Human Powered Propeller Query

[UoNMechEng]

Hello,

I am a Mechanical Engineering Student at Nottingham University and have a project to build a human powered speed boat that will attempt to get a new world record.

We are planning on a hydrofoiling hull (possible surf board) powered by one or two cyclists via a propeller.

We know that the max rpm for an average person is around 120rpm and an average bicycle derailleur has around a 1:5 ratio so a maximum of 600rpm.
An idea was to increase the gearing to 1:10 ratio and use two cyclists to help provide enough force to reach around 1200rpm.

Looking for your help on calculations for propeller pitch, blade area and diameter.
Using the online calculators, with an rpm of 1200, slip of 0.08, gearing of 1 (as rpm has already been geared up) and a final speed result of 20mph, I get a result of around 22" for the pitch. Is the production of a propeller with this pitch possible?

I am also looking for a more specific formulae for propeller pitch, blade area and the diameter that I will use in Excel to find the best outcome, are their any recommended formulae you know of?

Any help is appreciated.
Do you believe it is possible?

Many thanks.

Daniel
3rd Year MEng at UoN

 

[Home Cookin']

Re: Human Powered Propeller Query

I suppose you need to consider hull design as to whether you will have a planing hull or displacement hull. The typical motor boat and all speed boats AFAIK operate on a plane, which requires speed to get there. If you are unable to reach sufficient speed (really, force) to lift up and maintain a plane, the hull bottom becomes crucial.

You can also achieve higher rpm's and therefore force by trailing a great white shark with length of 1:2 ratio to your hull

 

[Texasmark]

Re: Human Powered Propeller Query

Hello,

I am a Mechanical Engineering Student at Nottingham University and have a project to build a human powered speed boat that will attempt to get a new world record.

We are planning on a hydrofoiling hull (possible surf board) powered by one or two cyclists via a propeller.

We know that the max rpm for an average person is around 120rpm and an average bicycle derailleur has around a 1:5 ratio so a maximum of 600rpm.
An idea was to increase the gearing to 1:10 ratio and use two cyclists to help provide enough force to reach around 1200rpm.

Looking for your help on calculations for propeller pitch, blade area and diameter.
Using the online calculators, with an rpm of 1200, slip of 0.08, gearing of 1 (as rpm has already been geared up) and a final speed result of 20mph, I get a result of around 22" for the pitch. Is the production of a propeller with this pitch possible?

I am also looking for a more specific formulae for propeller pitch, blade area and the diameter that I will use in Excel to find the best outcome, are their any recommended formulae you know of?

Any help is appreciated.
Do you believe it is possible?

Many thanks.

Daniel
3rd Year MEng at UoN

Anything is possible given the right amount of money, time, and effort.

I think you need to revisit your 8% prop slip calculation. Slip is the variance between turning a screw in a solid/semi-solid that doesn't displace, to turning the same screw in something that can displace. The heavier the load on the prop the more the slip regardless of what prop you are talking about.

Yes 22" is possible. Racing engines go a lot more than that. I run a 13+ dia 24P on my 17' fishing boat...all stock,

At slow speed as you will surely be traveling, a hydrofoil may not be to your advantage. I would think a flat bottom like comes on a river styled john boat would give you more surface area and a flat surface. You can plane out a john with next to no hp. I remember back in the '50's a friend had a Johnson 5 1/2 and could plane his 14' john. Planing gets the hull out of the water and reduces drag allowing what HP you have generated to translate to more mph and less SLIP. A Hydro needs speed to accomplish it's intended purpose. I used to have an 8' when I was a kid.

HTH,

Mark

 

[CaptainKickback]

Re: Human Powered Propeller Query

What is the current speed record you need to achieve?

 

[UoNMechEng]

Re: Human Powered Propeller Query

The current world record is 18.5 knots or 21.3 mph set by MIT in 1991. It is called the "decavitator".

The hull design will be hydrofoiled as the generating enough lift is not a problem as the craft only needs to be going max speed for 100 metres with as long run up as necessary.

Do you know what torque would be required to turn a 13+ diameter 24" pitch propeller at around 1000 rpm?

Thanks

 

[Philster]

Re: Human Powered Propeller Query

Important question: This is only about TOP speed, right? Not the top average speed? In other words, can you sacrifice acceleration for top speed? If the entire run of 100 meters is measured, then we must know that.

If you have 100 meters to clock a certain top speed, then everyone can answer with that goal in mind.

 

[UoNMechEng]

Re: Human Powered Propeller Query

yes sorry I should have made that clear,

This is all about top speed, you can have as long of a run up as you want.

The record is set by the boats time for 100 metres once it has reached top speed.

 

[CaptainKickback]

Re: Human Powered Propeller Query

MIT design + stronger legs equals new record. Lol

I assume you have studied that design. Should tell you a lot about calculations, etc.

My first thought is endurance of the crew. The longer the run up time, the more fatigue before entering the starting line. What i am saying is consider what your design can do to pop up on plane with less effort.

Good luck with your design and definitely keep us posted on progress and results.

 

[Silvertip]

Re: Human Powered Propeller Query

I can tell you that a 40 - 50 HP Mercury 3 cylinder engine with 1.83 lower unit gear ratio turns a 10-1/2 inch diameter x 13 inch pitch at 5500 rpm to achieve in the neighborhood of 35 -40 MPH. That combination produces approximately 3000 prop RPM at 2750 RPM or 1500 RPM at 1375 RPM. Note that the prop diameter is 10 inches. I'm not aware of any 22/23 inch pitch props in that diameter as they simply require too much power to twist so would not be practical on that size engine. However, 23 inch pitch props are available in 14 - 15 inch diameter ranges (right here on iBoats - click the Marine Store button at the top of this page. Good luck.

 

[Frank Acampora]

Re: Human Powered Propeller Query

FIRST you need to understand that the average male physical worker can sustain about 1/5 horsepower with bursts to a maximum of 1 horsepower --from an old Marks manual. This seems true as I speed skate and given the time it takes me to circle a ring at top speed and my weight, I am generating 1 horsepower over a period of 30 seconds or so.

Now given that your athletes are not average, figure in some increase. THEN decide how much horsepower a given prop will absorb at a given RPM. It is no good to decide upon a pitch and rpm that the operators can not physically acheive.

 

[Philster]

Re: Human Powered Propeller Query

If you could make it such that you alternate leg presses (one guy alternates with the other) to achieve the power, you'd produce more torque than those MIT guys could generate pedaling, and you'd want the proper gearing to use the massive relative torque to spin the prop.

Because human HP is inefficient, I'd want to capitalize on human torque and convert that via gearing to spin the prop. From an aerobic and anaerobic standpoint, given the distance at hand AND the benefit of a smooth cruise (pedaling is disruptive), if you could push power via leg presses and covert that to spin the ol' prop.... that'd be fine. Pedaling makes more sense for distance and endurance trials.

All this is moot of pedaling is a requirement.

 

[zagger]

Re: Human Powered Propeller Query

You will have to look at much more than propeller pitch. The prop design will be very important, like a two blade instead traditional 3 or 4. Adding riders will add weight which will increase required power to maintain planing speed. Instead of starting with a prop you should figure the hull design, total weight with the rider, drive system and parasitic loss, total drag you will have to overcome before planing speed. Once you know that you can calculate prop pitch and drive gearing. If you can generate enough torque through torque multiplier (gear case) to get on a plane than depending on the power of the rider you can increase the pitch of the prop for fastest top end. Come to think of it a variable pitch prop like an airplane one would be the best choice for this type of project. Good luck.

 

[mommicked]

Re: Human Powered Propeller Query

Are you allowed to use a flywheel or spinning mass to amplify the peddlers torque?

 

[QC]

Re: Human Powered Propeller Query

Because human HP is inefficient, I'd want to capitalize on human torque and convert that via gearing to spin the prop.

It is still horsepower that must be achieved. Speed (his goal) requires a calc that includes time, torque does not include any time calcs . . .

1000 lb/ft at 10 RPM is the same as 10 lb/ft at 1000 RPM as far as top speed is concerned, aka horsepower . . . torque x RPM/5252 = 1.9 hp in both examples.

 

[Philster]

Re: Human Powered Propeller Query

I'm using torque in a more relative way, wherein low-frequency movements (leg presses) are more akin to low-end torque than rapid pedaling is, which is more akin to upper-RPM horsepower, which was all qualified by how one's body operates aerobically and anaerobically. Given the distance and goal, and the need for a smooth plane, I like my 'make use of torque' idea.

Or something like that.

 

[cyclops2]

Re: Human Powered Propeller Query

I sure hope you are putting in a bicycle 10 speed setup to keep your foot speed at the BEST rate. That allows a larger & more efficient prop to be used. You will need to build your own SUPER THIN AIRFOILED prop to reduce prop drag to a minimum. Might as well use bike racing body suits & helmuts too.
Hull designers step foward

Should keep you out of trouble for months.

 

[Texasmark]

Re: Human Powered Propeller Query

If you could make it such that you alternate leg presses (one guy alternates with the other) to achieve the power, you'd produce more torque than those MIT guys could generate pedaling, and you'd want the proper gearing to use the massive relative torque to spin the prop.

Because human HP is inefficient, I'd want to capitalize on human torque and convert that via gearing to spin the prop. From an aerobic and anaerobic standpoint, given the distance at hand AND the benefit of a smooth cruise (pedaling is disruptive), if you could push power via leg presses and covert that to spin the ol' prop.... that'd be fine. Pedaling makes more sense for distance and endurance trials.

All this is moot of pedaling is a requirement.

Not being combative, but they could use the Johnny-pop two cylinder flywheel theorem....the engine was only there to spin the flywheel and the flywheel did the work especially when it was on a 20 foot x 8" belt connected to a hammer mill or harvester and there the kinetic energy was in the belt and the flywheel.

Mark

 

[Alwhite00]

Re: Human Powered Propeller Query

In theory you can gear it to the moon but in reality you can only exert so much pedal power to the prop - I also think a multi speed setup is the way to go as it would allow an easier take off and you could slowly ramp ut to speed.

What are the details on the record holding bike? (If any are available)

LK

 

[Tail_Gunner]

Re: Human Powered Propeller Query

View attachment 120101


Something like the above....foam frame wrapped in glass.....See if you cant get Ondarvr to chime in...His knowledge would grealy assist you in const,,,one of the best.

You want to turn the largest composite prop you can...blade area always wins the day at low rpm...Gearing is to simple just find use a 15spd bike to determine gearing. Until you build a sleek low profile hull prop size will very hard to get to...Why a composite prop???? Weight will win this day and there about 1lb compared to 5 lbs alum i think


Surfboard would be very unstable due to weight shift...i would think stability lightweight and narrow profile

 

[cyclops2]

Re: Human Powered Propeller Query

Beat this.