advised, IMHO. A diesel that is little more than 500lbs of scrap iron isn't doing anything for the boat's resale value, either, and in fact is worth even less than the EP one might replace the dead clankasaurus with.

Most sailing yachts can easily accomodate an extra 500 lbs or more of batteries, above and beyond the weight of the old diesel, full fuel tanks, and other diesel related stuff. However, space, ventilation, and accessibility considerations must be considerated. Yeah, that is still a smaller "fuel tank" than the diesel installation, but there is no reason other than cost and space to limit the new propulsion bank weight to the weight of the old diesel.

[valhalla360]

Originally Posted by GrowleyMonster

Of course it must also be remembered that diesels run best within a fairly narrow power band. Sustained operation at very low loads and speeds really isn't good for the engine. Plus there is a minimum idle speed. One advantage of electric is you can run it any speed you like, down to a dozen or a couple dozen RPM, and once you experience docking stern in to your slip with electric, you will never be truly happy bumping a diesel in and out of gear again. There is also no efficiency penalty to speak of, running a high power electric motor at low power. The only reason not to install an electric motor the same power as the usual diesel is cost. You can still run at half or a third of hull speed for extra range, if desired.

The power band usually isn't much of an issue for a displacement sailboat, unless you take it to silly levels, keeping the engine in the band where it's pretty near peak efficiency and plenty hot enough to isn't hard. If you really want to live with 2kt cruise speed, you should be comparing to a much lower HP diesel.

Bumping a diesel in and out of gear to control speed is an issue for high powered planing boats. Minimum idle speed isn't much of an issue (much different on a high speed power boat where idle speed might be 5-6kts). Of course, powering a high powered boat off electric is orders of magnitude more difficult.

I do agree: If you are purely going to use it to get in and out of the marina, it's viable but once you start talking about covering distance under power, it makes little sense.

[Adelie]

Originally Posted by valhalla360

….

I do agree: If you are purely going to use it to get in and out of the marina, it's viable but once you start talking about covering distance under power, it makes little sense.

I figure that using the sails is how you cover significant distance.

Sometimes it’s slower than I’d like, sometimes faster than I hoped for. On most boats it winds up being a pretty decent average.

[Mauruuru]

Originally Posted by GrowleyMonster

Of course it must also be remembered that diesels run best within a fairly narrow power band. Sustained operation at very low loads and speeds really isn't good for the engine. Plus there is a minimum idle speed. One advantage of electric is you can run it any speed you like, down to a dozen or a couple dozen RPM, and once you experience docking stern in to your slip with electric, you will never be truly happy bumping a diesel in and out of gear again. There is also no efficiency penalty to speak of, running a high power electric motor at low power. The only reason not to install an electric motor the same power as the usual diesel is cost. You can still run at half or a third of hull speed for extra range, if desired.

The weak point of any EP system is and always will be the batteries: charging efficiency and energy density. The ideal application for EP will always be short range or backup or maneuvering only motoring. Hybrid systems excepted, of course. Oh, and the technical expertise of the owner/operator. Further, there is no reason to replace a running diesel with EP. It is false economy. Replacing a dead and unrepairable diesel or gas engine in a boat mostly used for day sailing is a no brainer. A cruiser needs to think very carefully on EP, before going electric, mostly because of the batteries. And once again, replacing a running diesel with EP is ill advised, IMHO. A diesel that is little more than 500lbs of scrap iron isn't doing anything for the boat's resale value, either, and in fact is worth even less than the EP one might replace the dead clankasaurus with.

Most sailing yachts can easily accomodate an extra 500 lbs or more of batteries, above and beyond the weight of the old diesel, full fuel tanks, and other diesel related stuff. However, space, ventilation, and accessibility considerations must be considerated. Yeah, that is still a smaller "fuel tank" than the diesel installation, but there is no reason other than cost and space to limit the new propulsion bank weight to the weight of the old diesel.

So I don't intend to proselytize because I don't really care what people decide to use for their propulsion. I will tell you the issue is way more complicated but also much more straight forward than most will accept or acknowledge. No internal combustion engine will ever give you more than a 30% energy conversion efficiency and every step you take to convert energy to motion obviously is lossy. My point is take a diesel genset run at a very narrow speed band where it is tuned for max conversion efficiency, use high efficiency PMAC generator to make electricity, use that electricity for everything on the boat...drive power, cooking, AC whatever you choose. This gives max flexibility and when coupled with other sources of generation like regen or solar extends the effective range of that fossil fuel while creating maximum flexibility for sailor. This is the goal of Hybrid power applications. When you finally realize there is no perfect one solution, you rapidly decide to find an optimum one.

[CatLove]

Originally Posted by Mauruuru

So I don't intend to proselytize because I don't really care what people decide to use for their propulsion. I will tell you the issue is way more complicated but also much more straight forward than most will accept or acknowledge. No internal combustion engine will ever give you more than a 30% energy conversion efficiency and every step you take to convert energy to motion obviously is lossy. My point is take a diesel genset run at a very narrow speed band where it is tuned for max conversion efficiency, use high efficiency PMAC generator to make electricity, use that electricity for everything on the boat...drive power, cooking, AC whatever you choose. This gives max flexibility and when coupled with other sources of generation like regen or solar extends the effective range of that fossil fuel while creating maximum flexibility for sailor. This is the goal of Hybrid power applications. When you finally realize there is no perfect one solution, you rapidly decide to find an optimum one.

Which diesel genset are you using?

[Snerf1]

Originally Posted by Mauruuru

So I don't intend to proselytize because I don't really care what people decide to use for their propulsion. I will tell you the issue is way more complicated but also much more straight forward than most will accept or acknowledge. No internal combustion engine will ever give you more than a 30% energy conversion efficiency and every step you take to convert energy to motion obviously is lossy. My point is take a diesel genset run at a very narrow speed band where it is tuned for max conversion efficiency, use high efficiency PMAC generator to make electricity, use that electricity for everything on the boat...drive power, cooking, AC whatever you choose. This gives max flexibility and when coupled with other sources of generation like regen or solar extends the effective range of that fossil fuel while creating maximum flexibility for sailor. This is the goal of Hybrid power applications. When you finally realize there is no perfect one solution, you rapidly decide to find an optimum one.

This issue has been studied many times by different naval engineering outfits for at least 20 years. The same conclusion is always reached: the most efficient system with the highest ROI is direct drive diesel.

You aren't the first person to envision the system you outlined above. Hundreds (thousands?) before, with $billions in capital to invest, have previously wondered why the electro diesel locomative setup cannot be replicated with similar economic parameters for naval applications.

You can count me among them. Lol. Like all fantasies, physics is a real bitch popping everyones ballon. Go watch a few vids (or read some papers) and witness the same reaction everyone has. Then you'll understand why no one is running this commercially.

(Sure, you can build a personal toy system regardless of cost if you dont care, there's someone subsidizing you, or you're offsetting the expense with YT advertising revenue.)

[Adelie]

Originally Posted by Snerf1

This issue has been studied many times by different naval engineering outfits for at least 20 years. The same conclusion is always reached: the most efficient system with the highest ROI is direct drive diesel.

You aren't the first person to envision the system you outlined above. Hundreds (thousands?) before, with $billions in capital to invest, have previously wondered why the electro diesel locomative setup cannot be replicated with similar economic parameters for naval applications.

You can count me among them. Lol. Like all fantasies, physics is a real bitch popping everyones ballon. Go watch a few vids (or read some papers) and witness the same reaction everyone has. Then you'll understand why no one is running this commercially.

(Sure, you can build a personal toy system regardless of cost if you dont care, there's someone subsidizing you, or you're offsetting the expense with YT advertising revenue.)

Efficiency is not the only design considerations. Plenty of naval engineer outfits have found systems other than direct drive diesel to be the most appropriate in various situations. ROI depends on the

Short and medium range ferry boats tend to use diesel-electric because it offers quick changes in thrust and even quick reversal of thrust at the expense of fuel efficiency. This is needed when the vessel is docked and gotten underway several times each day.

There are a few very short ferry runs that have gone all electric, the ROI of doing so was good enough to justify it.

Cruise ships prefer to have Azipods and bow thrusters because together they offer the cruise liners the ability to dock themselves without the need for tugs at varying destinations that change seasonally.

Tugs use a whole whole range of different drive options that have nothing to do with efficiency.

In fact the only use where direct drive diesel is the predominant use is large long range cargo vessels where tugs for docking are available at each end and the need to reverse under self power is almost non-existent. While direct drive is not going to change for this use case, efforts are underway to explore alternative fuels (such as ammonia) and to develop wind technologies to supplement mechanical drive.

In the small and medium size commercial market places where fuel is relatively cheap they tend to use diesels driving transmissions with fixed pitch props. In places like Europe where fuel is relatively expensive, direct drive is used to turn controllable pitch propellers. In this case the savings in fuel justifies the increased upfront cost of the prop and its maintenance.

For the near shore fishing and short range cargo industries parallel hybrid electric systems have be found to be more efficient due to the large percentage of operation at lower speeds. Market development is just starting for this type of drive.

Electric drive for recreational vessels is not a "toy system", there are a number of commercial suppliers in this market. it doesn't need subsidies, in fact up front costs are lower for medium sized (30'-40') vessels.

Just because it's not something you would use, doesn't mean it won't perfectly meet other user's expectations.

[Mauruuru]

Originally Posted by Snerf1

This issue has been studied many times by different naval engineering outfits for at least 20 years. The same conclusion is always reached: the most efficient system with the highest ROI is direct drive diesel.

You aren't the first person to envision the system you outlined above. Hundreds (thousands?) before, with $billions in capital to invest, have previously wondered why the electro diesel locomative setup cannot be replicated with similar economic parameters for naval applications.

You can count me among them. Lol. Like all fantasies, physics is a real bitch popping everyones ballon. Go watch a few vids (or read some papers) and witness the same reaction everyone has. Then you'll understand why no one is running this commercially.

(Sure, you can build a personal toy system regardless of cost if you dont care, there's someone subsidizing you, or you're offsetting the expense with YT advertising revenue.)

I'm not sure what your research sources consisted of but the fact of the matter is that hybrid diesel electric system are being employed commercially in US NAVAL vessels. In effect the vessels are totally electric drive using diesel gensets running at optimum rpm to generate the electricity.

Electric drive gives many advantages but one of the major advantages is 100% torque at 1 to max RPM (not totally correct but theoretically possible) but way better than ICE can ever do. Thus the interests in electric propulsion are motivated by efficiency, flexibility, optimization driven engineering and operating concerns not just toy of the month.......