choosing a gear ratio should start with a ruller under the boat!!!! measure how large a propeller will fit on the boat. be sure to allow proper propeller clearence. The slower the propeller shaft, the larger the prop. for rule of thumb thinking purposes think torque will change prop diameter while rpm will change pitch.
every boat was originally designed for a specific engine (usually IC)and specific diameter of propeller. the propeller space was determined and set in fiberglass or wood. The pearson under discussion was designed for a atomic four engine that had a direct drive forward and was probably designed around a 12 inch propeller. It may take a 13 inch propeller as a max. any combination of motor HP and gear ratio must result in a 12 or 13 inch diameter propeller. the pitch can vary a bit due to prop availability
Your only option is to select your motor and battery system for the displacement, lwl and your boating needs. then run repeated prop calculations varing the gear ratio until a ratio is found that will allow the 12 or 13 inch prop. many prop calculators will automatically run different ratios.
every week i need to tell some boat owner thay wasted $4000 to $10000 repowering a boat simply they did not consider the prop space in the original calculations.
larry
--- In electricboats@yahoogroups.com, "hardy71uk" <p0054107@...> wrote:
>
>
> Another way of looking at it is ( ignoring gear loss) gears do not change power at all . since power is torque times speed for example if a gearbox doubles torque it will halve speed so the product remains the same .
> but motors , props, wheels etc all work most efficently at certain speed-torque combinations so the aim is to choose a gear ratio that matches the optimum speed-torque of the prop to the optimum speed-torque of the motor .
>
> Chris S
> --- In electricboats@yahoogroups.com, Kevin <pembertonkevin@> wrote:
> >
> > Torque is increased when reduction gearing is used. The amount of
> > reduction increases torque. boat drives rely more on torque than HP as
> > do most drives. The advantage of reduction drives is the lower load on
> > the motor that the motor will try to provide thus increasing the
> > temperature of the motor to the point of burning up the windings. Much
> > of the motor design relies on cooling the motor for the desired rating.
> >
> > You can get more power out of a motor if you can cool the motor enough.
> > External fans help with this, because the fan no longer relies on the
> > motor speed.
> >
> > Hope this helps.
> >
> > Kevin Pemberton
> >
> > On 08/02/2010 09:51 AM, Daniel Michaels wrote:
> > >
> > > Thanks I have been doing more research and found EMC-RT Motor which
> > > seems like it is going to do the trick. I am trying to find out now if
> > > I still have to use a gear reduction with this motor.
> > >
> > > Dan
> > >
> > > --- On *Mon, 8/2/10, Ron /<rlgravel@>/* wrote:
> > >
> > >
> > > From: Ron <rlgravel@>
> > > Subject: [Electric Boats] Re: Hello
> > > To: electricboats@yahoogroups.com
> > > Date: Monday, August 2, 2010, 11:46 AM
> > >
> > > HP will not increase, a gear reduction drops the output speed and
> > > increases the twist force on a slower turning application.
> > >
> > > --- In electricboats@yahoogroups.com
> > > </mc/compose?to=electricboats%40yahoogroups.com>, "Daniel"
> > > <nov32394@> wrote:
> > > >
> > > > Hello I just joined. I own a Pearson Triton 28' sailboat that I
> > > plan on using electric power for. I have a small amount of
> > > information but I always like more. One of the biggest questions I
> > > need answered is the speed of the motor. Lets start out with a
> > > golf cart type motor. Does it have the same power at 800 rpm as it
> > > does at 1,600 rpm? Do you want to use a reduction drive on an
> > > electric motor if you are going to run it at a slower speed?
> > > >
> > > > Does an Electric motor work the same as an ICE as far as gearing
> > > it down? With an airplane you get more hp the faster the engine
> > > goes so putting a reduction gear on gives you more hp.
> > > >
> > > > Dan
> > > >
> > >
> >
> > --
> > Ubuntu10.04, Acer AspireOne, Virgin Mobile 3G Broadband2go.
> > Doesn't get any better than this!
> >
>
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