I understand. Thank you. The greencat solution sells at about 4 times the cost you quote and weighs about twice as heavy. I suppose the hydraulics are included. In addition, motors are brushless and also regenerating. Motors and controllers are protected against overheating. Controllers are water cooled.
Luc
--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> The greencat has a neat arrangement. Would be interesting to know
> how much their pods cost by the time they were installed. The only
> significant difference with what we have is the low BAR prop with
> relatively larger diameter. This gives us higher prop efficiency.
> With clean hulls and calm conditions the prop efficiency is 72%. The
> outboard prop was getting around 40% efficiency.
>
> The drive unit is not much deeper than the main beam when raised.
> When the lw unit is hard up against the deck there is just a single
> blade that protrudes about 300mm below the beam and is toward midship
> of the beam. The prop blade is only slightly deeper than the well in
> the deck.
>
> The motors get just over 90% efficiency through most of the range we
> will use. For motoring we will run lw at 2.5kW and ww at 1.5kW to
> make best use of the installed battery capacity - 5kWh on lw and 3kWh
> on ww. Motor losses on the lw side will be 250W. The motor box will
> not get much hotter than water temperature due to all the immersed
> plate on the fairing and the motor is fitted with an air cooling fan
> as well as the conduction from the base plate. We do not have
> thermal protection on the motor but we will check motor case
> temperature once we do some motoring.
>
> Prop clearance is adjustable but the props cannot hit the hulls
> because the motor housing prevents travel.
>
> We have set the props quite deep to avoid ventilating in waves. You
> would not want the hulls to be deeper than the props. Bottom of the
> prop is almost 900mm below surface. On this boat the rudders provide
> the crash stop in shallow water - they are about 1.5m deep. The
> props are nylon and have some compliance plus a shear pin. They can
> take a bump particular with the stretch in the restraining rope.
> Owner plans to carry at least one spare prop. Each prop cost USD33
> plus postage so a trivial expense if that is all that gets damaged.
>
> Rick
> On 23/12/2012, at 12:19 AM, LucD wrote: