My first thought was that a jump from 4" pitch to 9" would result in overheating, too. I agree that 6" would fall within tolerances, especially since the torque/thrust is shared between two motors. As is the case, prop selection usually gets down to trial and error.
--- In electricboats@yahoogroups.com, David Brooks <avantiman@...> wrote:
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> I used Minn-Kota 101's on my British bilge keeler and the max speed was 4.5 mph at 60 amps. Stock pitch is about 4 inches. Be very careful re amp draw if you change the prop because of overheating. A 10x6 prop might give you the extra speed without overload.
> Also MotorGuide 3 blade props can be cut to fit and give a bit more speed and far better reverse thrust than the 2 blade Minn-Kota props. Please advise re vendor of used 101's as I have a possible use for one as a thruster motor.
> Thanks,
> Dave 613-798-3454
>
> --- On Tue, 10/5/10, alex <alex04032@...> wrote:
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> From: alex <alex04032@...>
> Subject: [Electric Boats] Need Propeller Guru
> To: electricboats@yahoogroups.com
> Received: Tuesday, October 5, 2010, 10:02 PM
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> Hey guys, my boat is almost done and pics to follow, but Im expecting the props will need adjusting and Id like to deal with that before launch.
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> I rebuilt an 18ft daysailor, 1200-lbs totally loaded, with six golf-cart batteries driving two 36v Minn Kota 101-lb-thrust motors rated 50 amps each. I estimate that is 3hp total at the props. My calc's estimate that a hull speed of 6mph can be reached with 2hp. Thats my goal.
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> Here is the tricky part. I dont know the rpm or pitch of the Minn Kota 101. Its 9"d, I hear its 4"pitch, but I dont know that or the RPM.
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> Rumor has it that at full RPM and small slip, the max boat speed for Minn Kota is 3.5 mph. If so, I want to increase the prop pitch and maybe diameter, too, so that I can reach hull speed. I have RMS amp meters on each motor and PWM controllers so I expect to be able to keep an eye on the motor amps/heating.
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> Can anyone analyse the Minn Kota RPM and prop ? Im preparing to buy a couple used 10x9 props and fix them to Minn Kota hubs. Any feed back on how this might result ?
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> p.s. I can buy used salt water Minn Kota 101's (1.5hp) anytime, including PWM controllers for about $450... thats a real watts/dollar bargain.
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> Thank you !
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