The Electric Boat Thread

All has not gone dead on the electric boat project front. Some things have been much harder, and taken far, far more time to sort out than I had hoped, though. The really big challenge for a very low powered boat such as this project is maximising efficiency everywhere in the system. I spent a lot of time wringing every last lost watt from the electrical systems, then discovered that some of the mechanical parts soaked up far more power to drive than I had hoped. After a lot of fine tuning, I now have a motor that is around 90% efficient at cruise power and a gearbox and drive system that only soaks up about another 5 to 6 watts.

The last challenge, before I get to integrate all this stuff into the boat, has been to get an efficient propeller. Boat propellers are generally pretty dire, I've found. Boat designers don't worry about prop efficiency too much, they pick a diameter that suits the boat and then just make sure the engine is much bigger than really needed, so they have some headroom to play with when it comes to losses. For electric power, particularly where I'm hoping to be pretty much solely reliant of solar charging, I've needed to develop a propeller that will do much, much better than the standard small diameter, wide blade chord, high rpm boat prop. I tried model aircraft propellers, and these do work very well, much, much better than a boat prop if they are made big enough and can turn slow enough to be efficient. The really big problem with them is that they collect weed extremely quickly, so are practically useless.

Luckily, the human powered boat people have been facing the same problem, as they only have a very modest amount of power to play with as well. A chap in Australia, Rick Willoughby, has come up with a neat way of making a folding prop. If the blades catch a bit of weed, then they fold back under the extra load and it slips off. Apparently this system works well. I've spent the last couple of days making a set of stainless steel blades. The starting point is a strip of stainless steel sheet, that is twisted to the correct pitch angles (checked with templates at four radial stations. This is then cut to a rough profile shape and has stiffening pieces silver soldered to the root section:

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The grotty bottom one is a near raw blank, the top is a partially finished blade.

The blades are then hand ground to shape, using templates to get the right aerofoil section at each point. This doesn't take as long as some may think, perhaps an hour or so per blade. Much of the time is spent checking to make sure both blades are identical and follow the templates accurately.

This is a shot of the finished blades in a partially finished hub:

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They will fold backwards (down in this picture) if a bit of weed gets caught on one. The other thing that helps this weed clearance method is that the prop only spins at around 400 rpm at cruise speed, as it's 13" in diameter, massive for a very light two person river boat.

The drive system for this uses a right angle gearbox. I'm currently working on the moulded fairing that fits around this to reduce drag. The motor is my re-wound, low Kv, Towerpro, fitted with Hall sensors and driven by a modified low voltage xeichang 116 six FET controller. The boat hull is one of these pedal boats, minus the pedals: http://www.swallowboats.co.uk/content/view/94/30/



Jeremy
 
Very nice work on the propeller Jeremy. It's a surprise to me that conventional boat propellers aren't very efficient. I'd always assumed that the wider blade profile was chosen because of the difference in viscosity between water and air. Over the years there must have been a considerable amount of research into blade efficiency, so I guess there must be other factors that affect the choice of blade section. You mentioned fouling – could cavitation become an issue? I imagine the slimmer blade design spins faster as well?
 
There a few generalisations when it comes to props. The blade chord is pretty much proportional to the amount of power you want the prop to absorb, so more power = wider blades (or more blades). Prop blades are really just twisted aeroplane wings, and just like aeroplane wings, long thin ones are much more efficient than short fat ones (think of gliders as being probably the most efficient wings going). The downside with long thin blades is that you can't spin them very quickly, as the maximum tip speed is limited by the shear strength of water. If the tip moves too quickly, then the pressure difference between the high and low pressure side of the blade will cause the water to vapourise, producing cavitation.

Big diameter propellers are a designers nightmare, too, because space need to be found for them. They need to be protected from hitting the bottom during accidental grounding and need to be well clear of the hull to avoid tip interference. They also need either lower rpm motors, or reduction gearboxes, due to the need to turn them slowly. A small outboard motor may only have a 6" prop and will turn it at maybe 2000 rpm or so, but it's total efficiency, from engine power to power in the water, may only be around 20% or so. Using a big, slow turning, prop, with long thin blades allows high efficiency, but at the cost of some installation headaches. I've made the whole motor lift up under the stern, like an outboard but fitted into a slot in the bottom of the boat. This gets around the ground clearance problem and also allows the boat to be trailered fairly easily (I hope).

The design software I'm using, Javaprop, can also design props for aeroplanes, all you have to do is change the values for viscosity and density. Given the same sort of requirements it designs props for either air or water that look pretty similar. I've had a lot of help from folk over on the Boat Design forum, especially the human powered boat people, who are working at similar power and speed levels.

Jeremy
 
Hi Jeremy... re protecting props... did you consider/discard a steerable nozzle a la Kort? To offer some protection to the prop plus obviate the need for a separate rudder?
Lock
 
Hi Lock,

I did look long and hard at Kort-type nozzles (specifically the Rice nozzle, as it's a bit more efficient than the Kort). After discussing it with people on the Boat Design forum, who had some knowledge of these things, I discounted it, not because it was inefficient, but because they are reputed to collect weed very easily (they apparently act a bit like weed vacuum cleaners).

My prop is steerable, as I've made the gearbox at the bottom of the leg able to rotate. I does still mean that I've lost a shallow water capability, but I'm reasonably happy with that compromise, as most of the time the boat will be used on inland waterways with at least 2 or 3 feet of water.

For another application, where the prop diameter is limited to 8" maximum, I am looking at using a Rice nozzle. This is for a sailing boat, that normally has a small outboard, but the designer wants to try efficient electric power. The idea is that an on board wind generator will be able to keep the battery topped up, allowing enough power for the motor to be used to get the boat to and from it's mooring.

Jeremy
 
I've now finished the prop and hub. Here's a picture with the blades open:

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and another with them folded back in weed clearance mode:

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I just need to get the leg finished now, so that I can give it a test.

Jeremy
 
Yea, that's awesome!! Good work!

Are you able to silver solder stainless with a low temp torch like mapp gas or propane?
 
Many thanks for the kind words.

I silver soldered those bits of 316 stainless together using Castolin Eutectic XFC1020 fluxed silver solder rods and an ordinary butane/propane mix torch, one intended for DIY plumbing etc. It takes a while to heat the parts up, but seems OK for small stuff like this. The only downside to using this stuff is the price, the silver solder rods are pretty expensive.

Jeremy
 
I've spent a fair while at sea (I have a Yacht Masters ticket), owned an old gaff-rig yacht (which I restored from a wreck) for a few years and have spent quite a few holidays cruising our inland waterways, so I suppose the answer is yes, I have spent some time "on the water".

There's no need for a shear pin, as this is a relatively deep water, very low power, boat intended for use on canals, rivers and lakes here in the UK. On the waters for which this boat is designed, weed is the biggest problem, hence the need to make the blades fold (using blade sweep or skew to resist weed entanglement has a massive impact on efficiency). The cruise power is only around 100 watts maximum, so there isn't enough power there to do any real damage, or shear a pin, plus that prop will only be doing around 400 rpm at cruise.

The boat has an easily driven hull that is designed to run at the legal speed limit on most of our inland waterways, 4 mph. The maximum speed that the boat will do is around 6mph, but at that speed it needs a lot more power, and that poses problems with regard to range, as the batteries are kept charged up by solar cells on the decks.

Jeremy
 
this is a relatively deep water, very low power, boat intended for use on canals, rivers and lakes here in the UK. On the waters for which this boat is designed, weed is the biggest problem, hence the need to make the blades fold ..... The boat has an easily driven hull that is designed to run at the legal speed limit on most of our inland waterways, 4 mph. The maximum speed that the boat will do is around 6mph
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Jeremy, I see! Given those conditions, I understand what your are working towards.
Is your prop shaft counter threaded, or is prop just held on by the socket/allen head?

That low 4mph w/6mph speed limit is interesting.
That is the low speed of our river current.
I saw your link to the Swallowboat and that kinda made me wonder how 'peaceful' of a river it was meant for. We call that style of boat: "Divorce Boats", cause after a while --- the two people may end up fighting each other over who is steering, and who is powering .... that type boat is a bit slow and "tippy", and sometimes prone to dumping a quarreling couple. :lol:
Anyways, we are more primitive river folk on a massive amount of flowing water.That Suchi-blade look of your prop made me wonder all the stuff it was going to encounter on its <15 mph tip-speed trip (turtles, fish , concrete, bottles, logs, etc etc).


Best of luck with your e-boat build!!
 
I think we're used to very different waterways!

Over here, we have a pretty extensive (by UK standards) inland waterway system, mainly man-made canals, but with a few modest rivers connected to the network and thrown in for good measure. The current in the canal network is near-zero, so all I really have to worry about is wind and weeds. The 4 mph speed limit on the canal network is to limit erosion, as they are pretty narrow (the locks only allow boats up to 6ft 10" beam and the canals in general only just allow two narrowboats to pass). The great thing about the canal and river network here is that it connects together most of the central part of England, together with parts of Wales and a little bit of Scotland, together. You can just about go right around the country on the canal and river network without needing to take the boat out of the water. It's all a left-over from the Industrial Revolution, when coal, iron and manufactured goods were all literally shipped around the country on horse-drawn barges, before the advent of the railways. Now the canals are really only used for leisure, but are arguably busier than when they were in commercial use a couple of hundred or more years ago.

A lot of the ideas in the prop have come from a chap in Australia who has been building and pedalling human powered boats for a fair while. Here's a link to his thread on the Boat Design forum, where the long story of his boat development is spelled out: http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345.html Along with all the serious development, he's been having a lot of fun going pretty fast for hours on end, all powered by his own efforts.

The prop is going to be pinned to the shaft with a 5mm stainless socket head bolt, not the pivot bolt shown. I haven't got around to drilling, tapping and counterboring the hole yet. I agree about the "divorce boat" and although I'm using the same hull, I have opted to make the seats reversible, so you don't have to sit there looking at each other if you don't want to!

Jeremy
 
Jeremy thanks for the update, and can't wait to hear about live action. How thick is the original SS stock used to make the blades? Are all those design details something you plan to share, or is it already over in the boatdesignforum?

John
 
The stainless was a bit of 1/8" thick (3.2mm) 316 sheet that I happened to have already. It's doubled up near the root, to get both some added stiffness there and to allow for the narrower chord needed there to reduce swirl. The post on the Boat Design forum where Rick first comes up with a folding prop design is here: http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345-25.html#post295095

All of the information needed to design and build these props is on that forum, but it still requires a fair bit of homework to get to understand all the interlinked factors. I was lucky, as I was already used to using Javaprop (a free prop design programme) so at least I didn't have to spend time learning to understand that bit. The main issue is getting to grips with all the information you need before you start designing, let alone building, a prop. The starting point was knowing the speed vs resistance curve for the boat. This told me how much prop thrust I needed for any given speed. It's then a matter of picking a prop diameter and rpm and iteratively going around a loop of changing one parameter at a time, re-running it through Javaprop and seeing where the optimum is. I probably spent a few hours running different props through that programme before settling on the 330mm x 356mm one I ended up building. With so little power to play with it's important to wring every little bit of efficiency out of it.

Jeremy
 
I think we're used to very different waterways!
Click to expand...
Yep! Like floating thru the looking glass. :shock: Our local US system is so much more like a huge crowded highway, and similar to navigate.
http://upload.wikimedia.org/wikipedia/commons/8/80/Mississippi_watershed_map_1.jpg
& http://en.wikipedia.org/wiki/Inland_waterways_of_the_United_States
Thanks for the thread link to the prop build. Reminded me a little bit of the Gossamer Albatross's tapered prop.
I'm curious as to why you didn't use brass blades for your initial prop trials?

On our river system, you need sudden power to get out of the way of these ...
031806_tow_coming%20_right%20_at_you_thumb.JPG

I currently am enjoying Jake's blog (http://www.portagetoportage.com/) . I have seen folks from all over the world in the weirdest craft: aluminum canoes stretched long and one welded on top of the other, 2 stroke mini-surf boards, hippy-yachts , large racing hovercrafts, etc but hardly any E-boats on my local rivers.
thank for posting your e-boat efforts!
Cheers to ya'.
 
Thanks for the links, we are definitely in different environments! My nearest canal on the network is the Kennet and Avon. Here are some photo's to give you an idea of what it looks like. It's a pretty standard British canal, virtually the whole network of around 2,200 miles looks much the same, with most of it running through open countryside.

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This a general view of a typical bit of the canal. The towpath on the right was originally to take the horses that pulled the canal barges along. Nowadays a lot of the towpaths have been turned into cycle paths, as they are pretty flat and make ideal routes for bikes, avoiding busy roads.

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This gives a better idea of the width. Generally, most of the bridges are just big enough to get one narrow boat through, so will often have an opening of only around 7 or 8 feet wide.

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Where the canal has to go over a valley (they are generally cut to follow the contour lines around hills) the engineers had to build aqueducts. This one is around 150 years old, built during the latter part of the canal building boom, when the railways were already threatening to take away the business.

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Where the canal had to go up and down hills, there are flights of locks like this one. As England is generally less than flat, most canals have quite a few of these and you can expect to do several each day when cruising. There is a fairly big flight of locks near me, at Caen Hill:

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It's the best part of a days work to get up or down this flight when the canal is busy.

One of the nice things about the network is that, as it was designed for commercial use there are lots of pubs alongside. When cruising it's pretty easy to have lunch at one pub, cruise on and spend the night within an easy walk of another pub.

Hope you enjoy the insight into our way of using the local waterways!

Jeremy
 
Tks for the pics Jeremy... I got to cruise the Fens and the Broads twice... as a young Canadian guy it was living a fairytale...
Lock
 
Glad they brought back good memories, Lock.

I had a sailing holiday on the Broads a few years ago, on the George Thetford, a Broads yacht with a Lynch motor for auxiliary propulsion.
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The George Thetford under sail

It was very capable propulsion system, as we had to cruise under power pretty much all the way up the Bure on the way out (a couple of days of electric powered cruising) and only needed to charge the batteries once during a weeks cruising, up at the top of Hickling Broad.

Jeremy
 
That's a nice boat, and it's only a few miles away from me at the moment. I think the reason she may not be that easy to sell is her beam, at 13ft 6in she's too wide for most of our canal network. She'd make a nice liveaboard, though.

The majority of UK canals can only accept narrowboats, up to 70ft long by 6ft 10in beam, set by the size of the locks and the width of the bridges. Only the newer canals, those built from around the mid 1800s onwards, are broad enough to take boats of Unity's beam. Much of the most scenic part of the canal and river network here was built in the 100 years or so before then, to the narrower width.

Electric power is gradually catching on here as a viable propulsion method for inland waterways boats. There are a few companies, like Solar Boat, who are quietly developing and selling electric boats. The curious thing is that, back in the late Victorian, early Edwardian, period, electric river launches were quite popular. With the development of the infernal combustion engine their popularity waned, and with it a lot of the style and efficient hull design that typifies some of these old boats.

My hope is to play a tiny part in trying to promote the use of electric power as a practical way to cruise our rivers and canals, in the hope that more may become interested in the idea.

Jermey
 
The Kennet and Avon is a lovely stretch of water. I spent a very relaxing week in a narrowboat on the canal with the family when my eldest son was just a toddler. My most vivid memory is from about halfway through the holiday when we turned a bend and were confronted by a motorway flyover. The noise and the smell and the starkness of the concrete came as a real shock after a few days of settling into the pace of the canal and watching herons and otter.

I also made the mistake of strapping my son's trike to the top of the boat. Some of those bridges are very low...
... but luckily there was a large hammer on board so I managed to straighten up the mangled trike after a fashion. It always listed to one side after that though.
 
I had a similar culture-shock moment years ago when cruising on the canals through Birmingham with some friends. Even in the middle of the city we were still in relative peace and quiet on the canal, and very definitely in "4 mph mode". We tied up in Gas Street Basin (which hadn't yet been developed as a tourist attraction) and decided to venture out on foot for a meal. We opened a wooden door and found ourselves instantly in the inner city mayhem of Broad Street - the overwhelming temptation was to just close the door and flee back to the quiet of the boat!

Jeremy
 
Jeremy Harris said:
4445094090_b21a3c7deb_o.jpg

It's the best part of a days work to get up or down this flight when the canal is busy.
Click to expand...

Here's where it's nice that your boat is lightweight. Bring a foldable canoe cart and use the path on the right. B.t.w. how do you pay for lock use and maintenance of the canals? Taxes or per use? In Sweden there's usually a 1-way fee for all the locks to go up or down a canal system. It is only for the locks though, so a canoe carried around the locks is free.

I tried to cycle the canal paths of southern England about 1990. At that time many were poorly maintained, and there was no cycling map. We started in Kensington (where my friend was living at the Imperial college student housing -- quite a contrast to the luxury mansions nerarby), and tried to make it out of London on the canal paths, but encountered barbed wire fences in industrial areas, sections were the path was not maintained and completely overgrown with bushes. Getting out and in of London was a nightmare. Cycling in the countryside was nice and pleasant. Still remember the ubitiquous Wetabix tomato and sausage breakfast in the hostels. Maybe I'll try again in some years when my kid can cycle along.
 
I've already been thinking along the lines of making a canoe-style portage trolley, as it would make a big difference at locks.

Over here, we pay an annual licence fee to British Waterways which covers as much waterway use as you wish for the period of the licence. You can either buy a short term licence (for a day, week or month) or a long term licence (for 3 months, 6 months or 12 months). If the boat is portable, then there is a 50% discount on the fee, and there is a 25% discount for electric power.

The towpaths on quite a lot of the canals are now pretty good; there's been a fair bit of work done in recent years to make them cycle friendly. Some of the less well used canals still have towpaths that are a bit rough, but their generally passable.

Jeremy
 
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