Saturday, January 13, 2018

Re: [Electric Boats] Direct Drive QS Hub Motors

 

Hi Jeremy
I have read somewhere that the maximum recommended propeller shaft RPM for small displacement hulls is 1800. Basically I believe you swing the largest diameter prop with the required hull clearances that can fitted into your hull at the lowest RPM to get the best efficiency. Their is also the physical limitation of cavitation to propeller RPM, goggle it for an explanation. Cavitation would not be the main reason for keeping the propeller shaft RPM down it would have more to do the design of the propulsion system. RPM limitations of Cutless Bearings, vibration and longevity of other components is more important. Most of the older internal combustion engines fitted to small displacement boats or Putt Putts are relatively low RPM designs. They are also fitted with reduction gearboxes, generally a 2:1 for forward. My selection of a low RPM, high torque hub motor is based on a straight forward swap out on a Bukh 10hp/ 2:1 gearbox box (Maximum engine shaft torque at 2400 RPM - 2:1 Reduction = 1200 RPM at the prop shaft) in the Nordic 17. Hopefully this will enable the standard 13" three blade bronze propeller (not sure of the pitch) to be retained. The only upgrades (assuming the shaft and prop are in good condition) to the propulsion system planned is a new cutless bearing and dripless shaft seal.
Mick 

On Sat, Jan 13, 2018 at 12:08 PM, 'P. Jeremy Baker' childscrick@yahoo.com [electricboats] <electricboats@yahoogroups.com> wrote:
 

Great post and group. I'm usually a lurker but have posted a couple times. Still landlocked. But my first question about this hub motor is regarding the rpm range? Is 1400 rpm enough? What is the rpm range on a diplacement hull? I'm too am attracted to direct drive. I'm sure propeller size, torque, has something to add.
 When my electric motorcycle project is done I'll shift my attention to boats in the Idaho panhandle. Thanks

Jeremy

On Jan 12, 2018, at 2:58 PM, mryanqld@gmail.com [electricboats] <electricboats@yahoogroups.com> wrote:

 

Hi My project this year is to build a small displacement electric boat. The base will be a fibreglass Nordic 17, 17 feet O/A and a displacement of 1.4 tonnes. The Nordic is a traditional double ended design originally fitted with a 10hp Bukh diesel. After several months of research for a drive system my best option at the moment is a 6000 watt QS Hub motor (1400 RPM 72Volt) and a APT 96600 sinusoidal controller. On the keep it simple theory it appears easy to connect the prop shaft via a polyflex shaft coupling to the 5x100 PCD wheels studs on the hub. This is direct drive. The hub motor will be fitted in a custom aluminium mount with polyflex engine mounts. A LiFePO4 battery pack will fitted as low as possible in the keelson area forward of the engine bilge. Am I missing something but why are all the kits available using high RPM motors which require reduction and avoidance of axial thrust loads. The hub motors you would expect are designed for axial loads as experienced in cornering of the vehicle. Also I would expect reasonable and adequate splash/dust protection from a hub motor. Additionally the disc brake rotor could be removed and replaced with a fan blade for increased cooling and ventilation. As I said I may be missing something and welcome advice and experience from this excellent knowledgeable forum. 




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Kind regards Mick 0414 264 312

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Posted by: Michael Ryan <mryanqld@gmail.com>
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