Engine Torque Curves

Jusy expanding on a previous suggestion but most mercruiser stuff starts its life on a chevy, ford, or chrysler engine line. if you have acces to the 2.5 l find out who made the engine. it will more than likely match up to one of the auto makers car engines. using a degree wheel, dial indicator and some time you can get camshaft specs. using the bore, stroke, compression ratio and a moderate volumetric efficiancy you can get a computerized dyno program from performance shops that may give you ball park h.p and torque curves.

 

Very interesting project... I looked into a similar conversion over the last few months as an alternative propulsion method. Found a lot of information available at the "electric vehicle" websites. Of course, these guys have been at the "electro-motive" table for a much longer time.

As far as motors go, you may be able to get some good info by contacting "Advanced DC Motors". They make some pretty beefy motors that are used in electric cars, golf carts, and lift trucks (forklifts).

I (sort of) abandoned the project when the costs, weights, and control complexities exceeded a realistic budget. The thought is still there though. Maybe someday...

Q. - are you actually going to build and test this system, or is this a strictly paper (theoretical) engineering exercise?

 

Marine engines have a totally different torque and advance curve than an automotive one. Check pcmengines.com for more info.

 

Good question. You are right - a project of this type is quite expensive and the weight issue is not to be ignored. I haven't checked this thread in a while, so I was surprised to see any more activity. The system design is complete (the detailed design work such as mounting, cable length, prop re-sizing, etc still has to be done). I am to give a presentation tomorrow to see if the project is to proceed.

Here's a recap of what was done. I could find no reliable information on the engine anywhere. As an above poster mentioned, the Merc engine was manufactured by GM. Neither GM nor Merc could ('would' is probably more like it) help me out. One poster offered an EXCEL spreadsheet to use in determining power/torque curves. This was a start, and probably accurate enough for my purposes, but I decided to create my own equations by taking known data from several smaller marine engines. I then extrapolated the data and found a curve that I felt confident in presenting to others and explaining where it came from. What I decided I needed, based on the new data was a 30-35 horsepower motor (the application of the boat is such that it seldom ever used more than 30% of the available power).

Here's where my biggest problem popped up. As pointed out by many (here and elsewhere), batteries are the limiting factor in a design of this type. Batteries have too main flaws in regards to marine design - they do not last long enough and they are heavy. I don't recall exactly, but it seems like the smallest rated 'off-the-shelf' voltage for a motor of that size was 300 V. A 300 V system requires twenty-five 12-V batteries. Figure a nominal weight (at the low end) of 60 pounds each, and you are looking at 1,500 pounds of batteries.

I then took a different track. By using the Displacement Speed Formula presented in Dave Gerr's Propeller Handbook, I determined the speed I could expect from variously sized motors From this, it looks as though a 20 hp motor will be quite acceptable (it may be possible to go as low as 12 hp in this application, which of course saves money, but it would sure be slow) From 20 hp on down, 120 V systems are possible, which slices the number of batteries to 10 (600 lb - still heavy, but acceptable).

The past couple of weeks I've just been waiting on quotes from motor and/or drive/controller vendors. As I stated, I am to present what I have tomorrow. I am presenting 2 options - one with a DC motor and the other an AC motor. Both have distinct advantages and disadvantages. Once again, it may be the batteries that will stop this project cold. With current battery technology, it looks as if a set of batteries should only be expected to last 6 months. That, coupled with their weight and the expense of the rest of the system, may or may not be acceptable.

For my money, I'd stick with the gasoline engine and be happy, but then again, it's not my money.

 

An electric drive system doen't absolutely have to depend on batteries, though trolling motor type systems are set up that way. However, trolling motors aren't often used for primary propulsion. The more "conventional" or practical system would utilize a diesel engine coupled to a generator (or alternator) then through the controls to electric propulsion motors. These motors in turn would be connected through thrust bearings to the prop shaft. Hence, a true diesel/electric propulsion system, not dis-similar to that used in d/e trains.

In another model utilizing batteries, the batteries are set in between a diesel "battery charging" generator and the control system/ motor, creating a longer "power train", but allowing a much extended cruising capacity. In theory, the generator could be sized close to the motor's ratings and the batteries would really only act as a reserve.

Google "Fast electric yacht systems" and "Vetus" to get a better view.

 

You are right, on larger boats, hybrid systems would be a good alternative. However, the whole point of my project is to go all electric. That said, batteries are the only viable way to supply energy. The only other option I can think of is photovoltaics, but they are too impractical.

 

The right DC motor

Do you need a 120HP electric motor? This is a large motor. Note also there are many different types of DC motors. Best bet may be to start with a shunt motor because they are easy to control. Pleae be careful. At this horsepower you will need lots of volts (240?).

 

President

Try This:

http://www.apicsllc.com/apics/WP_1/WP_1.html

We would be glad to provide you with more information.

Regards
Brian