1. The outboard cost more, was a little easier to install although I had to build the power tilt mechanism, is much quieter than the MARS inboard, has much better steering authority. Top speed is about the same for both boats.
2. Given that the prop is optimized (six blade, 9" dia) for use with the kort nozzle, I found no difference in speed vs. input power with or without the nozzle. I would bet it would work better without the nozzle if I could fit a "normal" 12 or 13" dia 3 blade prop. The nozzle makes a huge difference at very slow speeds. With it I can power load the boat onto the trailer, without it not even close. Once above a couple of mph, though, it seemed to offer no benefit. It offers excellent protection for the prop.
3. A bigger prop running at a slower speed (lower voltage, more amperage) might be more efficient but to my knowledge no other props are available. Motors are constrained by amperage more than voltage so the motor at 24v could only produce 1/3 as much power as at 72v. That's why everyone uses reduction gears or belts and higher voltage.
PS: The Mar/Apr 2011 issue of WoodenBoat magazine has a beautiful 30' half cabin electric cruiser on the cover and a lengthy feature story about it. It uses a 48v PERM 132 system.
1. Why switch to this propulsion system? Cost? Ease of installation? Performance? Powering Flexibility?2. Is the Kort nozzle on this outboard efficient enough to propel a larger vessel? Like the one I have emailed about earlier?3. How does prop rpm vs. voltage affect the overall efficiency of the propulsion system? I mean is there an optimum voltage (and, I assume, resulting boat speed) where this propellor provides the optimum efficiency or, as we are only talking a potential range of speeds of lets say 2-3 mph between 24 and 72 volts, is this propellor going to be able to be reasonably efficient for all voltages?I know I should be putting this to the manufacturer, but I would like an unbiased opinion.Thanks Denny! I appreciate your taking the time to answer my questions!On Thu, Dec 9, 2010 at 8:15 AM, Shawn Gates <shawngates.home@gmail.com> wrote:
Denny:Thanks Denny, I actually got alot of info off of your article in WB magazine. Sorry I forgot to mention that in my initial post.I used the dimensions from your boat to come up with a beam to length ratio slightly higher than yours. WL is just under 33'.Building is some time off as I have to finish building my house first.Also thanks for the wooden boat design forum suggestion; I will post there to see what people think of the hull design etc.Cheers!ShawnOn Wed, Dec 8, 2010 at 9:10 PM, dennis wolfe <dwolfe@dropsheet.com> wrote:
Hi Shawn and welcome to the group. You are starting off the right way, with a boat designed to cruise efficiently at displacement speeds.You didn't state the wl length but guessing 30' I ran a few numbers for a 7,000 # weight hull with a 300ah 48v battery bank. At 85% electrical efficiency and 80% depth of discharge you would get:4 mph 7.9 hrs 1.3 kw 1.7 hp5 mph 3.7 hrs 2.5 kw 3.4 hp6 mph 2.0 hrs 4.3 kw 5.8 hpYour 20 - 30 mile range at 4-5mph is doable with just the batteries.I don't know much about solar cells but averaging 2kw, especially in your neighborhood, takes a lot of loonies, weight and area. Electric boats are dirt cheap to run if you can recharge from the grid, very expensive otherwise.Best of luck with your project.If you are building your boat out of wood, be sure to check out the Woodenboat forum. The folks there would love to follow your building progress.Denny Wolfe----- Original Message -----From: Shawn GatesSent: Wednesday, December 08, 2010 3:25 PMSubject: [Electric Boats] Electric set-up for cruiser
Hello everyone:This is my first post, so please forgive any mistakes, etc..I have been reading some of the discussions going on and thought that I would join in, mostly to learn from your collective knowledge.I am interested in an electric drive for a new displacement cruiser. I know that most of you are sailors and your electric systems are set up to act as an auxilliary (sp?). My boating area is system of lakes, rivers and canals that stretch from Lake Ontario (Kingston, Ontario) to the Ottawa River (Ottawa, Ontario) Either way I get to the St. Lawrence or the Great Lakes.I am also very new to boat design but have put pen to paper ( or, mouse to autocad) to come up with a 33' double-ended cruiser that, given your experience with "slippery" displacement hulls designed for sail, I feel is worthy of consideration for electric power. I come to this conclusion after reading lots of books and articles (mostly, it seems by Dave Gerr) about hull shape and power requirements. I have also been inspired by a neighbour of mine who runs an old 30' Maine lobster boat converted to a hybrid system that has both an 8 hp DC motor and a 10 hp AC motor with a 10 kw diesel generator. His boat is as I said 30' and displaces about 16,000 lbs. Now, he only runs off batteries for a portion of his 4 hour cruise. (check out rideauboattours.com).I plan on installing the 8kw dc motor that is offered by Thunderstruck along with the associated electric gear. I'm hoping that, like Mundoo III (See WB magazine for article), to eventually run this vessel in the 4-5 mph off of some solar panels, but initially using 8 AGM 6 volt batteries from Lifeline (either 300 ah @ 20hrs or 220 ah @ 20hrs rate). I think that a range of 20 to 30 miles is a reasonable expectation given the speed and hull shape. I can only swing a 16" prop. probably with at least a 2:1 gear reduction (toothed belt). The boat I estimate to displace approx. a little over 3 long tons (7,000 lbs) I've also estimated a DL ratio in the 120 region (quite light for it's length, but then I'm pretty well confining myself to lakes & rivers.What do all of you think. I welcome any comments or advice. Thanks!Shawn
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