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Old 27-08-2018, 08:25   #1366
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Re: Oceanvolt Hybrid Motor

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Originally Posted by transmitterdan View Post
I like simple explanations so forgive me if this is overly simplistic.

So to summarize the argument the equivalency of EP 20HP to diesel 40HP is because the diesel is really only usable continuously at 20HP. And EP is sized so it can run flat out at full 20HP continuously.

Is that the theory in a nutshell?
I always understood, gas engines like to limit to around 60-70% of peak rating for continuous output.

Diesel can happily run at upwards of 80%. Hence in the old days, they would spec lower HP diesels for trucks because they didn't care about acceleration and you could run them hard.
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Old 27-08-2018, 08:28   #1367
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Re: Oceanvolt Hybrid Motor

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True, or you could be like me and just have an aversion to looking after engines and see electric as being more reliable with less maintenance. I accept its horses for courses.
People keep saying that but I've yet to see any documented evidence to support it.

As I mentioned in a recent post, electric vs gas golf carts, there really isn't much of a reliability difference and those are not emerging technologies where you can chalk it up being new technology.
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Old 27-08-2018, 15:19   #1368
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by valhalla360 View Post
Quote:
So to summarize the argument the equivalency of EP 20HP to diesel 40HP is because the diesel is really only usable continuously at 20HP. And EP is sized so it can run flat out at full 20HP continuously.


I always understood, gas engines like to limit to around 60-70% of peak rating for continuous output.

Diesel can happily run at upwards of 80%. Hence in the old days, they would spec lower HP diesels for trucks because they didn't care about acceleration and you could run them hard.

At 80% of RPM - which is generally about 50% of HP. So that summary is accurate as far as it goes.

The problem with that summary is twofold:
1. It ignores those situations where you require more that 50% of available power.
2. The 50% ratio is erroneously extrapolated to HP required at all speeds and conditions.



There are a number of other omissions in the argument that I won't bother to go into now.
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Old 27-08-2018, 15:35   #1369
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Re: Oceanvolt Hybrid Motor

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Originally Posted by StuM View Post
At 80% of RPM - which is generally about 50% of HP. So that summary is accurate as far as it goes.

The problem with that summary is twofold:
1. It ignores those situations where you require more that 50% of available power.
2. The 50% ratio is erroneously extrapolated to HP required at all speeds and conditions.

There are a number of other omissions in the argument that I won't bother to go into now.
My understanding was Percent of Rated HP, not of RPM.
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Old 27-08-2018, 16:15   #1370
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
My understanding was Percent of Rated HP, not of RPM.
http://www.ciar.org/ttk/mbt/engine.cat.c10.pdf

I think this Caterpillar link gives a good picture.

Max RPM = 2100
Governed to 1800.
Operating range 1400 to 1700 rpm.
Max torque = 1200 rpm.
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Old 27-08-2018, 16:25   #1371
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Re: Oceanvolt Hybrid Motor

The engine power curve showing HP obtainable at a given RPM is one thing, but in practice on a boat the HP delivered is determined by the propeller power curve. I need to look at the curve for my engine, but I can easily believe that at 80% redline RPM the engine is only delivering 50% HP to the propeller.
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Old 27-08-2018, 16:43   #1372
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Paul Elliott View Post
The engine power curve showing HP obtainable at a given RPM is one thing, but in practice on a boat the HP delivered is determined by the propeller power curve. I need to look at the curve for my engine, but I can easily believe that at 80% redline RPM the engine is only delivering 50% HP to the propeller.
Yep - the recommendation for my engine in a truck is 1500-1600rpm but it seems to me that for the prop we have the sweet spot is 1200 revs. (and much lower fuel consumption.)
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Old 27-08-2018, 18:55   #1373
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Re: Oceanvolt Hybrid Motor

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Originally Posted by DumnMad View Post
http://www.ciar.org/ttk/mbt/engine.cat.c10.pdf

I think this Caterpillar link gives a good picture.

Max RPM = 2100
Governed to 1800.
Operating range 1400 to 1700 rpm.
Max torque = 1200 rpm.
I didn't see anything in there documenting the max hp vs continuous hp limits.

Redlining the engine at 2100RPM is HP independent. Rev the engine to 2500-3000 in neutral and leave it there...you will be putting out very little HP but will likely blow the engine in a short time.
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Old 27-08-2018, 19:10   #1374
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Re: Oceanvolt Hybrid Motor

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Originally Posted by ssmoot View Post
Boosting an engine puts stress on the connecting rods, head, valve-train, pistons, beyond what they were engineered for. You could have a failure in 10 seconds or 10 years depending on how much boost.

That's really not at all similar to feeding so much juice to an electric motor that it ends up overheating after some amount of minutes and frying itself. If you have a thermal cut-off, there's no practical risk to this with any sort of reasonable input. You're certainly never going to see a working motor fry itself within 10 seconds without some sort of serious hidden defect already existing. Which is why pretty much every EV you see does it by design and under warranty. The same is not true for modifying your diesel. Bad things are going to happen if you try to get double the horsepower out of it.
So you are saying you can overpower an electric motor if you do the right design and put in safeguards....generally do it right.

But then compare it to home brew turbo charged engine with no design or safeguards installed as proof of your point. Had a 7.3l ford, only had 180hp (naturally aspirated) a few years later, essentially the same engine with a turbo was up to 260hp. Both were regarded as pretty much bullet proof designs.

In practice its the exact same problem. You can pump more power out of either but the more you pump out either:
- The motor won't last long if you don't do it right.
- Or if you do it right you can pump a lot more power out of either motor type.

If you do an apples to apples comparison either can be easily destroyed trying to pump more power out.
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Old 27-08-2018, 19:23   #1375
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
My understanding was Percent of Rated HP, not of RPM.
Nope.
Example Yanmar 3JH3E. Nominal "40HP @ 3800", Max continuous (36HP @ 3650 RPM):
Rated propeller HP at WOT of 3800 = 38HP.
80% of WOT = 3040RPM. Prop HP = 18 (approx).
80% OF HP = 30.4HP which is achieved at around 3500 RPM (92%)
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Old 28-08-2018, 02:40   #1376
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Re: Oceanvolt Hybrid Motor

Copied from the Yanmar 3ym30 operator manual:

Quote:
Maximum throttle (3600-3800 rpm) for less than 5% of total engine time. (30 minutes out of every 10 hours)
Cruising Speed (3400 rpm or lower) for less than 90% of total engine time (9 hours out of every 10 hours)
So in a 10 hour cycle you have to go above cruising speeds for at least one hour, I guess to burn the soot. But you should not go WOT for more than 30 minutes.

Based on these statements its safe to run the engine between 3400rpm and 3600rpm for days.

Looking at the attached 3Ym30 diagrams the engine has its peak output at around 3550rpm, as torque goes down quickly when going faster than ~3400rpm.

So at least the yanmar 3YM30 engine is made to run 100% output util it runs out of diesel.


But to me this is just not important, partly because I never needed to motor at 100% on both engines for anything longer than a few minutes. A cat like the 380 also just isn't made to motor into seas building after hours of 50kn wind.
There are of course different situations (tides, currents, limited time windows for landfall, etc), but for us so far the upgraded engines were of no use at all.




I'm a fan of going electric. I am ready to dump these decorative shade devices called sails. I don't see much of a difference between sailing and EP-motoring - both are just different ways to use the sun. I don't consider sailing a superior way of moving a boat. Its not even cheap compared to diesel (except long distances).
I sail because its quiet vs noisy diesel. Give me quiet & affordable EP and I'll become a motorboat guy.

Our cruising style (in the Med!) is really just hopping from anchorage to anchorage. Anchor 2-5 days, move 5-20nm, repeat. A EP cat with plenty of solar should have enough time to recharge the batteries while at anchor.
Those few 100-200nm hops between islands can be made with genset support, and I'm OK with 5-7kn avg speed.

But for us EP needs to be comparable in cost, maintenance, dependability, risk and reliability. And this I just don't see (yet). It's bleeding edge technology with all that is to be expected: immature components and high failure rates. High cost due to low production figures and no scaling effects. Suppliers that won't be around in a year, or who drop a product the day after you buy.
As of now you need to do EP as DIY, or be prepared to pay big bucks for immature technology that will not outlast a normal diesel installation.

Looking at the billions that go into research of electric mobility now, this will change. In a few years the know-how, battery technology, motors, components will trickle down from cars into boats.
At least I hope so.
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Old 28-08-2018, 09:47   #1377
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Re: Oceanvolt Hybrid Motor

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Originally Posted by StuM View Post
Nope.
Example Yanmar 3JH3E. Nominal "40HP @ 3800", Max continuous (36HP @ 3650 RPM):
Rated propeller HP at WOT of 3800 = 38HP.
80% of WOT = 3040RPM. Prop HP = 18 (approx).
80% OF HP = 30.4HP which is achieved at around 3500 RPM (92%)
I think we are talking about two different things as RPM isn't comparable between gas and diesel engines (or electric for that mater) and it's common to spec a smaller diesel engines (in terms of rated HP) because you can run it at a higher percentage of peak power (not RPM).

The problem with using propeller HP is that presumes a lot of assumptions and for the purpose of discussing electric motors, runs into the same issue.
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Old 28-08-2018, 10:45   #1378
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
The problem with using propeller HP is that presumes a lot of assumptions and for the purpose of discussing electric motors, runs into the same issue.
But you *need* to consider propeller HP in any reasonable discussion of marine propulsion. If you use different propellers for electric vs diesel propulsion, then you need to account for that. If there are inaccurate assumptions, explain what they are and why the inaccuracy matters. But you can't just say "it's different". The ultimate goal of a motor or engine is to deliver power to the propeller.

I've got a friend with a heavy 50 ft cabin cruiser and failing diesel engines. He *so* wants to go electric. He was believing the "4x diesel" electric power claims. I would love to see him happy with an electric solution. But the more we looked at the math and the reality, we realized that it just wasn't going to be a useful solution. This is one of the reasons I participate in these threads -- I'm actually hoping that someone can show me where I'm wrong.
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Old 28-08-2018, 10:55   #1379
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Re: Oceanvolt Hybrid Motor

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But you *need* to consider propeller HP in any reasonable discussion of marine propulsion. If you use different propellers for electric vs diesel propulsion, then you need to account for that. If there are inaccurate assumptions, explain what they are and why the inaccuracy matters. But you can't just say "it's different". The ultimate goal of a motor or engine is to deliver power to the propeller.

I've got a friend with a heavy 50 ft cabin cruiser and failing diesel engines. He *so* wants to go electric. He was believing the "4x diesel" electric power claims. I would love to see him happy with an electric solution. But the more we looked at the math and the reality, we realized that it just wasn't going to be a useful solution. This is one of the reasons I participate in these threads -- I'm actually hoping that someone can show me where I'm wrong.
In terms of the Magic Electric HP, I absolutely agree.

But if you put the same prop on, the prop HP will be the same for a given RPM at the prop regardless of power source.
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Old 28-08-2018, 11:50   #1380
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
But if you put the same prop on, the prop HP will be the same for a given RPM at the prop regardless of power source.
Exactly. It couldn't be otherwise -- the prop doesn't know what's spinning it.

I guess I was wondering about those invalid assumptions.
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