Tesla Powerpack enough of a game changer to move to single engine ?

[henryf]

Is the problem with boats the requirement to get up on the plane?

If you stayed at displacement speed does electric make more sense?

Cruise ships are all using electric motors these days. What about 2 really good sized generators to give built in redundancy. Modern battery storage used to power the boat systems when not under way. Possibly higher voltage than the traditional 12/24 volts. Ultimately we want to generate mains power for A/C, TV, cooking etc. Lighting and so on all low voltage.

Alternatively do you just use a generator all the time to power everything when not underway.

Interesting built in redundancy in that you can use 1 generator at a time. I can see huge advantages in terms of engine bay space. Would it work for larger, longer range boats ?

Henry

 

[Keen_Ed]

Cruise ships use diesel electric because the house loads are so huge. Propulsion is incidental.

 

[MapisM]

Would it work for larger, longer range boats ?

V V complex subject, H.
You might wish to have a look at the two links I posted in this previous thread, where you can find the interesting original Nordhavn webpage (2005 vintage, removed from their website several years ago):
http://www.ybw.com/forums/showthread.php?392481-Greeline-Hydrid&p=4700007#post4700007
Back in those days, they already envisaged all the advantages that you mention, and then some. And fwiw, I agree with most of those thoughts.
They actually built a couple of boats around them, and they were a mess - hence the project dismissal.
But that's because as I said their technical competence was nowhere near what the system complexity required, not because the principles were wrong.

 

[henryf]

I hadn't appreciated how technically difficult it seems. I just assumed you generated power and drove an electric motor

In terms of house power v propulsion power the reason I suggested larger longer range boats was because they have lots of house load, stabilisers (I'm thinking at anchor as well as underway and putting comfort in the domestic category), climate control, AV equipment, cooking, lighting (quite small with LEDs), and all the pumps, motors, computers, satellite comms, etc. oh, and of course the hot tub !

At slower speeds the power required to move can't be huge. Our 50 foot boats does 6 knots plus with one engine at tickover, 7.5 knots with both engines at tickover.

Henry

 

[henryf]

Right, so I've had a bath and thought about this.

What exactly is the difficult bit in using electric motors powered by generators. Two generators rated for continuous use. Because the electric motors are so small there's lots of space. Any problems just unplug them and slide them to under a hatch opening where they can be craned out. A days work to swap out a genny including 3 cups of tea and a hearty lunch.

In terms of propulsion the Nordhaven article seemed to imply everything worked better at fixed speeds (or was that just the generators). Cruise ships seem to be able to run at different speeds whilst using a couple of the pods.

Here's the clever part. If generators want to run at a constant speed then put any left over power into your battery bank be that conventional or these new flubber batteries due out. These batteries power stuff when the generators aren't running and if need be the generators switch off and the batteries take over for a while. A bit like KERS in F1

When you need full steam ahead Mr Christian both generators run together and combine though phase aligner thingy which
Hurricane can design over a weekend.

Is there anything I've missed ?

Henry

 

[Hugin]

Is there anything I've missed ?

Only that at full speed ahead nothing beats a diesel driving the prop directly.... that will always be the most efficient set up from around 60% power to full throttle.

At planing speed a series hybrid system (also known as diesel-electric with battery buffer) doesn't make sense in terms of efficiency (2X conversion losses), economy (very expensive up front) or weight (quite heavy with all the extra components)

 

[Hugin]

The Tesla battery packs are extremely limited in use. For example, you only get to recharge them fully 500 times before they're scrap. The good news is that that takes ten years; the bad news is that that's because they are limited to one full recharge per week.

Hold on, you are describing the new Tesla PowerWall product intended for household load-leveling over the week (10 kWh) or over a 24 hour period (7 kWh) The original poster mentioned units of 90 kWh each; which can only be the ~1300 lbs battery assembly used for Tesla's cars and not at all limited to a weekly or daily cycle. I see no reason why Tesla's car batteries could not work fine in a boat provided adequate cooling.... they are already designed to operate in a wet(rain/snow), cold(winter) and shaking (driving over all those potholes) environment.

Just so we discuss the same thing.

 

[Hugin]

Btw, @ the OP: which are the well known inefficiencies from running one engine instead of two, on planing boats? I'm not aware of any

Reduced drag of having only one set of appendages, spinning shaft and propeller compared to 2 or more sets. However this has to be held up against the advantage of possibly a larger total blade area of multiple props; allowing for a reduction in blade pressure, less slippage etcetera etcetera. There is of course also the internal friction of the main engine(s), which is likely to be smaller in one big engine compared to two small engines of the same total power. In terms of monetary savings I don't think these efficiency savings count for much in a leisure boat whereas for a cargo ship on the move 5000 hours annually it adds up.

In a sense, it's actually the opposite: it has been proven that surface transmissions (which is the best/most efficient propulsion for fast and big vessels) work better with a high "fragmentation" of power delivery - i.e. with 3 or even 4 props.

This is a special case; a surface drive is a high-speed application. In high-speed applications appendage and shaft drag is a significant component.... it requires a lot of extra power to overcome that drag resistance. Double the speed and you have 4 times more drag resistance. The surface drives are superior precisely because the appendages and the spinning shaft is moved up above the water and therefore doesn't induce any drag at all (in an ideal world). On the other hand only half of the propeller's blades are in contact with the water and therefore pressure on these blades quickly becomes very high if a lot of power is transmitted through the rather limited surface area .. which in turn triggers a lot of problems. The obvious solution is to add more propellers since it doesn't add much extra drag..... only extra cost (but that's another matter)

 

[henryf]

Just to be clear I am thinking entirely displacement. 12 - 13 knots would be lovely but I suspect costly from a power requirement perspective. I don't know long the boat would have to be to achieve this.

For planing boats I admit defeat from the outset, nothing but straight diesels.


Henry

 

[westernman]

The Tesla Powerpack won't change anything at all as far as propulsion is concerned. It holds the equivalent of about 1 gallon of diesel fuel in energy.

Cruise ships are diesel electric, because that works better for podded drives. Also they can vary the number of generators running to take into account the different speed they need to run at to arrive on time at the next destination.

The drives are podded in order for them to be able to dock without using tugs. This is a huge game changer for them.

Diesel electric is not the most efficient propulsion for a displacement ship at relatively low speeds. That is a large single diesel engine sized correctly for the ships cruising speed, driving a big (usually fixed and not controllable pitch) propellor. This is how almost all big container ships are set up.

Diesel electric may make sense for high speed planing boats - you can get more propellors in the right places etc. Also you may have a little generator for pootling along at displacement speeds and a second much bigger one for going at full speed.

However, the Tesla battery pack won't change anything there.