Human Powered Boat

PropSim

If anyone out there has experience using this program, could you please tell me what "# of Lines" and " Hub/ Diameter ratio" are? I'm trying to get an idea of the ideal prop. shape but I'm kind of a noobie at prop design.
I'm kinda stuck here...any help would be appreciated.
SG

 

Hello. Sorry I'm late to the party.

One question I've always had about HPV's is why people choose to trasform rotational force along the longitudinal axis to rotational force along the lateral axis.

In other words, why face forward and crank, and then have that power converted to turn 90 degrees to the original force? When dealing with human power, the losses seem to be a bigger part of the total force.

Now, obviously, with something like a children's pedal boat, such a configuration wouldn't be worth the oddness factor. However, when you're talking about an extreme vessel for trans-oceanic travel, it seems tempting to go for the most efficient system possible.

So why not a sideways-mounted pedals/nordic-track/whatever mounted to a direct drive propeller? Or, maybe, just the gear you're pedaling directly, attached to a splined shaft of the appropriate size to give you whatever gearing advantage you need. No fancy chains, no belts, no pinions, no gears (or maybe just that one gear, built into the driveshaft).

 

Hi, I'm also late to the party! I don't know how I could have missed this thread before. My particular interest outside of boats has been motorbikes.
I have owned chain drive and shaft drive also. I have also researched the efficiencies of each configuration of engine and drive system.
As it applies to a HPV we can take the example of a race track motorbike.
The crankshaft is ALWAYS transverse across the bike whether the cylinders are as an L or V or straight line. As the engine must be located between the wheels there needs to be a drive mechanism. On bikes this is a metal chain of high quality material with sophisticated linkages connecting crankshaft and rear sprocket which forms part of the rear wheel hub.
Any other configuration suffers power losses to a greater extent and is immediately non-competive.
It seems that with the relatively miniscule power available on a HPV that efficiency considerations are almost as important as the entire hull.
Therefore I must agree with Toot that there should be no change in drive direction on your craft.
BTW why is the drive system on your boat Immutable?

 

drive line efficiency

frosh & toot,
I may have spoke in haste earlier in this thread when I said that "the driveline is set", that is not a true statement. It is not set, rather we are looking at the final lay out by building a mock-up.
The reason why the CL shaft rotation is transfered 90 degrees is so I can be alligned along the Center Line, not 90 degrees to it. I just think that the increased efficiency due to less friction loss by direct rotation of the shaft is outweighed by my comfort in a seaway.
SG

 

Whew. Just waded through the entire thread. Fascinating. I had some thoughts.

More gears means more power loss. The Gossamer Albatross was mentioned a while back; I think it used a plastic chain from an outfit called Berg which was twisted through a 90 deg angle to connect with the pro shaft. It got more complicated in the final version, but it would be efficient and need no oil.
I suggest that the ability to have different working positions (sitting, recumbent etc) might be nice over a long effort like this.

In a following wind you will want to freewheel the prop to reduce drag. As an alternative, props that retract into a well have been around for a while, although your prop looks huge.

Good luck; its a wild idea.

 

the whole thread?

Ancient Kayaker,
If you REALLY made it through the whole thread....well, I appologize. That is one long, disjointed track...
A great deal has been said about efficiency of the drive line, even more has been discussed about alternative drive types, flywheels, props etc.
My idea for the drive line is to keep it as simple as is practical. My plan is for a free wheeling hub on the bevel gear side. I'm thinking oars will be an adequate reverse when I need one. I can see some miniscule advantages in using some unconventional materials such as a plastic chain and such but I'm unsure of the advantages I would gain in the long run. Bicycle chain is available everywhere in the world at a relatively low cost. Since my drive line is completly modular, I can easily repair or replace damaged or non-functioning components in a jiffy while underway with minimal tools. I consider that a plus.
My hope now is that we will be able to achieve at least 50% efficiency in the drive line (loss from friction) as to maintain at least 1/10 hp to the prop. which theoreticaly should give us around 3 kts.
SG

 

Freewheeling...maybe not.

You would think freewheeling would result in less drag, but it ain't necessarily so. Narrow two-bladed props at slow flow velocities usually generate less drag if they're locked. Sailboat auxiliary props often fall in this category, and I suspect yours would too. I've always rationalized this to myself with the idea that a freewheeling prop is more like a sort of disc pulling through the water.

Here's an explanation:
http://www.shaftlok.com/FreewheelStoryShaftLok.htm

 

On the freewheeling note. Aircraft with twin centreline props (Cessna Skymaster, Rutan Voyager, etc) usually lock and, if possible feather, the second prop when cruising on a single engine. There is considerably less drag this way, as well as less wear on the mechanicals.

 

SG, no need to apologize it was fun you should write a book. Point taken on chain: plastic chain on G. Albatross was probably for weight. If I can get info on efficiency of chain and gear drives from my mechEng buddies I will pass it along. Interesting point on freewheeling drag; helicopters with engine failure can use negative blade angle to coast down using just the drag described in ChrisF's link. Feathering was considered earlier I recall and rejected because of complexity; rubber-powered model aircraft use a different feathering concept where the blades pivot around a tangential axis instead of the conventional radial axis; these are long, narrow blades that point back along the airflow when not rotating; perhaps the torque could be used to raise the blades into position automatically. Feathering is only useful if the prop drag is likely to comare to the hull drag of course.

 

efficiency

An interesting point has been made regarding feathered or pivoting propblades, I wonder if it wouldn't be advantageous to have the prop. free wheeling (at the hub like a 10 speed) when not being turned by the cranks. Then I could increase or reduce my drag (on the prop) by locking the shaft. Let us remember that this is an HP/V not a sailboat, so when not under power, I'm DIW. I'm not "draging" anything, in fact...it is my plan to throw out the old sea anchor when currents are favorable, and hoist the wind gen, when winds are favorable.
I doubt the gain in efficiency would be notable for a (variable pitch, feathering or pivoting), aka "fancy" prop., when compared to the added complexity of the system.
SG

 

You don't want maximum efficiency?

Hi Sol, this is likely to be the biggest challenge of your entire life. How can you discard ideas that you and your designer would agree would lead to greater efficencies when you are going to be grateful when the time comes for every mile gained towards your destination. Complexity and cost should not even be issues, unless the complexity is directly related to unreliability and greater likelihood of breakdown.
Do you realize the monumental effort you are contemplating to take on? This is no trivial matter!!. If I was doing it, and I would love to, but at 58 years I fear that I am about 20 years past my prime, I would do anything necessary to gain even a 2% improvement in efficiency. Do you want to increase the odds that you won't make it even slightly? Please take a realistic view.

 

Global Challenger

frosh,
Yes, this most certainly will be one of the most challenging efforts of my life.
Which ideas that my co-designer and I agree on have I discarded?
Unfortunately,such things as complexity, efficiency and cost are issues but I have been adressing those issues to the best of my abilities.
I feel I have no delusions regarding this effort. I'm prepared to succede in the attempt, if that what happens, it will be from all the preperations and training that have taken place over the last 2 1/2 years since I initiated this project.
I believe I have laid the ground work for success. A read of the thread from begining to end shows alot of these efforts and honestly, anyone who makes general comments regarding previously argued points hasn't read the whole thread and lacks a full understanding of both my efforts and the efforts of the Global Challenger Association.
At barely 39, I'm not in my prime...but I am comitted to the effort to the end.
What would you propose to give me a 2% increase in efficiency? It sounds like something I'd be interested in.
SG

 

Hi Sol, firstly I must admit that I have not read every posting in the thread as I have been under enormous pressure at work just lately. However I have read all the recent ones and here are my comments.
First of all at 39 years of age I was doing my best slalom water skiing which I had been involved with since the age of 22. Unfortunately I had an almost life ending accident with large granite boulders at very high speed, and miraculously have no permanent disability proving all my doctors wrong. This accident occurred just short of my 40th birthday.
Don't sell yourself short because of age. You are, if physically fit enough, so close to your prime for a durability event that it does not matter.
Regarding the 2% increase in efficiency. This number is a guess and I have not done the calculations. Both Toot and I strongly believe that you will lose a minimum of 2% by using bevel gears to change the direction of the driving force by 90 degrees.
My other thought is that you should computer model the exact size and shape of the propellor, but this is not my field so I cannot do it for you.
There will be drag from the propellor even when being driven and this needs to be examined in the most minute detail to reduce drag taking into account expected RPM.
Also losses due to flexing of the propellor need to be eliminated. Therefore the construction material should be the very best known at the current time, with cost of propellor not to be considered at all.
If you are are resting and going with the current, the propellor should be capable of folding so that it resembles the shape of a birds body, with no rough edges or protruberences.
This is from an amateur but I believe that incorporating these measures in full will give a lot better than a 2% efficiency increase.
Best of luck and God speed to you when you make that fateful beginning to your journey.
Best regards, Sam

 

I got the following answer back when I asked a former colleague about the efficiency of chain and bevel gear systems:-

That's not as straight forward as you think (although maybe you knew that!!) Anyway, Efficiency is very dependant on many factors. here are some, but not necessarily all, of the factors:

Tooth profile accuracy
Tooth surface finish
Materials
Lubrication method (oil, grease etc)
Lubrication viscosity
Temperature
Contact Stresses (can generate tooth degradation if too high)
Bendinng Stresses (deformity of the tooth etc)
Type of mesh (bevel, spur, worm etc)

To name but a few!!!

Anyway, this is not what you wanted to hear right?? So, in my estimation, I would assume the gears will be grease lubricated and of commercial quality, not made of a high quality steel, and operating at normal ambient temperature.

I myself don't like bevel gears and if there is another way to reach the objective, would use it. Bevels have a certain amount of sliding action which will reduce efficiency and life. Spur gears are about the simplest and are pretty efficient. If Bevels are used. great care must be exercized when setting them up to make sure the mesh is right. Shimming on assembly is invariably needed. Also make sure they are rigidly mounted and not allowed to move under load. Oh, and don't even think of using a worm and wheel (yuk!!!)

Having said all that, If I had to design something after this nature, I would not go to great lengths with all the theoretical analysis (which for the most part is unreliable, and only used to satisfy customers like NASA etc) I would use about 85% for each spur gear mesh and about 70% for the bevel gear mesh. These are numbers out of my head based on previous experiences. Usually, for the space gears which are very accurate, high quality and are light grease lubricated having low contact and bending stresses, I would use 90% for each spur gear mesh.

Well, hope that gives you and your colleagues something to think about! good luck.

-OOPs, that NASA bit gives away my former activities, doesn't it! Hope it will be of use. Giving the overall efficiency of 0.85 x 0.85 x 0.8 approx 58%, you may wish to re-evaluate my earlier suggestion of the Berg plastic chain drive which can be twisted through 90 deg to eliminate the bevel gears, also rust- and grease-free. If it can give you an extra 25% ...

I have unearthed my copy of Gossamer Odyssey, which has some data on human power levels for up to 2 hours. It seems that 0.3 hp is exceptional for this kind of duration although 1 hp or even more can be achieved for very short times. For an effort which has to be sustained day after day in far from ideal circumstances I assume you are banking on far lower levels. Its data for combined hand and foot cranking is a little higher but only for a couple of minutes or so. Interestingly, the power levels from champion athletes is close for rowing and cycling, presumably limited by heart-lung capability. My apologies if you already have this info.

 

To Solomon Grundy, and Ancient Kayaker. I fully agree with the latest posting by the latter, even if this now makes a decision on the drive mechanism much more difficult. I think that just going for reasonable, instead of optimum efficiency is not a wise option, for an undertaking of this magnitude. Sol, you will need to get further EXPERT advice before making your final decisions on the above mentioned matters.