Subject: Re: [harryproa] Re: Twin Electric Thrusters
From: Rick Willoughby
Date: 12/21/2012, 4:49 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Luc

The prop torque can get to 190Nm so will easily overcome the weight of the thruster meaning it needs to be locked both ways.  There is a line from an eye off the side of the hull to one of the pivot arms that can be tensioned from the deck and secured.  It preloads the lifting line and needs to be released to enable the unit to be raised.

The prop has a maximum rotational speed of 700rpm.  Gearbox has a reduction ratio of 1/3.3.  We considered a planetary gearbox with an inline motor for submersible mounting of motor but the lowest price we found was over AUD500 and that is without any stainless shaft extension for the prop and shaft sealing system.  The right angle gearboxes we are using started out at AUD110 each but we added a pair of angular contact bearings for the thrust and a stainless shaft that brings total cost to AUD190 each.

There were other factors for the choice of gearbox.  We have already tested the gearbox we are using on the trial unit and four of the same boxes are used for the steering. They are simple, robust boxes; literally agricultural by design and intended use. 

We didd not get far enough into design of a submersible pod to consider the lifting load but it needs consideration.  As it is we can lift by hand (about 20kgf dead lift) but have also used the sheet winch to make it easy.  Pods off the side of the hull that can be raised and lowered would be nice if you can find suitable planetary boxes.

Rick
On 22/12/2012, at 4:09 AM, LucD wrote:

 

Rick, this is a very good price (OK that is without the high modulus rope ;-) Does the arm lock in vertical position? Apparently you do not advocate an engine pod behind the propeller. Is that because of the increased drag or a heavier moment with the engine weight at the very end of the arm?
Thank you.
Luc

--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> It has taken 17 months but we finally have a neat twin electric drive
> system for the 18m proa:
> http://www.youtube.com/watch?v=81tw5Xw4Wdg
>
> The units have been mounted beside the lw hull and ww hull to
> maximise turning moment. They swing up and out of the water
> laterally for sailing. The lifting ropes need permanent attachment
> points and will be thinner high modulus rope.
>
> Since the initial trials with the single Mars 3001 motor we decided
> on much more powerful Mars 1003 motors for the permanent
> installation. These have the simplicity of being brushed DC so could
> be run without controllers in an emergency by direct connection to
> batteries.
>
> The lw unit is not constrained by battery current so it can produce
> 9kW continuously on the 50V battery. The smaller battery on the ww
> side limits power to 6.7kW. We have not measured bollard pull but it
> will be in the region of 6000N with both motors on their current limit.
>
> The testing today was for maneuverability rather than speed test and
> the video shows how the 18m boat can be turned on the spot.
>
> Next step will be to get the hulls clean (again) and do some speed
> trials. The range should be around 9nm at 5kts solely from batteries
> without any extra charging. Decisions are still to be made on means
> of charging but plans are to at least set up some solar panels so the
> batteries can be charged between outings.
>
> Expenditure on the units now totals AUD8,000 in round numbers. This
> is for motors, gearboxes, props, controllers, batteries and aluminium
> housings plus fixings. This is less than the original 60HP high
> thrust outboard installation. Which is now for sale.
>
> The ww unit has ended up mounted lower than planned during design
> stage so it will be modified to get the motor housing out of the
> water to prevent the ploughing evident in the video. The lw unit is
> set at the correct height and wash is much cleaner.
>
> Props are 540mm diameter and prop shaft is 600mm below the surface on
> the lw side. Each drive unit weighs about 35kg. The lw batteries
> weigh 60kg and the ww batteries 40kg. Overall weight similar to
> outboard counting the mounting, starting battery and controls. The
> motor housings have been pressure tested for leaks as they are
> intended to take full immersion.
>
> Time will tell regarding durability.
>
> Rick Willoughby
> rickwill@...
>


Rick Willoughby




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