Efficient electric boat

[papawoodie]

Jeremy,

She looks sweet. The Winsome hull design is really elegant looking.

Keep us posted... we've all been waiting, too!

And Congratulations!!!

[MCDenny]

Jeremy, Your new hull looks beautiful. Now the fun starts - putting all those experiments into practice.

[MCDenny]

I posted a good bit back last fall on this thread about my experiments with modifying a cheap torlling motor to power a canoe with the hope that I could devise a practical electric auxiliary motor for the 18' sailboat I was going to build in the winter.

Well, winter has turned into summer (Rick- not for you, though) but the boat is finally done and I have some performance data to share.

It is 18' long, 5'4" beam and weighs 450 lbs all up but with no crew. It has one group 24 12v AGM battery weighing 53# with a C20 of 80 ah. The manufacturer (Cabella's via China, of course) claims a C3 of 74 Ah but I really suspect this is just wrong or measured to an (unstated) really low cell voltage. The motor is a Minnkota 36# thrust unit turning a two blade 10x6 APC pusher prop meant for model airplanes.

My goal was 4 mph for ten miles at 80% dod. I haven't actully powered it for ten miles but I did do a three mile test and the results indicate I can expect 12 miles range at 4 mph.

I'm indebted to Rick and Jeremy for their advice in developing the project.

Pictures tell the rest of the story:

Here's the boat


Range vs speed relationship


The motor installed in its well


The "dashboard" with 12v outlet, speed control off-on switch, throttle and direction knob, GPS and "glove compartment"


Behind the dashboard showing controller and wiring


Battery charger and master circuit breaker under the front deck hatch. You can just make out the battery (slightly darker grey) in front of the mast well

[Jeremy Harris]

Fantastic job, Denny, and as it happens very useful for something that I've been looking at for another boat. I'm going to send Swallow Boats an emailed link to your post, as your boat is very similar to their Storm 15 (see here: http://www.swallowboats.co.uk/content/view/69/30/) that I did the first short test with my original electric drive.

I'm tremendously impressed by the efficiency improvement that you've managed to wring out of this motor, particularly as the motor and parts are so readily affordable.

I hope that Rick is still following this forum, even though he's chosen to leave (a great shame, in my view, but understandable given the way he was so generous with his time). I'm sure he'd be as impressed as I am with the outcome of your lengthy experiments and development work.

Jeremy

[pedalingbiped]

I came across this website.
you pull to turn the propeller, then you push a pad with your feet to turn the propeller the other way.

can you really make a propeller that turns both ways to go forward?

http://www.forwardface.com/

[portacruise]

YES. One way clutches post #921 on

Pedal Powered Boats

P

Originally Posted by pedalingbiped

I came across this website.
you pull to turn the propeller, then you push a pad with your feet to turn the propeller the other way.

can you really make a propeller that turns both ways to go forward?

http://www.forwardface.com/

[noeryan]

Hey guys, I want to clear up a little confusion with trolling motors and sizing the props. I made this excel file to help you pick the size and shape of your prop. It is version one, and was made in a short bit at work. There is no calculation for drag of your boat... since each boat is designed differently. You will have to put in your own calculations here. But to give an idea, suppose you weighed your boat down with weights representing you and you pulled the boat with a rope. About how much does it feel like it weighs after you have brought it up to speed? You might could do this by pulling your boat with another boat and a rope with a large fish scale. Default was 20 lbs of force which I felt would be a decent boat. Maybe 15 foot long. The velocity is whatever you would like to go. If I recall, someone stated 100 RPM per volt? Choose what you wish.

The calculator will give you power required and thrust.

I'm an aerospace engineer so my thinking is with aircraft more so than ships. I haven't seen many calculations.

If this is popular and is of use for any of you, I will add aspect ratio, elliptical lift distribution, tapered chord, or whatever else you would like.

[BertKu]

Originally Posted by noeryan

Hey guys, I want to clear up a little confusion with trolling motors and sizing the props. I made this excel file to help you pick the size and shape of your prop. It is version one, and was made in a short bit at work. There is no calculation for drag of your boat... since each boat is designed differently. You will have to put in your own calculations here. But to give an idea, suppose you weighed your boat down with weights representing you and you pulled the boat with a rope. About how much does it feel like it weighs after you have brought it up to speed? You might could do this by pulling your boat with another boat and a rope with a large fish scale. Default was 20 lbs of force which I felt would be a decent boat. Maybe 15 foot long. The velocity is whatever you would like to go. If I recall, someone stated 100 RPM per volt? Choose what you wish.

The calculator will give you power required and thrust.

I'm an aerospace engineer so my thinking is with aircraft more so than ships. I haven't seen many calculations.

If this is popular and is of use for any of you, I will add aspect ratio, elliptical lift distribution, tapered chord, or whatever else you would like.

Thank you, very interesting. I will study it tonight. The motors I have are 75 rpm/Volt (12 kw) 130 rpm/Volt (6Kw) and 180 rpm/Volt (3 Kw) But in my view it is impossible to calculate every bit of friction and what you have given here is sufficient.(for me). Thanks Bert

[Jeremy Harris]

We've found that we can get a pretty good (better than 5%) value for hull resistance at any speed using either Michlet or Freeship/Delftship (Freeship is here: http://sourceforge.net/projects/freeship/ and Delftship is here: http://www.delftship.net/ and Michlet is here: http://www.cyberiad.net/michlet.htm). Rick Willoughby (who has now, unfortunately, unsubscribed from this forum) was a dab hand at getting results from these modelling programs, but they are pretty easy to get to work well with a bit of practice.

Once you have the hull resistance vs speed data, it's easy to plug the numbers into Javaprop (see here: http://www.mh-aerotools.de/airfoils/javaprop.htm and remember to change the density and viscosity on the back page to the correct figures for water) and iterate to get the best prop for your application. I've found Javaprop to be one of the very best freeware prop simulators going, it seems to give results that are very close to real-world performance (my background is aircraft design, too, and I've used it to size aircraft props with great success). Like your simple spreadsheet, it has to be used iteratively to get sensible answers, but it does give you full prop data (local chord vs radius, local alpha vs radius etc). It also allows varying Re across the disc, albeit at just four stations, together with varying sections. The latter makes a significant difference to the efficiency, as does the local chord, so is an important parameter to model.

The trolling motors present some additional challenges as they run a little too fast for best efficiency. Nevertheless, they are good value and, when modified with a better prop, as Denny has shown, do offer a pretty simple, almost off-the-shelf, solution.

As an example of how using this combination of models works, below is the hull resistance data from Freeship for my boat (it's modelled, but has been verified to be pretty close to real-world requirements by testing). I derived a 'best estimate' of thrust vs speed from the Freeship model, plus real-world resistance data and simply calculated prop output power required vs speed. The thrust and power needed are shown on the 'power and thrust' chart below. These numbers were then plugged in to Javaprop and the model run iteratively to get the best efficiency. The primary drivers are prop diameter and rpm and it will, of necessity, be a compromise, as the local blade chord has to be wide enough to take the loads (Javaprop can give some very thin, highly efficient, blade shapes, but they are impractical for boat use).

Knowing the key motor parameters (from bench testing) I was able to combine the hull resistance, prop efficiency and measured mechanical/electrical losses into a plot that gives power and efficiency over the boat's normal speed range, when fitted with a motor, reduction drive and propeller that was optimised for best efficiency. The final plot below shows this data.

I should be in a position to verify (or otherwise) the veracity of these figures in a few weeks, but, based on the extensive verification of the techniques I've used (from Rick Willoughby with his pedal boat experiments) I'm near certain that performance should be within 10% of my predictions.

Jeremy

[noeryan]

Could have saved 45 minutes yesterday! Thanks for the heads up on JavaProp.

[daiquiri]

Originally Posted by Jeremy Harris

I've just got back from a drive across country to the far side of Wales to collect the hull. I'm really pleased with the way it's come out, the Nick and Colin at Swallow Boats have done a superb job, and it's still reasonably light. Here's a couple of pictures, although bear in mind that it's not painted yet:

Jeremy,
the other one's name is Winsome, so you are fully entitled to call that beauty Handsome. It looks gorgeous.

[Submarine Tom]

What happened to old Rick W then?

-Tom

[Jeremy Harris]

Originally Posted by daiquiri

Jeremy,
the other one's name is Winsome, so you are fully entitled to call that beauty Handsome. It looks gorgeous.

Thanks for the compliments, "Handsome" sounds pretty good to me, I'll give it some thought.

With luck I should have the motor fitted by the end of the week and the solar panels fitted by the end of the weekend, with luck.

Jeremy

[Jeremy Harris]

Originally Posted by Submarine Tom

What happened to old Rick W then?

-Tom

He unsubscribed a few weeks ago, I don't know why. My guess is that he was spending too much time trying to help people out here. I know how long it takes just to do a fairly simple set of calculations in Freeship or Javaprop and was amazed that Rick was so generous with his time when asked to run multiple iterations for people here.

Hopefully he's still reading the forum and spending his free time working on something interesting. Pity he felt the need to leave, though.

Jeremy

[pistnbroke]

I picked this up on the british canal boat forum and thought the connection method was good as it kept the batteries equalised during discharge.
Note in the first diagram that the + comes from the opposite corner of the bank to the -. (not from the top left hand pos)
second diagram shows the cross link for equalisation...so 4 x6v is better than 2x 12v