Switched to Electric

DDW

Super Anarchist
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For dockside maneuvering, there is no doubt that electric wins, hands down. The ability to turn very low rpm and instantly reverse change the game. With the eProp on my dinghy, almost had to learn to drive again as it is very different. Now most larger sailing auxiliaries aren't so highly powered that a lot of transmission play is necessary. On my trawler (375 hp on a 36') idle is probably 4 knots so the transmission is guaranteed some exercise each docking. 

 

longy

Overlord of Anarchy
6,985
1,280
San Diego
on the return delivery I presume. in which case - they probably stuck a more adequate prop on for the job. I mean, if I catch the drift of this conversation - most of our diesels are oversized because our props are undersized. which leads me to..
No, the return was via Matson, on it's trailer.

 

MikeJohns

Member
485
133
Hobart
I think there is some advantage to having very low rpm torque. Typically, electric motors that are used as auxiliaries can make arbitrarily slow turns. That's kinda nice. ICE aux engines usually get set-up with a minimum turns in gear that occasionally results in more boat speed than wanted. So, we bump them in and out of gear to get lower average turns. It works but isn't ideal. It also, isn't humbug enough to motivate installing fancier transmissions.


................... diesels don't have to be run at a constant RPM. They should be used under considerable load; about 50% of max power minimum for longest life/best cooling efficiency.........
Interested as to where that comes from

50% .....at least 50% load for the first 100 hours is common for heavier built engines to bed everything in. 

After that, just under some load rather than at idle will do for longevity. Maybe you are looking at max energy out to life against cost ? 

The longest lasting engines I have ever seen, have been significantly derated and running say 1/5 of the max power available from the same base engine. 

Direct drive gensets are a case in point, when operating at 50Hz often a 30hp diesels is run at 1500 rpm and commonly with a draw no more than 2 or 3kw they can easily get over 5k hours without anything other than routine service.....  

 

Fah Kiew Tu

Curmudgeon, First Rank
10,376
3,470
Tasmania, Australia
For dockside maneuvering, there is no doubt that electric wins, hands down. The ability to turn very low rpm and instantly reverse change the game.
Or, as I keep saying, a controllable pitch prop.

The Sabb diesel I have has a pitch control lever that enables going from full fwd pitch to full reverse in a couple seconds or less. You can also put the prop in fully feathered position and use it as a paddle wheel.

They are really neat devices. But - not cheap to make compared to a fixed pitch prop.

FKT

 

DDW

Super Anarchist
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The best maneuverability is a reversible transmission and variable pitch. That lets you pick the prop walk you want to use. 

A problem with variable pitch is you cannot vary the true pitch, only the angle of the blade, so you have to pick what pitch you want to be efficient. Some of the variable pitch props have no twist so not super efficient anywhere. 

The "you have to run a diesel hard" myth is very slow to die. There are millions of diesels sold in cars and light trucks (many times the number in boats), they run at < 1/3 their power capacity almost their whole life. Even heavy trucks are very typically idled overnight to keep the AC running. It doesn't seem to hurt them. The slobbering and other problems with older injection systems is much less a problem with newer, and not a problem with common rail. 

 

Zonker

Super Anarchist
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Canada
The longest lasting engines I have ever seen, have been significantly derated and running say 1/5 of the max power available from the same base engine. 
Yeah, but that's not the quite same thing. The injectors and turbos on those engines are NOT the same as the one putting out 5x the power. The timing and cams will be different. Each is optimized to put out the power according to the rating.

If you take your max rated engine and run it at 20% load you will get a lot more carbon build up and slobber. The injectors are not as good at metering small doses of fuel. This is more for mechanically controlled motors i.e. smaller sailboat motor; more modern electronic injectors are better at metering smaller amounts. I'm sure the higher output motor will last nearly as long as the de-rated engine if run gently, but you'll be doing more maintenance on it. 

(Your derated engine is also running much slower, so mechanical components are less stressed.  Thus 1000 hrs @ 1500 RPM is not the same as 1000 hrs at 2700 RPM.)

----------

The 50% figure came from a study I read about maintenance costs (including overhauls) for a series of large engines for a stationary (floating) powerplant. I think it was a Wartsila document but can't be sure now. Recently I was involved in a USCG proposal where you had to design the generators to always be at 50% load or greater and this determined generator capacity. Not sure if that was just a coincidence. 

 

167149

Super Anarchist
Yep. I like the idea of electric drives but this biz of a 10kW electric drive is the same as a diesel engine of 3X the (theoretical) output just because it's using magically more efficient electrons instead of carbon is pure wishful thinking, to be polite.

If a much smaller electric motor can replace a much larger diesel, the boat never needed that size diesel in the first place. So it was originally poor engineering design and nothing more, most likely driven by marketing.

Period.

I thought about this before I built my boat which is why I have a 3:1 reduction transmission and a big propellor - 22" diameter. I wanted to be able to transfer the engine power to push, not cavitate a small prop. Wouldn't matter what the power source was if you can't transfer it efficiently to thrust.

And before anyone goes to 'yes but you drag a big bucket when sailing' - it's a feathering prop so, no I don't. What I did was spend money.

FKT
suppose the barge model seagull is an example of this, if (big if here) you can get them running AND keep them running it can be quite staggering  to see just what those buggers will shift

 

mckenzie.keith

Aspiring Anarchist
847
282
Santa Cruz
Knew I'd get in trouble if I generalized about electric motors. Yes AC induction motors don't have high zero RPM torque; I was thinking about DC PM motors.
Well, some AC induction motors have very high zero RPM torque when line connected. Of course nobody is going to run an induction motor to propel a boat unless they use a variable frequency drive. Once you add the variable frequency drive you get controlled and limited full torque from very low speed (let's say 10 RPM). If you have a shaft encoder you can even run at full torque at zero speed indefinitely (might need a fan on the motor though). I think it would possibly be interesting to use a normal induction motor to power a boat, but they are so heavy. Might have to use a smaller one and overload it a bit.

One thing about induction motors is that the rated power is much lower than the maximum power. A motor rated for 20 HP will put out 20 HP 24/7 for many years. But it can put out 40 or 50 HP without stalling. It may tend to overheat if operated at that power level for a long time. But a diesel will stall if you try to get double power out of it.

In my opinion, if you have a 30 HP diesel (30 HP topline advertising number), you can probably replace it with a 20 HP induction motor and call it even. The 30 HP diesel won't put out 30 HP continuously, and the 20 HP induction motor WILL put out 30 HP. Maybe you can even get away with 15 HP.  But this is just because the ratings are different and the overload response is different. Not because electric HP are magical.

 

Kris Cringle

Super Anarchist
3,261
2,894
Interested as to where that comes from

50% .....at least 50% load for the first 100 hours is common for heavier built engines to bed everything in. 

After that, just under some load rather than at idle will do for longevity. Maybe you are looking at max energy out to life against cost ? 

The longest lasting engines I have ever seen, have been significantly derated and running say 1/5 of the max power available from the same base engine. 

Direct drive gensets are a case in point, when operating at 50Hz often a 30hp diesels is run at 1500 rpm and commonly with a draw no more than 2 or 3kw they can easily get over 5k hours without anything other than routine service.....  
My old Nissan diesel evolved like this. It was originally designed to run water pumps in the 3rd world and had a mechanical governor that kept RPMs to 2600. After that, the engine was adapted to marine by Chrysler/Nissan, to forklifts and eventually to a Nissan pickup truck that had a diesel option in the 80's. 

Through that evolution the only thing that changed was the governor. For the PU truck, it had a pneumatic governor fitted that allowed rpms to over 4,000. It also had a medium governor of some kind. Although my present engine SD22 started in a Nissan PU (that rusted out at 70K miles), I just swapped the pneumatic gov for my mechanical and marine cooling gear.

Her days of redline 4,000 are over. She's been put out to pasture in a sailboat. 

 

Zonker

Super Anarchist
10,129
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Canada
Good if you like to approach the dock at high speeds and then BAM into reverse.

Sometime I think tugboat throttles could be a binary switch "On/Off" - or at least some skippers drive them that way.

 

weightless

Super Anarchist
5,608
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The tug drivers around here occasionally show off serious throttle tickling skills. I think the crew boats just have full reverse - off - full forward.

 
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Good if you like to approach the dock at high speeds and then BAM into reverse.

Sometime I think tugboat throttles could be a binary switch "On/Off" - or at least some skippers drive them that way.
I met a guy with a DIY electric setup with two 6V batteries, wired with switches for 6V or 12V - two speeds, high and low, plus reverse. Simple and cheap, it worked fine for him. It probably would for me too.

We had a 5kt idle on the Maple Leaf 50, so lots of on/off operation.

 

Bull City

A fine fellow
7,185
2,819
North Carolina
Very good article in the latest WoodenBoat (March/April 2022 #285) by Stan Grayson about his switch to electric propulsion. First, a Torqeedo OB for his inflatable dinghy, and then an electric inboard for his Pisces 21 daysailer.

 

Kolibri

Member
484
574
Haleiwa, HI
Going sailing this weekend again and it finally looks like we will get some good wind. The last few times out it's all been around 5 kts of wind at best. I will finally have a chance to play around with regen charging and dial in my Monitor windvane with stronger wind. Forecast is for 10 to 20 kts on Friday dropping off slightly each day through the weekend. 

 

Kris Cringle

Super Anarchist
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Electric propulsion is the theme in the March April Good Old Boat. Yet some groups and forums are still saying, "You can't" 

Screen Shot 2022-03-02 at 7.26.35 AM.png  

 

thinwater

Super Anarchist
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143
Deale, MD
^^ The articles don't say "it's great" either. Like this thread, they explain that electric power is a matter of compromise, and by and large, they are happy with the compromises. You have to read all the numbers and decide if the compromises suit you.

(I am one of the authors.)

 

Fah Kiew Tu

Curmudgeon, First Rank
10,376
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Tasmania, Australia
^^ The articles don't say "it's great" either. Like this thread, they explain that electric power is a matter of compromise, and by and large, they are happy with the compromises. You have to read all the numbers and decide if the compromises suit you.

(I am one of the authors.)
I think of it in these terms.

Would I install a diesel engine with a fixed tank capacity of 8 litres, and having to be filled via a 3mm orifice?

If that works for you, you'll likely be delighted with an electric drive system.

Once again, it's not the drive itself, it's the range and recharge time that are the issues. There are use-cases that work because people keep their boats in powered slips and don't go far.

FKT

 

DDW

Super Anarchist
6,698
1,228
Electric propulsion is the theme in the March April Good Old Boat. Yet some groups and forums are still saying, "You can't"  
I rarely see anybody say "You can't". There are quite a few people who say "I wouldn't" or "not practical for many uses". Which is an entirely different thing. 

 

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