Shaft Angle

mr hot rod- Thanks for the info. I'll definitely be getting that book! I will be drilling the shaft hole at some point in the near future, and I dont want to mess it up LoL

CDK- According to a few people that have built EV's with that motor, they say the motors efficiency raised when they ran the motor at 144 volts. They didn't provide documentation, so hard to say for sure. Probably couldn't hurt from a performance stand point (other than weight-which is the hot topic ) NetGain says 190volt max/160volt constant for the peak voltage.
I'm thinking about running a v-drive so that it will give me some more flexibility for weight distribution-ability to move motor back towards the transom as needed. Thanks for the input though!

 

A V-drive will take 15% of power. The least efficient type of transmission, and the one more prone to failure in the long run.
A bad choice.
Lister

 

I've never heard that before. I have specified V-drive transmissions many times, and there is nothing in them that inherently reduces power any more than a conventional transmission, in my experience. The main drawback with V-drive gears is that the shaft seal ends up under the engine, and it is a lot harder to reach for service.

Eric

 

Data is hard to find, but according to Daniel Clarkston, director of product engineering at Mercury Marine's MerCruiser division, a stern drive loses about 13 percent of its power compared to 8 percent for the V-drive :

http://www.boatingmag.com/article.asp?article_id=223&print_page=y&section_id=2​

__________________
Paul Kane Chelsea, PQ

Building the Glen-L Hot Rod : http://www.boats.chelseacoachworks.com

 

iF YOU HAVE A ELECTRIC MOTOR HOW BIG IS IT WHAT THE ACTUALL SIZE ??
WHY NOT MOUNT IT AT THE FRONT END OF THE SHAFT WITH A PLANETARY GEAR BOX AND A RIDGED COUPLING . dONT FORGET THE THRUST OF THE PRP IS TRANSFERED TO THE SHAFT AND WILL BE PUSHING ON YOUR MOTOR SO A THRUST BEARING COULD BE NEEDED !!
ON SUCH A SMALL BOAT WHY DO YOU NEED A GEARBOX ANYWAY ?? WHAT KIND OF RPMS ARE YOU LOOKING AT ?? RACING PROPS AND VERY SMALL AND SPIN AT REALLY HIGH RPMS SO REGUARDLESS OF RPMS THERE MUST BE A PROP TO SUIT YOUR APPLICATION !!
THERE IS A LOT OF HOO HAA AND NOT MUCH CONCRETE INFORMATION . iF THE HP IS SMALL WHY LOOSE A GOOD PERCENTAGE THROUGH A GEARBOX THAT WEIGHS QUITE A FEW KILOS AS WELL . ALL THIS BLAH BLAH IS GOING NO WHERE JUST ROUND AND ROUND !!

 

tunnels- The motors actual dimensions are 9.25" diameter, the motor housing is 15.92" with an overall length (including both end shafts) of 20.19" It weighs 143lbs.
As far as the power specs, the only documented dyno figures are @ 72 volts with a 350 amp controller. (here's the dyno numbers- http://www.go-ev.com/images/003_16_WarP_9_SpreadSheet.jpg ) If I run higher voltage (which IS an option) it will raise the rpms at which it gets those power numbers. A higher current controller will allow for more torque, but my understanding is that a prop will have better grip at higher rpm (please correct me if I'm misunderstanding this) so a bunch of torque at under 1K rpms probably isn't going to help me much. However if I step up the rpms to the prop with some sort of tranny, I could take advantage of the motors good low speed torque and still get the rpms the prop needs to grip. Would using a 4 blade prop with a high pitch allow me to run lower rpms but have decent speed? As far as speed goes, I would be thrilled if I could get it to the 35mph mark to start with. Not very fast for this type of boat, but it seems decently fast on my buddies ski boat (and it would be nice to be able to keep up with it) I dont know how much slip to expect from this boat/design either, so there are some things I just cant be specific about at this point. But if there was a prop that would work well in the 2000 rpm range, that might be a good place to start. Are there diesel powered, direct drive setups? Maybe could match props of that setup since diesels tend to run at lower rpms then their gasoline cousins. Once I can figure a good starting point, then I could tell what kind of slip the boat will have, how high up the rpms will go (wich I can compare to the dyno to see exactly how much power it takes for a given speed) and then I'd know for sure if a tranny is needed. I would like to use a direct drive setup (no tranny or v-drive) if it's possible to get a prop to work at these low rpms, because the more efficient, the longer the run time...

 

nsmoracr,

Sorry if I'm a little late to the party, how is the project going? The reason I'm posting is that I'm basically doing the exact same thing, warp 9 motor and all. I'm building the boat from scratch with a projected displacement of 1200 lbs and LOA 16ft. My shaft angle will be 12 degrees and and I will be running between 135 and 150 volts of LIPO batteries...total pack weight is just over 200lbs.

I kept the shaft angle as low as possible for my design length and overall layout, but really, it comes down to your hull design, and CofG that determines the angle. I've seen a lot of boats that have too flat an angle only to require trim tabs or ballast up front. Thrust acts along the prop shaft. If you draw an imaginary line along this shaft and the CofG is behind and above the line, the thrust will apply a bow up moment on the hull. If the CofG is in front of and beneath this line of action, a bow down (plowing) moment applied to the hull. If there is too much bow up moment, the boat will porpoise. If there is too much bow down moment resistance will increase rapidly with speed.
At below 12 degrees shaft angle there is not an appreciable difference in efficiency due to thrust direction itself (you can do the trig and see) as long as your moments are optimized. Drag on the hull itself contributes to the sum of the moments as well, as does hydrostatic pressure and wind resistance.
But for a rough guide, I would shoot for having the shaft line of action provide a slight bow up moment.

As for my design, I have an Impulse 9 (a slightly smaller version of the warp) in my daily driver electric car so I know what the netgain motors are capable of. The car has a 1000amp motor controller and does 0-60 mph in around 7 seconds. The motor puts out over 100kw at 5500 rpms with my current setup, and it doesn't seem to be stressed at all. I have maintained 23kw at highway speeds for 20-30 minutes with my current battery pack.
The boat is a classic style runabout intended mainly for silently cruising around the lake while being capable of up to 50 knots or waterskiing for short periods. I have already done one electric planing boat so am pretty confident I will achieve this goal, but you never know. Conservative calculations estimate that with about 220lbs of Lithium polymer batteries the boat will be able to plane for about an hour at 80 percent DOD.
I went with the warp 9 over the impulse due to the continuous torque capability to avoid overheating while operating at higher power levels. There is no reason you need to run a transmission if you prop it right. Boats like the one you have run high revving V-8s with overdrive transmissions such that they are spinning a very small 2-bladed prop very fast, although they are not very efficient at low speeds. You could probably get away with a moderately sized prop with a lot of cup and still be able to have decent lower speed efficiency and be able to spin it up to the rev limit of the warp 9.

I put together a spreadsheet that calculates torque and power of the warp and impulse 9 motors vs. rpm for any voltage you enter and could provide it to you if you'd like. It also calculates the current required to power the boat with a specific prop for my design for the warp 9 and impulse 9 (how I decided between the two), but you could modify it for your boat if you could come up with a power vs. speed curve. I hear the new generation warp 9 motors have been operating at 192 volts with no problems which is very exciting because the power of these motors is proportional to the square of voltage. At these levels the warp 9 motor would be able to maintain a flat torque curve (250 lbft at 1000amps) from zero all the way to its 5500rpm rev limit. E.g., at 130 volts the warp 9 will only provide 100 hp at 3900 rpms while at 150 volts it can provide 140hp at 4500 rpms. Imagine what kind of power White zombie is getting at 2000amps and 200volts per motor! And those are the smaller impulse 9s like in my car. And as for whether or not white zombie is really producing the kind of power they claim, who cares? All you have to do is look at the amount of power required for a similar door slammer powered by an ICE engine. You'll likely find it to be in the neighborhood of 500 hp...at the wheels. And as to whether or not you can put that kind of power to the water, I don't see why not if a mild v8 can with a similar torque curve at the voltages you're talking...not to mention blown hemi drag boats.
I say go for it, I don't think you'll be disappointed. BTW, you could do 35mph in that boat by hooking the warp 9 up to a friggin paddle wheel.

 

Oh yea, and CDK is right. If you use 72 volts and 100ah you won't go very fast at all, no matter how much current your controller puts out. But if you use 144 volts and 50ah you will have about 4 times the power. Always use the maximum controller voltage you can because the higher the voltage, the more current you can pull at a given rpm. And torque is directly proportional to current. With series dc motors a good rule of thumb is that doubling the voltage allows you to draw twice the current at twice the rpm.

 

I would put a 2 stroke 75hp outboard on our boat. It will be a lot lighter, faster, less problematic and cheaper. And I don't have to worry about shallow water or shaft angle.

 

I almost did an outboard actually because it would be easy. Ended up being deterred by the price, noise, and looks. Imagine a chris craft barrelback style boat with an outboard. A new outboard of the power levels I was looking at was significantly more expensive than an electric setup with twice the hp and 4 times the torque. Clean and silent and much more reliable. And the boat will be much faster and only 75 pounds heavier with better weight distribution...