Use of flywheel to enhance human powered drivetrain

[r2ak24]

Hey , I’m participating in a sailboat race that forbids gas or electric engines. Paddles and oars are popular with smaller boats while racers over 25 feet rely on peddle drives. As we are poor substitutes for engines these devices work but not very well !
My thought is to add a flywheel, as heavy as possible, to the mix so the peddle drive is used to spin the wheel and have the prop spun after that . I’m hoping by using the bicycle gears the flywheel can be spun faster than a direct drive and the weight of the wheel can offset some of the resistance of water on the prop .
Hoping someone can advise as to the merit, or lack of , on these ideas . Thanks!

 

[Baluncore]

Welcome to PF.

I’m hoping by using the bicycle gears the flywheel can be spun faster than a direct drive and the weight of the wheel can offset some of the resistance of water on the prop .

Interesting idea.
Why are flywheels not also used on bicycles?

To improve pedalling, I would investigate the gear ratio between the pedals and the propeller. Humans operate comfortably at about 70 pedal strokes per minute, and synchronise their breathing.
Also, use cleats or toe straps, to get the pull on one pedal, to oppose the push on the other. That will produce smooth power over a full turn, without a flywheel, and keep you in your seat.

 

[Filip Larsen]

To the extend that it is human muscles that needs to power the whole drive train, including the power needed to spin up and maintain flywheel rotation, you will not be able to get more total power by adding a flywheel. Due to friction you would more likely get a bit less power from the muscle into the boat/water if you include one.

The only situation I can think of in which a flywheel may potentially make sense if input or output torque or power varies a lot and you want something in the drive train to smooth out this variation.

 

[berkeman]

Welcome to PF.

I’m participating in a sailboat race

Um, why are you worrying about driving a propeller in a sailboat race? Are these races commonly held in becalmed conditions?

 

[r2ak24]

To the extend that it is human muscles that needs to power the whole drive train, including the power needed to spin up and maintain flywheel rotation, you will not be able to get more total power by adding a flywheel. Due to friction you would more likely get a bit less power from the muscle into the boat/water if you include one.

The only situation I can think of in which a flywheel may potentially make sense if input or output torque or power varies a lot and you want something in the drive train to smooth out this variation.

Getting more torque in the drive train I think would be an advantage. As long as a not too large prop is used it seems like the weight of the wheel would help maintain a constant rpm . As a posed to direct peddle drives where the prop stops as soon as the peddles do .

 

[r2ak24]

Welcome to PF.Um, why are you worrying about driving a propeller in a sailboat race? Are these races commonly held in becalmed conditions?

It’s a 750 mile race up the inside passage from Washington to Alaska . It can take a week or so and calm or no wind is common.

 

[Averagesupernova]

I can see it being an advantage if you could somehow have bearings good enough to allow this flywheel to spin for hours and hours with little loss. So, pedal even when the wind blows. Not that I've read the rules in your race, but this sounds like charging a battery while the wind blows and then throwing the switch. You mention that is not permitted, so, I would look into the rules concerning ANY energy storage scheme.

 

[sophiecentaur]

Hoping someone can advise as to the merit, or lack of , on these ideas .

You are basically after a flywheel storage system. There are examples of systems where a flywheel is used to store energy for a short while but they are only practicable for a limited range of applications. See this link. Your particular application is an unusual one but it may be worth while doing a google search with some 'inventive' search terms. I couldn't find anything for you in a brief search. Also, look around you. Are there any such systems in the boats you see out on your training sessions?

Just another comment: rowing a boat with a well designed hull and good oars seems to work pretty well for long distance (oceanic) records.

 

[Flyboy]

Just another comment: rowing a boat with a well designed hull and good oars seems to work pretty well for long distance (oceanic) records.

Seconding that. The hydrodynamics of the hull are going to be far more important than any type of energy storage. You would need a lot of mass, a fast spinning flywheel, and a pretty efficient gearbox to make it very useful. And even given that, the endurance of the system would be minimal. Might be useful for a burst of energy when desperately needed, but otherwise it’s probably more trouble than it’s worth.

I think, from a practical perspective, your efforts are better spent on making the propulsion system and the hull as hydrodynamically efficient as practical. The place where I would put such mechanical complexity would be in the propeller, in particular in making it able to streamline when not in use. I know such propellers already exist for sailboats, as the excellent Acorn To Arabella project showed a few years back, but they might not be optimized for human power. Some investigation would be in order.

 

[r2ak24]

You are basically after a flywheel storage system. There are examples of systems where a flywheel is used to store energy for a short while but they are only practicable for a limited range of applications. See this link. Your particular application is an unusual one but it may be worth while doing a google search with some 'inventive' search terms. I couldn't find anything for you in a brief search. Also, look around you. Are there any such systems in the boats you see out on your training sessions?

Just another comment: rowing a boat with a well designed hull and good oars seems to work pretty well for long distance (oceanic) records.

Hey ,
Thanks for mulling this over . I agree oars are solid choice but as the boats get bigger oars become impractical as the rower gets higher off the water.
As for designs in use now , there’s nothing more innovative than a 10 speed fitted to a prop or paddle wheel .