Hybrid human/electric 6kt AIRBOAT - design proposal

[lockhughes]

Hello all. My first post here. (It's a long one, sorry!)

I'm a long-time small boat sailor (Tornado cat made of plastic snot <sigh>).

I've been wanting a proper pulling boat for a while now (sweeps, NOT paddles!), and am contemplating building same. Something like a stitch-and-glue main hull, with "outrigger" mini-hulls (so a trimaran configuration) for stability (guests and picnic), using the supports for the outriggers to support the oarlocks for the sweeps. It'd be an exercise machine for me, suitable for no-wind days, and spring and fall between sailing seasons.

I have three "problems". Carpal-tunnel in my wrists, always having to look over my shoulder ahead, and weedy, crowded, shallow lagoons and harbour.

At the same time, I am also trying to work up a proposal for an electric-powered (read "zero emissions here) 40-persons ferryboat service across the 1 mile stretch of Toronto harbour.

I have been accumulating the results of my www research into the ferryboat as a web site at:

http://groups.yahoo.com/group/QCYCTender/

Anyway, back to my little airboat...

My research into electric propulsion has led me to eBoat forums and the HumanPoweredVehicles-Boats mailing list, where folks concern themselves greatly with efficient hull forms and drive systems for low-speed craft.

The current world speed record for human pedaled craft is about 20kts over a sprint distance. This was an athelete pedaling a 2:1 geared TEN FOOT air propeller! A project of MIT.

That was about 12 years ago, and at HumanPoweredBoats meets since then, air propeller boats have been turned away routinely as dangerous, for obvious reasons... Here's a video some may find amusing:

http://lancet.mit.edu/decavitator/v...dRun.better.mpg

I'm no athelete, I don't need to go 20kts, and I don't need the danger (I have the Tornado catamaran for that <grin>).

The power-assist Yahoo group (mostly bicyclists) and the HPV-Boat folks concern themselves with transmission systems involving chains and gears and gearboxes and shaft seals and underwater struts and weeds and shallows (well, the bike folks seem to have the weeds/shallows problems licked <smile>.

So my idea (maybe crazy - I'm no engineer or boat designer, as you will see!) is to get *all* the underwater struts,props,rudders out of the water and into the air, and to pedal an electric dynamo for electricity, transmitting the power by *electric wire* directly to the (air)props:

This is a snip from my msgs with the HPV-Boat folks:

I have an idea (now) for a hybrid HPVessel for two persons, which I hope is not OT here, because I will try and address some of the design aspects you good folk have been considering - stuff like cadence and transmission losses and weeds and ...

I see air props have been verbotten at events. I
understand concerns about safety. Other than safety, what other concerns might there be, considering an air prop vs water? As a long-time sailor, I am aware of parasitic drag in rigging and topsides,etc., but wouldn't this drag (air props, *cages*, support structure) in the air be less than the drag of rudder and struts, etc in the water, because of the different densities of the two mediums? I'm guessing too though, that props in the water are more efficient, because of that same higher density, of water?

You see, I like that Decavitator!... and yes, I know the derivation of the boats name! I wonder if the safety concerns and bans would explain the lack of apparent interest in this List, or are there other reasons?

What if the air prop was smaller, and there were two (or more?) of them, something like this:

http://www.marlec.co.uk/products/prods/rut503.htm

Don't know if all can see that - it's a wind generator with a smallish propellor with a ring at the prop tips.

I have read a *lot* of msgs all about problems with rudder/strut/seal/propellor designs and practical considerations. If everyone were using air props, I guess there would be a different set of problems to face!!!

About cadence, and transmission losses... here's my thought:

I'd like *my* HPV boat to have an electric dynamo
connected to electric motors driving the air props - two 5 foot diameter props at least. You pedal the dynamo and the energy is transmitted by wires to the motor. Not by u-joints or shafts or chains. Catamaran configuration. 2 persons, plus picnic. drink holders. Recumbent, so it's easier to reach stuff like picnic and drinks... and perhaps to reduce a little windage.

My objective is not some speed record... It's comfort and distance. Perhaps a 5-6kt cruising speed, with possible bursts to 10K range in frisky mode.

The electric motors and dynamos I'm talking about here are one and the same. You spin the motor and it produces electricity.

I've have been trying to educate myself a bit lately about electric motors. Today we have available rare-earth, permanent magnets mounted on a rotor, inside wire windings. These little (and big) motor/dynamos have ONE moving part, and are claiming efficiencies of over 90%. I can buy ones off the shelf today which will run just fine, fully submerged.

So for my little HP cat, I'm guessing an efficiency of 81% between the pedals and the prop? I'd introduce bicycle gears that I can shift, so there's some more loss there too...

But otherwise, it'd be an almost solid state
propulsion system? No shaft seals, u-joins, gear
boxes.

... and no rudder. With a little electronics, I
would steer the boat by changing the speeds of the props. These little electric motors will spin in *reverse*, if the current is reversed. So now, I'm stopping, backing up, and turning within a boats length if I wish, just by twiddling the joystick - yeah, I'm steering and reversing by joystick.

With this configuration, the weedy lagoons around
here would not be so problematic.

Now I fear I'm getting a little offtopic so *snip* here if you think so...

You guys bring up cadence. And how two persons
need to be "sync'ed", or - de-coupled, if they're of different strengths (or temperments <grin> )

So at this point, I introduce a little bit more
electronics, and a battery. If the two pedalers are driving separate dynamos, then they are free to pedal at whatever speed they wish. If the pedaling isn't smooth, doesn't matter, `cause the electric smooth out the power by the time it gets to the prop.

If the plan is to go for a leisurely cruise, the
one pedaler or both can still pedal at frisky speed - and STORE their power for later, in the battery. In picnicing mode - boats pulled up on the shore - if there's some wind, the props turn into wind generators, and STORE wind energy. Tired on the water and taking a break from pedaling? Props spin in the wind again.
On the subject of dynamo/motor drive combinations, I've just found this outfit:

http://www.autork.com/e/product/product.html

The product of several years of research at a Swiss university. I see they have two electric/human hybrid bicycle manufacturers using their system now, so I hope that bodes well for this technology/approach!!! As their site promotes, going straight electric for a transmission systems provides flexibility and facilitates the introduction of additional elements eg solar/wind charging, etc.

Anyway. I'll stop here. I would appreciate any
feedback, very much!!! I'm probably wildly over or under estimating some simple fundamental law of physics or the state of current technology <pun intended>...

For purposes of any discussion here at WB, my little airboat will have two gorgeous little wooden hulls, stitch-and-glue, finished bright.

Fair winds, and... leave a clean wake.

Regards

Lock Hughes

[John E Hardiman]

Laughlin;

I thought long and hard about posting a reply or even a private message. However, in the interests of this forum I decided to post this.

I belive that this forum is not the place to waste bandwidth and storage to provide a detailed commentary on a topic that has nothig to do with hull material selection. E-mail me at jehardiman@worldnet.att.com for a detailed breakdown of why this is SOoooo wrong. I can give you a synopsis of my experience and reaserch with the qustions you ask.

I have visited your website and while your attempt at "green-ness" is laudable, I will give you some of my stardard replys when confronted with a client who has a similiar proposals:
1) Physics is physics and you can't change that no matter what your rank.
2) They're called "rare earths" for a reason.
3) High efficiency does not equate to low entropy.
4) Any man-made product cannot be zero emission by definition.

Remember, overall "green-ness" must look at the entire picture, not just that something is electric or human powered or even solar powered. As I have said before, the fix may be worse than the problem.

[On Vacation]

http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=5;t=005704 and
I belive that this forum is not the place to waste bandwidth and storage to provide a detailed commentary on a topic that has nothing to do with hull material selection.

Two examples that fits your sentence.

[ahp]

Have you ever considered using a diesel engine? Consider. A human, as an engine that converts very expensive fuel into mechanical energy is about 1.0% efficient. A diesel is about 30% and uses very cheap fuel. Which extracts the least from the environment?

When you say human powered, I hear coolie. This is progress?

Perhaps a degree in engineering should be your first step. I have one but I haven't time to educate utopians.

[bainbridgeisland]

If you are really interested in human powered vehicles, take John up on his offer and e-mail him. Having designed a human powered vehicle that held the world’s record for many years, he knows what he is talking about.

[John E Hardiman]

To All;

My bad... I keep forgetting that ATT changed my e-mail address. It is now officially:

jehardiman@att.net

and I updated my profile.

[ 08-21-2002, 11:25 AM: Message edited by: John E Hardiman ]

[Bruce Taylor]

Please hold this discussion on the forum where we can all enjoy it. Questions about alternative methods of propulsion are quite appropriate here.

[John E Hardiman]

Originally posted by Bruce Taylor:
Please hold this discussion on the forum where we can all enjoy it. Questions about alternative methods of propulsion are quite appropriate here.Bruce;
My adversion is not to a discussion about propulsion, but to what appears to be the tenet of the proposal. While I may be able to point him to the right references or line of action, am I actually doing what he intends, i.e. a green policy.

It's like using a titanium bicycle; you will never "save" the energy used pedeling due to the amount of energy "spent" to refine, transport, and fabricate the metal in the bike. It is better to built a single bus and burn oil than to manufacture all the bikes needed to do the same job.

Should I help Laughlin "hoist himself with his own petard"? My ethics say no.

[lockhughes]

Boy... tough crowd <smile>.

Gentlemen.

In my first post, I began by explaining that the boat I want will "be an exercise
machine for me."

And I mentioned that I wished to address three problems:
"Carpal-tunnel in my wrists, always having to look over my shoulder ahead,
and weedy, crowded, shallow lagoons and harbour."

And later I said "My objective is not some speed record... It's comfort and
distance." I suggested the sort of cruising speeds and distances I would like to
be able to accomplish comfortably.

I mentioned a project I have been working on, but this was intended only as an
aside and background to explain my interest in electric propulsion. I'm sorry if
this coloured my whole message "green", because that was not my intention.

Perhaps the Decavitator video was a little over the top...

Here's a short video of a (pedal-powered) boat with an airprop, the Crosstrek,
cruising *slowly* through a patch of weeds (you may have to cut/paste this into a new/
empty browse window to see it):

http://www.angelfire.com/trek/boat/XTREK3.WMV

I am primarily interested in the relative merits of air props vs. water. And the use
of electrics to store and transmit power rather than shafts and gears and fuel tanks.

To John Hardiman
You said:
I belive that this forum is not the place to waste bandwidth and storage to provide
a detailed commentary on a topic that has nothig to do with hull material selection.
I poked around the WB site John, and I could find no reference that defined the
nature of each forum. Other than the titles given to each. When I look in the Designs/
Plans Forum, I see subject headings including rowboat questions and motorcycle
engines and diesel weights and make your own bouyancy bags. The Miscellaneous
Forum seems a gam.

If you would suggest a forum that would be more appropriate for any musings about
hybrid propulsion systems etc for small boats, well, then, I'll ask our WB hosts if
these messages can be moved.

John, you also said:

E-mail me at jehardiman@worldnet.att.com for a detailed breakdown of why this
is SOoooo wrong. I can give you a synopsis of my experience and reaserch with the
qustions you ask.I appreciate your offer.

"bainbridgeisland" pointed out your background with HPV's (boats? he didn't say).
I may have naive ideas for my little air boat, but I'd be a fool not to try and hear
what you have to say. Even without knowing your background, the very reason
I posted here in the first place was in hopes of feedback. Good and bad. In spite
of the various shoals that can be encountered in these (public) forums, one really
positive aspect, I find, is that these threads are available later to all, so that others
may research these subjects.

So for that reason alone, I am reticent to turn to private emails. For you, it may be
an issue of privacy, in which case, that's fine with me. Personally, it's OK with me
to take my lumps in public, if I (and others) learn more in the process.

Finally John, you said:
Remember, overall "green-ness" must look at the entire picture, not just that
something is electric or human powered or even solar powered. As I have said
before, the fix may be worse than the problem.and I agree with you 100% on this... but can we refrain from talk of "green-ness"
in this thread? I just want a quiet little pedal boat for the harbour! If I tap with the
HPV-Boats folks, I don't mention batteries. We talk about the really heavy
picnic <smile>... So here, instead of "green-ness", how `bout we refer to it as
"quiet" or "odor-free" propulsion?


ahp?
You said:
Have you ever considered using a diesel engine? Consider. A human, as an engine
that converts very expensive fuel into mechanical energy is about 1.0% efficient.
A diesel is about 30% and uses very cheap fuel. Which extracts the least from the
environment?I need the exercise ahp... and I see too much oil in the harbour waters. Also, I hope
to be able to move around in relative silence. Something I've come to appreciate
from years under sail. BTW, I got to drive an electric vehicle today for my first time.
Twice. An interesting experience, which I invite everyone to try.

Cheers all

Lock

ps... just to reiterate:
I am primarily interested in the relative merits of air props vs. water. And the use
of electrics to store and transmit power rather than shafts and gears and fuel tanks.

[On Vacation]

["Carpal-tunnel in my wrists, always having to look over my shoulder ahead,
and weedy, crowded, shallow lagoons and harbour."]

If you are not promoting green-ness, just go to Wal-mart and buy yourself a paddle boat. There I have solved your problem. You will get all the exercise you need with no diesel or pollution. But then again, I contribute to global warming when I do it.

["I am primarily interested in the relative merits of air props vs. water. And the use
of electrics to store and transmit power rather than shafts and gears and fuel tanks."]

Storing electric in batteries will never give you any exercise.

[ 08-22-2002, 08:01 AM: Message edited by: oyster ]

[Matt Middleton]

Just some thoughts- the only reason you'd use an air propeller on a boat is to avoid hitting whats under the boat, whether that be weeds, a log, or the ground. The only boats that I've seen use air propellers are the airboats common here in central FL. These boats generally use airplane engines as well as airplane props, and these engines put out between 100-150, maybe 200 HP to power a relatively light aluminum or steel skiff to the same speeds that a 40 hp outboard would achieve. For that and other reasons, an underwater propellor would be the way to go unless you just are wanting to do something fun & different.
As far as using a generator/wires/batteries/motor as a transmission, that's what's commonly done in railroad engines. The diesels are not mechanically coupled to the wheels at all. This allows the train to use full power (keeping diesels at optimum rpm) at any train speed, which is essential to get them moving. The "electric transmission" is the best way to get the continually varying "gear reductions" to start a train rolling, not so necessarily used because of superior efficiency. Mechanical might be more efficient, all told.
That said, I think a mechanical transmission (let's say like a bike) would be better for your project in several ways. It will probably be more efficient (just my opinion, because my schoolbooks aren't in front of me.) The mechanical transmission will weigh much less. Parts will be much cheaper. Parts will be more readily available when the old ones are broken down by the harsh environment you'll be asking them to work in.
All that's just an opinion, so take it for what it's worth.
Also, here's something that's a little different, but proven:
web page (http://www.gartsideboats.com/catrow2.php#pedal)

http://www.gartsideboats.com/pgimages/blueskiesrud.JPG

It may well be worth purchasing some plans like these to get you headed in the right direction.

[John E Hardiman]

OK: Setting green-ness aside....

oyster is on the right track smile.gif , a paddleboat is what you are asking for. I would suggest a sidewheel hull with feathering wheels equipped with brakes and clutches as well as a rudder. Most likely ~16-18 feet LWL, ~2 foot hull beam, 5-6 feet width over the wheelboxes to make it trailerable. Wheelshafts driven by foot-crank, bow and stern seats. Remember to place the wheels at the transverse wake wave crest at the design hull speed. Get a copy of Saunders, Hydrodynamics in Ship Design, with attention to Sections 10, 32, and 72.

Some of my rules of thumb about human propulsion.

The human body is high torque, low rpm; Design for "cruising" HP of ~1/4-1/2 @ 60 rpm, max HP of ~3/4-1 @ 60-70 rpm for a few minutes before the lungs can't keep up with the oxygen demand. Max rpm is ~80 for anything useful even with a light load.

Some of my understanding about high efficiency propulsion.

Propellers need to be long and thin high pitched and slow turning, with root to tip taper and negative sweep. Air propellers are theoretically more efficient (i.e. less drag) however this is totally irrelevant due to the limited environmental conditions they have this advantage in (i.e. DFC). A good water wheel would be 24-30 inches in diameter and totally in the hull wake to recover energy, which rules it out for a shallow draft craft.

The move toward electric propulsion in some types of ships (cruise liners/ferries, warships, and self-unloading container) has nothing to do with improved efficiency of either the electric motors or the propulsor. It has to do with space, weight, and cost savings. All the types of ships that have high electrical loads at sea, or need to share power between deck gear and propulsion can save space, weight, and cost by fitting medium speed gensets for the maximum load only, rather than having engines for both the propulsion and electrical loads.

As I said, e-mail me if you want more depth on any of the topics.

[On Vacation]

Another alternative.
http://www.seacycle.biz/

[rkrough]

This intrepid inventor once had a cart with a sail mounted to it that used a electric fan to provide the wind. His initial testing and field trials went well. However the craft on it's maiden voyage suffered an electrical malfunction while crossing a very deep chasm .Possible adaption to a boat though the extension cord may prove to be a bother. I think Acme sells the componets.
http://www.bostonbrace.com/images/wileycoyote.gif

[lockhughes]

Just adding another 1000 words to this thread.
This vehicle was spotted yesterday at the NEDRA (Nat'l.ElectricDragRaceAssoc.) Nationals.

Over 30kts of speed (on land).. Looks like four batteries at the stern. HEY! He forgot the pedals <wink>

http://us.f1.yahoofs.com/groups/g_7047675/AirCar!!!.jpg?bcNXOd9AYOV072R7

[TomRobb]

I'd suppose that the drag on those wheels is orders of magnitude less that for a boat.

Harry Brian makes, and I think sells plans for, a sort of decked canoe that peddles a largish plastic fin that moves the craft, fish-like, through the water - much like the human powered submarines we see on TLC or Discovery channel. No arm/wrist involvement at all.

If you like rube-goldberg/Tom Swift projects, peddle/battery transmission will use up plenty of your disposable time and cash.

[On Vacation]

Nice hobby. And you know , you can start now and maybe show it off at the next Earth Summit. You can rig an coal style furnace to burn the trash and create your own steam too for your return trip.

[ 09-02-2002, 03:16 PM: Message edited by: oyster ]

[imported_Steven Bauer]

Have you seen the pics of my Thistle? It's a Harry Bryan designed 12' lapstrake decked canoe with a pedal powered fin drive. I've had no problems going straight through thick lilly pads and floating seaweed.
Here is a link to the Imagestation album:

Thistle pics (http://www.imagestation.com/album/?id=4291900137)

If you search in Building/Repair for Thistle you'll see more info about this fantastic boat!

[bainbridgeisland]

Expanding on John Hardimans' point about air propellers: Since a human produces relatively low power, your air propeller will need to turn relatively slowly to be efficient. The problem with this is that even modest wind will change the angle of attack of your air propeller, making it very inefficient.

[ 09-05-2002, 01:32 AM: Message edited by: bainbridgeisland ]

[lockhughes]

Hello Steve

Originally posted by Steven.Bauer:
Have you seen the pics of my Thistle? It's a Harry Bryan designed 12' lapstrake decked canoe with a pedal powered fin drive. I've had no problems going straight through thick lilly pads and floating seaweed.
Here is a link to the Imagestation album:
Thistle pics (http://www.imagestation.com/album/?id=4291900137)
If you search in Building/Repair for Thistle you'll see more info about this fantastic boat!Interesting. Couldn't see anything at imagestation without logging aboard, so will hunt for more info on this fin drive!
Thanks
Lock

[lockhughes]

Originally posted by bainbridgeisland:
Expanding on John Hardimans' point about air propellers: Since a human produces relatively low power, your air propeller will need to turn relatively slowly to be efficient. The problem with this is that even modest wind will change the angle of attack of your air propeller, making it very inefficient.Thanks BBI. Sounds like a v.good point. Don't know how an electric assist might compensate.

For the record, re the "craft" in the pic:

It's a "Wind Wagon" by Bill Bruder. Some more details:
He hit a speed of 39.17mph on Monday. Had to "throttle back" at 39+ `cause his frontend was going airborne.
(A record speed though, for Bill.)
It has a 62" ultra lite prop built by IVO prop.
36volt golfcart motor running at 48V but "capable of more".
The current motor is series wound.
About 2500 RPMs
The rig dry weighs 247lbs. plus Bill.
4 batts, 48 V NAPA Orbital Deep Cycle Marine

He did three runs down the track and about 30 min. of himself and others driving it plus cooling people off during photo shoot. This was on one charge.

Bill figures at 3 to 6 mph he can most likely go two hours on one charge - but he has never tried a distance run (!)

He says it runs well at lower rpms also.

BTW, believe I have found my joystick controller -they make `em for "battlebots" (robotics) where they're controlling drive motors independently. Cheap too - $40US. Up to 42v systems... They mate these with Lynch brushless PM motors, which sounds about right. 24 to 48 volt, 1730 to 3450 RPM, weighs 21lbs, 15hp max., 8hp continuous.

Thanks for the feedback re angle of attack.

Lock

[lockhughes]

Hello Tom
Originally posted by TomRobb:
I'd suppose that the drag on those wheels is orders of magnitude less that for a boat.I'm sure you're right. This fellow is shooting for 40+ mph. I'm sure when he moves his weight fwd, adds fairings, winglets, whatever, he'll be hitting speeds somewhat greater with the same HP. I'm shooting for only 6+mph.

Harry Brian makes, and I think sells plans for, a sort of decked canoe that peddles a largish plastic fin that moves the craft, fish-like, through the water - much like the human powered submarines we see on TLC or Discovery channel. No arm/wrist involvement at all.
Understand. Sounds interesting. It's the addition of any sort of power-assist that complicates matters. That's where I hope an "all-electric" transmission might offer some simplicity and flexibility. The Swiss Autork technology is used to multiply pedal power 2x on the pedal/electric bikes in production. I'm assuming the multiple could be make variable from zero assist to 20x or more... to multiply the (approx. 1/2 hp x 2 persons) 1HP human power I have to start with. But the goal would still be 4-6kts with zero assist. I see 1-person pedalled catamaran configs (water prop) where the mfgrs claim 6kts is do-able/comfortable.

If you like rube-goldberg/Tom Swift projects, peddle/battery transmission will use up plenty of your disposable time and cash.Hehe... yeah have too much time right now. Hope the cash to play with some of this technology won't be *too* harsh. Looking for off-the-shelf mostly. 2nd-hand bits and pieces, whatever.

Thanks for the feedback

Lock

[Matt Middleton]

I've ridden one of those pedal-power catamarans- the one I rode even had arm levers, so you could get the full body workout (similar to the ones on exercise bikes.) You steered by leaning your body, which caused the aft ends of the hulls (hinged from the main part) to act as rudders. It responded to forward and reverse inputs pretty well, but IMO would've been better with just leg power and steering operated by hand.

Every time I think about your idea, I think that an underwater propeller is better. Air is much more compressible, and it seems to me that it would be compressed by the propeller. Since compressing air requires power, you've got wasted energy, most of which would've been used as propulsion on an underwater prop.

I also had another thought I wanted to add, that applies to air and water. My sailboat has an outboard, and it has been equipped with a special prop and a ring around the prop to increase efficiency. It is somewhat nozzle shaped, to increase the speed of the water leaving the prop. Now I don't know how much truth there is to that claim (Note: boat was equipped this way when I bought it.) But I do know that an amount of air/water pressure is lost radially off of a prop. A ring around the prop would constrain it to help with propulsion.
It's the same reason you put end plates on the wings on a race car: so your pressure doesn't spill of the sides of the wing.

Not only that, but such a ring around a prop on a kick-up skeg (like the one I sugggested above) would serve to protect the prop even more from stumps, maybe even weeds.

Anyhow, those are just some thoughts I wanted to add. And I hope they make sense to someone else than me. ;)

[John E Hardiman]

Originally posted by MattM:
My sailboat has an outboard, and it has been equipped with a special prop and a ring around the prop to increase efficiency. It is somewhat nozzle shaped, to increase the speed of the water leaving the prop. Now I don't know how much truth there is to that claim (Note: boat was equipped this way when I bought it.) But I do know that an amount of air/water pressure is lost radially off of a prop. A ring around the prop would constrain it to help with propulsion.
Is the ring actually part of the prop, or is the prop just in a nozzle? The effect (i.e. increased thrust for a given diameter/rpm/speed of advance) is similar but the physics are different. A ringed prop effectively increases the apparent aspect ratio of the blade, while a nozzle either increases or decreases the apparent advance coefficient. Ringed props are generally fitted to slow turning shafts as the torque lost to drag increases with the square of the prop diameter. Nozzles are fitted to allow more thrust to fast spinning wheels at slow speed (think towboats or outboards on sailboats)or slow spinning wheels at fast speed (think pump jets) by controling cavitation losses. As a note, neither ringed propellers or nozzled props are more efficient absolutely than a well designed wheel of the same diameter, they just manipulate for more thrust at a specific advance or diameter.

And yes, a major loss in propellers is radial flow. This can be prevented by good blade design. However, material and structural considerations begin to dictate blade shape in large high power wheels.

[Matt Middleton]

Hi John- it's a propeller inside a nozzle.

But from your description, I wonder if it's pointed the right direction. I have a 9.9 outboard on the back of my sailboat, and the nozzle (if I remember correctly) is installed such that the big end is facing forward. If it's putting the same amount of water through a smaller diameter opening (at the rear), isn't it increasing the velocity of the water at the exit, and so decreasing thrust? And from your statement, maybe even inducing cavitation at higher engine speeds? Seems I'd want it the other way around. The boat seems to perform OK while motoring, but I don't use more than half throttle and still make decent speed.

One cool thing about it- the prop wash doesn't noticeably disturb the surface of the water. You can see a long trail behind, but it's all underwater. I had figured that was because the water wasn't spilling off the prop blade ends.

Any more thoughts on this effect would be interesting to hear.
Matt

[lockhughes]

Hi Matt

Originally posted by MattM:
Hi John- it's a propeller inside a nozzle.
<SNIP>
Any more thoughts on this effect would be interesting to hear.
MattThe nozzle is often called a "kort nozzle" on a water prop Matt. I gather it's termed a "ducted prop" on an air prop.

The kort is useful for tugs (as John mentioned). Applications where you're not moving but want more thrust, as I understand it <and I have only a limited understanding of all this>

I gather that korts are best as designed for a limited speed range, outside of which the drag takes over.

I'm interested in what these folks are doing:

http://www.karvi.com/technology/tech-speednozzle.htm

As I understand it, they're learning how to make kort's more efficient (faster speeds or better fuel economy) at speeds greater than zero. It *sounds* to me that the best opportunities with a kort extend around a designed and limited range of speeds?

I've seen an ad around for years, for a kort retrofit for outboards - this may be what you inherited?

Don't know if you can see this, but here's a recent message thread on korts:
http://boatdesign.net/forums/showthread.php?s=0a5a47fbfa5cef7cc2ca99c2493c4b0e&threadid=731

Here's another thread:
http://www.eboat.org/forum/index.php?board=20;action=display;threadid=65

This was/is a convo among a bunch of eboaters (electric motorboats) - and they take their efficiencies pretty seriously...

I was impressed by the fellow that "threw together" a kort in his shop, and the gains he reports from even a "simple" nozzle.

This gentleman sells an outboard with a kort nozzle included:

http://www.qis.net/~jmgraham/resrun.htm

and he claims great positive things for a kort also. (Yeah, ok, so it's an *electric* outboard again... humour me <g>)

I'm stalling on your question about the nozzle being backwards maybe... sure I read an explanation somewhere about kort theory and which is right. Hopefully John will chip in. sorry

The hovercraft/skimmer crowd use ducted fans for lift and "free" 3-blade props in the air for propulsion, when I look at most of their designs. I'm trying to chat`em up a bit <wink>. Their "ultralight" skimmers work with little 12hp engines on the (propulsion) props.

Lock

[lockhughes]

Originally posted by MattM:
I've ridden one of those pedal-power catamarans- the one I rode even had arm levers, so you could get the full body workout (similar to the ones on exercise bikes.) You steered by leaning your body, which caused the aft ends of the hulls (hinged from the main part) to act as rudders. It responded to forward and reverse inputs pretty well, but IMO would've been better with just leg power and steering operated by hand.
ps... "arm levers" Matt? musta been spilling your drinks all over the place. That's no good.
Think picnic here <smile>

Lock

[imported_Steven Bauer]

OK, I don't think everyone used to have to sign in to view an album. Did Imagestation change this? I don't think I changed anything. Oh well, here are some Thistle pics:

http://www.imagestation.com/picture/sraid26/p33253a79c7f9ba34a69021d09a6fc937/fd846edc.jpg
the fin doesn't all show up in this pic.

Here is a close-up with the fin extended backwards - which happens when you run over some lilly pads

http://www.imagestation.com/picture/sraid26/p1d1f1f755c3aaa256912f347507b8bc4/fd846e9b.jpg

And in action

http://www.imagestation.com/picture/sraid26/p991e25894ef287d9c252658629d07246/fd846e5f.jpg

I have some more that I haven't loaded to imagestation yet.

Here's a shot from the plans

http://www.imagestation.com/picture/sraid18/p5cdc1392e70aac4d187d5b99be860677/fdcc3acf.jpg

Am I going crazy here?
How about the pedals?

http://www.imagestation.com/picture/sraid26/pc1adcb8edb9b84afe750fa617021477b/fd846edf.jpg

[John E Hardiman]

Originally posted by MattM:
...the nozzle (if I remember correctly) is installed such that the big end is facing forward. If it's putting the same amount of water through a smaller diameter opening (at the rear), isn't it increasing the velocity of the water at the exit, and so decreasing thrust? And from your statement, maybe even inducing cavitation at higher engine speeds? Seems I'd want it the other way around. No Matt, the nozzle is correct. You most likely have a Kort type accelerating nozzle. This type of nozzle is used to prevent cavitation at low J values by decreasing the angle of attack of the blade. They do this by accelerating the flow into the propeller, i.e entry diameter is larger than the diameter at the prop. As axial continuity must be satisified, velocity in the axial direction must speed up prior to action by the prop; the slower the Va the larger precentage it speeds up. This tends to flatten out the efficency curve and thereby improve efficencies in the low J region. It is mainly used in situations where more than enough Hp is available to achieve maximun efficiency, but the depth of submergence is low and the disk area loading (thrust per square foot of disk area) is high, such as shallow draft towboats and outboards. Remember, unless the blade is specifically designed for cavitation, it will lose thrust proportinal to the amount of cavitation experienced. Once you have cavitation started, you must effectively stop the prop to remove it. A lot of boats will "dig holes in the water" if the throttle is advanced too fast at low speeds.

I can point you to books and papers that discuss this much better than I and follow the coventional wisdom in this matter. I'm a member of the "lunatic fringe" of prop design and some of my ideas will get you beaten up by the "classical" prop designers out there if you voice them.

[John E Hardiman]

bump

[imported_Daniel]

What about a jet drive (read pump) instead of props? Seems to me you could do the gearing to get neccesary RPM's to turn the impeller(s).

ahp wrote:

Perhaps a degree in engineering should be your first step. I have one but I haven't time to educate utopians. I say.... :rolleyes:

[ 05-21-2004, 07:38 PM: Message edited by: Daniel ]

[Paul Pless]

Jet drives are very inefficient. I have a 75 hp Yamaha Enduro Outboard, that has been converted to jet drive via a foot swap, it is now rated at 50 hp for registration purposes.

[Hal Forsen]

Today's Orange County Register (CA) had this article concerning a race between solar powered ply boats built by local High Schoolers. The race was sponsored by the Metropolitan Water District of So Cal.
I hope this link works;
http://www2.ocregister.com/ocrweb/ocr/article.do?id=96068&section=LOCAL&subsection=LOCAL
HF

[imported_Daniel]

Paul, is that because its a conversion kit and not specifically designed, or does this apply to all jet drives?

[Paul Pless]

Daniel,

I'm sure an engineer will be along shortly to clarify, but I'll give it a shot.

With a prop the direction of the water never really changes. The flow hits the prop from the front and goes out the back. For, one thing with a jet, the water gets sucked up and then twisted and turned about 270 degrees before being squeezed out of the nozzle. In addition to the lifting and redirection of the flow there is the matter of frictional losses as well as the fact that the water is being forced through a nozzle.

In my mind there are only two advantages of a jet drive: Shallow water drive and reduced appendage resistance in really fast boats (drag boats for instance). My boat will run in about 3 inches of water trimmed out and on plane.

All of the outboard maunfacturers use the same lower unit, even on new jets sold from the factory. Its made by an Australian Company and sold through a distributer in San Leandro, California. The name of the company is Outboard Jet Drive. I bought and rigged my in 1998, this was before it was easy to get a jet straight from the manufacturer. A friend bought one already converted at the factory two years ago and his lower unit is identical to mine.

Paul

edited to add:

Just like with conventional outboards and propellers, different impellers are available. These vary the accelleration and top speed potential of the drive, but not by as much with a prop. I used to run the high speed impeller, its a 3 blade cast aluminum unit. Now I run the most aggresive acceleration impeller I could find, its a forged steel 4 blade unit. The boat is noticably quicker to get on plane (important in whitewater) but I've only lost three miles an hour on top speed.

[ 05-22-2004, 09:25 AM: Message edited by: Paul Pless ]