RE: [AtkinBoats] New member question.
The MARS motor was designed by Briggs & Stratton in the US for battery floor polishers. I wasn’t aware that it was being made in China, but that’s the way of things these days and even if that’s true, US quality control still applies I would think. Hey, if they can make Cadillacs in Bulgaria (or where ever it is) then I guess anything is possible.
The thing that attracted me to the MARS is that it is brushless. That means it has no moving parts (well, aside from the armature of course) so it is practically silent and there is no servicing. It also has permanent magnets instead of field windings – less to burn out and the whole thing is smaller and lighter. Also, because it has no moving parts, it is also a bit cheaper to buy although it needs a different controller which will be the same, if not a bit more, so perhaps that evens out.
The MARS operates up to 36v and will produce 7hp continuously and 15hp peak (for 30 seconds I think it is) and unless you are headed into really rough weather, the Trojan T105’s are the obvious choice if you don’t want them to operate upside down. There is a little bit of occasional maintenance however.
Calculating the horsepower you need is a whole different ball game – it depends on the efficiency of the hull – it’s drag coefficient particularly. There is some free hull design software called DelftShip (formerly FreeShip) that, if you can get your head around it, will ultimately give you a graph of drag (and therefore required horse power) to achieve any given speed for your particular hull. It’s not an easy product to learn though, unless you’re already into the 3D computer modelling world. (I’m not and it was a real struggle!!).
In general terms though, 7hp for a 16’ boat in relatively sheltered waters should by a good proposition and given that 1 hp equates to 746 watts, you can work out how long any given battery pack will last – more or less. (That’s very rough, not much better than a wet finger in the air because there are a lot of other factors, but it gives you any idea anyway).
Alan, I haven't quite decided yet. The MARS motor is made in China and I have had some bad luck with other brands and types of Chinese electrics in the past and have since avoided purchasing them. Denny Wolf, an electric boat enthusiast , has had good luck with the MARS product and recommended it to me however I am leaning more toward the Advanced DC Motors model no. A00-4009 made in Syracuse, NY and sold through EV America (Bob Batson) in Wolfeboro, NH. Bob's phone number is 603-569-2100 and he is most helpful and knowledgeable. This motor runs on 24 - 144 VDC ......at 36 VDC it develops 4 hp ......at 72 VDC, it will push a VW "Bug" at 45 mph (according to Bob). It is series wound like the starter motor on a car. It weighs 43 pounds which is heavier than the MARS. At this point I believe I will use the A00-4009 motor but won't need it for a couple of months. For batteries, I would like to use the Life-Line AGM (Applied Glass Mat) type but 6-volt units cost $300 each and Trojan T105's (open cell type) cost around $150 each and both types have basically the same run times fully charged. The run times, range, and current drain calculations given below were furnished by Bob Batson based on the 36 VDC motor and T105 batteries (6 cells @ 6 VDC each):
Speed (MPH) 3.5 4.6 5.8 6.9
Motor HP (total) 0.4 0.9 1.7 2.9
Total Current (amps) 9.4 22.3 43.5 75.2
Time (Hours) per pack 13.1 5.5 2.7 1.5
Range (miles) 45.2 25.1 15.7 10.8
The above calculations were based on my boat (the Victor Slocum) at a displacement of 900 pounds. I hope the above is of benefit to you.
----- Original Message -----
From: Alan Boman
Sent: Friday, September 04, 2009 7:31 PM
Subject: RE: [AtkinBoats] New member question.
John – are you using the MARS electric motor ?
I am building the "Victor Slocum".....a 15' 10" design that has turned out to be 16' 4" .....and will be powered with inboard electric. I could not find a Palmer Baby Husky (6 hp) in GOOD CONDITION that was specified for it and believe that small diesels are too expensive, too noisy, too much vibration, and are basically overkill for a small boat like this. I am using 18 mm Okoume for the bottom reinforced with another panel of 18 mm Okoume in the area where 360 pounds of batteries will be located for 36 VDC operation. The frames are gusseted 18 mm Okoume, planking is glued lap 9 mm Okoume, stems, chines, outwales, inwales, breast hook, and quarter knees are laminated Honduran mahogany. I think I will use African mahogany for seats......or perhaps Northern White Cedar....haven't decided on this yet. I'm using a 10" diameter X 6" pitch 3-blade Michigan Wheel bronze prop.
6300 Campbell Hill Road
Belton, Texas 76513
----- Original Message -----
Sent: Thursday, September 03, 2009 7:41 PM
Subject: [AtkinBoats] New member question.
I am interested in building a boat for a large lake, shoal draft exploring. The boat must be rather low to clear a couple of low bridges. Locally, pontoons will not clear, bass boat types will. So far, I feel like the Rescue Minor will be a good choice, but it's a little longer than I can build comfortably in the space I have available. I like the plywood construction for trailering. Also trailering and launching would be easier with a shorter boat. Perhaps one or two passengers would be all that would be necessary.
So..Rescue Minor would be my choice, but longer than I prefer. Given the 900 or so designs in the Atkins portfolio I hope the members can help me find a similar but shorter design.