Rick,

I will be following your posts avidly. Please include costs when you get to your desired performance. 

Just as a ballpark, would you expect a regular Harry (40' lee hull) to need a system about half this size?

- Gardner

Sent from my iPhone

On May 22, 2012, at 8:17 PM, Rick Willoughby <rickwill@bigpond.net.au> wrote:

 

Gardner

This boat is fitted with a single 60HP outboard located amidship.  It is on a transom that can be raised and lowered.  The outboard can be turned independently with intention of being able to vector thrust but and side flow bounces off the hull and does not give net side thrust.

The boat does not respond well to rudders unless it is doing 3kts.  So getting it alongside a berth is not easy if there is any wind.  

When sailing the transom is below the level of the cabin floor and deflects a large amount of water upwards when driven through a wave.  Also when motoring in waves the outboard is constantly ventilating and over revving.  

A better solution would be two smaller high thrust outboards located out near each hull.  To match what can be done with the electric thrusters swinging big props would require at least 25HP outboards.  By the time these are mounted with electric start and remote control you are looking at maybe $16,000.  Discount the time of two retirees playing around, the cost of usable electric system should be about one third of this.

With outboards there is a need to carry a volatile fuel and there is a need to refuel.  With the electric a solar panel or two will keep the batteries charged from week-to-week.  For cruising the cabin top will hold about 1.5kW of panels.  This will be useful to hold a few knots if there is no wind - higher if you have battery capacity.  

So if the boat is essentially a sailing boat for cruising then the electric system is not bound by a fuel supply.  Also if the power is only needed to get on and off a mooring or marina pen then electric is very convenient.

From a reliability perspective we spent most time on Monday fixing the electrics in the 60HP outboard.  It is the 4th electrical problem with the outboard in 6 months.  This time it was the little microswitch used in the throttle to interlock starting in gear - contacts were not making.  The electrics on the thruster can be waterproofed better than what you get with typical outboard installation and the thruster has fewer electrical connections than the outboard.

So electrics have merit but most current commercial versions do not suit the proa.  And the good marine systems are still expensive.  IC outboards have about 80 years of serious development.  Electric propulsion for leisure marine use is at an early stage of development.

We have even contemplated using an electric transmission by coupling two Mars motor directly with one acting as a generator run off a little diesel.  The motors are three phase synchonous so reversing could be done with contactors and throttling the diesel would give speed control.  Following along this line there are submersible bore pump motors that come into consideration, being small diameter so would be mounted underwater in line with the prop.  These could be run off a standard 3-phase generator.  Coupled to a planetary box, a low power motor has the ability to swing a very large prop.  Two 4kW motors could make way in 60kts of wind if it was needed.  The system we are working on will hold up to about 45kts. 

Rick

On 23/05/2012, at 9:30 AM, Gardner Pomper wrote:

 

Rick,

I think I missed the posting when you talk about why they went with electric thrusters? Each time I have seen the topic raised, it seems like the electric motors end up costing more and weighing more (with the batteries) than an outboard. Is it just that it is cool?

- Gardner

On Tue, May 22, 2012 at 5:53 PM, Rick Willoughby <rickwill@bigpond.net.au> wrote:

 

Luc

Each situation can be different so needs its own analysis.  However if you aimed to do 10kts under motor the system needs to be designed to do that in its own right.  You would treat any output from the sail as assistance.  This approach is required because the prop and motor need to be matched so maximum rpm and target boat speed are matched. 

In the case of the 18m proa the system using two Mars motors will be capable of 8kts in calm conditions with a clean hull.  That requires 7.7kw.  If the target speed was 10kts then the power demand goes up to 14kw.  So the last 2kts take almost as much power as the first 8kts.  The possibility of doing this depends on how you derive your energy.  For day sailing you might carry enough fuel to do it and have a large charger capable of producing the extra 7kW.  7kW from solar panels requires very large array.  7kW from a battery bank for more than a few minutes requires very large battery.  Sails are more effective at moving the boat in wind than a wind turbine so wind turbine would not be beneficial.

Using a propeller as a turbine is not ideal because the blades are optimised for thrust.  Running the prop backwards as a turbine might be a little more efficient, which would be possible with bi-directional rudders.  The controller we have enables full 4-quadrant operation meaning it can drive or brake regeneratively in either direction so it is not difficult to use the unit as a generator.  If you want to sail at 15kts with the prop/turbine spinning then the system has to be designed for this condition or at least able to tolerate the mechanical stresses of severe overspeed and overvoltage condition.  It probably means you are going to have to design a system capable of 40kW or so.

The immediate objective with the electric drives on the 18m proa is to get the boat controllable under power so it can be easily docked.  We feel two units separated across the beam is the best way to do this.  Two directional units separated longitudinally would also work for docking but there is about 10% extra power required for same speed due to the thrust being offset from the drag.

I also believe a prop mounted on a rudder will introduce unwanted characteristics particularly at high speed under sail.  It would need to have retractable fairing to avoid this and more complexity.  I know of a small sailing dinghy that did it well but sailing speed is around 6kts.  I do not know of anything bigger but they might be out there.   

Rick

On 23/05/2012, at 5:04 AM, LucD wrote:

 

Rick,

Rob has drawn the 60' Seabbatical with an e-prop on each beam mounted rudder. The e-prop can travel along the edge of the rudder to be immersed or retracted. The rudder itself can also be retracted (together with the e-prop). This is very clever.

To simplify, what about fixing the e-prop in its optimally immersed depth but modulate the control as to power the e-prop to keep the speed at, let's say, 10 knots when not enough sail power, to regenerate power and slow down the boat some when sail driven above 15 knots, and power the prop just enough to neutralize drag in between those speeds? Electronic complexity for mechanical simplicity.

Am I overlooking something?

Thank you in advance.

Luc

--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> Roger
> I spin my latest HPB props at 7X cadence. At 10kts they are spinning
> over 700rpm:
> http://www.youtube.com/watch?v=ONk3fUnHamI&feature=relmfu
> By comparison the electric thruster prop will have an absolute
> maximum rotational speed of 800rpm - so not much difference. The
> cause of shaft vibration in sailing boats is more often inclined
> shaft rather than imbalanced prop.
>
> The nylon prop has a taper and keyway so it is well connected to the
> shaft.
>
> The unit ran smoothly with really nice control. It is possible to
> set motor speed to just hold against the wind while leaving the mooring.
>
> The two old batteries have not been used much so they should not be
> slugged. I suspect the active plate area is low so I am hoping a
> deep discharge and recharge will increase the active area.
>
> The test batteries are only 85Ah - one is the starter battery for the
> existing outboard. Two were used infrequently as forklift starters
> and one is new so we could get 48V. The target cruise power is 2kW
> meaning we want to pull at least 50A at a steady state eventually.
> The existing batteries are hopelessly inadequate for long term use as
> burst current is 200A for each motor or 400A total. I prefer a
> battery that can hold this without significant voltage droop for 5
> minutes or so. A decent set of batteries is a major investment and
> we need to be confident that we can engineer a reliable system that
> fits neatly into the proa operation. I suspect from a power
> delivery point of view lithium batteries are going to look very
> attractive.
>
> The thrusters have to be compact enough to fold up out of the way
> when sailing. The existing outboard transom can only be lifted about
> 400mm clear of the water and acts as scoop/brake when the boat drives
> through waves. Main objective with thrusters is to get steering
> leverage from two thrusters and mount them nearer the hulls so their
> immersion does not vary so much. Existing outboard prop can be in
> open air when the boat is over a trough.
>
> Rick
> On 22/05/2012, at 7:54 AM, Roger L wrote:
>
> >
> > As you probably know, as wet cells charge/discharge they shed a
> > conductive sludge which settles out and shorts the plates - I
> > believe it is a function of the purity of the lead plates....with
> > possibly some sulfur compounds involved....although I don't know
> > that for sure.
> >
> > I do know that it is possible to take most battery cells apart -
> > some require removing a sealant or even cutting the top of the
> > case. Then the plates can be lifted out, cleaned, and reassembled
> > with fresh acid. I've done that with some success.
> >
> > There are chemical processes where cadmium or magnesium salts are
> > used to flush out the sulphation without disassembling the battery.
> > I've had less success with that method.
> >
> > Yes, the large diameter props do need to be unusually strong. We
> > made models from wood and plastic and had them cast in aluminum. Of
> > course all that torque makes for a bit of a problem at the
> > connection to the drive shaft, so additional thought is needed to
> > make it very strong where the prop bolts to the shaft. Human
> > powered props don't turn all that fast, and so perfect balance and
> > geometry is not as critical as with faster turning outboard types.
> > Roger L.
> >
> > ----- Original Message -----
> > From: Rick Willoughby
> > To: harryproa@yahoogroups.com.au
> > Sent: Monday, May 21, 2012 3:21 PM
> > Subject: Re: [harryproa] Re: 18m Proa Electric Thruster Test 3
> >
> > Roger
> > The old batteries have sat around for years without any use. We
> > plan a couple of slow discharges to about 20% voltage from full
> > voltage. It may not work in which case we have to decide on what
> > permanent batteries will be.
> >
> > The first tests we did used a large model aircraft prop that was
> > 32" diameter. It was very efficient but it does not have the
> > strength to handle the 250 to 300kgf that each thruster will be
> > capable of. The props we found are quite low BAR with blades
> > aspects over 2 so they are quite efficient. In the final design at
> > 5kts in calm conditions the props will be achieving 75%
> > efficiency. The existing outboard prop is 45% as the same
> > condition - just too small.
> >
> > Rick
> > On 22/05/2012, at 12:47 AM, Roger L wrote:
> >
> >>
> >>
> >>
> >> Rick, I'm curious how you are going to restore life in the old
> >> batteries. I've tried restorations by cleaning the internal plates
> >> and also with cadmium salts - both with varying degrees of success.
> >>
> >> What is the rpm & torque or ratio? I watched some years a go as a
> >> human powered prop was developed for a high torque/low rpm bicycle/
> >> prop drive. It was quite different from a gasoline motor driven
> >> prop. Apparently there are standard naval engineering formulas for
> >> prop shape. We used several reference books.
> >> good luck, Roger L.
> >>
> >>
> >> --- In harryproa@yahoogroups.com.au, Rick Willoughby
> >> <rickwill@> wrote:
> >> > Next step is to try to restore some life in the old batteries that
> >> > have sat around for 7 years or so then do another test closer to
> >> >the 4kW motor rating or even into overload if the batteries can
> >> hold the voltage.
> >> >
> >> > Two thruster will not improve low end efficiency compared with a
> >> > single unit but they will give heavy weather performance
> >> similar, or
> >> > better than, the 60hp outboard. The tiny 14" prop on the
> >> outboard is
> >> > cavitating quite heavily even at slow cruise around 6 knots. But
> >> > worst situation is the ventilating that occurs in anything over
> >> 0.5m
> >> > waves.
> >> >
> >> > Rick Willoughby
> >> > rickwill@
> >> >
> >>
> >>
> >
> > Rick Willoughby
> > rickwill@...
> >
> >
> >
> >
> >
> >
>
> Rick Willoughby
> rickwill@...
>

Rick Willoughby

rickwill@bigpond.net.au

Rick Willoughby

rickwill@bigpond.net.au