Replace Diesel with electric engine

[Adelie]

Originally Posted by moseriw

...

So why discussing it?

No my problem are people who want to braeak any rules of nature by propelling at 6+ knots for 10 hrs with EP which is NONSENSE!

And the next stupid nonsense is to buy a genset für 15-20.000 USD to drive with EP when the diesel engine cost 12.000 including a new gearbox. (for the 300 NM's they use it during the season.)

And the next stupid nonsens is to replace an engine because it has uahh 3000 NM on it and it is sooo good to have it new.


My Ford Lehman is of 1981 and only God knows how many miles it did. But it does not suck oil and it does not smoke and yes I had to repair the starter and change all heat exchangers and...
it was no problem at all to do it and I bet it will do the next 40 years on 1800 rpm workload instead of the 3200 rpm of the new lightweight engines that give up within 5-6 years.

And it is soooo stupid to renew things just for the supervised good feeling.

We are discussing it because this is a discussion forum.

Why would it be impossible to motor for 10hr at 6kt using EP?
Let's say 6kW will get you 6kt on Jedi's 20m, 25t vessel. To go 10hr he would need a 60kWhr battery. If you want to be nice to the battery and only use 80% of capacity then it's a 75kWhr battery. At 48v that's 1,560Ahr. That's a $30k bank at $500/12v-100Ahr LFP battery. If you DIY'd the battery, it's more like $10k.

It's not impossible, it just takes, money, effort and space.

Let's say he drops to 4kt and it takes 2.5kW to maintain that speed and he still wants to go 60nm.
That would take 37.5kWhr, or a 47kWhr battery. which would be about $19k.
If it takes 2kW to make 4kt then its a $15k battery bank.

[valhalla360]

Originally Posted by Dirk01

100 diesel hp ist without inner friction and without power for the oil & water pump, the generator, the belts, ...
Electric power is measured at the prop shaft.
Real life says 10 kW EP is nearly 20 hp diesel power designation. Let it be 60kW and it's fine.

ICE are typically rated based on power at the crank shaft. So unless you add a big after market alternator or engine driven fridge compressor...it's pretty comparable.

You might gain a little from the omission of a transmission but that's a few percentage points not 60-70%.

Of course, if you start adding accessories, you have to find a way to power those on an electric boat, so there is no free lunch (or you can use those alternate solutions on an ICE boat and skip the oversized alternator).

[valhalla360]

Originally Posted by Adelie

We are discussing it because this is a discussion forum.

Why would it be impossible to motor for 10hr at 6kt using EP?
Let's say 6kW will get you 6kt on Jedi's 20m, 25t vessel. To go 10hr he would need a 60kWhr battery. If you want to be nice to the battery and only use 80% of capacity then it's a 75kWhr battery. At 48v that's 1,560Ahr. That's a $30k bank at $500/12v-100Ahr LFP battery. If you DIY'd the battery, it's more like $10k.

It's not impossible, it just takes, money, effort and space.

Let's say he drops to 4kt and it takes 2.5kW to maintain that speed and he still wants to go 60nm.
That would take 37.5kWhr, or a 47kWhr battery. which would be about $19k.
If it takes 2kW to make 4kt then its a $15k battery bank.

Probably the biggest issue with this is using more realistic power demand. Maybe with a 15kt tail wind, he can get 6kts on 6kw for 20m 25t boat.

In any kind of realistic use case, I just don't see that kind of performance happening.

Now if you are a purist sailor and only use it to get in and out of port before setting the sails, it's quite viable. If you use it more like a typical coastal cruiser, it's very limiting.

[Adelie]

Originally Posted by valhalla360

Probably the biggest issue with this is using more realistic power demand. Maybe with a 15kt tail wind, he can get 6kts on 6kw for 20m 25t boat.

In any kind of realistic use case, I just don't see that kind of performance happening.

Now if you are a purist sailor and only use it to get in and out of port before setting the sails, it's quite viable. If you use it more like a typical coastal cruiser, it's very limiting.

With a 15kt tailwind he’s going to exceed 6kt using 0kW.

[Adelie]

Originally Posted by valhalla360

ICE are typically rated based on power at the crank shaft. So unless you add a big after market alternator or engine driven fridge compressor...it's pretty comparable.

You might gain a little from the omission of a transmission but that's a few percentage points not 60-70%.

Of course, if you start adding accessories, you have to find a way to power those on an electric boat, so there is no free lunch (or you can use those alternate solutions on an ICE boat and skip the oversized alternator).

Transmission is about 3%. Bearings are about 1.5% each

On an electric boat you don’t need to power an alternator so that’s one less thing.

[valhalla360]

Originally Posted by Adelie

With a 15kt tailwind he’s going to exceed 6kt using 0kW.

If the windage is that bad with sails down, no way he makes 6kts with 6kw in calm conditions.

[valhalla360]

Originally Posted by Adelie

Transmission is about 3%. Bearings are about 1.5% each

On an electric boat you don’t need to power an alternator so that’s one less thing.

As I said...if you need a 300amp alternator, you would need some way to replace that output on a BEV boat.

Say you install solar panels on the BEV boat...well you could do the same thing with ICE and skip the oversized alternator.

But regardless....even with a few percentage points lost for the transmission, no where close to the magic HP numbers electric proponents are claiming.

[Adelie]

Originally Posted by valhalla360

If the windage is that bad with sails down, no way he makes 6kts with 6kw in calm conditions.

I was making a joke. Jedi is a real sailor. He has indicated up-thread that he sails at 6kt in 9kt of wind.

[Adelie]

Originally Posted by valhalla360

Probably the biggest issue with this is using more realistic power demand. Maybe with a 15kt tail wind, he can get 6kts on 6kw for 20m 25t boat.

In any kind of realistic use case, I just don't see that kind of performance happening.

...

On what basis do you believe that 6kW is not enough for him to make 6kt?

The drag curve for boats is very non-linear

[valhalla360]

Originally Posted by Adelie

I was making a joke. Jedi is a real sailor. He has indicated up-thread that he sails at 6kt in 9kt of wind.

I know got it the first time...if you have to explain it and all that.

[Adelie]

You didn’t seem to have gotten it which is why I felt a need to explain it.

[valhalla360]

Originally Posted by Adelie

You didn’t seem to have gotten it which is why I felt a need to explain it.

Apparently, my abbreviated response didn't get thru...

If you have to explain a joke, it's generally not very funny.

[valhalla360]

Originally Posted by Adelie

On what basis do you believe that 6kW is not enough for him to make 6kt?

The drag curve for boats is very non-linear

True but on a 34ft cat with a hull speed of around 7.5, we took around 6kw to make 6kts.

Yes, there are efficiency improvements with WLL but it still takes more power for a larger boat to go the same speed (at least when not running up against hull speed).

But in real life use, say going against a 10kt headwind, that could easily double the power needed to maintain 6kts. Of course, as previously stated, if your a purist sailor, it's not relevant but I've already allowed that you are a purist, electric is viable...but as someone else brought up, if you are purist, you are probably not using the diesel much anyway and it will survive just fine for decades.

[s/v Jedi]

Originally Posted by valhalla360

True but on a 34ft cat with a hull speed of around 7.5, we took around 6kw to make 6kts.

Yes, there are efficiency improvements with WLL but it still takes more power for a larger boat to go the same speed (at least when not running up against hull speed).

But in real life use, say going against a 10kt headwind, that could easily double the power needed to maintain 6kts. Of course, as previously stated, if your a purist sailor, it's not relevant but I've already allowed that you are a purist, electric is viable...but as someone else brought up, if you are purist, you are probably not using the diesel much anyway and it will survive just fine for decades.

You underestimate the importance of waterline length. Your hull speed is 7.5kts, my hull speed is 12kts. In order to go 6kts, I only have to do 50% of hull speed, you must do 80% of hull speed. Looking at the graphs, the difference is stunning.

When we have a 10kts headwind, we don’t need a motor at all as this means we can sail. Anything above 6kts wind we can sail and so can everyone if equipped to handle light conditions. Just choose the tack with best VMG and go.

For us it is a really big thing that we need to visit a fuel dock; we would love to eliminate this dependency and we won’t even be surprised if it becomes a necessity in our lifetime. Mechanical propulsion is the only thing we need fossil fuel for as we have successfully switched to solar power for everything else incl. galley, watermaker and even A/C.

[moseriw]

Just choose the tack with best VMG and go.

Yes, does not matter if you have 500 Miles to go. Wind will shift.
But if it is 2 p.m. and you want to go 12 Miles to the next marina.
Upwind with engine 6 knots 2 hrs.

On the tack 4 knots 12 NM x 4 = 48 NM / 4 = 12 hrs

Oh nice, you do not have to pay the marina as you will not reach it.