electric boat, proper rpm and propeller

Displacement?

Is the transom submerged at 10 knots?

What area have you got to mount solar panels?

Rick W

 

displacement=2.65ton
yes
area=13.9875 m^2
thank you for helping

 

I have done the attached sketch of the boat you describe. You will have to advise if I am close to the mark.

The boat drawn will require 17kW to do 10knots if the propulsion can achieve an efficiency of 75%.

Good solar panels can produce up to 160W/sq.m in strong sunlight directly overhead. So the required area of panels is:
Area = 17000/160 = 106sq.m

With your available 13sq.m you could produce 2080W. This will achieve a speed of 3.5kts for the boat I have drawn.

The transom drag is significant. If I have shown it deeper than it is in your boat then this should be modified to get a more accurate calculation of performance. A photograph of the boat would help.

Rick W

 

Electric outboard for small(12ft) dinghy

Hi,
I have been reading with great interest this topic on propeller design and electric outboard as I am looking at converting my aluminium dingy to electric propolusion.
I live in Perth, Western Australia so availabilty to your full range of products may be limited.
I currently have a 12ft aluminium dinghy with a 9hp Mariner(mercury) engine.
Can anyone suggest a suitable electric outboard?
Kind Regards.
George.

 

George
You really need a good reason to spend the money to replace a petrol outboard on a small dinghy intended for planing.

The only commercially available electric outboards are rated around 4HP. Something like these:
http://www.electricmotorsport.com/store/ems_marine_electric_outboard_motors.php

There are some others but most are more expensive. The ones shown are USD prices as well.

So you can get an outboard of considerably less power than the existing Mercury. The next step is the batteries. Lead are heavy. For a 4HP outboard you would ideally need about 240kg (three adults of weight) of batteries and they will set you back AUD3000. By the time you do this the boat will be way to heavy to plane. It will be like a barge.

For AUD3000 you could get lithium batteries that would weigh much less and enable full power for about 50 minutes. They might get you on the plane one-up but it would be borderline. You might need a special prop.

I expect by the time you have spent AUD6000 your little tiny will be overcapitalised. Its performance will also be considerably reduced. It will be a little quieter though.

If you are doing it simply to reduce noise with the intention of just mooching along then a Minn Kota or Torqueedo might be worth consideration:
http://www.minnkotamotors.com/
http://www.torqeedo.com/en/hn/home.html

Also be careful with things like static thrust on electric outboards compared with combustion engines. It has no meaning to moving a boat through the water. It only has meaning if you want to tie the boat to a pier and measure the force you can produce. I have no idea of the value in doing this exercise. None the less it seems to be something that helps sell electric outboards. It seems the makers get close to fisticuffs over this nonsense figure accusing each other of exaggerated claims.

You will find most of the developments with electric powered boats are in hull design where the designer starts with efficiency in mind at the outset. You can get impressive results from electric motors matched to an efficient hull and prop.

Rick W

 

Electric propulsion for dinghy

Thanks for your valuable reply Rick.
Kind Regards.
George.

 

Hi i'm John, i'm thinking of purchasing a wide beamed canal boat 57ft by 12 ft which will weigh somewhere in the region of 22 tonne.I would like to power it by electric motors , however i have no knowledge on the subject. I'd like to know what sized motors ,best type of propeller and drive system ?Also best type of batteries taking into consideration that i will be living on the boat and have all the electric amenities that you would have in a house. Would it be possible to link it all to a generator that would drive the motors when the batteries are low , charge them at the same time and run the electrics on the boat? Please note that i will be also incorporating solar panels on the roof of the boat. Can anyone help? Regards John M.

 

22 tonnes ...
Try anti gravitation solution before going electric ?
What about air drag ? Important ?

Power needed will depend of the way you will need to move, speed in heavy weather/water condition is expensive in energy. In lake use it can be low.
Power generator efficiency will count too as KWH to litre of oil ratio is wide !

 

John
It will be an expensive method of propulsion. It can be done. I do not know of any system that you can buy so you are on a long and expensive learning curve. You need to have considerable engineering expertise. An electrical qualification and license would be handy or at least befriend someone this knowledge.

I can help with power and things like that. I expect the boat already has a prop so best to start with this to check its suitability.

Rick W

 

Thanks Rick for your reply, may i point out that the boat will be used on the british canal and riverways system and i know that there are several boats of equivilent or larger size using quite a simple system driven by lynch motor. (Refererance magazine Waterways world and canal boat.) My problem is calculating propeller size ,motor size and batteries adequate to store power to give the most efficient drive and run all the systems on the boat . I would presume that any form of power drive would be inefficient and would relate to 1 or 2 HP being driven through the propeller. (Hey but these boats were pulled fully laden by one horse from the eighteenth to early twentieth century)
The maximum speed on the canal system which for the most part is still water is 4 m.p.h and the navigatable rivers would probably run up to 4 notts.
Regards John M

 

If you accept to run your boat only when wind and water stream is calm, energy need will be significantly lower.

 

using javaprop

using javaprop for finding props for electric boats. Great tool!

Some questions:
1.
To test efficiency penalty, if blade chord is increased, the "modify card" was used. However, running "desing" for modified chord fails? The "design" returns original optimum chord data, and omits modified chord data totally? Did I miss something?
2.
For water propellers, there are no typical foil profiles? Water prop profiles are in practice thin ones, and the entry is guite sharp. Actually entry and trail profiles may be about similar (symmetry). Used E193 and ARA D profiles in javaprop to approximate an actual water prop forms.

Great tool to play "what if",
redu

 

O.K.
It was possible to compare e.g. blade cord increase beyond that optimizewd one. It could be done in the "analysis" section of Javaprop.

"Advance ratio" = v / (n*D) [v = boat speed m/s, n = revolutions per second, D = prop diameter] is something I do not understand? Why to use this "advance ratio" figure?

redu