... the ROCAT story

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

  1. cristofa
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    cristofa Junior Member

    ... some interesting points have been made - it's late here so I will respond tomorrow
     
  2. rwatson
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    rwatson Senior Member

    I am curious as to why the 'rowing pod' is not self bailing ?

    Whats the point of the solid transom ?
     
  3. cristofa
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    cristofa Junior Member

    ... the seatdeck has a 6mm drainhole to let rainwater out - seawater very seldom comes on board. And the seatdeck shell would have to be much stronger/heavier if it didn't have a back.
     
  4. cristofa
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    cristofa Junior Member

    In my story, I have tried to explain the processes by which I arrived at the eventual solutions but, in the light of some responses, it is evident that some of my explanations lack clarity and need to be revised. This was a long, hard, trial-and-error and intuition based design and development project, and nothing exists on the boat by accident.

    The story is here because I thought it might be of interest to the forum, and that some members might learn something from it - as I would from the anticipated discussion and informed, constructive observation and criticism.

    I do realise that the story is long and not everybody will want to plough through it, so questions will arise which are covered in the narrative - that's fine, I will do my best to answer any queries.
     
  5. cristofa
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    cristofa Junior Member

    This is a quote from Rowing Injuries -Identifying and Treating Musculoskeletal and Nonmusculoskeletal Conditions THE PHYSICIAN AND SPORTS MEDICINE VOL 28 - NO. 4 - APRIL 2000

    "Low-back pain. The rowing stroke puts extraordinary pressures on the low back. The back begins the stroke flexed, and during the middle of the stroke the back opens up, but remains flexed, in a motion similar to an incomplete dead lift. Loading the back in flexion places large forces on both the back muscles and the disks. In one review (3), low-back and knee injuries were the two most common injuries found in collegiate rowers."

    ... the full report can be read here - back injury is a serious problem for rowers

    ... agreed - I called them 'early adopters' but they knew that they were part of the development process. As you can imagine, I didn't have the resources for extensive 'beta testing'.

    ... OK

    ... again, as you can imagine, that was the subject of much discussion! I am confident that there is high end market potential - in fact, one of the orders was for the ROCAT to become deck jewellery on a very large new super yacht - but, relative to the sales potential of the core boat, I believe that market is very small. Which would net more is, clearly, the crucial question? I believe the cheap boat also has huge market potential, but the margins would be very tight.
     
  6. rwatson
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    rwatson Senior Member

    Please note I didnt say 'transomless', I said 'self bailing'.

    The 'seawater very seldom comes on board' is not a valid statement in my experience - you can be on a millpond until some powerboat 100 yards away sends a half metre of water at the wrong angle. - and all of a sudden you have a bathtub.

    Also,in previous descriptions you talk about, and illustrate quite rough conditions for operation. A small breaking wave, say as when you are forced to land in small surf - would make the experience very uncomfortable.
     
  7. upchurchmr
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    upchurchmr Senior Member

    6mm is smaller than holes we use in aircraft for drain holes.
    And those don't take care of waves coming in like Watson talks about.

    The picture of the boat going into a big wave is pretty impressive, wish we could have seen a video. But it looks like the seat back will deflect most of a head on wave. Waves from the side and rear would be my concern, again repeating Watson.

    As much as you disdain the Virus, it will not fill up.
     
  8. cristofa
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    cristofa Junior Member

    rwatson - I'm afraid this is down to semantics and language - when you said "Whats the point of the solid transom ?" having just talked about the 'rowing pod' AKA the seatdeck, I thought you were talking about the back of the seatdeck. So what were you talking about?

    What I find very strange, and completely fail to understand, is how someone who has not seen the ROCAT, let alone rowed it, let alone spent time in it in a force 7 among large Atlantic rollers with whitecaps, can flatly contradict the designer and developer of the craft who has spent many many hours rowing it in all sea states and weather?!!!

    In all the time developing that boat, more rainwater arrived in the seatdeck than seawater - really. As I said above, nothing on the boat is there by accident - every detail was considered - can you not see that, if the seatdeck had needed more drainage, it would have had it.

    And the point about a forced landing in surf - the ROCAT is not designed to operate in surf but, if for some reason you were forced ashore through some surf, water in the seatdeck would probably be the least of your problems.

    upchurchmr - did you look at the video linked to in post#5?
     
  9. rwatson
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    rwatson Senior Member

    Sorry if you got confused, but there is only one transom that can catch water on the boat - and that is the back of the 'seatdeck'

    I have attached a photo from your website - showing a wave you made it over.

    It could easily have been a bit higher or crested more, then the seatdeck would have filled up. Its not down to how perfect your design is - its just physics
     

    Attached Files:

  10. cristofa
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    cristofa Junior Member

    ... there is nothing in the definition of 'transom' relating to catching water, however, supposing that to be the case, when you asked "whats the point of the solid transom ?" I replied "And the seatdeck shell would have to be much stronger/heavier if it didn't have a back." How does that not answer your question?

    ... that is absolutely not the case - I was there! (Also, bear in mind that the production boat has 50% more buoyancy than the boat in that picture to cater for heavier rowers in the American market.) I have been out in some very big seas and I have never felt that 'this is getting scary - perhaps I shouldn't be here' - the boat just lifts to every passing wave and water does not come into the seatdeck.

    When developing a product like this, you don't suddenly go out into a 3m Atlantic swell and hope for the best - you gradually gather confidence in the boat's performance by exposing it to a wide variety of conditions. This is why I find it so very odd that, with no experience of the boat whatsoever, you feel qualified so glibly to dismiss my hard-won knowledge.

    ... did you look at this 'rough sea trials' video

    then there's another here of the boat in a more tranquil setting which shows the stroke
     
  11. upchurchmr
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    upchurchmr Senior Member

    Cristofa,

    I did view the video.
    The boat handles those waves well, which I personally expected from my own experience.

    That particular sea did not threaten to fill the seat deck at all, but there was not much of a breaking sea. It also did not represent the wake from a heavy power boat.

    Its always possible to find a worse sea state, its also not possible to design for every condition, and its reasonable to not go out in worse conditions.

    That boat works well, I've stated a concern for really bad conditions, let me leave it at that.
    In fact, my boat has nothing to protect the rower from a really bad breaking wave, I have been concerned about that and was just trying to understand the difference between yours and mine - and a reasonable "compromise".
     
  12. SukiSolo
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    SukiSolo Senior Member

    I can vouch for the state of the seas off Penzance and Mounts Bay. In fact almost anywhere exposed down in the SW of Cornwall or Devon. It is a true Atlantic swell that has crossed the continental shelf but still has quite a punch to it. That Rocat handles those waves well, and I think in many ways that area is a good test bed for such a craft. Although I have not witnessed a full hurricane strength there, I have sat through a Force 10 and it was er, interesting. Fortunately in the good confines of Penzance Sailing Club.

    I have built conventional rowing shells before and I quite like the static seat concept. Mainly because as stated the weight transfer allows a smoother less pitchy ride. It also allows potentially slightly different hull forms, maybe even planing?

    Cristofa, those automotive tools made parts whereby the vehicles were crash tested and measured. It was used partly as validation for FEA analyses and also to genuinely see what happens. As most of us know, with the best will in the world, sometimes (probably most) some small unexpected weird thing occurs which had hither too been overlooked ;) I am a great believer in prototypes and testing and not a fan of get it 'right first time' straight from the drawing board/CAD system, no testing. Not that it will be far away, just nearly always a few small niggles to sort. Your process shows that up perfectly, a good example of correct product development, thanks for sharing.
     
  13. cristofa
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    cristofa Junior Member

    Posting the ROCAT story here has been an interesting experience for me - I have dipped in to boatdesign.net before, but I have never put up something important that I felt would genuinely intrigue and inform.

    When I made the hulls in one piece, the process was unique - I suspect it remains so - is nobody here is interested in how it's done. Using epoxy primer in the moulds instead of gelcoat is also unusual - does that not raise some questions? And what about casting foam blanks as cores for infused carbon braid parts in closed moulds - (almost) everything was produced by vacuum infusing epoxy in closed moulds?

    Instead, I am expected to defend the size of the drainhole in the seatdeck by someone with no experience whatsoever of the boat - I would be very interested to see chapter and verse of the physics that decrees that the boat will inevitably, in due course, be swamped.

    So, only slightly off topic, here are two pictures of what weather can look like where I developed the ROCAT - the first is of Penzance harbour and the second of nearby Porthleven - there are days when I would prefer to watch the storm than be out there in it.
     

    Attached Files:

  14. cristofa
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    cristofa Junior Member

    ... the slip by the sailing club is the one I used most of the time during the ROCAT's development. Even when it was blowing a hooly, it's very sheltered inside Penzance harbour so I could launch there and then ease out of the lee of the lighthouse pier into the rollers knowing I could duck back in if I felt unsafe - I never did feel unsafe!

    Sukisolo, if you are down this way again, do get in touch - contact details on the website. Oh, and if you like storm pictures, there are some more in the coast and sea galleries of the photography section - this year has been especially good for storms!
     

  15. SukiSolo
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    SukiSolo Senior Member

    Thanks very much Cristofa, I like a lot of your work and it would be good to meet. I was down at Mounts Bay in '12 (for a week) and we never got a single SW or S big swell, believe it or not. Mind you sipping a pleasant English wine whilst having a private viewing of the Mount was a pleasant way to spend a very warm summer evening, watching the night sea breeze set in :). Convivial company of a lot of good sailors and watermen.

    Hope to be down that way again. I don't mind the drive too much, passing Stonehenge at 2.00 am I wondered where the traffic was!. All about timing, come summer holidays.

    Casting the cores is not that unusual I believe, I'm sure I've seen it. Certainly it is a process I have considered/designed for, but not marine. Not all are post blown. You may have a trick for the moulding of certain foils used on sailboats. Some are very crude by modern standards and could benefit from your thinking.

    I enjoy all types of craft, and am always interested in the thinking/concept and trying to get behind it. There is a wonderful quote from Le Petit Prince (St Exupery) which says something along the lines of 'all the work, all the blueprints and time for something so simple' . It sums up a lot of good design, simplicity is so hard to achieve, but so worthwhile.

    Yes, we have had a very stormy winter. Nothing quite like Oct 87 but we don't get 100mph often, but equally we don't get too many 70mph+ stuff again and again in a couple of months. Personally I've only lost a chimney cowl and an aerial mounting bracket but that is light damage. Not got flooded, no serious power cuts (my woodburners anticipated those), no food shortages etc, escaped lihtly. Mind you a chainsaw in the car was an essential tool back in Dec or Jan for fallen timber...;)
     
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