Electric Propulsion on Catamarans

[44'cruisingcat]

Originally Posted by deckofficer

Even taking into account the 110 lb weight savings of the Cruise 4.0s over the Yamaha 9.9s? Plus the weight savings of 6.08 lbs per gallon of gasoline?

(16) 200 ahr LiFePO4 cells weigh 232 lbs. This would be a 10.4 kwhr bank and your Seawind should use less than 300 whr per mile, so that works out to 35 miles. Would that be enough?

How slow would you need to motor to only require 300 Whr per mile? 6 knots in Seawind 1000 would take about 5 kWhr.... enough gasoline to motor 35 miles at 6 knots would weigh somewhere around 15 lbs. Enough batteries would weigh what? 500lbs? Kind of makes the 110lb saving disappear pretty quick.

And IS 35 miles enough? If you cruise much of the East coast of Aus it isn't even close. We did a 95 mile passage yesterday for instance.

[BigBeakie]

The thread seemed to have run out of steam, or should I say watts, lately.

So let me ask for purposes of planning battery capacity for an electric propulsion cat, what would you say is a reasonable maximum period to run motors at full throttle? Under what circumstances would you need to run wide open?

I can think of:

1 Running against current into or out of a lagoon passage.
2 Getting off a lee shore anchorage in a big blow.
3 While setting a parachute anchor. Again, big wind.
4 MOB situation (drop sails and get back quick)
5 Showing off when drag racing a diesel powered boat

All of these would seem to be relatively short time periods of WOT, so anything I've overlooked?

[valhalla360]

Originally Posted by BigBeakie

The thread seemed to have run out of steam, or should I say watts, lately.

So let me ask for purposes of planning battery capacity for an electric propulsion cat, what would you say is a reasonable maximum period to run motors at full throttle? Under what circumstances would you need to run wide open?

I can think of:

1 Running against current into or out of a lagoon passage.
2 Getting off a lee shore anchorage in a big blow.
3 While setting a parachute anchor. Again, big wind.
4 MOB situation (drop sails and get back quick)
5 Showing off when drag racing a diesel powered boat

All of these would seem to be relatively short time periods of WOT, so anything I've overlooked?

If you extend #1 into a longer channel, such as entering a river port on the wrong part of the tide (yeah, it's nice to claim you would always time it right or you would simply wait but realistically...), it could easily push up into 2-3 hours and if you are fighting a 4kt current, opening up the diesel is actually significantly more efficient as your SOG increases drastically relative to the extra fuel burn.

#2 could easily be several hours.

Another one to add, if there is a medical emergency that is of moderate severity but not bad enough that you want to call for rescue (ie: someone has a very painful sprain, possible fracture or a deep cut where you have stopped the bleeding but want to get to a doctor quickly).

Drag racing doesn't work so well. The battery bank to support a 600-1000hp electric motor, would either be huge or you wind up with a 1/2 mile range before needing to be towed back with dead batteries. If you are talking about cruising sailboats, I've yet to see a drag race so it's not a particularly high priority.

[mbianka]

Originally Posted by BigBeakie

The thread seemed to have run out of steam, or should I say watts, lately.

So let me ask for purposes of planning battery capacity for an electric propulsion cat, what would you say is a reasonable maximum period to run motors at full throttle? Under what circumstances would you need to run wide open?

2 Getting off a lee shore anchorage in a big blow.

All of these would seem to be relatively short time periods of WOT, so anything I've overlooked?

My experience in getting off a lee shore (at least on my EP powered monohull) is you don't need as much propulsion as you might think. Same goes for trying to make it around bouy or bridge. A small amount of electric propulsion allows one to point up nicely to avoid dicey situations (or just avoid another tack) quite easily. The only time I ran WOT was getting out of narrow channel against the flood into 25 knot headwinds and that was just for a few minutes.

[Tropic Cat]

Originally Posted by Stumble

...I will leave you with this quote from Richard Woods "I still think solar powered electric motor cruising boats smacks too much of perpetual motion to be credible."

Ever met Richard? Solid guy. If he says it, you can make book on it.

Derate all Solar panels to 75% of advertised power output to mirror reality.

Unless the math has changed since I was in my EE classes 747 watts still = 1 horse power.

Where are the efficiency numbers for the electric motor drives?

In anyone's power calculations, you're left with an electric drive system that can give you hull speed for around 10 minutes or 2-3 knots of boat speed for a couple of hours or so.

Electric motor drives will be disabled by a lightning strike, so not usable in tropical climates. (I live there and have been struck by lightning... not a lot of fun) and in short is just not ready for prime time. If it was, I'd have it on my boat as I love the concept, but not the reality.

No boat owner should rely on electric drive with current technology, as there are times you need your engines when things go bad out there.

When these systems can motor at 6 knots for a minimum of 5-6 hours and the batteries weigh less than 600 pounds, and I can recharge batteries in less than an hour (WITHOUT A GENSET) ... I'll buy one myself.

For now, a diesel just works.

[colemj]

Originally Posted by Tropic Cat

Electric motor drives will be disabled by a lightning strike, so not usable in tropical climates.

Unfortunately, many of the new diesel models can also be disabled by a lightning strike.

Mark

[BigBeakie]

Thanks Guys, great feedback. FYI we are considering 40hp electrics with 13kW battery per motor so WOT gives about 30 minutes before the 6kW generator kicks in.

Valhalla 360: Yes I've been looking at long river entrances as one scenario. Bundaberg has a reasonable length passage but the tidal current is pretty modest, so not an issue. One thing I am investigating is what adverse current and wind conditions would stop the boat, but havn't reached a conclusion yet.

As for the lee shore scenario, I am assuming if there is that much wind that once we get off shore a bit that sailing would then take over, maybe with engine assist to point higher. Is that a bad assumption for some reason?

The drag racing was a joke, but I have actually been on a boat that "tested" their hull speed with another boat, for fun.

mbianka: That is what I am hoping, that WOT would be an infrequent requirement and for limited time. The question is would 30 minutes be enough in conditions of South Pacific cruising?

Tropic Cat: I am not planning a 100% solar electric propulsion system without any generator. The 30kW Torqeedo Deep Blue's are about 97% efficient & will give about 30 minutes WOT on their designated battery, not 10 minutes. On the genny, it looks like we will be able to potter along at 5 to 6 knots for a long time. I have not heard yet a cogent argument as to why such a hybrid system is not viable...but I am still listening, and very open to hear what are the show stoppers. Lightning is certainly a big consideration for an electric boat, for sure. But as colemj points out, that is not exclusive to electric motors.

But the point is well taken, lightning strike is certainly a worry. We will be tropical cruising, and perhaps "sheltering: in equatorial waters during the cyclone season, so we expect our fair share of lightning. I am investigating isolation strategies & Faraday cage to try and protect electronics as much as we can.

Keep the ideas coming!

[colemj]

Originally Posted by BigBeakie

I am investigating isolation strategies & Faraday cage to try and protect electronics as much as we can.

The motors themselves won't be highly susceptible to lightning, and will be grounded to the seawater through the shaft anyway (?). I think your main concern will be the control electronics and charging systems. Maybe a spare controller?

Mark

[BigBeakie]

Colemj,

Yes exactly, grounding will be via the shaft drive & will have to have protected redundancy (hence a proper faraday cage for storage re induction charge) for critical electronics for both propulsion and navigation.

There's no guarantee of course, you can only do what you can do. A corollory of Murphy's Law is that once you have spent all the money on contingency planning, the event is much less likely to occur

[mbianka]

"As for the lee shore scenario, I am assuming if there is that much wind that once we get off shore a bit that sailing would then take over, maybe with engine assist to point higher. Is that a bad assumption for some reason?As for the lee shore scenario, I am assuming if there is that much wind that once we get off shore a bit that sailing would then take over, maybe with engine assist to point higher. Is that a bad assumption for some reason?"

That was my experience. I plowed out of Mattituck Inlet into a northwest wind blowing 20 to 25 knots. Thought it would be a piece of cake sailing east the fifteen miles to get around Orient Point. But, forgot about the fetch and waves pushing me sideways toward the rocky north shore. I tried a little EP (did not need to go WOT) and was able to point up enough that I could see the distance to shore increasing and the lee shore would not be an issue. I also like that it is quiet propulsion and allows one to think things through even when things are kind of rough.



"mbianka: That is what I am hoping, that WOT would be an infrequent requirement and for limited time. The question is would 30 minutes be enough in conditions of South Pacific cruising?"

I've only drift dived though places like Rangiroa Tiputa Pass . I'm not familiar with any of the other cuts in the South Pacific . Though I would think 30 minutes WOT would be plenty of time to get through most places. Though personally I like to wait for favorable currents in places like Hell Gate near me. I did that even when I had a diesel.

"Lightning is certainly a big consideration for an electric boat, for sure. But as colemj points out, that is not exclusive to electric motors."


If lighting hits your boat you are probably not going anywhere for a while no matter what your propulsion is. Here in the northeast we do get our share of lightning and have not had a problem in seven years. You do know most boats already do have an electric motor (the starter) already. If I did get hit and things failed I could remove and replace the motor in about twenty minutes (or less) same for the controller. Battery charger even less. Parts are easily shipped by air and for my system available off the shelf. Spares are also easily carried if you felt the need too.

[BigBeakie]

Thanks Capt'n Mike, that's good to know.

Heard some stories about cruising South Island New Zealand and getting out of some deep sounds/fijords by short tacking with engine assist to get out in a big blow. That could perhaps push our 30 minute window of WOT but as you say, less power would probably suffice.

Another use of WOT I just thought of is getting out of & into river entrances over the bar. We have several of those on the Oz east coast and some of them can be really hairy. Coming in you need enough horses to stay on the back of a big wave until it breaks, and then put the throttle down hard to get through the break zone before the next monster rears up behind you. We've had some real heart pounding episodes on the Wooli bar in a dive boat, so doing it in a cat would be challenging, to say the least. At least the cats track well.

It really helps to have enough horsepower when you need it, but for short periods.

[yamez4u]

Electric motor drives will be disabled by a lightning strike, so not usable in tropical climates. (I live there and have been struck by lightning... not a lot of fun)

This might be the stupidest thing yet I have ever read on this forum. So how did your engine work without it's alternator? Did your boat sink because all your bulge pumps stop working? Must have sucked having none of your heads working? Your boat is full of electric motors, they take lightning strikes as well as anything else on a boat. If electric motors had some magic ability to be "super" effected by lightning, we would all have mandatory diesel powered bulge pumps on our boats. Most new large ships are electric hybrid drive, I have never seen an electric container or cruise ship dead in the water from a lightning strike.

[Tropic Cat]

Originally Posted by yamez4u

This might be the stupidest thing yet I have ever read on this forum. So how did your engine work without it's alternator? ....

Are you for real? A post from someone who doesn't know that diesels don't need an alternator, spark plugs, a coil or an ignition system to operate.

Bilge pumps are very necessary when your boat takes on water. But whatever possessed you to assume a lightning strike would automatically hole a boat? This guy has never been struck by lightning. Does he even own a boat?

I hate it when folks post on topics where their only knowledge is apparently off of sailing forums.

My experience is real life...

My lightning hit

And it made good reading in Southwinds.....a sailing magazine.

[colemj]

Originally Posted by yamez4u

This might be the stupidest thing yet I have ever read on this forum. So how did your engine work without it's alternator? Did your boat sink because all your bulge pumps stop working? Must have sucked having none of your heads working? Your boat is full of electric motors, they take lightning strikes as well as anything else on a boat. If electric motors had some magic ability to be "super" effected by lightning, we would all have mandatory diesel powered bulge pumps on our boats. Most new large ships are electric hybrid drive, I have never seen an electric container or cruise ship dead in the water from a lightning strike.

We took a lightning strike that took out our alternator and bilge pump (and almost everything else - including things with electrical motors like the windlass). The engine works just fine without an alternator and the manual bilge pump wasn't affected. Our heads are manual.

Large ships have lightning protection systems that can route strikes around the electrical systems to ground and have surge arrestors sized for lighting strikes on their electrical circuits. While these can be added to small boats to some extent, it is a poor comparison to use and does not make the point you wished.

Mark

[seandepagnier]

Originally Posted by Tropic Cat

Derate all Solar panels to 75% of advertised power output to mirror reality.

What reality is this? I have a better reality, measure watts coming out of your panels in actual conditions. The rated power has no standard and therefore can be arbitrary.

Unless the math has changed since I was in my EE classes 747 watts still = 1 horse power.

This is true.

Typical diesel propulsion systems in most yachts are so horrifically inefficient (tiny propeller spinning fast, not optimial pitch/camber for slower more efficient drive speeds etc) as well as being rated at maximum possible power (electric is continuous power and can peak at 3x this for bursts of a few minutes with sufficient cooling)

You will in almost all cases find that an efficient electric drive equivalent to a diesel in practical use will have a much lower horsepower (1/3rd or less)

Where are the efficiency numbers for the electric motor drives?

Cheap brushless run 80-85% through most of their range. Cheap brushed motors 65-75%. Some brushless can achieve 90% or better.

In anyone's power calculations, you're left with an electric drive system that can give you hull speed for around 10 minutes or 2-3 knots of boat speed for a couple of hours or so.

This is incorrect. My system could drive the boat 2-3 knots forever as well as charge the battery with the excess solar input. Motor used 150 watts to go 2 knots, and 7 "50 watt" solar panels producing 250 watts.

Electric motor drives will be disabled by a lightning strike, so not usable in tropical climates. (I live there and have been struck by lightning... not a lot of fun) and in short is just not ready for prime time. If it was, I'd have it on my boat as I love the concept, but not the reality.

This is completely false. Brushed motors will not be disabled. Only the controller will be destroyed in a brushless motor, not the motor itself. A cheap controller for a 2hp motor costs $35, it is feasible to put one in a metal box.

A gps will also be disabled, so I guess they are not usable in tropical climates (despite the fact that lightning strikes occur outside of "tropical climates" depending on season, and also don't often occur everywhere in tropical climates..)

No boat owner should rely on electric drive with current technology, as there are times you need your engines when things go bad out there.

There are _never_ times when you need an engine of any kind. It is and always will be purely for convenience only. This was proven thousands of years ago using wind and sail alone as humans colonized the planet.

When these systems can motor at 6 knots for a minimum of 5-6 hours and the batteries weigh less than 600 pounds, and I can recharge batteries in less than an hour (WITHOUT A GENSET) ... I'll buy one myself.

For now, a diesel just works.

In 70 years from now, when the co2 is 800ppm, your great-grandchildren (if any survive) will curse you in your grave for taking away their right to walk outside without getting a headache. How can you be so selfish?

Originally Posted by colemj

The motors themselves won't be highly susceptible to lightning, and will be grounded to the seawater through the shaft anyway (?). I think your main concern will be the control electronics and charging systems. Maybe a spare controller?

Mark

Either that, or simply sail until you get a replacement controller in the unlikely event of getting struck. Also consider adding switches to disconnect the controller from the wires to the batteries during lightning storms,as well as all wires going up the mast. These switches must be double pole to include power and ground.

The charging systems can be bypassed if needed.