Calculating power requirements for an electric 'shop boat' ...

[kengrome]

I may get a contract to repair boats located in various places around the Philippines (7000+ islands here). In anticipation I am designing a large power boat that has a workshop and living accommodations built into it, complete with everything my employees and I need to do the work where no electric, water, food. materials, equipment or accommodations are available.

The boat will be a power catamaran that carries everything we need including an electrical generator with power enough for all our equipment. My thought is that since I must buy a generator anyways, why not buy one that's big enough to power two electric motors -- one in each hull -- for the boat's propulsion?

I'm designing for 32,000 pounds displacement at 20 inches draft. Assuming 500 pounds per HP I will need only 64 HP to push the boat at displacement speed. But these are long and slender hulls with a LWL of 56.5 feet and a BWL of 5.4 feet so I actually have a L/B ratio at the waterline of more than 10:1.

This makes me wonder:

- What is the realistic "hull speed" of this boat?
- Could I reach this speed with less than 64 HP?
- How fast can I push this boat using twice the HP?
- What would be a recommended electric propulsion motor?
- What losses should I figure from generator to propeller?

If I do not change things I should be able to use an 18 inch diameter propeller -- two of them actually, one beneath each hull -- but this can change if necessary since I'm only just beginning to make decisions about this boat. I welcome your thoughts, suggestions and insights ...

:)

[Jango]

Speed change with twice the HP (All things being equal - weight etc.) :

sq. rt. of 2 or 1.4 times mph (knots)

[klick]

There are many motors that would meet you needs. I've been wanting to convert a boat to electric with a high power motor such as this:

http://www.evparts.com/prod-MT2143.htm
or
http://www.evparts.com/prod-MT2119.htm

Really any of the large electric motors they have there are powerful enough for what you need. As you can see, the smaller one above is about 28HP continuous and the other is around 35HP continuous, as rated by the manufacturer. However temporarily those motors can be pushed extremly hard, even the manufacturer will admit that 100 to 200HP is easily achievable but it wouldn't be for very long at all, even with water cooling. Crazy EV dragster people have pushed that ADC 9.1" to over 500HP, I think you have to replace the whole brush assembly to push them that far, but i doubt you're looking to do this anyway.

Regardless, the continuous rating would be what you're looking at, but that would require a very generous generator, and in reality hybrid solutions aren't all that efficient for marine applications, or for any application that requires a constant speed for a long time. You would also need a substantial battery bank to even handle the load that it requires, and that would weigh thousands of pounds, and even at 65HP it would only last 15 minutes, and that battery bank would only last a thousand cycles TOPS, if you buy the most expensive sealed deep cycle lead acid batteries there are.

I'd still like to do it, despite most of the shortcomings, but for you i'm not sure it's worth the risk. Even if you were really rich and could go lithium ion it really wouldn't buy you much, a million dollars worth of cells still coudln't get you that far, unless you go 5knots.

Ross

[kengrome]

Hi Ross, thanks for the reply.

I wouldn't be using any batteries, instead I would simply use a big generator to power the motors directly. There's the AC/DC issue to consider too I guess. Most generators output AC but I presume I would need DC motors if I want forward/reverse propulsion without a transmission -- unless I can get reversible AC motors.

In reality hybrid solutions aren't all that efficient for marine applications, or for any application that requires a constant speed for a long time.In this case I might be better off using a small power generator for my shop tools, and a couple of diesel engines for the boat's propulsion ...

[SheetWise]

In this case I might be better off using a small power generator for my shop tools, and a couple of diesel engines for the boat's propulsion ...


Don't give up so easy. There are solutions to all of these issues -- some of them more elegant than others. Maybe you'll be the one to find the right balance ...

[the1much]

Ken,,get ahold of Kaptjer.,, he talked to a company that sells electric set-ups for boats,,,,,make it seem like you wanna buy it from them,,, give them all the #'s ,, and i bet they tell ya what ya need, and that they would be happy to sell you the set-up and batteries for a little under $15,000.00 ,,maybe twice as much if they like ya,,hehe ;)

[Guest625101138]

Hi Ross, thanks for the reply.

I wouldn't be using any batteries, instead I would simply use a big generator to power the motors directly. There's the AC/DC issue to consider too I guess. Most generators output AC but I presume I would need DC motors if I want forward/reverse propulsion without a transmission -- unless I can get reversible AC motors.

In this case I might be better off using a small power generator for my shop tools, and a couple of diesel engines for the boat's propulsion ...

You could use a complete AC system but to use industrial components would be very expensive. Probably around three times the cost of separate diesels at the scale you are considering. Any fuel gains would be doubtful as well because even a good electrical system will only get around 90%. If the diesel has a narrow efficiency window then this could be more than made up.

The EV automative technology does not suit the boating application. There are big gains in the energy recovery with EV systems and they focus on this. So much so that it will be allowed in F1 next year. This will really power the development. Sadly this does not help boats much where regeneration is not required.

The scale model stuff that is being produced for electric helicopters and airplanes is brilliant but just too small for most boating applications. I figure it will not be long before we see the cheap electronics coming into a wider range of higher power applications.

These are the sort of motors you should be looking at:
http://www.baldor.com/products/detail.asp?1=1&page=6&catalogonly=1&catalog=IDNM2334T&product=AC+Motors&family=Inverter+Duty%7Cvw%5FACMotors%5FInverterDuty&winding=10WGW586&rating=40CMB%2DCONT

I have not looked closely at controllers but something like this is required:
http://www.hitachi.us/supportingdocs/forbus/inverters/Specifications/SJ300_Specs_RevG.pdf
Some prices here to give you an indication:
http://www.inverter.co.uk/electric-motor-controls/inverters/3-phase-low-cost.htm

If you shopped around you might find something purpose built for traction application but I think you are at the small end of this.

The gap between the high power hobby stuff and low power industrial stuff is huge at present. You may find something that is bridging the gap if you look hard enough.

The firm that I found (FEYS) building small boat systems no longer seems to operate. There are some firms offering electric at the top end. If you have solar collection to batteries on a sailing boat then it makes a lot of sense. There are some advantages with electric but I do not think you would appreciate them too much on a work boat. You also have to consider what expertise you have to fix the things when they go wrong. In the worst case I guess you could hard wire the motors to the alternator and effectively have an electric gearbox off the engine.

Rick W.

[Ratch]

I cannot answer your question but I can point out some thing you might want to look into. From what little I understand an electric motor rated hp is not the same as an engine something to do with the electric motor being better because it can maintain equal torque across the rpm range. I too would be interested in learning exactly how they compare.

For the AC motor look at those used in cooling towers on commercial air conditioning systems. They are designed to work in wet environments and not much more than a standard motor. How this compares to a proper marine motor I have no idea. Teco sell a lot of these where I am so would be a good place to start.

For the motor speed control you would use a VSD (variable speed drive) this will give you accurate speed control and direction. I know Danfoss make very good ones but there are many manufacturers to chose from.

Remote control of the VSD is easy they are designed to be run by BMS systems (computer that runs the Air Cond). They will all be able use a 0 to 10 volt input i.e. 1.3v will give you 13% speed. So a 50 cent trim pot and a $2 toggle switch will give you very accurate motor control.

I am guessing that you would be looking at $5-7k au for each motor including VSD. reconditioned motor would be even cheaper.

[FAST FRED]

ON EV autos the ONLY "gain" is in heavy city traffic , stop & go , one block at a time.

On the highway the conventional cars do better .

There is ZERO upside to a direct genset electric motor for a simple boat.

If you had 15 gensets , a variable hotel load , and variable speed and thruster requirements (AKA a large Cruise Ship , doing without a Berthing tug) it might be worth the engineering and operating costs.

Pro boat builder went all through the std boat setups , and a cheap shaft , marine gear box and prop will never be beat for a long distance run .

FF

[Dieseltwitch]

Hello, Im new to this forum, I am an avid EV designer. I am also an electrical engineering student here in colorado.

While going electric may cost you more money it does have some advantages. The amount of tq available is massive! and the speed of the motor can easily out strip any diesel motor setup (10,000 RPMs) AC electric motors are unique in that they can provide a flat tq curve for getting going then transfer that tq to hp to keep the motor running at the most efficient point. what your looking to build with the diesel gen set running the motor is called a Series hybrid. I have one of the planing board right now. I even some day would like to use a turbine gen set as the power source. the site i use for motor and inverters is Metric Mind (http://www.metricmind.com/). hope this gives you a good jumping off point. if you have any question I would love to help you out.

Also -
Im not sure as to the power requirements of power to push a boat through the water. in search of this is how i found your post. if any one has any calculation on this mater i would love to get my hand on them.

[TollyWally]

Hey Diesel,
Interesting link, I bookmarked it. You appear to have a pretty good grasp of an interesting and somewhat misunderstood area of technology. You could be a valuable addition to the forum here. :)

You need to get your hands on a couple books by a guy named Dave Gerr. One is the Propeller Handbook, the name of the other escapes me at the moment. I can't put my hands on it right now but it will be easy to find at the library or Amazon. Those books will get you all set up in short order.

I wouldn't put a whole lot of effort into the Grome project. He is long on quick computer renderings and abstract theory, extremely short on follow through.

[Luckless]

What about stealing a design idea from farming? Run both the prop and your generator off the same engine? You're not likely to be in high demand of both at the same time after all.

It would mean a more complex gear system, being able to disengage the generator or the prop at will, but it would likely be more fuel efficient than running an engine to turn a generator to run an electric motor.

But I'm guessing Power Take Off units aren't all that common on marine engines, I wonder if it would it be faster to add such a thing to a standard marine engine, or easier to take a land based setup and rebuild it for marine use?

[Ad Hoc]

kengrome

It has been almost a year since you posted your question above.
Have you made the boat yet, what is she like, are you sailing around the philippines..???

[Dieseltwitch]

Wally - Thanks for the kind words. I would love to answer any questions you might have about electric drive systems. I looked the books and all three by him are on the way! Go Amazon! lol I know that most people on forums do a lot of talking and a lot less actual building, and thats ok! I like going over ideas in my head and some times they are nice to get over with other people.

Luckless - Im a little lost as to why you would need to worry about disengaging the motor from the prop. If it was designed as a hybrid system the motor/generator could be place any where on the boat. I think I may just be reading your post wrong.

Ad Hoc - LOL

[Ad Hoc]

Dieseltwitch

Well, reasonable question....did he or didn't he. Makes the debate more realistic then, otherwise everyone is just "philosophying" about, well...er...what might be not what is or should be by now. Just adds credibility to the posting , that's all :)

[TollyWally]

Diesel,
I don't have any specific questions but I am interested in the whole subject.
I need a little firmer grasp before my questions would do me much good. What I remember from high school physics seems to fly in the face of many people's enthusiasm about electric power. But as always the devil is in the details.

The torque possibilities of electric motors fascinates me. I look forward to your participation here on various things electric. There are some pretty smart people here who will help you with your various questions with hull dynamics and power once you get enough of the basics down to understand the lingo. Gerr's books will give you a good grounding from which to work.

[Dieseltwitch]

Ad hoc -
I know I was laughing about your passive aggressive way of calling him out. I see a lot of people I wish I could do that to. In school i hear way to much about some ones father or brother that did this or did that or is "gona do". I just think its funny

Wally -
Your about where I was at 5 years ago. I hope people don't miss understand my excitement for electric motors as a hate for diesels. Personally I love diesels. Hence the name. All my friends say I have diesel fuel for blood! I went to school for diesel maintenance back in high school and my teacher told me something that got me thinking. he said (yelled), diesels were never made to be put into cars and trucks, they where designed be turned on, run at their most efficient point and then left there for a very very long time. he told me about a car he had designed "on paper" mind you, that would use a small diesel engine to power a large hydropump and then have small motors on each wheel. basically a hydrostatic car. he claimed it would be the "most efficient thing on four wheels!" when I asked him why, he said simply. We produce power in the most efficient way and use it in the most efficient way. gears, shafts and clutches are very in-efficient! he also said that you could increase the overall efficiency by turning off each motor one at a time as you get going. Why drive all four wheels when you really don't need to. later as I learned about AC motors and drive systems I realized that they do exactly what he was thinking about. lets take some work I've done for EV's as an example. I personally drive a VW Jetta TDI for my daily driver. It has a 100HP 4 cylinder Diesel turbo (175 - lbs-ft). When I look at the power curve I see that I can only get max HP around 3500 RPM (only one spot) and there is no way to choose the power of the motor just the speed. When I did the math I found that I only need 14 hp to maintain 70 MPH on flat. but at 70 mph my engine runs at 3500 RPMS, so what happened to the rest of the 86HP? Nothing! its literally blown out the tail pipe and taken away as heat in the cooling system. So this is where electric motors and battery systems come into play. Electric motors have the advantage of being able to have both their speed and power regulated. allowing them to produce the needed power at almost any given RPM. the batteries allows us to store large amounts of energy and use it when needed. this storage ability allows us to use smaller generator to move larger items. think of batteries as a power accumulators much like those found in hydraulics systems. They also act as a buffer allowing us to run our generator at its most efficient point. why make 100HP when we only need 14hp, that wouldn't make much sense. basically the generator will run independently of the the electric motor. When the system comes on line the computer looks at the charge in the batteries if the batteries are below a given set point the computer turns the diesel-genset on and begins to charge the batteries when they are full it shuts off. Now the electric motor can run when ever the drive wants it to, and it will have full power, no waiting for the motor to spin up, having a massive storage tank of power to draw from. the way I am sizing my generator is so that it can handle the power needed to move the car in the worst possible driving situation. allowing me to keep both my generator small and my battery pack small, This can be applied directly to boats, in fact it might even be easer to do. you could have a number of small jet pumps ( cause the least amount of drag when not in use) have relatively small electric motors for each pump. when you are trying to plain out or just get going you could use all of the pumps/motors. once you plane out you could turn off a number of the pumps, allowing the boat to maintain plane and still use very little power. or you can run all the motors and just turn down the power to each one . the net power use would be the same in each case. In the end you use each component todo work at its most efficient point. Doing the most work with the least amount of effort (little waste).

Note - The diesel engine could even be supplemented with a gas turbine, they are even more efficient then a diesel engine if it can be run at its most efficient point and have that power harvested.

"Work smarter not harder"
"Noise is nothing more then wasted power!"

Gas engines are around 10-20% efficient
Diesel engines are around 30-40% efficient
Turbine engiens are around 60% efficient
Electric motor are around 90-95% efficient (from the power produced at the generator to the end power produced at the motors shaft!)

Sorry I went on a rant there, hope this gets those gears turning Wally. let me know what you think. Sorry I didn't have any examples of boats, I just got a hair up my ass one day to start looking into making a diesel-electric boat. (still looking for a donor craft)

[Dieseltwitch]

here is a link to a Turbine-electric hybrid (series) bus!
http://www.designlineinternational.com/regional_div.cfm?subpage=704452
Take a look. sadly they took down a lot of the pictures that showed how it worked but you'll get the idea.

[Luckless]

Luckless - Im a little lost as to why you would need to worry about disengaging the motor from the prop. If it was designed as a hybrid system the motor/generator could be place any where on the boat. I think I may just be reading your post wrong.


Well, for a safety stand point I would want a system that completely disengaged and locked down the connection between Engine and Prop. The idea being that you use a fairly standard inboard engine to directly power the prop. When stopped you can switch the engine from powering the prop, to powering the generator.

Now, I'm not sure about you, but if I'm tied up at some dock, gunning my engine at full speed to power my tools, I really don't want a simple clutch or something being able to slip and engage the props, or someone easily being able to pull a single lever to do it.

Basically I ask why you would bother to run the props off electric motors, by running a large fuel engine to turn a generator,... Sounds like a fair bit of extra weight to carry on the boat. But I will agree it gives you far more flexibility in placement of gear, just at the cost of fuel efficiency.


(I once worked on a project to implement secondary backup redundancy for a system. There was a primary with redundancy, a back up with its own redundancy, the secondary back up, and the secondary back up redundancy. After such a project I look at safety systems a little oddly I think.)

[Dieseltwitch]

Actually no, you can go with a much smaller motor then you normally would. you use the most power when you accelerate out of the hole, once you get moving the amount of power you need is greatly reduced. this allows you to size a motor to the exact size that you would need to just to keep the boat moving. A small battery pack can provided a buffer to get the boat going and then allow for harvest and storage of the diesels power. Again I'm sorry for the lack of boat examples. but here you go. the hybrid I am designing for my car, will only require a 40kW diesel engine (53 HP), thats half the size of the 100HP engine that I currently have. and half the weight and almost 3 times the efficiency. This is due to the fact that when that motor runs it will ONLY run at its most efficient point! To really understand why electric motor are superior to ICEs in broad range power production you need to look at the power curves. I will try and find some for you. but basically an electric motor can produce 300% its rated tq at 1 RPM and hold that 300% to nearly 60% of its max RPM. while a diesel engine needs time to build up to its max Tq and then once it goes past it, the tq drops off rapidly. thus is it more advantages to harness the diesel power at it most efficient point and then use the electric motor to do the actual work.

[Ad Hoc]

Dieseltwitch

Very interesting. I must point out though, owing to the lack of examples as you state, i'll add one for you. Your suggestion of "..you could have a number of small jet pumps.." is where the "master plan" of falls down. To drive a jet boat efficiently, you need the largest size of jet possible, in the same way as you need the largest diameter prop you can use.

Ideally the velocity of water coming out of the jet needs to be the same as the velocity of the boat. As the velocity of the water through the pump increases (in selecting a smaller diameter jet), your efficiency decreases. Not to mention problems with increasing cavitation.

As for being pass-agress....well, where would we be without asking a few questions?? ;)

[Dieseltwitch]

True, I was thinking hypothetically. sounds like a jet drive would be best left to high speed craft. What about using a set of Voith Drives? These have intrigued me for some time. Then you could not only reduce the amps at each motor but also steer them independently from a single power source. my only other choice would be some time of pod drive system. Either way you get the idea. I would have to run some simulations to see what drive system would work best for what application using a hybrid system.

[Ad Hoc]

The basic problem with eletric plants for propulsion on boats in a word "weight".
Great for large cruise liners (as is now the norm). Smaller boats, the weight will kill the design.

[Dieseltwitch]

You are right in this! I don't see small run about benefitting from a hybrid system. I would be interested in finding the power need to keep a craft moving at a given speed. I have a method that works to find the power needed to keep a car or truck rolling but have never tested with a boat. if any one is up to the tanks the process is very simple. any takers? all you need is a stop watch and the specs for your boat. ie weight

[speedboats]

Going back to the original post application, in a multi-hull setup it would be easy then to run 2 drive systems but have a single motor. As was suggested, this gen-set would then power any tools needed for the workshop.

To isolate the drives from the generator -or power source- would be as simple as an heavy duty battery isolation switch (no energy means no go...)

As was stated, the best effiency for water propulsion is as big as practical, being large diameter jets or props. As max torque is available with an electric drive from 1 rpm, then electric is awesome for spinning these, whereas say a gasoline or diesel (and we have this problem with larger diameter jets of 12" or more) wants to spin at 3500 - 4500rpm the jet wants to be at 2800 or less.

The example here was for a displacement vessel, where the power requirement doesn't 'drop off' once the boat is free of the water, although with a prop the amount of energy required to maintain x speed will lower once that speed is achieved, the same isn't always true for the jet. Think of a jet as a water pump (which is all they really are), to acheive 2500 rpm will require the same energy input weather the boat is loaded, unloaded, at speed or stationary. The jet is unaffected by what the vessel is doing.

I like the idea of electric, which is the reason I've got 'into it' for a potential car project (finances always dictates other things). Not so much the green aspect, but more the beauty of efficiency and raw available power. As has been stated, the need for alot of power in a car is really for short durations, then to maintain 60mph only requires minimum hp to overcome wind drag and rolling resistance. Seeing it in boats (particularly smaller run-abouts) may be a little hopefull. 200lb for the electric motor, plus the gen-set and all the bulk that comes with it would make it prohibitive. In the original example where it would be a vessel with a workshop and a generator would already be onboard to power tools etc, it makes sense to utilise the same generator to run the drive system would save capital expense and weight of more engines for a dedicated drive system

My 2cents

[Ad Hoc]

speedboats

"...Going back to the original post application..."

That is the whole point. This thread is almost a year old, so, what was selected what was done, since we can talk about X,Y and Z until the cows come home...but what was actually done. There seems to be a deafening silence in this regard!

[speedboats]

I don't disagree with you, but the topic caught my eye all the same and am interested in comments of others none-the-less. Perhaps, while hypothetical, the concept may have merit and be worth discussion. Peoples ideas (especially about electric) and technology would have and has changed over a year.

As you say, it is somewhat disappointing not to get a reply about how, if at all, things got on with said project

[speedboats]

'till the cows come home'. I take it you are not a native of Japan?

[Guest625101138]

........, it is somewhat disappointing not to get a reply about how, if at all, things got on with said project

The answer is here:
http://www.bagacayboatworks.com/

I have not heard from Ken since the end of 2008.

Rick W

[Ad Hoc]

speedboats

well, i'm surrounded by Cows reared for the famous Kobe beef, other than that, no :)

Rick, thanks...pity, Cebu nice place.