Using electric motors instead of Diesel on your cat

[valhalla360]

Originally Posted by Sailingcouple13

no one said it was cheaper! it the standard now.

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Again, can you provide a source. The gunboat website didn't show anything regarding electric has standard and a general internet search turned up nothing either.

Are you sure you don't have it backwards and the diesels are standard and it's a $75k upgrade to go electric?

[cwjohm]

It's in there current specs and pricing sheet provided by the factory. Not up on site yet. It was a big part of their presentation in Miami. OceanVolt 15kw 48volt motors on saildrives, polar power 20kw 48volt DC diesel gen. 16kw lithium ion phosphate propulsion bank. Top speed 9knts. Weight savings about 2000#s.

First of all no way is this cheaper than a pair of 39Hp Yanmars which they say is standard on their site. I also believe you have this the wrong way around in that this is $75K more expensive than the Yanmars.

I understand Rainmaker installed larger Yanmars. Perhaps someone can confirm this. I would certainly think a 55" cat even with as low water resistance of Gunboat would require at least 54 HP.

Secondly, it would be madness to go bluewater with 15Kw electric motors, especially in the sort of conditions in which Rainmaker was lost, and there is NO WAY you will see 9kn in any reasonable sailing conditions.

[Sailingcouple13]

I do not have it backwards...it is listed under options as: The Old Iron Propulsion Package (in lieu of standard electric) $75,000.

That is the standard so if you want Diesel it cost more. From what I understand the space savings in the engine compartment is going to be designed into the interior. Therefore if you want the old system it will be more than a drop in. This is a production boat now not custom.


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[Sailingcouple13]

I do not have it backwards...it is listed under options as: The Old Iron Propulsion Package (in lieu of standard electric) $75,000.

That is the standard so if you want Diesel it cost more. From what I understand the space savings in the engine compartment is going to be designed into the interior. Therefore if you want the old system it will be more than a drop in. This is a production boat now not custom.


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[Sailingcouple13]

I think if someone told this group the sun was going to rise tomorrow, they would say you are not well informed.

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[Sailingcouple13]

I did have the speed incorrect 8knts.

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[valhalla360]

Originally Posted by Sailingcouple13

I think if someone told this group the sun was going to rise tomorrow, they would say you are not well informed.

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Easy, we see lots of odd comments on the forum and many times they are unfounded or only part of the story. It does appear they are pushing the diesel electric option but...

There is still something that doesn't sound right.
- Do a pair of 39hp diesels even weight a total of 2000lbs? I can't see how they could possibly cut 2000lbs when the diesel electric system still has weight.
- If 20hp (generator size) is plenty of power, why are they spec'ing just shy of 80hp in the diesel version? Seems like a pair of small 15hp diesels would be sufficent to exceed the 8kt cruising speed and still provide the extra power for short surges that the batteries provide.
- What would justify the $75k cost? Assuming it is a new build and not a retrofit, they have the design for the diesels already, so moving some bulkheads shouldn't cost much.

My guess is there is more to the story.

[Sailingcouple13]

I imagine the weight savings includes, less one full fuel tank. If I were marketing it I would.

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[Ulstue]

It looks like that Gunboat precisely calculated everything that is needed for that particular system, not for the other. For example, sound insulation, tanks, other batteries for the diesel etc. So that you have an actual comparison for the whole complete different system.
Concerning hp: a 40 hp diesel in normal driving uses not the whole 40 hp, but only as peak power. The electric motors in the system can produce the same peak power into the water. They will not only supplied by the generator, but from the batteries.
I suspect the performance of e-system is sufficient. The only question is how long ...

[valhalla360]

Originally Posted by Sailingcouple13

I imagine the weight savings includes, less one full fuel tank. If I were marketing it I would.

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They say one less 75gal tank, so there is around 500lbs in a worst case situation of full tanks but I'm sure the big battery bank will balance out a good part off that.

I'm not saying it won't be lighter but I struggle to see how it could be 2000lb lighter.

[Dockhead]

Originally Posted by Ulstue

It looks like that Gunboat precisely calculated everything that is needed for that particular system, not for the other. For example, sound insulation, tanks, other batteries for the diesel etc. So that you have an actual comparison for the whole complete different system.
Concerning hp: a 40 hp diesel in normal driving uses not the whole 40 hp, but only as peak power. The electric motors in the system can produce the same peak power into the water. They will not only supplied by the generator, but from the batteries.
I suspect the performance of e-system is sufficient. The only question is how long ...

Only problem is that the diesels are 40hp (or 39 hp to be exact) EACH. That's 78 horsepower, versus about 40 horsepower peak power - unsustainable since the generator only makes 20kW or about 26 horsepower -- TOTAL.

The battery bank completely full holds theoretically 15kW/hours (expressed wrong on the Gunboat flyer). So you will spend half the bank's total theoretical power covering the difference between generator full theoretical capacity and peak power demand of the electric motors for 20 minutes or so.

Otherwise you need to be content with 26 horsepower -- maximum even theoretically sustainable power -- in a vessel that size -- and query whether that genset is rated to produce its maximum rated power continuously -- most aren't. Hmmm. Sure wouldn't want to be caught off a lee shore in that vessel. When you need engine power in a hairy situation you REALLY need it. Speaking from experience here.

[valhalla360]

Originally Posted by Ulstue

It looks like that Gunboat precisely calculated everything that is needed for that particular system, not for the other. For example, sound insulation, tanks, other batteries for the diesel etc. So that you have an actual comparison for the whole complete different system.
Concerning hp: a 40 hp diesel in normal driving uses not the whole 40 hp, but only as peak power. The electric motors in the system can produce the same peak power into the water. They will not only supplied by the generator, but from the batteries.
I suspect the performance of e-system is sufficient. The only question is how long ...

No they spec'ed a pair of 15kw (20hp) electric motors (40hp total) with a 20kw (26hp) generator to replace a pair of 39hp diesel motors (78hp total). 40hp motors can't develop 78hp.

Yes, the batteries can supply the missing 14hp but they are still providing drastically less power and only for short bursts. If they only need 40hp total, why were they not providing dual 20hp diesels as standard?

Either they overpowered the diesel version or they underpowered the diesel/electric version (maybe both).

I'm still think there is something untold in this story.

[Ulstue]

Whether nobody really thinks as far before installing this system in a Cat for millions of dollars?

On the side of the system manufacturer, Torqueedo / Moonwave one can read that one can choose between
"Electric Propulsion: rotating or fixed Saildrives up to 30 kw per hull or shaft drives up to 60 kw per hull." What is 41 to 81 hp per hull.
"Battery Capacity: From 26 to 104 kWh"
"Generator: 1 or 2 @ 22 kW, 1 or 2 @ 50 kW"

Surprisingly, it seems that the german engineers who designed the system are not complete morons.

[Dockhead]

Originally Posted by Ulstue

Whether nobody really thinks as far before installing this system in a Cat for millions of dollars?

On the side of the system manufacturer, Torqueedo / Moonwave one can read that one can choose between
"Electric Propulsion: rotating or fixed Saildrives up to 30 kw per hull or shaft drives up to 60 kw per hull." What is 41 to 81 hp per hull.
"Battery Capacity: From 26 to 104 kWh"
"Generator: 1 or 2 @ 22 kW, 1 or 2 @ 50 kW"

Surprisingly, it seems that the german engineers who designed the system are not complete morons.

That's much more reasonable, but that is definitely not what is written in the Gunboat brochure shown above in this thread. There it's definitely 15kW per hull, with a single 20kW generator. Total of 26.8 horsepower sustained or 40.2 horsepower for battery-assisted bursts.

Chris White Atlantic 57 -- a similar sized boat -- has two 55hp Volvos, total 110 horsepower. Now to be fair you have to deduct the drivetrain losses to get shaft hp -- but that's still at least 100 horsepower -- 2.5x more than the electric Gunboat's burst power and nearly 4x more than its sustained power.

What is wrong with this picture? As someone said, either the diesel cats are grossly overpowered, or this electric one is grossly underpowered -- it just ain't right.

I spent a couple of weeks on a Norseman 43' cat I chartered, a much smaller vessel. It had two 27 horsepower Yanmars for 54 hp total. It was NOT overpowered; on the contrary, I thought it was rather underpowered for any kind of strong conditions.

[Ulstue]

Right, what's in the Picture above is definitly nonsense for a 50 - 60 feet Cat.