Finaly starting my Electric Kayak project.

[Bazaki]

Hey guys,

I want to build a FAST boat at electric power, my idea of the setup is the following equipment:

15 KW Brushless Predator 37 from Plettenberg
A Jeti Spin 300A
A whole bunch of Lipo's from hobbycity.com
And a 10-15hp stock outboard motor to replace the petrol engine with the brushless.

And install this outboard on a inflatable rubber boat.

And I expect this to happen :
http://www.youtube.com/watch?v=SrqqvDiNyYY

Only a bit cheaper since those guys ask about 10.000 Usd for only the outboard 11kw.


The part I don't understand is the efficient of the prop, should I use a very large thin prop ? or would the originale be fine too ?

I can use the brushless directly to the shaft on the outboard, 170kv x 40v (under load) with 20% less rpm since the prop/boat has al lot of drag, that would make about 5600 rpm. An original 10-15hp outboard also has 5000-6000 rpm.

Any thoughts ?

 

[Jeremy Harris]

First off, you need to try and optimise the whole system (motor, reduction drive, prop, batteries, controller and most of all, boat hull) to get even close to the performance of an ICE powered fast boat with electric power.

Next, you need to compromise on range or speed, as you can't have both. Although LiPo's are good, they are puny at storing energy when compared to a tankful of petrol/gasoline/diesel.

I'm building an electric river launch and have had to work pretty hard at getting the best efficiency from every little bit of the whole system, just to get a boat that will do around 5mph for 8 hours or so, carrying two people, on a LiFePO4 battery pack that holds around 1kWh.

An inflatable hull is a poor choice, because it's heavy and horribly inefficient. Something like a very light hydroplane hull would be the best bet for speed with just a few hp. Some of the early plywood hydroplanes went very well on modest amounts of power.

Next, your motor needs to be fitted with a reduction drive with very low losses. Ordinary outboard motor legs are pretty awful and soak up lots of power that should be going to the prop. I ended up making a direct drive system with a re-wound motor (to get a very low Kv) because I found it tough to build a low-loss reduction drive leg.

Finally, the prop needs to be carefully matched to the motor/reduction drive and the speed and thrust requirements of the hull. Generally, standard outboard props are pretty poor, as they have a very high wetted area and so soak up lot's of power. A large diameter, high aspect ratio (thin bladed) prop will probably give a worthwhile efficiency improvement (maybe 10 to 15% better than a standard prop) but will catch weed easily and need to be custom made.

All told, it's a lot harder to make a decent boat propulsion system than it first looks, as I've been finding out!

Jeremy

 

[Bazaki]

Thanks, great to hear I'm not the only one :wink:

I believe a 10hp Yamaha would have 10hp OUTPUT power. As for an E-motor we watch our Amps and Volt, count it and say: My setup has 7.5KW, that's the input, a lot of heat will be produced by the controller and motor I think, I there a basic rule of about 10% loss ? Or more ?

So an stock outboard is pretty bad, I see, but if a outboard has an petrol engine that delivers 10hp output, and I replace it with an E-motor with at least 20hp Peak and 15hp continu power, what would be the differences ? I assume that I get the same power out of this outboard.

Btw, my batteries have to run for 10min and that's fine. I just want to get to destination asap. Now I have a stock 800 Watt 12v outboard which takes me about half an hour, so I want to go fast as possible, the destination is about 1 mile, and I have to go back ofcourse.

As for the inflatable, watch this :
http://www.youtube.com/watch?v=FT4m-c1UnMY&feature=related

These kids are very light, but I see a lot of small inflatables with 5-10hp that go really fast.
http://www.youtube.com/watch?v=mygFpbfq3Fw&feature=related

So my plan is to make a E-outboard with an overkill of power, so I loose the half I still go 30km/h in plane.

 

[northernmike]

Guys, I had to share this.

I got a model cedar-strip canoe kit for Christmas, and Googled it's maker, Bear Mountain Boats...

Look what they're up to! http://www.bearmountainboats.com/launch.htm#

 

[jmygann]

Torqeedo Travel 801 Electric Outboard Motor Test & Review on Sea Eagle PaddleSki and Foldcat

http://www.youtube.com/watch?v=eHTJjH-C2Tw

I had a Paddle Ski with a motor and SLA