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Old 27-10-2016, 13:37   #151
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Re: Oceanvolt Hybrid Motor

7 knots at 7 kW would need a VERY light and efficient cat. I'd estimate we need around 12 kW to do 7 knots.
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Old 27-10-2016, 13:48   #152
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Re: Oceanvolt Hybrid Motor

Is there any problem with running an oversized generator at optimum efficiency for very short periods of time to top off low batteries? It is my understanding that the new lithium batteries can accept high amounts of energy to recharge quickly, exactly how a big generator would provide.
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Old 27-10-2016, 13:56   #153
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Re: Oceanvolt Hybrid Motor

oceanvolt and sail combo is entirely possible. a no brainer, if i wasn't a powercat guy. but my argument for huge generator and huge diesel capacity is based on where i'm coming from. and that's the impractical energy demands of even the most efficient powercat
















Quote:
Originally Posted by BigBeakie View Post
It's important to understand the realistic cruising possibilities of EP. The idea of needing 1,000 gallons of fuel to drive the EP for a big motor cruiser via DC genset is very sobering.

Since we are looking at a multihull forum, I think it's right to realise that multihulls are probably the best application for cruising with EP. Why? Because the useable range and hull speed at CRUISING speeds are entirely achieveable with multihulls that have suitable displacement and hull form.

For continuous motoring, the "7 at 7" is an achieveable goal, that is, 7 knots of cruising speed using 7 kW of power, in slight seas for a 45' cruising cat with reasonable hull form and displacement. Big fat hulls on heavy condomarans will get less performance, and slim 'n slippery hulls with a light boat can get more.

What you find is that there is a sweet spot for cruising hull speed vs kW consumed, and you can run the DC genset to generate that kW battery charging so you do not eat into your propulsion battery reserves. So you run on a nett zero battery use.

OceanVolt do that analysis for you, and they err on the conservative side. The speed vs kW used curve shows that you can get more speed, but you use MUCH more power to get that extra knot or two, compared to the sweet spot.

We will be using a 10kW DC genset on our 50' cat to give us a bit more grunt for adverse conditions when/if necessary such as tidal sets or coral pass current. BUT, we plan on sailing the boat, because it sails so well. When we are becalmed, "7 at 7" will do us just fine using 3 liters/hour on the DC genset running at maximum efficiency. We are deciding now on how much diesel tankage we'll need, but one thing is for sure, it sure ain't 1,000 gallons!!!
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Old 27-10-2016, 16:50   #154
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Re: Oceanvolt Hybrid Motor

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Originally Posted by 44'cruisingcat View Post
7 knots at 7 kW would need a VERY light and efficient cat. I'd estimate we need around 12 kW to do 7 knots.
44'cc,

How'd you come up with your "estimate" ? What is it based on?
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Old 27-10-2016, 18:49   #155
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Re: Oceanvolt Hybrid Motor

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44'cc,

How'd you come up with your "estimate" ? What is it based on?
8 knots on 15 kW
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Old 27-10-2016, 20:14   #156
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Re: Oceanvolt Hybrid Motor

As a matter of interest "License to Chill" Alibi 54 has just gone on sale. Among many other attributes it had 20KW Electric Drives backed by 22KW generators and 25KW Li.Ion batteries when first built.

All ripped out now and retrofitted for diesels. This is one of many who have been attracted by the lure of electrics and had to pay a high monetary price to refit the boat when trialling in real world conditions.
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Old 27-10-2016, 22:03   #157
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Re: Oceanvolt Hybrid Motor

I'd like to see the design that gets 7kts at 7kw in a 45-50 (the post was mixing the two up).

I'll give you 10-1 odds it's either imaginary or the major drawbacks have been glossed over.

45-50' cats typically have motors in the 40-75hp range PER HULL...and suddenly approx. 10hp total will be plenty. I can see if you are willing to accept lower performance, you can cut back on HP a bit but this is just silly.

I keep seeing this problem with electric propulsion, rather than admit where it's viable and grow from there, you get these crazy claims.
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Old 28-10-2016, 16:55   #158
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Re: Oceanvolt Hybrid Motor

Ok guys, I'll tell you what.

To all the naysayers, I promise to post here on CF a full, complete, data rich, warts and all, report of our OceanVolt 15kW installation on our 50' FreeFlow cat, 13.5 ton cruising displacement, after our sea trials.

We will bake a crow pie onboard and serve it with humble sauce, and anyone is welcome aboard to come to see the EP performance for yourself.

Either you all will be eating the pie, or I will.

BTW, we may get an appetizer soon, as there is a bigger cat being launched with the same OceanVolt system, and I hope to get some sea trial data from that installation in early 2017.

Stay tuned......
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Old 28-10-2016, 17:50   #159
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by BigBeakie View Post
Ok guys, I'll tell you what.

To all the naysayers, I promise to post here on CF a full, complete, data rich, warts and all, report of our OceanVolt 15kW installation on our 50' FreeFlow cat, 13.5 ton cruising displacement, after our sea trials.

We will bake a crow pie onboard and serve it with humble sauce, and anyone is welcome aboard to come to see the EP performance for yourself.

Either you all will be eating the pie, or I will.

BTW, we may get an appetizer soon, as there is a bigger cat being launched with the same OceanVolt system, and I hope to get some sea trial data from that installation in early 2017.

Stay tuned......
Hi BigBeakie

I would love to hear more about your system, as I am researching hybrid systems as well.

This is 2x15kW motors? Powered by a single 10kW generator?

So you can run either 1@10kW or 2@5kW long-distance (using generator).

And assuming battery power is available, you can go as high as 2x15kW for short periods?

And the calculations for your boat estimate 7 knots of speed using 7kW? I assume this is 2x7kW?

What are you doing for the house battery bank? Is it separate from the propulsion battery bank? And how is it charged?

Best regards,
- Fabian
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Old 28-10-2016, 19:12   #160
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Re: Oceanvolt Hybrid Motor

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Hi BigBeakie

I would love to hear more about your system, as I am researching hybrid systems as well.

This is 2x15kW motors? Powered by a single 10kW generator?

So you can run either 1@10kW or 2@5kW long-distance (using generator).

And assuming battery power is available, you can go as high as 2x15kW for short periods?

And the calculations for your boat estimate 7 knots of speed using 7kW? I assume this is 2x7kW?

What are you doing for the house battery bank? Is it separate from the propulsion battery bank? And how is it charged?

Best regards,
- Fabian
Hi Fabian, glad somebody is interested

That is a yes to all your questions except no, for our full cruising displacement of 13.5 Ton, we expect a balanced continuous cruising speed of 6.6 knots. The "7 at 7" is realistic for a somewhat lighter and slimmer hull and no, that is 7kW total consumption, not 2x7kW=14kW.

For house bank we are adding a few more Super B LFP's beyond the 16kW propulsion bank, and at this point we are thinking to keep it simple as one big bank vs the complexity of separating them.

BUT, bear in mind that this is A) a very good sailing cat, so we do not anticipate using the genset much unless becalmed in under 3 or 4 knots wind, B) we have a very healthy 3 kW solar installation, and C) the regeneration of the OceanVolt SD15's is impressive as we sail...so "empty bank anxiety" is not as acute as on some other installations. The system also has very good battery monitoring & alarms, and the display is viewable from both the cockpit and saloon.
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Old 28-10-2016, 20:29   #161
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
Hi Fabian, glad somebody is interested

That is a yes to all your questions except no, for our full cruising displacement of 13.5 Ton, we expect a balanced continuous cruising speed of 6.6 knots. The "7 at 7" is realistic for a somewhat lighter and slimmer hull and no, that is 7kW total consumption, not 2x7kW=14kW.
Yes, I'd say somewhat lighter alright. We weigh around 6 tonnes all up, LWL 13.5 m and LWL:BWL around 12.5 : 1.

And we can't do 7 knots on 7 kW. Probably more like 5 knots.

With the numbers you're quoting, I'd suggest your long term motoring speed (on 10 kW) will likely be less than that.

One suggestion - make sure, when you do your sea trials, you have a reasonable cruising load aboard. It does make quite a difference.
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Old 28-10-2016, 21:36   #162
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Re: Oceanvolt Hybrid Motor

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Is there any problem with running an oversized generator at optimum efficiency for very short periods of time to top off low batteries? It is my understanding that the new lithium batteries can accept high amounts of energy to recharge quickly, exactly how a big generator would provide.
The problem is efficiencies. While lithium batteries are better than old lead acid, there are still losses converting mechanical energy to electrical to battery back to electrical and finally back to mechanical for propulsion.

It's more efficient to simply hook the diesel up to the prop shaft directly.

Also, if you check around, a 20kw generator will be much larger than a 20kw propulsion engine. Add in a large battery bank plus the electric motors and the weight/cost savings largely go away.

Electric or Electric Hybrid is completely viable if you limited to weekend sailing. When you want more than a couple hours motoring, it quickly becomes impractical.
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Old 28-10-2016, 21:40   #163
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by BigBeakie View Post
Ok guys, I'll tell you what.

To all the naysayers, I promise to post here on CF a full, complete, data rich, warts and all, report of our OceanVolt 15kW installation on our 50' FreeFlow cat, 13.5 ton cruising displacement, after our sea trials.

We will bake a crow pie onboard and serve it with humble sauce, and anyone is welcome aboard to come to see the EP performance for yourself.

Either you all will be eating the pie, or I will.

BTW, we may get an appetizer soon, as there is a bigger cat being launched with the same OceanVolt system, and I hope to get some sea trial data from that installation in early 2017.

Stay tuned......
No one said it couldn't be done. If you make an extreme boat geared specifically for efficiency at the expense of all other design criteria, it can be done. But when you claim unrealistic capabilities and compare only on length, it's misleading.

So why are you avoiding telling us more? Yeah, you can make a boat that in specific ideal conditions can do 7kts on 7kw but I'm betting your crow pie will be served on a completely impractical boat.
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Old 28-10-2016, 23:09   #164
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by BigBeakie View Post
Ok guys, I'll tell you what.

To all the naysayers, I promise to post here on CF a full, complete, data rich, warts and all, report of our OceanVolt 15kW installation on our 50' FreeFlow cat, 13.5 ton cruising displacement, after our sea trials.
Which Freeflow is that? Nathan Stanton has designed a 46 and a 52, but no 50 that I am aware of.
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Old 28-10-2016, 23:27   #165
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Re: Oceanvolt Hybrid Motor

My understanding it is a new updated vessel yet to be released.
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