Enjoyed your Archimedes Project blog wi photos. Enjoyable for me; hard work for you. Thanks
--- On Sat, 8/11/12, Carter Quillen <twowheelinguy@yahoo.com> wrote:
From: Carter Quillen <twowheelinguy@yahoo.com>
Subject: Re: [Electric Boats] Electric Outboards?
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Date: Saturday, August 11, 2012, 9:09 AM
Chris is right, Eric said the Torquito was the most "efficient", not the most powerful. But in Woody's defence, Eric's contention that you "must" have 1 kW/ton is definitely up for debate. It's a "rule of thumb", that's all. The specific hydrodynamic of each vessel, the efficiency of your drive drain and prop, along with cost and "your" desired performance are all things to consider. You might need, or want, as much as 2 kw/ton or more but you can easily get by with less than .5kW/ton in a hybrid, which I would consider a sailboat to be in one sense. I mean people got by without any auxillary power in sail boats for thousands of years. Kind of depends on how good of a seaman you are and what kind of conditions you want to operate in. However, I do think it is safe to say that if electricity is your vessel's only form of propulsion, 1 kW/ton might actually be a minimum power level but I'm pushing an almost 20 ton boat quite well with 5 kW, that's like .25 kW/ton. It's pretty slow in heavy weather but so far I've always been able to maintain control, albeit, in slow motion sometimes. In calm water I easily reach about 85% of hull speed with an acceleration factor of 2 mph/min. That's a bit slow off the line but once I get up to speed, no problem. I really prefer the control of the electric throttle when docking and I've never come up short of power for that. So much depends on the individual boat and it's captain. Admittedly, I do generally kick in the diesel in heavy weather or when I want to get somewhere in a hurry and it's good to have the 40 hp diesel backing me up for safety reasons but once I get my full 5 kW of solar installed this Fall, I'll basically have a never ending gas tank when I'm done. And personally, I'm perfectly content to cruise for free at about 5 mph on the inland waterway whenever the sun is shining. So I would say that the major part of any design criterion for an electric propulsion system is really about what you want from that system, along with how much money you have to spend, and not necessarily a target of 1 kW/ton. Like I always say, "Don't let your thumb get in the way of good engineering". Carter Quillen, PE
From: chris Baker <chris@currentsunshine.com>
To: electricboats@yahoogroups.com
Sent: Friday, August 10, 2012 5:54 PM
Subject: Re: [Electric Boats] Electric Outboards?
Hi Woody
You have misunderstood Eric's very clear statement.
He states that the Ray Electric will not deliver the same range for a given speed.
You mention nothing of this, but instead quote power, speed and acceleration. So in fact you are not differing at all, just using different measures.
Have you ever done any range tests comparing the Torqeedo and the Ray Electric?
Can you share with us the details of the testing that you did?
Cheers
Chris
On 11/08/2012, at 7:33 AM, woody wrote:
Beg to differ with you on the statement you made! "So I can say that it has been prove that it takes at least 6.7HP (5kW) to push a Catalina 30 at 6kts in calm conditions, often requiring more power if the drive isn't really efficient, like your traditional outboard driveleg and propeller. It has been my personal experience that the Torqeedo outboards are much more efficient than traditional outboards, putting them close to the same efficiencies as many electric inboard installations, but the Parsun or Ray Electric will not deliver the same range for a given speed. And one of my main objectives has been to get the maximum range for given speed from the same batteries. Perhaps other people have other priorities...."
I have tried and tested both the Ray Electric Outboard and the Torqeedo, and the Ray Electric was a All-Round winner with more Power, Speed and Acceleration. Woody
Hi Donald, That's just not true. 5HP cannot not push a 10,000 pound sailboat with a 25 LWL, more specifically a Catalina 30, to hull speed. And suggesting that it would be possible with a 12,000 lb Catalina 34 or 13,500 lb Catalina 36 (there is no Catalina 35) is horribly misleading. A 5HP motor will move the boat around, better in calm conditions than in heavier winds, but you will not hit hull speed. A Catalina 30 requires about 300 lbs of thrust to hit 6.7 kts and a 5HP motor or engine, inboard or outboard, doesn't come close. We've observed many times in this group that 1kW of power per ton will push an auxiliary sailboat (all sorts of designs) to about 90% of hull speed. That last 10% will come close to doubling the power demand. So I can say that it has been proven that it takes at least 6.7HP (5kW) to push a Catalina 30 at 6 kts in calm conditions, often requiring more power if the drive isn't really efficient, like your traditional outboard driveleg and propeller. It has been my personal experience that the Torqeedo outboards are much more efficient than traditional outboards, putting them close to the same efficiencies as many electric inboard installations, but the Parsun or Ray Electric will not deliver the same range for a given speed. And one of my main objectives has been to get the maximum range for given speed from the same batteries. Perhaps other people have other priorities.... Fair winds, Eric Marina del Rey, CA --- In mailto:electricboats%40yahoogroups.com, donald bland <dlblandjr@...> wrote: > > You can easily push a catalina 30 or even 35 to hull speed with 5 hp...
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