Re: [Electric Boats] Prop size for 10500lbs 30 ft. coronado sailboat

 

Ken  in short I agree with some data he could have a cracking system

On 2/28/2012 3:21 AM, KEN wrote:

 

missed that detail and I agree with Andrew about the supply voltage! (bigtime!) jumping from 36 to 48v is a big deal, and probably a safer bet to drop down to 24v. sure its gonna lose some rpm and hp output for doing it, but maybe gain some reliability. true about the old type speed controllers being much less efficient, I dont think its something "un-doable", especially at lower voltage, horsepower, rpm, etc. gear ratio and prop pitch are definitely gonna be success vs fail.   http://go-fast.com/boat_speed_predictions.htm as a ballpark estimater toy, plugging in 10,500 lbs, 6hp, hull constant of 275, projects a potential 7mph. kinda jives with the 6.4 mph 3/4 hull speed, 8.5 top hull speed I'd ballparked. dropping to 2/3 voltage, if hp output follows suit.. maybe 6 to 6.5 ponies there. it might be pretty good in a 5 to 6 mph range, where the speed calc is indicating a 2.9 to 4.25 hp demand, like 1/2 to 3/4 of the guestimated 6 to 6.5 hp. (its all theoreticals to me, I sure wont deny it.)   not doubtin your opinion at all Andrew, I'm a deffo rookie to this stuff.. and some of us rookies are on the "run what ya brung" kind of budgets. we also like to tinker, which also has to be within a realm of realistic (somehow!). I do think if Bob gets some calculations together, it could work out fairly decent. gear ratio, prop pitch, motor rpm etc. water being definite constantly variable load, currents, windage, its all gonna mess with stuff, calculations too. a golf cart might run 5-10 minute bursts, 12-15mph, is definitely a different kind of duty. wouldnt think it impossible to safely adapt with some decent efficiency from it tho. I'm open and curious about opinions and criticisms, only helps me learn more-better!   I'd also think a handheld tach would be more than just handy to see the motor's free spinning rpm's at 24v, and whether it can reach 80-85% of that under full load, as an indicator of a prop pitch being too much a load, they arent real spendy. its likely more important than what kind of hp the motor can actually put out, reliability-wise. same for keeping good track of the motors temp until its behavior well known stable. --- On Mon, 2/27/12, Andrew Gilchrist <andrew@fastelectrics.com> wrote: From: Andrew Gilchrist <andrew@fastelectrics.com> Subject: Re: [Electric Boats] Prop size for 10500lbs 30 ft. coronado sailboat To: electricboats@yahoogroups.com Date: Monday, February 27, 2012, 10:00 AM   I'll be matter of fact here - it sound dangerous to me the proposition your float is essentially a motor used to push 1500 lbs with short term usage, spikes dropping down rapidly to a very low average amperage and lots of cooling time, will now propel 7 times the mass at 50% more voltage than previously, through a underrated old  tech speed control, through liquid. the load could be 10.5 times that of the buggy; and its long term 100% duty cycle instead of the short time light load of the buggy  Establish the amp draw of the controller  - but things don't look great a 36v  controller being run at 48v and probably a much higher load than the cart could create if it is a resistive coil set up ditch it its dangerous and wasteful and a 10hp motor - is that max power or continuous power whats the kv - the the torque per amp and the efficiency levels * first  make sure your charger is correct type for that battery type and you have a battery management system on it. * Make sure everything is well insulated * establish the motor kv, peak rpm,  92% of peak rpm and amp draw at max efficiency * get your prop pitch and use it to establish how fast the prop will try to push the boat at 92% of peak rpm; if its 20 knots you are barking up the wrong tree all round - if its 2-3 knots that may be survivable  * ditch the electro mechanical controller and well overrated  PWM type if you persist with the current setup try running it at the dock and so you can observe the controller directly - if it is electromechanical it will probably glow red hot - unworkable -  have fire suppression ready At the very least you need an overrated PWM controller Andrew On 2/27/2012 11:21 PM, Robert Jorgenson wrote:   48v battery supply 36 v controller 10 hp General electric DC motor can the golf cart controller handle the load? what size Prop will be most efficient???????? fire hazzard lithion ion batteries =factory sealed 24 v battery packs in heavy alluminun box. what size prop should work well?? I realize I will have to experiment but i need a starting place. was not getting consistent voltage even though the battery cells read fully charged. battery terminals factory sealed with foam. removed foam from top of connectors two of the nuts on top of batteries required a 360 degree turn to bring them to he same torque as the other 14 9/16 nuts. this is why I have had an electrician guide me thur such a simple p ocess as battery instalation. Capt. Bob 435 678 3436 Shockwave Golf of Mexico Equal opportunity Crew openings with Drivers licens Mpving 30 ft Coronado from blanding, Utah 84511 to Houston Texas, one ton Chevy stick shift Individuals will be incouraged to cruise for a couple of weeks in golf of Mexico What tourque should the 9/16 nuts on the battery terminals be set at???????? -- AJ Gilchrist Fastelectrics 0419 429 201

--  AJ Gilchrist Fastelectrics 0419 429 201

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