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Cadence · 01-10-2014, 11:44

Quote:

Originally Posted by FloatingDutchMn

You are absolutely right, this is fundamental to the issue. However, the engine that is in the Neel 45 gives it a cruising speed of 10kt. This is due to the efficient nature of the trimaran design.

Electric engines up to 20kW make sense, after that they are too big, heavy, so the question is what cruising speed can be achieved with a single 20kW engine. Or will 2 be required to achieve a satisfactory cruisng speed, say 7kt+.

Given that from a safety point of view a generator needs to onboard in any case, then the generator size becomes the question, and AC or DC generator.

Am I reading the last couple of posts correctly 20KW, 40KW? I gest what are we pushing a tractor tug?

FloatingDutchMn · 01-10-2014, 11:48

Oceanvolt have a 15kw engine which they state is good for a monohull up to 40ft. For cats they recommend 2x10kW. So, I think 15-20kW engine is what is most likely going to be required.

**a64pilot** · 01-10-2014, 11:53

Quote:

Originally Posted by Cadence

Am I reading the last couple of posts correctly 20KW, 40KW? I gest what are we pushing a tractor tug?

I was wondering that too, isn't 20KW about 27 HP?
Now I don't understand why, but for some reason electric motors seem far more powerful than there HP rating would suggest, seems like a 2 HP electric motor will do the work of a 5 HP gas engine.
How much will this boat weigh?

Cadence · 01-10-2014, 12:00

Quote:

Originally Posted by FloatingDutchMn

Oceanvolt have a 15kw engine which they state is good for a monohull up to 40ft. For cats they recommend 2x10kW. So, I think 15-20kW engine is what is most likely going to be required.

My Guess that is for someone that is looking for diesel electric power not a minimal weight situation such as the OP?

barnakiel · 01-10-2014, 12:15

Quote:

Originally Posted by FloatingDutchMn

(...)

Electric engines up to 20kW make sense, after that they are too big, heavy, so the question is what cruising speed can be achieved with a single 20kW engine. Or will 2 be required to achieve a satisfactory cruisng speed, say 7kt+.

You can google out tables that let you convert available power / displacement to speed.

As someone said, you go slower, you get further. Notice sprinters do not run marathons. Physics.

I think also one of Dashews' books discusses the physics and mathematics involved in detail. Look them up.

You can also go into HR website where they discuss range under power and see how they did. Except I think that a tri with fine hulls may be more power efficient in flat water.

b.

libramax · 01-10-2014, 12:35

Just from reading the other threads on elec. propulsion, there is also the issue of using a prop (size and pitch) that is matched to the torque curve of the electric engine. So I think the conversion of diesel hp to electric hp is quite complex and involves other factors that affect speed and range.

I think the key issue was briefly mentioned but not highlighted: There don't seem to be good Li-ion batteries available right now at an acceptable price point (and who knows when). I've been looking at suppliers of Li-ion batteries online for a home-based off-grid system, and they all sell dodgy Chinese batteries with slick websites full of hype. I was about to order some anyway, but then found scary stories about them on the BBB, and am back to looking at other batteries (nickel-iron, which are not suitable for boats).

dannc · 01-10-2014, 13:06

Quote:

Originally Posted by MasonMcD

To be fair, up until the 20th century, all we had was renewables!

Quote:

Originally Posted by valhalla360

Actually coal powered the industrial revolution back into the 1800's. Most early steam ships were coal powered. Even before that it was used for heating and oil was used in lamps.

Does that mean whale oil is renewable?

Sorry, I could not resist.

To the OP, a few issues back, there was an article in Passage Maker magazine about trying to power a boat via solar power that might be of interest and I think the same author had an article in Professional Boat Builder in the last year or so as well.

Later,
Dan

Stumble · 01-10-2014, 13:07

Quote:

Originally Posted by FloatingDutchMn

You are absolutely right, this is fundamental to the issue. However, the engine that is in the Neel 45 gives it a cruising speed of 10kt. This is due to the efficient nature of the trimaran design.

Electric engines up to 20kW make sense, after that they are too big, heavy, so the question is what cruising speed can be achieved with a single 20kW engine. Or will 2 be required to achieve a satisfactory cruisng speed, say 7kt+.

Given that from a safety point of view a generator needs to onboard in any case, then the generator size becomes the question, and AC or DC generator.

I think there are two seperate issues here.... 1) is a fully electric boat reasonable and 2) what specifications are required if you go this route.

I know all about trimarans, I actually own one (a much smaller Corsair 750). And while I love it, there are issues that will impact this decision.

First you are correct that a trimaran needs less power on a day to day basis. Lower weight, less wetted surface area, and clean lines all make them very efficient moving thru the water. Where you get into trouble however is that the same motor that works fine on light air days won't work when it's windy.

The very things that make a trimaras so slippery thru the water also increase the wind load substantially. Thanks to the appendages and nets, bridgedeck, ect. So motoring into a strong breeze for a trimaran requires a lot more power than motoring the same size monohull.

What I have found for most electric conversions is that people spec the electric drive based on calm weather days, but when it comes to motoring off a lee shore because the anchor drug they don't have enough reserve power to do anything. This is a reasonable solution for some boats (my electric race boat) but it's acceptable (to me) for a cruising boat. Particularly a high latitude boat where high wind speeds are predictable.

In short then, installing a 20kw motor probably will get you to 7kn on a calm day, but it probably won't allow you to motor into much breeze... Which is exactly where you need it the most. So in my eyes a large motor (or two smaller ones) is required. Not for the day to day operations, but for the times you really need it to be available.

For me this requirement then drives the answer to 1). Which is that unless you can spec an energy storage system capable of providing 40kw or so of power for a reasonable amount of time (which I don't think you can) you need a diesel generator. Sizing this becomes tricky as well since the larger the battery bank the smaller the generator can be. But frankly in the size of the battery's that seem reasonable I don't think it matters much. You are still going to need something like a 30kw generator to provide enough reserve capacity for propulsion.

**estarzinger** · 01-10-2014, 13:09

I can't add anything to the technical discussion, but I can comment on the high latitude conditions. . . . Cold (may have an influence on battery performance?). Quite a bit of fog and rain and hail (perhaps 2/3 days with no real sun). Lots of zero wind with ocasional gales, not much 15-20kts.

This season in the NWP the minimum motoring percent in the fleet going thru was 50%. Now these were heavy monos, so you might do a bit better, but a cat will have similar challenges sailing in zero wind and headwinds.

When we spent 3 years in Patagonia we got a Honda because there was no where near enough sun and not enough wind in the protected anchorages. . . . And we have an extremely power efficient/low consumption boat.

Now in the tropics it is a whole different story. You should be able to sail on and off the anchor every day, and have good wind or solar or both. It should be no trouble at all so long as your systems are simple . . .

The big systems questions are heating in the high latitudes and refergeration in the tropic. Realize you do not actually need refergeration and if you do without you greatly reduce your daily energy nut.

Stumble · 01-10-2014, 13:11

Quote:

Originally Posted by Cadence

Am I reading the last couple of posts correctly 20KW, 40KW? I gest what are we pushing a tractor tug?

No you are reading them right. Propulsion demands for a sailboat are generally orders of magnitude higher than electricity production, but HP and KW are convertible. The trimaran we are discussing comes with a standard 45hp diesel, 45hp works out to ~41kw. Of course the boat if it has a generator installed probably has a 5-7kw thus indicating the relative difference in power needs for propulsion versus everything else.

FloatingDutchMn · 01-10-2014, 13:16

Did anyone actually make it through the NWP this year? Reading Jimmy Cornell's blog suggested that conditions were unlikely for anyone to make it through, although 2-3 boats were still going to attempt when most considered the risk of getting stuck in winter ice too high and turned around for US coast or Europe

FloatingDutchMn · 01-10-2014, 13:41

Stumble, thanks for your input. You raise some very valid points for consideration.

The power requirements in rough and windy weather dictates the engine requirements for catamarans and trimarans. Having 2x20kW is probably required for the bad conditions, which is at the same level as the volvo D2-55 that normally is fitted. 2 engines is also good from a redundancy point of view, even though electric engines are very reliable. I would imagine that in normal cruising running 2 engines at the lower end of the rpm range will extend the range for a given battery bank versus a single engine running at much higher rpm for the same nominal speed.

An alternative is a hybrid engine, run on electric when possible, run on the diesel when situation dictates

Cadence · 01-10-2014, 14:00

Quote:

Originally Posted by Stumble

No you are reading them right. Propulsion demands for a sailboat are generally orders of magnitude higher than electricity production, but HP and KW are convertible. The trimaran we are discussing comes with a standard 45hp diesel, 45hp works out to ~41kw. Of course the boat if it has a generator installed probably has a 5-7kw thus indicating the relative difference in power needs for propulsion versus everything else.

That is what I was questioning. Yep, as I recall 756 watts /Hp. I might be +/- it's been a long time. The OP was and should be, concerned about weight. At 20K/ 40K as people where posting the electric gen. and motor weight would be defeating his goal. My original post was,

I wish I could help. I guess that's still the case just trying to dispel maybe some out of reality info..

**estarzinger** · 01-10-2014, 14:19

Quote:

Originally Posted by FloatingDutchMn

Did anyone actually make it through the NWP this year? Reading Jimmy Cornell's blog suggested that conditions were unlikely for anyone to make it through, although 2-3 boats were still going to attempt when most considered the risk of getting stuck in winter ice too high and turned around for US coast or Europe

yes, 7 boats made it thru east to west (5 sailboats) and 2 west to east (1 sail boat).

Jimmy is a good friend, but he arrived to early up there and gave up waiting about a week too early.

There was one section this year where you did need significant motor power to get thru before it closed in. Two under-powered sailboats did not get thru in time and got trapped and had to be broken out of the ice by ships.