Monday, February 27, 2012

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

 

math fun..  what's the RPM of the motor?  30 ft square root x 1.56 is 8.544 mph as a basic potential hull speed, and energy demand starts going up sharply about 75% of that..
is 6.4 mph. 5280 ft per mile divide by 60 minutes is 88 feet per minute for 1 mph..
so 6.4 mph about 564 feet per minute, 8.54 about 751 feet per minute.
(I'm really just "quick ballpark estimating" with this, no doubt others can do better!)
 
6.4 + 8.54, divide by two, about 7.47 mph, and about 7/8 of a 30 ft hull speed, if the waterline is about 30 ft.. is about where I'd expect to put a ballpark speed limit..
where aiming at max hull speed and motor under load being 7/8 of that, or 87.5%,
motor under load might reach 80-85% of free spin rpm if geared-propped right.
(is thinking not to stress it lots and get it heating up)
 
6" pitch is a foot every 2 revs.. 5280x2=10,560, divide by 60 (minutes) is 176 rpm..
per MPH if I'm thinkin straight.. so 176 x 7.47mph = about 1315 rpm?
where a larger diameter 12" pitch at 658 rpm (more gear reduction) is probably better,
more blade surface and less prop slip, but that gets real complicated too!
 
how big a prop? what motor rpm? what gear reduction?
maybe my ballparkin' is worth a darn as a starting point example to the math?
motor RPM and what gear reduction is there to play with are pretty big factors.
how much clearance from output shaft to hull for a prop radius-diameter too.
theres lots I dont know, and lots of unknown variables too..
motor RPM and gear ratio is the first thing I'd be looking at.
 
hope its somewhat a help there, again, I'm sure no expert either.
 


--- On Mon, 2/27/12, Robert Jorgenson <falcolnxp@yahoo.com> wrote:

From: Robert Jorgenson <falcolnxp@yahoo.com>
Subject: [Electric Boats] Prop size for 10500lbs 30 ft. coronado sailboat
To: electricboats@yahoogroups.com
Date: Monday, February 27, 2012, 7:21 AM

 
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????????

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