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Discussion in 'Boat Design' started by Guest625101138, Jul 14, 2008.

  1. OldNick
    Joined: Dec 2009
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    Location: Perth, Western Australia

    OldNick Junior Member

    Thanks for all that Rick. That chart is great. It's interesting to see that you look at watts rather than torque. Also that the torques are derated at speed mainly to provide longevity.

    I think in all of this the fact that the prop will just cavitate if I/we really jump on it is probably the most reassuring.

    hmmm..gearbox ratings and seal losses. If we always pedalled with two I would go up one and assume we are sharing most of the load (one input shaft and one output would always be there). But then there comes the matter of pedalling alone.

    You are right. I do need to rate myself. I just hate gyms. :( I did my knee cartilage a few years back and had to do physio and it drove me mad.

    I took up biking for fun, but it does wonders for my knees. So water bikes are the obvious extension.
     
  2. OldNick
    Joined: Dec 2009
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    Location: Perth, Western Australia

    OldNick Junior Member

    Ian, I found their website. It's a bit vague and messy, but I can enquire. That certainly looks a hefty gearbox. Do you have a model / part number that I can ask about?

    Also where did you get the seat, what do you think of it and what sort of $$? I see Rick commented that the seat is the second most important part of the getup.

    Nick
     
  3. I57
    Joined: Feb 2008
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    Location: Melbourne, Australia

    I57 Senior Member

    Gearbox

    Old Nick
    I haven't got a part or model number for the gearbox best way would be to send a pic. Person I was dealing with was called Alok, email is
    involute@airtelmail.in ,don't know if still current but give it a try.
    The seat I made myself out of wood and fibreglass, in fact I have made everything except the gearbox. Getting the right shape for the seat is a big problem and I still get a sore back after a while.
    I use Java prop for the propeller design and make my props out of fibreglass,
    haven't broken one yet. For different power and speed levels look at changing props, a few different props that can be changed is easier than trying variable chain ratios. My current prop is 400mm dia and I turn about 70-75 rpm at the pedals. Before this I had a 450mm dia prop and it felt lke riding a bike in too high a gear.
    My prop shaft is 8mm dia spring steel and works very smoothly with minimal drag. The tighter the curve the shorter the life, Rick has all the technical info in that area. When I first saw the flexible shaft I couldn't see how it worked but now I reckon its the best way to go. My theory is the less parts making up your drive system the less chance of something breaking, and I've had my share of chains coming off broken universal joints and stripped gearboxes.

    Ian
     
  4. OldNick
    Joined: Dec 2009
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    Location: Perth, Western Australia

    OldNick Junior Member

    Your idea of less moving parts sounds fine to me.

    I posted a link to a plumbers' supply place that has 3m long 8mm spring steel. So I was Ok with that idea.

    A couple of pics would be great! That gearbox does look solid.

    realoldnick@gmail.com is probably best. My email account is touchy about attachment sizes.

    hmmm...I was wondering if anybody had tried glass or carbon fibre for props. Interesting. I hate glass, cause it makes me itch. But in small amounts I can take it. I will check out that prop design software. Sounds fascinating. If I never build a successful boat I will have fun trying.

    If I decide to go with glass, I may pop back and ask for pointers: moulds, mixes, resins etc.

    The seat. Bummer about the back. Any idea of the cause: angle, shape? Making a seat does not scare me, but getting the right design would be tough. I was looking on eBay and there was a glass recumbent seat for sale for about $105 delivered from UK. It had no covering. It was just the hard seat. But it seemed good value. They claim the same seat is used on many recumbents. I was wondering if it was a knock-off of somebody else's :)

    Now that you have a skeg for the shaft (I am pretty sure you posted) what bearing arrangement do you have?

    Thanks for all this

    Nick
     
  5. I57
    Joined: Feb 2008
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    Location: Melbourne, Australia

    I57 Senior Member

    Some answers

    Old Nick
    With the pics if you have problems with gmail maybe posting pics here might be better.
    With the prop I make them around a 10mm square tube with a short length of square rod at the end of the shaft. This makes changing props easy and there is no chance of the prop slipping under load.
    The seat shape I got from trawling through a lot of recumbent bike pics, but is not the ideal shape. Maybe need to custom mould my back in the same way they make orthotics for shoes. Getting an inflatble lumbar support cushion which should work as I will be able to inflate, deflate it to suit. The difference with a bike is you are moving around and changing your position and I don't have a problem riding. Being in the same position without being able to move around is half the problem. The other half is years of wear and tear from canoeing and running, which is why I got into pedal boats!
    The skeg is only there to prevent the prop being lost if the shaft breaks. It has a short length of tubing at the end and has no bearings the friction being minimal.

    Ian
     

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  6. OldNick
    Joined: Dec 2009
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    Location: Perth, Western Australia

    OldNick Junior Member

    Yeah sure post them up here. It's not gmail though, it's my normal email account with wireless Bogpond that gets all snitty.

    Ah Ok, I have not ridden a recumbent bike, so I was not sure how much you moved about on them. Adjustable air seems good. Nice and comfy. Do you have any cushioning on the seat at present?

    My old bod has a bit of wear and tear as well, from farm work and driving machinery. I have always had crook knees and pedalling really helps.

    I see the idea on the prop. What about sheering, like a sheer pin for props? I can certainly see that the square will stop any slip, but I would be worried that it was too good.

    Your setup looks very nice and lightweight...not that this will matter with my setup...or with me on board! :( The best way for me to save weight is to eat less!
     
  7. Submarine Tom

    Submarine Tom Previous Member

    Old Nick,

    If you eat less you will loose muscle mass. If you exercise and eat good

    food you will maintain muscle mass and loose fat.

    -Tom
     
  8. Tiny Turnip
    Joined: Mar 2008
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    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    Nick, my build was very much driven by being able to achieve the result quickly - very difficult for me to find time for anything these days, hence the ready made seacycle units. Also good when much of my boating is saltwater. I bought factory recon units, which were a lot cheaper than new.

    Thanks for your thoughts on the broaching. I've little experience of sailing cats, and have always found them difficult!

    IIRC, Fangle would start to get slightly out of line when surfing. A quick response on the steering brought her back without any drama, and unless the waves were much steeper, I can't say there was any danger of a broadside capsize anyway. And just not fast enough to pitchpole. In truth I think its not an issue, I wouldn't be tempted to take her out in any worse conditions I don't think - having sufficient power for steerage against the wind would become very marginal very quickly in anything stronger.

    Any need to correct the steering with only one pilot was not noticeable, and certainly isn't an issue. Fangle has a rope steering system that you pull to port or starboard, and it is not as indicative of direction as a tiller would be.

    I wouldn't say that the larger prop would allow you to propel the boat any faster, just to pedal slower for a given boat speed. Boat speed 'on the water' is limited by the pain of pedalling, i.e. the resistance. our 4 knot ish cruise all day would be at a very gentle cadence of 50 -60 rpm. Rick's initial calcs did suggest that the ideal prop diameter for my set up would be much nearer to the 12" prop than the 16". Paul keencyclist would pedal at around twice that cadence, of preference. It might be that, rather counter intuitively, as a pair of poorly balanced engines, it is preferable for Paul to pedal the smaller prop and me the larger one. I will probably fit both 12 inchers when the weather improves.

    I would emphasise that one of the great unforseen delights of the boat is the controllability - being able to pedal very gently into the wind over a good fishing spot, then drift back down wind, hands free for the rod, is an absolute delight. As is feeling your way amongst rocks and shallows, peering down at the slowly revolving prop, as you watch for the bottom, or being able to stop pedalling for approaching seaweed.

    (Also very comfortable to pee while still sat down, straight into the water - a real benefit on a long trip!)
     
  9. OldNick
    Joined: Dec 2009
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    Location: Perth, Western Australia

    OldNick Junior Member

    Ok, yeah. If you are pedalling at 50-60 RPM the there is heaps of speed left. I just was not sure what the limiting factor was. As you say it's about the pain factor :( and fitness.:rolleyes:

    Sounds like you have the right idea about keeping Fangle under control in a following sea. My sailing cat (International 23, basically a 23' surfcat) from many years ago had a large-ish skeg that helped tracking, but was a pig when making the cat tack. So I would suggest that as a last resort. Cats are not known for looking after themselves as well as monos.

    I am actually amazed you were so happy in F6 on open sea! That makes for a very capable boat open at 18' and I am given confidence that you could paddle into, and handle the boat in, those conditions.

    Did you see much flexing between the hulls? I ask mainly because that was one of my worries with an unrigged cat, the rigging being such an important part of the overall structure. I know you mentioned the hulls moving apart a bit. Have you sorted that? Normally the rig would prevent that happening.

    I agree that unless you are experimenting as Rick does, or the build is at least as important as the product (that's me: I usually go too far) the "make it do it" call is a tough one. Nice work on refurbished units! They are pretty well as good as new and you can save a lot of dough.

    Haha! peeing, Yes. You are certainly set up there. The stories I have heard about expedition kayaking leave me underwhelmed.
     
  10. OldNick
    Joined: Dec 2009
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    Location: Perth, Western Australia

    OldNick Junior Member

    Sorry. It just a quip. My main point was that saving a kilo here and there may well be best achieved by trimming your own bod, for many people. But I do agree with you. I will save weight by eating better! :)
     
  11. Guest625101138

    Guest625101138 Previous Member

    Haaaaaa! The warm glow.
     
  12. OldNick
    Joined: Dec 2009
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    Location: Perth, Western Australia

    OldNick Junior Member

    A mate of mine and his mates have done some quietly serious expeditions (Esperance to Perth, camping on the beaches, paddling when all ports were closed at 45kt winds: Geraldton to God-knows where, including I think a 36 hour stretch along the Zuytdorp cliffs: Bunbury to Perth solo) and he reckoned that some of his boats will simply never get rid of the stink. That was what put me off.

    As an aside, he also competed in every Avon Descent from its inception until maybe 5 years ago. I think his best was 4th overall, and he always rated very high (1-10) in his class/age.

    I am completely in awe of the guy and AFAIK he has never rated a mention, or tried to. One of his cohort started making videos, but it never came to much, again AFAIK.

    And so I bathe in the glory of others...:eek:

    Nick
     
  13. OldNick
    Joined: Dec 2009
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    Location: Perth, Western Australia

    OldNick Junior Member

    Maybe I should rephrase that last line? eeeyouuu!

    Nick
     
  14. Tiny Turnip
    Joined: Mar 2008
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    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    I would say that 4 kts was cruise all day without getting out of breath. Gently tapping it up a bit from that to a reasonable level of exertion, gets Fangle up to 5, 5.5kts *fairly* comfortably, but beyond that, even supremely heroic pedalling that would only last a couple of hundred metres at most, makes not a huge difference; we just can't supply the power needed as the graph steepens. Because of issues with the seacycle units, we haven't tackled a serious sprint speed trial yet.


    To be fair, although it was a measured 6, we didn't take Fangle out beyond the bay in these conditions, and we did get a fair amount of shelter in the lee of the island. It would have been a different story in the middle of the sound.

    No flexing really. The spars on the Dart are ovoid mast sections, and thus don't allow the hulls to rotate around them. The deck structure helps to brace things together somewhat. When the hulls migrated apart, one of the retaining clips wasn't in place, and I now run an additional roofrack tiedown strap through the front spar, which also gives something of a hand hold, and a tie on point for gear.
     

  15. OldNick
    Joined: Dec 2009
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    Location: Perth, Western Australia

    OldNick Junior Member

    Ok. Still 4 kt gets you a fair way there and back for a couple of hours' or so pedalling, considering the size of the boat you are pushing and the fact that you are taking it relatively easy. I just did a quick check on google using daft logic's distance calculator, and an hour's journey gets to some nice places from my starting point.

    I would be doing river boating or maybe estuary. It can get pretty tough in the sou'westers on the Swan, though, if you hit the shallows on the N/E side.

    The Hobie stays together and is bolted, so no movement. I will be interested to see how much it (it's not a she yet:) ) does flex. That will be a while: I am looking at up-river work to start with.
     
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