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Old 15-11-2016, 21:29   #286
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Jim Cate View Post
Backing up a moment... the requirement for 280 tonnes of bollard pull... can that be correct? I find it hard to imagine that a prop that a racer would be willing to drag could possibly generate that kind of thrust, no matter what sort of engine/motor was attached to it. Or am I missing something here?

Jim
Good catch, I missed that.

Nope, you're not missing anything. The salesman was dead wrong again.

"The engine needed to create a bollard pull of 280 tons for 15 minutes"

The requirement according to the current rules is "Traction value of 280 daN at a fixed boat (boat tied to the dock, traction measured with a dynamometer) for 15’.

Not sure what the "single quote" represents, minutes or feet

But daN = dekaNewton.

And 280 daN = 0.2855 metric tonnes force.
(or about 630 lbs for the non-metric among us)

So they were only out by a factor of 1000 in their claim.
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Old 15-11-2016, 21:52   #287
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Re: Oceanvolt Hybrid Motor

It's interesting to read the next bit after the erroneous bollard pull figures stated by the Commercial Director being interviewed:
"We thought this was going to be really tight for us, but we achieved it."

So there supposed 15kW (20HP) system is apparently being stretched to its limit to maintain 630lbs of pull for 15 minutes.
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Old 16-11-2016, 00:14   #288
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Re: Oceanvolt Hybrid Motor

Sorry for the noob question but what is wrong with using the prop to generate power under sail
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Old 16-11-2016, 00:56   #289
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Re: Oceanvolt Hybrid Motor

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Originally Posted by cameron82 View Post
Sorry for the noob question but what is wrong with using the prop to generate power under sail
Nothing is "wrong" with that. But most propulsion props are terribly inefficient at converting water flow into torque. They are designed to work the other way around. But if a boat is sailing in wind conditions where a brake would not change the speed much then a prop can generate some electricity and there are systems that do that. But the systems are complicated and most cruisers aren't sailing at hull speed a high percentage of the time. So most of the time a prop generating electricity would slow the boat and thus sort of defeat the purpose for many sailors.

Dedicated prop generators like Watt & Sea use a more optimal prop design and they tilt up out of the water for when sailing speeds are lower. That type system is very effective and also expensive.
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Old 16-11-2016, 00:56   #290
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Re: Oceanvolt Hybrid Motor

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Originally Posted by cameron82 View Post
Sorry for the noob question but what is wrong with using the prop to generate power under sail

Nothing as long as the drag from the generator doesn't slow the vessel to the point where it cannot generate power.
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Old 16-11-2016, 01:51   #291
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Re: Oceanvolt Hybrid Motor

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Originally Posted by SV DestinyAscen View Post
Garbage videos are probably why people are so cynical. Doesn't take a rocket scientist to recognize that electric motors deliver near peak torque at 0 rpm. From a standstill I would expect an electric system to out perform anything that relies on combustion compression to turn a crankshaft - electric cars, diesel-electric locomotives, etc.

The concern everyone has that the sales people curiously avoid is whether you can power a certain boat at hull speed for 48 hours. I'll never live to see battery technology advance to allow that, but if it does - I can see people adopting it for the RIGHT application.

It is the same type of barrier to entry that electric car companies have to address - range anxiety, the difference is that electric car companies that are doing well aren't doing garbage comparisons videos like tying a Tesla with a Mercedes luxury sedan and making them tow each other.
m


torque provides acceleration, and so your electric boat will shoot out of the blocks faster. Great if you're a nitro supercharged 1/4 miler fan. once you get up to cruising speed, then the energy demand is identical for electric or diesel. if your boat requires 25 kw to cruise at 7 knots on diesel, it will need exactly the same from an electric motor. 25 12v x 200 ah batteries will propel your electric boat at 7 knots for 1 hour. if you need to cruise for 5 hours, you'll need 125 batteries. They weigh over 5 tonnes. A 5kva charger will take much more than 25 hours to fully recharge. You'll need a much bigger than 10 kva gennie. So you have to add that weight and the diesel used to drive it. You probably will have to sleep off the boat or learn to cope with the thrum of a gennie running all night.

You can eliminate all those batteries by installing a diesel electric generator. You'll need a 25 kw generator which happens to use exactly the same diesel motor you pulled out in the first place.
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Old 16-11-2016, 02:04   #292
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Oceanvolt Hybrid Motor

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Originally Posted by dlymn View Post
m





torque provides acceleration, and so your electric boat will shoot out of the blocks faster. Great if you're a nitro supercharged 1/4 miler fan. once you get up to cruising speed, then the energy demand is identical for electric or diesel. if your boat requires 25 kw to cruise at 7 knots on diesel, it will need exactly the same from an electric motor. 25 12v x 200 ah batteries will propel your electric boat at 7 knots for 1 hour. if you need to cruise for 5 hours, you'll need 125 batteries. They weigh over 5 tonnes. A 5kva charger will take much more than 25 hours to fully recharge. You'll need a much bigger than 10 kva gennie. So you have to add that weight and the diesel used to drive it. You probably will have to sleep off the boat or learn to cope with the thrum of a gennie running all night.



You can eliminate all those batteries by installing a diesel electric generator. You'll need a 25 kw generator which happens to use exactly the same diesel motor you pulled out in the first place.

Because of the losses in conversion you would have less output available.
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Old 16-11-2016, 04:21   #293
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Re: Oceanvolt Hybrid Motor

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Originally Posted by four winds View Post
I've never seen a 300w panel at 20kg. That's 44lb and the panels I have seen are closer to 70lb.
Five of these should do:
R60 60 Watt Rollable Solar Panel - PowerFilm Solar
with properties:
Weight: 1.816 kg or 4 lbs
Power: 60 Watts
5 times that is 300W and 20 lbs or 9.08 kg

Haven't seen any panels with less weight for power than those flexible types, but it needs more area but typically cost less for power. Should be good for high power cases in catamarans.
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Old 16-11-2016, 05:21   #294
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Re: Oceanvolt Hybrid Motor

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Originally Posted by 44'cruisingcat View Post
The point is, they are claiming the use of their motors will result in MORE speed than just the sails will produce, yet with no additional energy input.

It's simply physically not possible.

And yes, if people claim this they are either lying or mistaken.

If it were true, then you'd have perpetual motion.
There is no need for additional energy input, it's enough to reduce the losses already there, namely those from hull drag. Nothing to do with perpetual motion.
A boat doing 8 knots 50% of the time and 6 knots 50% of the time has greater average drag than the same boat doing 7 knots 100% of the time. There is the reduced losses.
In addition, if sailing directly downwind under spinnaker at 8 knots the boat is slowed down to 7 knots by electrical energy production, the apparent wind will increase providing more driving force from the sails. This might also increase propulsive power from the sails.
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Old 16-11-2016, 05:37   #295
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Re: Oceanvolt Hybrid Motor

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Originally Posted by transmitterdan View Post
Nothing is "wrong" with that. But most propulsion props are terribly inefficient at converting water flow into torque. They are designed to work the other way around. But if a boat is sailing in wind conditions where a brake would not change the speed much then a prop can generate some electricity and there are systems that do that. But the systems are complicated and most cruisers aren't sailing at hull speed a high percentage of the time. So most of the time a prop generating electricity would slow the boat and thus sort of defeat the purpose for many sailors.

Dedicated prop generators like Watt & Sea use a more optimal prop design and they tilt up out of the water for when sailing speeds are lower. That type system is very effective and also expensive.
Not so if the prop is connected to a drive leg that allows rotating the leg 180 degrees about a vertical axis, so the prop works backwards as a turbine. It won't be as efficient as a purpose made turbine, but still far from terribly inefficient like it would be if used forwards facing. Props made for water use are not airfoil sections with parabolic/elliptic entry, but have both sharp leading and trailing edges, that work reasonably well either way. It's only the concave/convex faces that must work the correct way, one always on the low and the other always on the high pressure side.
The main problem with water turbines is that they don't produce anything at the dock or anchor (unless in fast current, not hopefully the case or anchor might drag), which is most of the time for many cruisers. Windturbines do work, but are usually disturbingly noisy. Hence most favor solar or fossile fuel generators.
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Old 16-11-2016, 05:48   #296
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Cap Erict3 View Post
Because of the losses in conversion you would have less output available.
True, but efficiencies might change in either ICE loading or prop.

Usually direct transmission on boats don't allow changing gears to load the engine most efficiently on lower power, but electric transmission does allow optimal revs for the engine for any power level.
Also gear ratio on boats is usually not optimal for efficiency, but selected from commercially available transmissions that are produced by manufacturers more from cost efficiency perspective than fuel mileage.
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Old 16-11-2016, 06:21   #297
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Stumble View Post
Here's the problem in a nutshell...
48MJ/kg diesel
.5MJ/kg - lifepo4 batteries
.17MJ/kg - FLA batteries
you should have used the lower heat value for diesel (exhaust water as vapor not liquid) 43,7 MJ/kg and multiply that with the engine efficiency.
Hence more like 18 MJ/kg available at the shaft for a small diesel at near optimum load depending on engine model.
18 MJ/kg means same as 200 g/kWh, some boat engines consume 10% less fuel, others 15% more at optimum, while all loose efficiency at low load.
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Old 16-11-2016, 06:23   #298
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Just Another Sa View Post
True, but efficiencies might change in either ICE loading or prop.

Usually direct transmission on boats don't allow changing gears to load the engine most efficiently on lower power, but electric transmission does allow optimal revs for the engine for any power level.
Also gear ratio on boats is usually not optimal for efficiency, but selected from commercially available transmissions that are produced by manufacturers more from cost efficiency perspective than fuel mileage.
Actually, a typical cruising boat will have no need for changing gears. Gear changing is only needed when you need a vehicle to operate over a wide range of speeds and thus the engine cannot stay in it's ideal RPM range without multiple gears.

For a cruising boat, it only needs to be set up for optimum operation of the diesel at cruising speed which most production models do a pretty good job at because it's an easy change for the manufacturer to spec the ideal prop and that costs nothing and provides better performance. (You do hear of one-off or repowered boats having issues or boats with significant bottom growth but not really relevant to the discussion as it's usually the result of a poor.)

Starting from a standstill it's less efficient but since the prop slips in the water, it's not an issue and so unless you are running a short distance ferry that starts and stops constantly, the diesel drivetrain is pretty much at it's peak efficiency.

Keep in mind, it's not only the transmission that determines the ideal loading on the engine. The pitch of the prop effectively is part of the gearing. So if you originally thought you needed a 2.3 gear ratio and the closest available is a 2.4 gear ratio, you just adjust the pitch slightly and you wind up with effectively the same load on the engine and you stay in that nice efficient RPM range for the diesel.
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Old 16-11-2016, 06:49   #299
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Just Another Sa View Post
you should have used the lower heat value for diesel (exhaust water as vapor not liquid) 43,7 MJ/kg and multiply that with the engine efficiency.
Hence more like 18 MJ/kg available at the shaft for a small diesel at near optimum load depending on engine model.
18 MJ/kg means same as 200 g/kWh, some boat engines consume 10% less fuel, others 15% more at optimum, while all loose efficiency at low load.
So if we assume your numbers are correct (they are not but for the sake of argument...), diesel still has 36 times the energy density of the very expensive Li battery banks. (105 times for lead acid).

Even if you assume 75% efficiency losses (assuming an engine that is running horribly as a typical diesel does significantly better) converting diesel to mechanical energy and the batteries have 0% efficiency loss, it's still an order of magnitude more available propulsive energy.

If they ever get that ratio down into the single digits (at reasonable prices), there will be a revolution. Until then batteries simply do not store enough energy to meet the typical cruisers expectations.
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Old 16-11-2016, 06:53   #300
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Just Another Sa View Post
Not so if the prop is connected to a drive leg that allows rotating the leg 180 degrees about a vertical axis, so the prop works backwards as a turbine.

Yeah, tons of cruising boats have sail drive legs that rotate 180 degrees...

In the real world we have propellers that are designed to turn out best efficiency at something like 500-1000 shaft RPM producing 5-10 knots. No cruising boat can drag that same propeller through the water and get even a tiny fraction of 500RPM from the prop while producing significant power. The design of the propeller is all wrong for that application. A propeller designed to transmit 25HP to the water at 1000RPM can't produce even 1/10 of that power as a water turbine traveling through the water at 5-10 knots so they are pretty inefficient as power generators.
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