... the ROCAT story

Discussion in 'Boat Design' started by cristofa, Apr 22, 2014.

  1. cristofa
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    cristofa Junior Member

    .
    ... I thought it was about time I told the story of the birth, development and end (so far) of the ROCAT rowing catamaran, so I have put it up here

    http://www.cristofa.co.uk/-/galleries/rocat

    ... I hope it contains some useful information and I will be happy to answer questions here or on the website (if I can get the commenting to work)
     
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  2. DCockey
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    DCockey Senior Member

    Thanks for the post. It's a very interesting story.
     
  3. SukiSolo
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    SukiSolo Senior Member

    Nice product, hell of a lot of work, well done. Hope it still goes somewhere, it deserves to. I know those seas off Penzance, and yes you do get a nice Atlantic swell when out a mile or two. Glad to see someone else has had serious stick out problems, I've part broken a couple of plugs before now. Unfortunately yours was a lot more expensive. I think I'll resort to testing smaller bits in future to actually test the release prior to a large part.

    Good luck with future projects as well.
     
  4. alan craig
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    alan craig Senior Member

    Interesting development story, I hope you find a buyer for it. The one piece hull manufacture looks very valuable if it is unique but it's hard to quantify what is saleable as it is now in the public domain. Also the hull might have a future with forward facing rowing, pedalling or electric power.
    I once developed a back packable open canoe to the prototype stage and didn't get any further so I have some sympathy for you.
     
  5. cristofa
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    cristofa Junior Member

    ... thanks David

    SukiSolo, what really pissed me off about the great stickup was Marbacote's arrogance. We knew what we were doing and used the product correctly so, the fact that it didn't release clearly pointed to a bad batch. But they didn't, apparently, give a dam - they knew we were small and couldn't afford to do anything about it.

    Alan, because I started the project from scratch with no pre-conceived ideas, I looked very hard at the possibility of forward-facing rowing. However, I abandoned it because I reckoned the necessary extra lever reduced the efficiency too much - OK for pottering though.

    Here's a link to some rough sea trials in proto-2
     
  6. SukiSolo
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    SukiSolo Senior Member

    Back in the early 90s' when we were working with some serious CADCAM boys, who made prototype press tools for the automotive industry, I saw some bad 'stick out'. They were using the so called correct wax and quite thick layups to allow say 100-200 parts in 2mm (SWG14) steel and even thicker at times. In the end they used Carnauba wax then PVA, more carnauba then more PVA so that gives you an idea that these problems are not new. Most of their tools were carbon/kevlar and some glass. Usually they worked fine but some of the steel parts presses were pretty powerful say several tens of tons, so they would occassionally break. Impressive ground table though, big enough to put a car or pickup on and measure deflection after crash testing.

    Since then, and after trying other release agents, I have ended up in a similar mode especially if the moulding involves epoxies with whatever fibre. Some of the spray ones (agents) work well if not massively curved and almost self contained but stuff close to say a semicircular section - like half a hull, can be a pain. Polyester with gelcoat is much better in my experience but neat epoxy straight on the surface of the tool can give problems. Having said that about Polyester, I will not use Beeswax as it is guaranteed stick out as two broken plugs can attest. One wrecked mould with epoxy, even with the carnauba but no PVA. Hence I get a little paranoid...;)
     
  7. upchurchmr
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    upchurchmr Senior Member

    I saw the length is 5M, the weight is 33KG.
    What is the width overall and the width of each hull?

    Mostly, what was the cost?

    Very nicely done work.

    I am puzzled at the need for the seat tray or whatever you called it.
    And also the benefit of the two armed mechanism to carry the oar locks.
     
  8. cristofa
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    cristofa Junior Member

    SukiSolo - am interested to read the automotive industry used composite tooling for press tool prototypes. On the whole, I guess we were lucky that we had very few release problems and we used epoxy throughout.

    upchurchmr - the overall width was 1.8m and the hull width was 250mm. The boat cost £3,800 for the first 10 early adopters and that was due to rise to £4,200 thereafter - these prices were not enough to cover costs for small-scale handmade production.

    I'm not sure I understand your puzzlement over the seatdeck - that's where you sit; it also provides a platform for the rigger and a place to stow your kit.

    The rowing mechanism is entirely novel and is more efficient than the conventional sliding seat stroke - it also reduces the risk of back injury. Have a look at the animations in the proto-1 section of the story, and here in the original website. The significant feature is that the hands are stationary during the power stroke and your back is properly supported.
     
  9. upchurchmr
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    upchurchmr Senior Member

    What I don't understand is the complication of the crossarm coming off the foot board/ roller, thru a link to the articulated arms beside the rowers seat compared to the Virus setup: http://www.rowvirusboats.com/virus/kataram.html
    Sliding riggers are not unknown, I built one myself (not anything like the finish of yours) and it worked well, but did not have the complicated linkage. I would like to know the benefits of your design.
    Your animation clearly illustrated the motions used in a sliding rigger, but it fundamentally is the same as the Virus and Piantendosi sliding rigger motion. Am I missing something?

    I do appreciate the significantly better construction of the hull compared to the Virus and the reduced weight (33kg vs 38)

    Again the seat deck offers significant protection from waves, but is it necessary? The Virus does not have room for stowing kit, I understand that point. The Virus will have significantly less weight to provide seating.

    I'm interested in your comparison / comments.
     
  10. Squidly-Diddly
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    Squidly-Diddly Senior Member

    they should broaden their target customer by touting the wide cat stance for other on water activities, like fishing, birdwatching or picnicking.

    even include add ons for small motor or sails.
     
  11. cristofa
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    cristofa Junior Member

    ... yes, upchurchmr, you are missing something! The ROCAT rig is emphatically not the same as the conventional sliding rigger as found on the Virus and the Piantendosi*unit.

    The sliding seat and the sliding rigger were both invented at about the same time in the late 19th century, and the geometry of the two strokes is exactly the same. In spite of the fact that the sliding rigger arrangement is better than the sliding seat - because the rower's mass is stationary relative to the boat - the sliding seat prevailed. But, from an ergonomic point of view, both strokes are a disaster because all the effort generated by the legs is applied to the oars via an unsupported back.

    With the ROCAT rig, the legs are pushing against the seat back (like a leg press in the gym) while the arms anchor the stationary oar handles during the power stroke. Meanwhile, the legs' force is transmitted directly to the centreline of the oar (so it doesn't twist the rigger) which is acting as a third class lever during the power stroke. Once the legs are extended, the rowlock becomes the fulcrum and the oar becomes a first class lever for the finish. This sounds much more complicated than it is, but it makes an enormous difference. I permanently damaged my back rowing competitively in my teens and cannot row a sliding seat boat now, or an indoor rower - but I can comfortably row the ROCAT for hours on end.

    And re the Virus Kataram - a Ford Escort with a BMW M3 are both cars which have 4 wheels ...
     
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  12. upchurchmr
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    upchurchmr Senior Member

    Cristofa,

    I am a mechanical engineer.
    The only difference I can see between your unit and the others is that you have too many parts.
    The pivot for the oar is always at the same place. Wether you move the pivot directly thru a set of cross arms (Virus or Piantendosi) or your method is immaterial. The force is still balanced from the blades to the pivot to the handles.

    In fact the forces are actually self contained in the oar/ persons body.
    There is no need for a back to the seat, except for comfort when leaning into the stroke. The rowing force is transmitted to the boat thru your seat, quite well. In fact if you are not leaning aft during the recovery, then fwd during the power stroke, you are not applying as much power as is available.

    I understand if you have a back problem you might not want to pull with your arms, but I have continuing lower back problems and have no problem with the stroke in a unit similar to Virus, etc. "Unsupported back" is a red herring for the majority of people.

    My interest in your explanation was to understand why your boat costs so much.
    Too much mechanism certainly hurts, as does things like carbon fiber and custom made molds.
    I have a strip planked (wood) catamaran with a rigger similar to the Virus. Its 11' long and weighs 50#. I believe it could be reasonably built 10# lighter. Works fine, in a lake, the ocean would probably require your longer length.

    The complicated flattened aft hull seems to me to be of little use, even my 11' boat does not pitch thanks to the sliding rigger.

    Now when I am trying to understand the principles of how the boats work there is little reason to talk about BMWs (which I like a great deal)

    You certainly have a high quality product, much better than anything I have built. No criticism was ever implied.

    One jerk in my buisness is quoted as saying "better is the enemy of good enough". But it is a good point whether we are talking aircraft or rowing catamarans.

    Good luck with your project, I won't bother you any more.
     
  13. Skyak
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    Skyak Senior Member



    Thanks for sharing this product development story -very thorough and candid. The early shows got me thinking that this was a big buck program but as the development story continued I anticipated that there would not be a happy ending financially. I have ideas of what should have been done and what can be done but the former is useless now and the latter seems to be all too abundant (from sources that are not investors at least). If you want to hear it (privately or otherwise) let me know.

    If you are looking for investment or to sell there is a forum here.

    http://www.boatdesign.net/forums/marketplace/


    About the swing-arm addition to the sliding rig -I wondered why myself. Sliding rigs are rare and I have never seen the swing-arm. It does counter the lateral movement of the oar stroke which makes the pull very linear and nicer than crossing hands. It got me thinking about the rest of the mechanism -does it have to be that large and could it have a more desirable leverage curve. If the mechanism provided leverage the oar could be shorter.
     
  14. upchurchmr
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    upchurchmr Senior Member

    Skyak,

    Nice point about the swing arm allowing the hands to have a linear motion.
    I missed that.
     

  15. Skyak
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    Skyak Senior Member

    It's a bit subtle as an onlooker but I think the linearity would be very welcome to the rower.

    Limiting the backs contribution to the stroke is a big deviation from 'normal' rowing that is competition focused. But this is not a big market loss because they reject the sliding rig anyway because it is superior. Are similar back problems common among competitive rowers?

    The one thing I agree with is that the best plan for the rowcat tooling as designed is to go upmarket. The prices of the early units were too low -I think you should refer to them as Beta testers. The production cost should be examined to be sure it all results in customer value, but the big hurdle is 'customer acquisition cost' -margin for high end sales. I would love to do the sales and marketing plan because it is high end. One design racing and a cheap version are things to consider AFTER the high end is an established success. Even mentioning them before makes the plan seem unfocused.
     
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