Design for a electric outboard for an inflatable.

[hansp77]

This thread is started to follow on from the ideas developed in my thread about building a sail set up for a Sevylor 360 (or any other such inflatable)http://boatdesign.net/forums/showthread.php?t=13097

Sail idea has been abandoned- for now.

Instead I would like to build a small car battery powered outboard.

Seaspark has helped me with the suggestions of using a salvaged auto windscreen wiper motor, possibly a large model boat prop, and possibly constructing it in a long tail design.

So far this sounds pretty good,
If anyone has any advice, theories, speculation or experience, then please chip in,
Thanks,
Hans.

[hansp77]

OK,
I have done a fair bit of research regarding electric outboards,

the results don't look too good.
A lot of the feedback I have found has been pretty negative.
For one, in order to get any decent power and usage time, it seems that one needs to upsize beyond twelve volts, to 24 or 36.
Once this starts happening, the battery(s) start to become very heavy and impracticle for a inflatable, and to lug around. (not to mention increasing the cost).

So, even if I do successfully build this thing myself, the power and time of use it gives me, with the size of battery that I am prepared to carry, may not fullfill my needs.
From the specs I could gather on Windscreen wiper motors, it would seem that the RPM would definately be too low (42-68 rpm), requiring a gearing system (Or could it be a larger slow turning prop?)
the torque of these motors is said to be pretty high 21 Nm - 26 Nm (whatever that means)...

Hmm.
Maybe I shall have to backtrack, and think about that sail again...

if anyone has anything to add here,
go for it..
Thanks,
Hans.

[Figgy]

Get a trolling motor off ebay or any other "used" source. I would NOT go through the hassle of building one myself, but thats me. You only need a small one anyways.
You said it was like $500 (for the sail kit), you could have a shop whip you up one for a fraction of that if you took in your own materials and cut/weld sheets.

[hansp77]

Haha,
I must be a sucker for punishment...
I seem to love to go through just about every hassle I can find
It all seemed to start when I bought one big wooden sailboat in need of just a little minor work...

Aside from the the $$$, I do really like making things myself,
even with the odd disaster or two...

Another big hassle that is tempting me is to build a trickle charge wind generator-
apparantly you can salvage the motors out of Fisher Pykel washing machines, and they make great generators...
http://www.sustainability.ofm.uwa.ed...me/dirty_linen

Not that I even need one at the moment.

I have even been thinking about trying to make some sort of simple human powered prop set up for the inflatable. (I really don't seem to enjoy paddling the damn thing).

Anyway its all just a bit of fun.
My study has me locked up with books and theories and essays and essays year after year, and these sort of projects help to keep me sane.

[alexlebrit]

If you're thinking human powered, it's well worth joining the HPB list http://www.ihpva.org/mailman/listinfo/hpv-boats which is full of people who seem to know lots about it, and who all seem to use RC Model Aero-props, which are apparently better suited for the low revs you get with human power, and there's http://www.humanpoweredboats.com. But you probably know both of these anyway.

Then again, perhaps they might also be suited to the low revs you'd get with a wiper motor?

[gonzo]

An inflatable is as inefficient a hull as it gets. The loss of power through drag is very high. Also, it is difficult to attach brackets and mounts.

[hansp77]

Yeah thanks Gonzo,
I sorta know that already,
but the issue is not to achieve maximum efficiency or anything, or to have the best engine mount, etc..
it is simply to get the thing moving through the water without having to paddle it myself.

I would be interested to know what you think would be the best way to do this.
I would like to avoid a petrol (gas) outboard,
I am considering trying to build a simple (and yes inefficient) sail,
or any other reasonable options that may be suggested.
Thanks.
Hans.

[Ari]

Originally Posted by hansp77

Yeah thanks Gonzo,
it is simply to get the thing moving through the water without having to paddle it myself.

I would like to avoid a petrol (gas) outboard,
I am considering trying to build a simple (and yes inefficient) sail,
or any other reasonable options that may be suggested.
Thanks.
Hans.

This is what fisherman in my place do..cut a nipah palm leave..use it as sail. The safest sail to use when the wind is too strong for even a fraction of cloth.But the wind must be strong enough.. Care to try ?

[SeaSpark]

Hoi Hans,

Just had a look at your " Picture and Story Thread", You really need a more efficient dingy than the Sevylor 360.

Another suggestion: build a "quick and dirty" catamaran for cartop transportation. This will be a good platform for any kind of propulsion so you can experiment at will. Personally i don't mind rowing i even rowed skiff's for a while (until i spotted a sailing boat on the water that made me think "what the hell am i doing here", happened all the time when i was out in a skiff"). Inflatables are a b... to row especially the kind of Sevylor ones so i can imagine your quest for alternate propulsion.

Whatever kind of propulsion you are going to use, it will probally be low powered so you need an efficient hull.

[hansp77]

Jeroen,
you might be right.
I haven't had to do it yet, but I would hate to have to paddle out or back against a head wind.

I have been keeping my eye out for a cheap tender, and was pretty pissed to miss that Sabot, but maybe I should build something.

I have a bit of 9mm Meranti ply peices and scraps left, but would still probably have to buy another sheet or two, and I still have plenty of epoxy. I also have a lovely big pile of wester red ceder, and then a fair bit of salvaged wood- oregan and various hardwoods.
Hell I even have a friend or two who will probably help me build it.
Back to the drawing board eh!

Thing is, I still have a bit of work to do for the real boat.
I have to build a pushpit and put my staunchens back on, I have to attatch the splashboards back on, and I have to then fix my main winches to the splashboards and deck...
So, I am a bit hesitant to leap into another building project.
But really, I should hope we could build a tender over a weekend and a fare few beers..

[Frosty]

I have heard of, but never seen long tail type outboards made from strimmers,--- you know those long hand held grass cutters. I believe they even have a centrifugal clutch.

On the other hand if you really like knocking stuff up yourself, I think a windscreen type motor would be as good as it gets.

Perhaps sealed in PVC water piping like a T piece so that the wires can run up to the supply and the handle. You can get hefty ends for the pipe fittings and knock up some seal arrangement. Probably have to increase the size of the shaft with a bush to get a seal to fit,-- maybe 2 seals with a grease bath in between them. I think the RPM would be fine , but you would need to prop it accordingly,---perhaps a houshold fan!!!!!! and cut the blades down a bit to handle the torque.

[hansp77]

I have had many a thought about those 'strimmers'. Here we call them whipper snippers. I think they would pack a bit of power. Other than altering the end to put a prop on and waterproof the shaft, it would require very little alteration.
Noisy though- half the bay would probably hear heading out to my mooring

[hansp77]

Just found a great link for a one step attatchment to turn a whipper snipper into an outboard engine.
Only problem is it isn't for sale yet.
http://www.designawards.com.au/ADA/0...GN/060/060.HTM
Check it out.

[Frosty]

Whipper snippers??? I suppose every country must have there own name for those things, but I think your right running it quietly would be the biggest problem. I cant think of any single 2 strokes that do run quiet,---exept one-- I think it was a little 2 stroke Suzuki generator, they seem to be pretty quiet. Perhaps an exhaust off one of them?

[SeaSpark]

With a longtail kind of setup you don't need seals, when you use a piece of old windsurfer mast mount the prop with bearing at the thin end and the motor at the thicker end above water level.

Boatbuilding party! Joepie! great idea.

Concidering migrating to Australia and make a living as a dinghy service ferryman.

I am talking about a windscreen wiper motor for a car or truck here "ruitenwissers" in dutch.