Pedal Powered Boats

[Guest625101138]

Ian
Thank you for the acknowledgement of the MM.

I use a bearing at the shaft tube to centralise the shaft in the tube. When in operation the thust will force the shaft against the front of the tube if the thrust is not taken by the strut. I also use bearings in the shaft strut. These are not all that important because the prop will unload at the strut once operating. I carry the thrust at the gearbox. Maybe a little at the strut but it is not particularly rigid so most goes to the box. It has plenty of capacity to handle the thrust.

The other thing you could do is make the strut detachable. It could be mounted in a tube that runs to the deck and you use a wing nut at deck level to keep it in place. Remove the whole shaft for transport and storage. I have a thumb screw at the gearbox and strut to remove the shaft so I do not need to carry tools.

If you let me know when you plan to have a test I might come over for a visit or you could have the first outing at Lysterfield. Today was too good not to spend a bit of time on the lake so I went out for a couple of hours early in the day and just went around a few times. It was a perfect day.

Rick W

[I57]

Rick, thats a good idea about a detachable shaft, may have to try it as setting up and launching with a big skeg is awkward. The way I have made it all of the thrust is taken at the skeg with the shaft detaching from the gearbox to make the boat easier to carry.
Hope to try it at the end of this week as going to Cairns next Sunday for a week, so see how I go for time. If going to the lake will let you know.

[I57]

Tried out the new boat today for the first time at Patterson River and despite very windy conditions performed well and nothing broke. The flexible shaft feels very smooth compared with the universal joints, didn't crank it up a lot as conditions were not good. It's very stable so will raise the outriggers a bit and see how it goes, outriggers tended to wobble up and down so might add a second pole. Should be out at the lake on Saturday for a better test, sorry no pics.

Ian

[Tiny Turnip]

Rick - congratulations on the MM - sounds like man and boat performed well. That is a serious distance. Getting me motivated for an early start to the season, though we've had a real cold snap here in the UK, harbours freezing up, which is pretty unusual.

Good luck Ian - glad to hear the maiden voyage went well - look forward to some pictures of the boat in action.

[Guest625101138]

Originally Posted by I57

Tried out the new boat today for the first time at Patterson River and despite very windy conditions performed well and nothing broke. The flexible shaft feels very smooth compared with the universal joints, didn't crank it up a lot as conditions were not good. It's very stable so will raise the outriggers a bit and see how it goes, outriggers tended to wobble up and down so might add a second pole. Should be out at the lake on Saturday for a better test, sorry no pics.

Ian

Ian
You should be able to raise the outriggers to the point where they just skim the water. If too high the boat will tend to flop although with a good ruder you can balance it dynamically.

What time do you think you will be at the lake?

Rick W

[Guest625101138]

Was sent this link regarding a new pedal powered fishing kayak. I expect it would be faster than a Hobie:
http://www.nativewatercraft.com/medi...lti_propel.cfm

Rick W

[MLampi]

Originally Posted by Rick Willoughby

Was sent this link regarding a new pedal powered fishing kayak. I expect it would be faster than a Hobie:
http://www.nativewatercraft.com/medi...lti_propel.cfm

Rick W

I would have to disagree, Rick. The apparently rather poor propeller and the tunnel hull, plus the relatively short hull lengths all contribute to a fairly slow boat. I expect there to be a bit of aeration of the propeller once you start going at higher speeds. This would limit the top speed to perhaps 6 mph.

Otherwise, the boat seems to be a nice craft for fishing and general tooling around.

Michael

[Guest625101138]

Originally Posted by MLampi

I would have to disagree, Rick. The apparently rather poor propeller and the tunnel hull, plus the relatively short hull lengths all contribute to a fairly slow boat. I expect there to be a bit of aeration of the propeller once you start going at higher speeds. This would limit the top speed to perhaps 6 mph.

Otherwise, the boat seems to be a nice craft for fishing and general tooling around.

Michael

Mike
You must have a higher estimation of the Hobie than I do. Having seen a few in operation close by me in recent weeks, including another twin in the Murray Marathon, I can honestly say they do not perform well.

The one in the Murray had fresh crew at each check point and still only managed to complete the last day where they delayed the clean up sweep to try to get as many finished as possible. It completed that day at slightly faster than half my speed.

The twin Hobie that went in the 2006 race had a more dedicated crew but they were still very slow.

Rick W

Rick, could a flexible shaft work with, say, 500 HP., a twelve foot run, and six inches of bend over eight feet?

[Guest625101138]

There is another thread that covers what was called a rope shaft used in a high performance vehicle but it is different to what I do. THere is also a lot of discussion there on the allowable fatigue range.

I would need to know the rpm so I can look at the torque requirement.

My operation is predominantly in fresh water and I use spring steel. Spring steel in small section is very good material so high yield. I get Range 2 material shown in the attached. You can see it is good stuff.

The allowable stress range for infinite life is around 40% of yield. I can determine this. It is a function of the shaft diameter and the curve radius.

You can get some high strength stainless steel but they cost a good deal. Typical shaft material may be OK if the stress range is low.

You need to maximise the bending radius and minimise the shaft diameter with some margin on the allowable torque.

If you could go the full 12ft it would help. Might see what could be done with layout if the required shaft material is too exotic.

Of course the length of shaft working in air would need to be checked for resonance. I have never checked if resonance in water is possible if the shaft diameter goes up. In my application the water dampens any tendency to vibrate. Also if you put the thrust load into the shaft it could increase stress significantly and need to be allowed for so I would suggest a strut able to take the thrust in most applications.

Rick W

1300 RPM max shaft speed. I´ve been using 2" SS. I don´t know of a thrust bearing that can be used under water. I´ve been all over nitinol and titanium and can´t sort it out. I´ve been thinking Shaft-Saver bearings would spread out the loads better than Cutless ( in fact, I don´t know why we ever use anything other than a Shaft-Saver in a water lubed bearing). It seems, particularly in light of what you said in the other thread, that I could go down to half the shaft size with aligned thrust - that would mean 1.75" should be no problem in stainless ( 1 1/2" would be about half of 2" , I figure). I could use all 12´ to bend - I was just trying to keep side loads off the reduction gear with a straight shot to the first bearing just aft of the stuffing box.I just don´t know what can take the stresses, the catastrophic splintering failure of nitinol scares me (most of what I can find is on medical equipment sites), which grades of titanium, etc.. I will post future posts on the other thread, sorry, guys. I thought that is where I was...too much time at the terminal today.

[Guest625101138]

Mark
How good are you at engineering? You should check these numbers as I have done them very quickly.

If you could get material similar to my spring steel then a 40mm shaft would give you a safety factor of 3 on the torque I calculate of 2740Nm. It has a shear yield of 7.3E8MPa.

The bending radius with a drop of 150mm over 2.5m is 21m. The spring steel will give infinite life at this - just. You would like a bit more length. Alternatively you could reduce the diameter to 35mm. Safety factor on torque drops to 2.2. Still OK if you have good connections and do not apply thrust through it. The yield for direct stress I am using here is 1.22E9MPa.

If you have some shaft material in mind then give me the properties and I will look at it. I need Young's Modulus, the shear yield and the tensile yield. If there is published data on the endurance limit this is also useful.

The other question is - why do you want to straighten the prop shaft? It does not seen to be a very large prop.

Rick W

Rick, not formally schooled in engineering but awake during class in high school. I can live with the safety factor of three if I accept the idea of a keyless (hense keywayless) shaft. I am comfortable with solely a well-fit (lapped) taper or, at most, an abbreviated, shallow keyway near the small end of the taper.
The shear yield pressures mean nothing to me other than using your spring steel figure as a reference point, assuming spring steel is stronger and has a higher modulus of elasticity (Young´s modulus?) than anything I might use. Your torque figure is on, of course, not counting rounding errors, mechanical losses through transmission, bearing losses, and whatever loss of bending the material itself. Probably a good idea to estimate everything on the safe side anyway. Good connections, I do, but not "applying thrust through it" I do not understand. I think this brings me back to an underwater thrust bearing which I have no idea of. 150MM over 2.5M fits right in with what I need but I don´t know why the 21 M radius applies.
To the other question; I do not want to straighten the propshaft - I just don´t believe that the transmission should accept a side load. I don´t know the allowable figures on this but "none" comes to mind. The prop I have now is 26" (66cm) dia. and pitch. I know what you´re thinking ( why does he need to bend so little?) and the engine sits pretty low in a wide, radiused keel and I´m planning either a step or prop pocket to accommodate some of the diameter.
Rick, because I don´t have an engineering background, I was hoping YOU had a suggestion as to what shaft material I might consider. Nitinol is the first thing that "springs" to mind because it´s used extensively in medical and dental drills on a smaller scale but that is just the problem - I don´t locate anything large enough to use, it might have to come from the Orient. Titanium is available and not that costly but the fact that it is not already widely used is cause for my scepticism. I don´t even know enough about it to theorize about what might be a good grade but I have a little experience with titanium tools as used when working with large magnets (imagine hybrid torsion bar/straight slot screw driver - wierd). I suspect some phone calls to distributors of SS, titanium, and nitinol are in order. - Mark
Comparing straight shaft to I/O or pod (not to mention what you have done with your craft!), it is obvious that efficiency is to be gained by aligning to flow, but with the set-up I am attempting, the smoothness is the real brass ring - why isn´t it being done already?!

[Guest625101138]

I can suggest some shaft materials. The young's Modulus will not change much if they are steel alloys. The yield strengths will change.

I would like a sketch of what you have and what you want to achieve.

The main reason I went to the curved shaft was because I could not stand the vibration. I already have a very efficient prop and these tend to create more vibration because it is only two blades and the blades are high aspect.

I have never done an analysis of the efficiency gain by running the shaft horizontal at the prop but I do not think the benefit is huge. If you are only after an efficiency gain then it has doubtful merit. This is more to do with the prop diameter than the angle it runs at.

The point I make is that you have to be certain about what can be achieved before going to the trouble of doing it. If you have a vibration problem then the inclined shaft is the likely source.

Rick W

[Tcubed]

Hate to disturb a nice exchange, but can't resist dropping this curio here to amuse some of you.