Efficient electric boat

Looks good. Efficiency wil not be affected much by the bevel gear at the lower end. You will loose about 2% unless you have it packed in grease. Use oil. See http://www.roymech.co.uk/Useful_Tables/Drive/Gear_Efficiency.html

You could get rid of this inneficiency by putting the motor at the bottom of the shaft where it would be better cooled and also add a little to stability like a little keel. Higher voltage will help you reduce copper losses, at the risk of frying yourself. 100V will kill you quite nicely in a salty environment.

Interesting stuff. Electric drive is the way of the future. The electronics is pretty good now, controller efficiencies have been better than 90% for several years now, what is still troublesome is the batteries, weight and longevity. Ultracapacitors are potentially a replacement for batteries, and offer the longevity, but still cannot match a battery for weight and volume, but we will get there eventually.

 

I'm putting together a BluePoint special electric outboard. BluePoint is the name of the Japanese angle air drill that has a 2:1 bevel gear and ball bearings in the drive. I'll run for a bunch of hours with various elec power combos, but chiefly I'm interested in getting some data on apc vs. torqeedo props. Changing one to the other is a twist of the chuck key. Hopefully I can download a foto. Those interested in powering up a brushless might consider ARO air drills, which I believe use roller bearing planetary. BluePoint has bushing planetary, which I chose not to use.

 

You want to be careful it does not pull out of the chuck and you loses the prop. It would be more secure if you pushed rather than pulled.

The most suitable of the two will depend on the application. I assume you are considering the 400 x 400 APC prop. The APC will not handle much thrust without the blades bending or breaking. However up to the point of failure you should find the APC prop to be more efficient.

Rick W

 

Hi Jay,

Looks like you got a Torqeedo kayak prop, too. That's an 8 x 8 isn't it?

Are you testing durability running in water? Judging efficiency by measuring static thrust (bollard pull) or testing it for speed vs amps in a boat?

There is lots of "armchair" testing on the web but not much actual test data from the real physical world. I look forward to your results.

I just started the head scratching phase of desigining my electric aux drive for the 18' sailboat I am building. Got the trolling motor laying on the bench next to the boat hull trying to envision taking it in and out, fairing the hole in the bottom of the well for minimum drag both motoring and sailing, physical structure of the well, etc, etc.

 

Hi
you may want to check the pro-pulse composite props. with adjustable pitch.
The axis may be large, but with some modifications you may be able to better it.
One may want to consider a wheel (like the mississippi boats) for efficient low speed propulsion, no shaft in water ... it is basically the most efficient olympic rowing boats propulsion system, they go pretty fast.
I tried fins with my catamaran and it was surprisingly fast. Perhaps the blades could have an S shape and flex like fins.
If only we could get interesting results for wakesurfing behind boat, the speed is about 11 knts. Exhaust is a problem, the energy surge for take off can be added to the axis with a combustion (gas, methanol, ethanol, propane, H, etc) and electric possibility (see fastest electric motorcycle drag race ...) .

 

No heavy battery weight, reduced losses compared to going thru battery, complete freedom with ergonomics, reduced and simpler mechanical components (no heavy gearbox or right angle components), no rudder needed. This has been done with land bikes by Andreus Fuchs who you can find on google. Or look in these archives under efficient electric boats under my name.

Hope this helps.

Porta

 

The APC 16X16 was successfully used in Bob Stuarts spinfin which was a human power application (1 hp? peak) so APC can handle some torque to this level without failure. With more recent development we have even stronger RC carbon fiber composites and hand laid carbon props which are very stiff and lightweight. There are still some carbon RC Bolly's around at various shops even though the company went down. MCDenny ran a bunch of tests with different APCs and his report and pictures are in the archives of this list. Electrics can be geared down to an optimum ratio with a good range of different acceptable RC props. You may have to seal the BluePoint if the the angle part will be submerged.

Hope this helps.

Porta

 

Hi all,

I'm back in action again, following a bout of surgery, and am back working on the project.

To bring things up to date, here's a precis of activity over the past few months.

When I discovered that the right angle gearbox I bought, a 2:1 Mitrpak, had high losses (around 14 to 15 watts, even after many hours running, and when warm) I looked at going direct drive. I built a direct drive "pod", with a rewound RC outrunner brushless motor, but this really turned the prop a little bit too fast for good efficiency. I did make some nice folding prop blades for this motor, using a mould made from a much-modified APC 12 x 10 model prop. I used a unidirectional carbon fibre core, with some bidirectional glass, set in epoxy resin filled with fine bronze powder. These blades were both strong, and heavy (for good spin out) but the pitch was too fine for anything other than direct drive, and the overall efficiency was only around 55 to 60% (electrical input to propulsive output).

Although the right angle drill gearbox that I used originally (see the start of this thread) worked pretty efficiently (losses were about 5 watts), it was very noisy and clearly wasn't built for continuous running (my guess is that a drill only gets a few tens of hours use through it's life at maximum torque). I decided to re-visit the Mitrpak gearbox, as this was clearly well-made and relatively quiet. I took it apart and discovered that removing the thick internal grease and replacing it with high contact pressure gear oil got rid of around 4 watts of lost power. I then realised that I didn't need the top, input shaft, oil seal, as I could fit a gasket to the sealed leg that coupled to this face and fill it with oil. The top seal was consuming another 5 watts or so, so getting rid of this, and replacing the grease with oil reduced the Mitrpak gearbox losses to around 5 to 6 watts, which I think is acceptable.

To support the prop, I've machined up a long Delrin housing, that bolts to the output flange of the gearbox and holds a PTFE bearing. The prop shaft is a bit of 12mm stainless rod, drilled and pinned to the Mitrpak output shaft. The input shaft is another bit of 12mm stainless rod, drilled and pinned to the input shaft and fitted with a slotted pin drive that engages with the extended motor shaft. The motor is a modified RC outrunner, fitted with Hall sensors and driven by a much modified electric bike brushless speed controller. Maximum prop speed is now about 750 rpm, cruise speed should be about 550 to 600 rpm.

The new folding blade prop is in the middle of construction, using a modification of Rick's method, using 316 stainless steel blades.

The hull has been delayed, as the company that are building it for me are snowed under with work. I've been getting on with the rest of the propulsion system, though and have finished the battery pack (a 12.8V, 80Ah, LiFePO4 pack), mains charger/balancer, solar charge control system (shunt regulators and a Fatmax MPPT for the solar panels) and now have 108 6" x 3" raw solar cells to build into a few panels to go on the deck.

I'll try and take some photos in the next day or two to give an idea of progress.

Jeremy

 

Good to see you back here.

I should have warned you about the grease in Mitrpak. We fill them with the light oil rather than grease. Other boxes I have used come filled with oil. I also drain that and replace it with transmission fluid.

Rick

 

I'll admit to being surprised that the grease caused so much friction. The tell-tale was the way that the gearbox unloaded power consumption dropped off after a few tens of minutes of running, as the grease warmed up. I couldn't think of anything else that would cause the gearbox to absorb 3 or 4 watts less when it was warm, other than drag from the grease.

By coincidence, the oil I've chosen is ATF, probably for the same reasons as yourself, because it seems to be the thinnest oil that's readily available and that still has good film strength when used with gears. The other two side effects of filling the gearbox, and part of the leg, with oil have been a marked reduction in noise and the provision of hydrostatic balance at the output shaft seal. Hopefully, any tendency to leak will be to let oil out, rather than water in.

Jeremy

 

Jeremy
On the ocean pedal boat the drive leg has two Mitrpak boxes connected with a flanged tube sealed to the faces. The seals on the output shaft of the top box and the input shaft on the bottom box have been removed. There is an oil fill point in the top box. This ensures a positive head on the prop shaft. Oil might get out as the seal wears but unlikely water will get in.

Also I was a little surprised you have gone for additional support for the prop shaft on the box. I have used as small as 9mm shaft swinging a 600mm diameter prop. The thrust loads are within the rating of deep groove ball bearings. I have not seen published data for the Mitrpak box but I would be surprised if your thrust would cause a problem.

Also where did you get you solar cells, what did they cost and how good are they?

Rick W

 

Rick,

I'm not sure that the output shaft bearing was really needed, but felt that the shaft would benefit from having some side support. The bearing has virtually no drag, as it's a relatively wide clearance PTFE bush, but might just limit any damage to the gearbox bearings in the event of the prop hitting anything hard.

Here are some quick and dirty pictures of the dismantled leg, without the fibreglass fairing that streamlines it. I've also attached a picture of the prototype moulded folding prop blades - these are 12" x 10", modified APC blades, with a slightly thicker section and a greater root depth for strength.

They were made by laying up an epoxy gel coat, loaded with fine bronze powder, into the mould, then adding a 200g/m² glass cloth layer on each half, then adding carbon fibre roving down the centre as a core. With the mould halves then assembled, I poured more bronze loaded epoxy in and put the whole thing in a vacuum chamber to get rid of any bubbles. The result is very resin-rich, but remarkably strong, all the same. The bronze powder massively increases the weight of the blades, when you hold them they feel very like solid bronze.

Unfortunately, these were destined for the direct drive pod, but that is really too inefficient. Their pitch is too fine for the gearbox leg, hence the switch to stainless blades.

The solar cells I have came from Everbright Solar in the US. They were very good to deal with, the cells were extremely well packed and the price was reasonable. Here's a link to the pack I bought: http://www.everbrightsolar.net/108-3x6-evergreen-solar-cells-pretabbed-diy-panel-kit-wires10836.html . I've not built a panel up yet, but have tested one of the cells. It's performance was close to the spec (bearing in mind that it's mid-winter here in the UK!) so I think they will be OK. To maximise the panel output I've bought one of these fine Australian products: http://solarmppt.com/product_info.php/products_id/33

Jeremy

 

Jeremy
I am interested in what you are doing with the cells. In particular I would like to know more about connecting them and how you will provide weather protection and cooling.

Should I get some to play with? I can get 170W panels here for AUD800. They are Chinese made and have a 25 year warranty. However they weigh 15kg. Your set up will be about 175W for maybe 8kg depending on how you protect them.

Rick

Rick

 

I like the idea of an electric boat. The off-the-shelf electric outboards by Torqeeda seem like pretty darn good devices, as long as the speed target is reasonable (say 8 to 10 knots).

However, it seems that just using a diesel generator really makes more sense than solar panels and battery given the current state of the art. I was surprised that the weight of batteries for the Atrim/Kozloff designed boat was about 5000 lbs. The equivalent weight of diesel with that same amount of KW is about 10 lbs (a couple of gallons).

Now, I know of the tremendous research going on in this area, and my last mission to Mars uses solar panels and batteries (the MER rovers Spirit and Opportunity). There are solar panel breakthroughs coming. There are solar to fuel systems coming. There are fuel cells also coming.

Soon, I think hydrogen fuel cells, where the hydrogen is created via solar panels, will be a really, really good way to do things on boats.

But by soon, that's probably 2020.

That's one reason I think going with a generator and electric outboards makes sense today: it will be relatively easy to replace the generator with a fuel cell in a decade, and the design of the boat will be more suitable for the future (MUCH lighter displacement without all those batteries).

Most importantly, one is still driven to design a very easy to motivate vessel, because those electric outboards are still only 2KW propulsors (4KW electricity input).

 

The current technology is really good enough for a boat if you treat it as a package and are prepared to pay the premium for the latest technology or do it yourself as Jeremy is doing.

He should end up with a day boat suitable for two people to cruise at around 4kts without ever having to worry about liquid fuels.

The bigger the scale the better it gets for the electric with solar. Think how much fuel you need to motor around the globe with a diesel. It is range where solar has a big advantage. The batteries are needed to give steady performance but the weight of these are coming down.

The solar cells Jeremy is using give 180W for 6kg. That is 30W/kg. In the tropics you could get about 6 hours of effective sunlight in an average day. So the enegy density for a solar array on a daily basis is 180Wh/kg.

A good diesel will require 200g/kWh, which is the same as 5kWh/kg. So a kg of diesel is equivalent to about 30 days from a solar array of 1kg.

Hence if you intend to have a range beyond 30 days between ports the solar array wins out.

A feature of the solar array is that you do not need to ever worry about running out of fuel. There might be times when you sit outside a dangerous entry waiting for sun to charge batteries but you do not need to be concerned with running out of fuel.

Unlike a sailing boat the solar array does not require regular tending. There is nothing flogging in a heavy blow. No need to get out in heavy weather to reduce sail. The solar boats use the same system for coming into a berth as it uses elsewhere - no need for an auxiliary, which is dead weight most of the time in a sailing boat. THe boat goes where it is pointed no matter what the wind is doing - at least to its seakeeping limit. The boat does not stop when the sun goes down or the wind drops because it has battery storage. From a day-to-day basis there is a need to manage energy collection and consumption but that is typical of other piloting demands.

The biggest problem I can see right now is finding the needed areas suitable for placing the solar array. I like the flexibility that a home made array offers.

Rick