How well does transverse mounting work when you pedal alone? Seems like more weight on one pontoon, unless the position is adjustable.
That's why I wanted a split box driving either 1 or two props, joining the pedallers together. You can pedal alone and if one pedaller is stronger than the other it does not matter.
That gearbox takes me away from transverse pedalling again, though. AFAICS.
So a supported shaft? Just a simple pillar that holds the end of the prop laterally? I feel that it can get more complex than that, because if you need forward and reverse thrust, you need fore and aft support as well, and friction is then going to start playing a part, with thrust bearings needed.
I am guessing that the least efficient setup is the "outboard leg", with two lots of gears and I assume also the need for seals on the lower end. Also more drag to cover the gears and shaft. Small prop, high speed etc.
Starting to look at unobtanium here....if only I could....
I think my design would be for 60-70 cadence and 100W max. This is not a racing boat, but a better way to paddle, for us. I guess that I can say 60 cadence and 200W with two people, but then I would need to have gearing to allow for just one, if the cadence is to be maintained.
I know I pedal faster than my wife. I guess my happy cadence under moderate conditions would be 60-80. It's really hard to tell, because we ride MTB cross country and that's all over the place, whereas a boat will be a fairly steady load, whether high or low. My wife has to consciously think about keeping up 60! She tends to sit in too high a gear and pump. I guess I can use sprockets to allow different cadence. This has to be a nice even experience and you can always change sprockets.
Hence your idea about a recumbent trainer. The only thing there is load. It would be hard to know what sort of push I am going to need, on average, to work the boat. I guess they would be able to set it up for a given "power", or drag that I can then calculate power from?
I suppose I need to start looking at desired speeds, cadence, power and prop sizes to get gearing right. Maybe a derailleur setup! 27 speed boat!
Have you pedalled in wind/waves yet? That would interest me. Have you made any alterations to the setup (prop size etc) and have you "calibrated" yourself?
And how have you gone with the damage to the drive. Sorry if I am asking stuff that has been covered in this thread, but it's so huge, and I also searched your posts and did not see anything.
OK. I have been doing some more reading and found quite a bit on the thread.
Tiny Turnip your posts are most encouraging, because as I said I have a very similar platform to work with.
Rick, you pointed to the MITRPAK gearbox.
I checked out some Oz ones as well, as I think you also suggested.
Using very rough figures.
The MITRPAK one says that its [i]static[i] torque is 275 (no units so I am assuming pounds-foot?) or is it pounds-inch? That's 275*~1.4 nm = 385 nm!
The Oz ones are talking maybe 11 nm at around 300 RPM with a 15 mm shaft.
Even at pounds-inch (32 nm), that makes the MITRPAK one nearly 3 times as capable. What happens as the shaft speeds up? I could not find any charts of torque capability vs RPM.
Also, let's say I have the capability to push max 80kg (~800n)with each leg. The pedal arm is 180mm. That's 144 nm. Divide by 4 for the chain ratio and you have 36 nm. With two people that's 72 nm. Seems that two strong people could tear a 12-15mm shaft gearbox to shreds.
I remember you commenting that a cheaper Asian leg was "geared to protect the workings" and that made for very fast pedalling.
Where am I going wrong? Thing is I am looking at pushing a big boat, maybe with passengers. So it won't just slip away under sudden heavy pedalling.
Again, sorry if this has been covered.
What do you think of this
My gearbox is a 3:1 Involute gearbox, they come from India and are a bit on the heavy side but will stand up to a lot of use. Don't know if they are still available but if you want to contact them I can give you their email address.
I got mine for US$300, but you get your moneys worth.
My boat is a proa and the reason for this is to avoid putting a hole in the hull. I sit half on the boat and half over the water allowing the shaft to spin free. The gearbox is mounted on an aluminium frame which is bolted to the boat. I use Ricks idea of the spring steel shaft, the shaft is connected directly to the gearbox without the need for chains or universal joints. The shaft bends up to allow launching off the beach or getting over rocks.
What about for your cat you used the same setup on each hull, it would mean two gearboxes. Advantages would be ease of setup and avoids major work on the boat, two could peddle at the same time or if one needs a rest the shaft could be bent up out of the water minimising drag.
Here are the main posts featuring my boat, Fangle:
My initial postings were on this short thread. Unfortunately photobucket has deleted my pictures because I have been inactive, but there's nothing missing that is not repeated elsewhere.
Propellor for pedal powered catamaran
The Dart 18 setup works well. It was a simple build, and the boat is responsive and robust. Our 15 mile circumnavigation of Gigha was very gratifying; we completed it in 4 hours, half the time the island's 8 man gig took a few days earlier. The handling is confidence inspiring. We have had it out in a force 6 three times, and in 6ft plus swells, and it behaves very well. In those conditions, we were starting to feel the effects of the windage on the steering, and the power needed to maintain steerage, particularly through the wind, was noticeably increasing. In following seas in these conditions, Fangle felt a little as if she wanted to brooch, which surprised me, as the rudders are large, but it may just be we need more time on the water to get familiar with the handlng. We didn't get to a point where we could travel faster than the waves, so there was no burying into the back of the wave in front, though the hulls are brilliant into a head sea.
The seacycle drives are twisted chain, and are fine, but are proving a little temperamental. The chain tension adjustment slips a little over time, and is slightly aggravating to adjust. Oil will leak from the units if they are laid down, they need to be upright not to leak.
I have used both the 12" and 16" propellors, and the only difference on the water seems to be the comfortable cadence.
I wouldn't worry about power differential between the engines. My principle other engine, Paul, is a very keen club cyclist, (Audaxes, 6 bikes and practice rollers at home!) and we found no issues at all in steering on our circumnavigation. It may be that the differential in fitness between Paul and me shows itself in sprints, which we haven't gone at seriously yet, but no issues at all in 'cruise all day' mode.
Fangle is very happy with one person only pedalling, - the drive legs kick up, though not fully clear of the water. It is noticeably harder and slower than with two, as you would expect.
There is some twist in the yokes and the cantilevered front end of the longitudinal beams as you pedal. It would be nice to get them more rigid, but its difficult with the way the yokes pick up the drive legs, and it would make the assembly/breakdown more complex.
I chose a Dart as a donor boat over a Hobie purely because the cross members are straight rather than curved, and I wanted a large flat deck for picnics, fishing, creels and pitching a pup tent on.
I could ramble on for hours, but if there's anything you'd particularly like to know, I'll do my best to answer.
There's some shots inside the seacycle drive p15, #220.
If the chain tension is too tight, the drive tends to bind under load. The problem I had was actually with the plastic propellor. Having bent it, when pedalling hard, the forces on the propellor made the damaged and weakened blade flap back and forth, which felt like a hard mechanical knocking in the drive unit, but wasn't at all.
No callibration done yet, but it is on my to do list!
You can break most things if you try hard enough. Olympic sprinters can shred cycle cranks. They have to control their power.
You have to consider what you can realistically sustain and design for that. I can sustain about 120W. I can peak at 630W. I do sprint but for short duration.
The torque ratings are given for long life at steady torque.
The Mitrpak ratings are given in inch-lbf. The boxes are similar capacity for size. The ZP range from TEA use higher strength steel so ratings are somewhat higher. I do know the shear pins in Mitrpak are light on.
If you want to look seriously at a gearbox then you should do some power testing and decide where you would like to work. Get on a recumbent machine at a gym and cycle for an hour or so at what you find most comfortable. Record the power and cadence. This will give a realistic design level. Most boxes will take 10X the continuous torque in ultimate. The torque rating does not drop much at the rpm used on these boats.
I have attached the rating information for the TEA boxes. You will see the ZP2 is rated higher than the DZ2. I have used both of these. I prefer the DZ2 as it has less seal drag. I have used the ZP2 for maybe 100 hours and it has not yet run in. The seal drag is high. It has 14mm shafts. It is rated at 496W at 300rpm.
In terms of breaking things, the prop will just turn. If you give it heaps of the mark the prop will suck air and just spin free. You will find it gets very hard to apply the maximum leg force at speed. I expect two people might break the DZ2 but not the ZP2. The 1/2" or 11mm Mitrpak would be light on for two riders; OK for one.
Using a box heavier than needed adds seal friction and associated losses.
I happen to have the Hobie, which needs a bit of work (the foam in the deck has collapsed ) but which I bought pretty cheap.
TT's boat is similar to your idea in positioning (only, hang another hull and person off where the ama is ), and as I say the idea of hanging out over the middle is brilliant. As you say it avoids a stuffing box.
A 3:1 box looks good. As you say, no chains. What's the shaft diameter on that gearbox? That seems to be as good as any indication of power handling in my totally non-engineering experience.
The main thing I like about chain drive is the ability to change ratios fairly easily and even have a multi ratio setup..
But I am looking seriously at DIY (I have to, TT ) and using the flexed shaft. I think I would use Rick's idea of a flexible leg to the shaft, so I can reverse as well as forward. A bit of extra drag in my situation means very little.
I was looking at the idea of a tee-box and single prop for balanced drive and also no need for two props, which are either expensive or take a bit of practice to make, especially if I am going to experiment (and it sounds as if I will). However what did occur to me was the fact that two props vs one prop is going to make a huge difference to swept area, power per prop etc.
Maybe I can actually help (hope I am not trying to teach gandma to suck eggs). What made you feel the boat was broaching? Force on the rudders or.... ??
One thing you did mention was the fact that putting yourselves forward of the main beam made the cat sit bow-down a bit. That would cause a broaching tendency. The stern will lift and surf and the bow will dig in and provide a nice pivot for the broach. But if you had "crew" or gear aboard on the aft deck, that might go away.
The other thing is rudder balance. If the rudders are balanced to suit the sail plan of the cat as sailed, they may not suit the sail-less setup. In fact the entire cat is set up to deal with a rig. A rig is itself adjustable, but you don't have that choice.
I know that when I built a cat, I went out in tough-ish weather . I was really working to keep the boat straight because of helm when surfing waves. I built new rudders that had some forward balance and that problem was gone.
When you pedal with only one, do you notice any need for rudder to correct the one-sidedness? In your case, having the props almost amidships would minimise that problem, I guess. Also, I would imagine you cop a double whammy, with cadence dropping as well.
With the different prop sizes, would you look at using the larger size to go faster (harder work, same cadence)? What sort of cadence do you work at for say, 4 knots? That's the sort of speed I am looking at. No records to break on an 18' cat!
I see the prop prices are actually quite reasonable for this unit. Interesting. Even though you damaged one, it's not the death-knock to replace on.
Re the curved spar. I intend to make a deck as you have done, and make it flat but with a lintel to allow for the curve. Ironically the curved sheer may be more of a problem!
I really like the Dart to look at. Nice powerful simple lines.
I too can go on!
This may be of interest
That's for Oz, but it looks as if plumbers' supplies may be a place to look.
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