University project

[joshqatar]

Hi there,

I am currently in my final year at university in the uk, and undertaking a major design project on Industrial Design and Technology. For this project I am designing a Human Powered Water Propulsion Device; basically a cross between a surf board and a pedalo/kayak. The user lies on the front board, with the drive below the surface at the rear driven by a single propeller. The foot pedals that power the drive are connected to two 'yankee screwdriver' mechanisms; each yankee runs at about 250-300 rpm.
Given this I am having trouble specifying the correct propeller for this product. Obviously if the diameter is too large the user will not be able to generate enough power to move the product, too small and it will bairly move. The product needs to move about 7mph/11kph in the water.

My knowledge of propellers is fairly limited, I need some advice as to how I go about specifying the prop diameter, pitch etc.

Any information anybody can provide would be very much appreciated.

Regards,

Josh

 

[rndn]

Re: University project

First, welcome to the forum. Second is that there has been pictures of hand cranked trollling motors posted on this form as well as Ebay. You may want to look at the prop design on one of those to get close to what you're looking for. Hope this helped.

 

[steelespike]

Re: University project

I'm not an expert but can give you the basics of prop theory.
A 12 inch pitch prop in theory moves 12" forward in one revolution.this disregards slip.12" pitch at 200 rpm is 200 ft per minute.I believe you can get
standard props in pitches up to about 22 to 24 inches.I think you can see how it multiplys out.
Modern day steam boats which turn something like 500-800 rpm run large diameter high pitch props.Of course they have pretty good power to turn these props.Metal props are going to be too heavy perhaps one of the "composite" props would work.Don't know what the material is.
Power Pulse brand comes to mind.These are a 4 blade an advantage for your application.These can be changed over two pitch settings.You may have to fabricate a prop from a metal or plastic fan blade like on a house fan.You could custom shape blade size and pitch.

 

[Silvertip]

Re: University project

Moving at 7 MPH in water by human power is going to take a person of stout stature and of very good physical condition. Prop diameter certainly has a bearing on your project but prop pitch is more important as it determines just how much water the prop gets hold of and translates that to forward movement. A 12-1/4 inch diameter x 15 inch pitch prop is common on a 50 Hp outboard motor installed on a 15 - 16 foot boat. You can draw your own conclusions but I'm thinking you need something like a trolling motor propeller. You can look at those right here on iBoats. Try MotorGuide propellers. You can also Google "marine propeller theory" and get up to speed rather quickly on the propeller characteristics.

 

[tommays]

Re: University project

hello

if you google "human powered boats" there is allready a lot of info on what worked and failed

The fast stuff got up on hydrofoils (over 20 MPH) to reduce drag

 

[joshqatar]

Re: University project

Thank you for the help guys. There is a lot of information to sift through. Just got to find what is relevant to me now!