Pedal Powered Boats

Flex Shaft

Rick
Got the boat on the water today using the flex shaft and it worked great. A bit of pushing and shoving to get the shaft connected to the gear box and out into deep water but once I started pedalling it was a breeze. Boat is a bit on the heavy side with all the changes I've done to it, the outrigger poles started to have a bend in them so may have to beef them up a bit. A guy in a canoe paced me for a bit with his GPS and gave the speed at 10kph, need to work on my fitness. Now the boat is finally reliable I can spend more time in it and less working on it. Going to try to get out this Saturday at the rowing course in Carrum, I suppose Lysterfield lake is still low.

Ian

 

Ian
If the shaft is only mild steel it may still have survival issues. Make sure the prop shaft cannot slip out of the strut if the shaft breaks. I use a tight fitting nylon fairing piece as a retainer.

Lysterfield is getting better. It is slightly higher and the cold weather has killed the long weed. Still needs heaps of rain.

If the weather is OK (not raining heavily) on Saturday I will come down to Carrum. It is better for exercising than the lake if a little boring.

Rick W

 

TT
Is Gigha the island to the west of Glasgow? If that is it then it seems just a small hop across to Ireland. A couple of hours if you choose the weather window and currents are not against you.

Rick

 

Ian
You did not say what diameter the shaft is.

I am taking length of 2.4m, drop of 0.6m and diameter of 10mm. Using these values the mild steel shaft is close to yield. It will not last very long. If you do not use a strut with a shaft retainer then you will lose the prop.

I have some 1/4" or 8mm spring steel you can have. The 10mm is stiffer than you need.

Rick

 

In USA, I believe spring steel goes under the name of piano wire or music wire. It is very inexpensive at the local hobby shops in the proper diameters, but have not seen lengths beyond 4' or so. The only graphite I've found that might take the torsion is fairly lightweight tube with braided fiber on the outside and straight on the inside, but in much larger diameters compared to the spring steel.

Hope this helps.

Porta

 

Flex Shaft

Rick
Shaft is 8mm dia mild steel 2.4 m long driving a 450mm dia prop, gear ratio is 3.3 to 1, dimensions are shown on attached drawing. I hadn't thought about losing the prop if the shaft breaks so will fit a retainer, losing a prop would be a disaster.
If gear ratio were higher say with a 8 to 1 gear ratio would this be less stress on the shaft? Higher revs, less load?

Ian

 

Ian
The life in this situation is related primarily to bending stress not torque. The shaft is bent back and forth every revolution.

With 661mm drop, 2167mm horizontally and 8mm diameter you are at yield. You may see the paint cracking before it fails. It is probably strain hardening. I doubt that you will get 50km out of it.

I would make a tension strut to support the prop and have a collar on the shaft in front of the strut so that when the shaft fails the prop is not lost. Carry a paddle so you can get home.

Rick W

 

10mm shaft

Rick
Don't know if I'm wasting my time or not, but if I had a 10mm mild steel shaft of length 2500mm using the dimensions shown on the dwg would it be under less strain. There would be a 2 to 1 gear stepup between the crank and the involute gear box giving a 6.6 to 1 gear stepup and using a 300mm prop. The shaft would be at a less severe angle which should reduce stress,
don't know if 8mm would be better or would it be to rubbery.

Ian

 

Ian
The easy fix is to replace the mild steel with better steel or aluminium. Going thicker reduces the life. Going longer is better but 2.5m would not be enough to get infinite life.

I have some spring steel that would be suitable.

If you you put in a strut you can keep going till it breaks. Carry a paddle so you can get home.

You would need 10mm thick aluminium. It is not as good as spring steel but a lot better than mild steel.

The spring steel is around 4 times higher yield strength than mild steel so endurance limit similarly higher.

Rick

 

Flex Shaft

Rick
Thanks for the offer of the spring steel, my concern is how hard it is to work with. How hard is it to drill a hole in it? With my current setup the shaft is connected to the gearbox with a bolt and the prop is fixed in the same way.

Ian

 

Ian
It is possible to grind it. I have cut a thread in one shaft but it destroyed the die. It can also be bent in tight radius.

I now machine up connecting pieces. It only takes a few minutes.

Give me the diameter of your gearbox shaft - save me trying to find my Involute box.

Also the angle of inclination of the shaft just to check that the 1700mm length I have will work. (I can use the last drawing if it is accurate.)

Finally the hole size through the prop - a photo or rough scale drawing of the hub would be good.

Rick

 

Spring steel shaft

Rick
The involute gearbox shaft is 17mm dia with a 4.5mm dia hole, the prop has a 4.5mm dia hole. Attached a drawing showing dimensions and angle of gearbox, flex shaft shown is 1700mm long. The difference between your setup and mine is the gearbox being 320mm above the deck, resulting in a longer shaft. Gearbox can be angled to suit the shaft, only a minor change to the support frame.

Ian

 

Ian
I would extend an aluminium tube from the gearbox to the water and then the curved portion from the water level to the prop. The fist 600 to 800mm would be tube - effectively rigid. I will see what I have with 17mm ID or close to it.

The curve as you have shown will be too severe even for spring steel.

Rick

 

Flex Shaft

Rick
With the first 600mm to 800mm being rigid would this still allow the boat to sit flat on the beach? Don't put yourself to any trouble with this.

Ian

 

Canoe, Hybrid

A couple of things to toss out here to get discussion going again:
I would like to build a sternwheeler canoe in order to cruise and camp. This would not be a racer, but I would like to achieve a faster cruise than paddles. My current thinking on this is a feathering wheel, hull width, with pedal power. I would like to travel everywhere a standard canoe can. Anyone with a design for a simple, reliable, light feathering mechanism? I am familiar with the Denbeigh style cantilevered wheel, and have thought of using cam followers on tracks to feather. Would this actually be faster than paddling?
Any progress on making a hybrid displacement/hydrofoil boat? I thought people were looking in this direction for the next increment in speed. By displacement/foil hybrid I mean taking a short, light hull (think cheap kayak) and adding an underwater "torpedo" that has some displacement (less than the weight of motor and boat) and less wetted area than a "standard" long hull. This would mount foils for lift, the prop and rudder. I imagine a toothed belt running through struts could drive the prop reliably. The displacement of the torpedo would allow running on the foils indefinately.
All comments welcome.
Tim Greiner