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Thread: Inflatable Proa

  1. #71
    Join Date
    Mar 2018
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    London, England, UK
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    Default Re: Inflatable Proa

    Quote Originally Posted by tink View Post
    My mate has a Gumotex Polava and it is awesome, he takes it down places that makes my ply canoe complain with strange creaks and needing a paint job. That said you could replace yours another six times for the price of it. The more expensive canoes are a lot heavier and because of the pressure have a very big pump which may be an issue flying.
    I see the Gumotex has solid seats across the hulls - that is one of the advantages I've been expecting from my design with a perimeter of gunwale planks - it would be strong enough to stretch a canvas seat across (eg. from a director's chair) and would help to constrain the width (when on water it's a hell of a lot wider than the spec says, and it's quite inconvenient when trying to paddle hard).

    The Sevylor also needs a bigger pump than the one they sell - but not because of high pressure - because of the lack of it - the huge floppy hulls need a huge volume at 2-4 psi (actually much the same as the Gumotex). I find it's a lot quicker and actually less effort to just use lung power (though the extra humidity won't do many favours).

    What I really need to make & take is a bellows with a 1 inch diameter nozzle to fit OVER the valve (the iron-age carrier-bag type bellowspaleometal blogspot.jpg has no bulky plates and would be ideal).

    The Gumotex weighs twice as much so probably costs 3-4x as much to make - but because of the semi-professional market they need to charge 7x as much for making small batches of a specialist product.

    As usual I want something in between.

    While looking that up I saw Sevylor have brought out the "Adventure" - in 2012 apparently but the first time I've seen it. With much thinner sides made from 3 stacked cells and a polyester outer skin - at roughly twice the price (under 200) it's quite close to my brief - I'm quite tempted, it would be a hell of a lot easier to paddle hard - but it's 4 Kg heavier which might translate into more difficulty to squeeze into hand baggage - the Riviera is quite tight in the cheap bag I use, and it might be pricey getting something 1cm bigger all round and bang up to the limits - and it might still be impossible to fit it in.

    I'm still considering tailoring a tarp sleeve here to fit round my old one and constrain it better (and give more abrasion resistance) - I'm going to have to think about this a lot... Welding it is the obvious choice.

    Anyway, I will be saving the no-kayak designs for after I've got my old kayak sailing well - I might just want to go on and prove I can sail a lilo or a rubber ring with just junk (though I'd definitely clamp a tarp pocket around maybe 2 or more) maybe just cram empty pop bottles into a cylindrical tarp bag 10' long like a giant sports bag! (I'm a big fan of that catamaran "Plastiki").

    Regards.

  2. #72
    Join Date
    Dec 2011
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    North East England
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    1,286

    Default Re: Inflatable Proa

    Came across this and thought of your project, I like the way the frame tucks under the tubes of the inflatable, look at the videos

    https://www.canoavela.it/inglese/index.asp

  3. #73
    Join Date
    Mar 2018
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    London, England, UK
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    Default Re: Inflatable Proa

    Quote Originally Posted by tink View Post
    Came across this and thought of your project, I like the way the frame tucks under the tubes of the inflatable, look at the videos

    https://www.canoavela.it/inglese/index.asp
    Thanks Tink - I'd say that's a Sevylor Riviera Plus - but a different colour - the velcro pads are in exactly the right places to support the 2 adult + 1 child seating.

    That means they have added 14Kg of boards and aluminium tube.

    It does look good though.

    But it reminds me of another reason I chose a proa approach - it means I can put the mast on one of the hull gunwales (I've chosen the windward one to minimise luffing moment) - so the cockpit is clear for shunting (though I will be ducking a lot even if/when I go for 2 masts) - but if I was tacking I'd still try to keep it clear - at one point when I was still trying this kind of direct approach to the problem I seriously considered stepping the mast across both gunwales as an inverted Y so I could slip under it when needed.

    Incidentally, I found your comments very helpful about the CofP being forward of the sail's geometric centre. I will have to be especially aware of this because getting it wrong would mean the sail lurching leech-forward - and being nearly right would still mean no feathering at all or a massive elevator to self-set.

    This consideration changes everything - it means the A (∆) sailplan for a 2-master is completely unworkable** and the B (◄) sailplan for a 2-master is workable if I move the mast from the geometric centre at 1/3 to the midline of the sail which is actually at 25% average chord and still won't hit the other sail when the masts are 6' apart.

    (** in the diagram 04-01-2018, 11:32 PM - the post # numbers have just re-appeared - it's #63)

    On the other hand the B◄ gives me the headache of nowhere to put an elevator except above the sail like in your lateen diagram with it's baby (elevator) on the yard above. It would need a very stiff yard because a tail elevator is always a tail wagging the dog.

    Again, as you suggested, a single elevator controlling both sails would be good, but the only foolproof 360 degree solution I can think of is to have rotating masts carrying sprockets linked by a bike chain - ideally under the deck (which would be a lot easier on a wooden boat).

    I may have to schedule the self-setting 2-mast rig for 2019... Unless I cross my fingers and assume the sails will always rotate exactly together - so the tail of one only needs to go past the tack of the other. I think that needs a diagram - but at least it's something I'd happily trust to scale model tests...
    Last edited by Saedilla; 04-29-2018 at 04:02 PM.

  4. #74
    Join Date
    Mar 2018
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    London, England, UK
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    Default Re: Inflatable Proa

    I meant to say the Canoavila Boipeba (apparently some kind of turtle) is obviously built around a Sevylor Tahiti Plus (not the Riviera - that has no + version anyway) and Tahitis do come in the same slightly odd green that's in the Boipeba assembly video, but not the more festive livery shown in the main picture.

    I'm still trying to make a goer of the "< delta" format "glider" rig (for want of a better term) - because using elevators to trim a bellying sail (even a tight one) is a bit of a nightmare - the angles are all over the place, so I'm thinking of putting a fairly tight soft envelope around a complete triangular frame (with a tapered trailing edge).

    Obviously this adds a bit of weight - but surely someone has tried this before?

    I know I'm "all ideas backwards" but how far off-beam am I really?

    My own diagrams below make it look like I can solve all the remaining trim problems this way - so please criticise them as much as you can - there must be something wrong here (and I'd rather not find out the hard way)...
    Proa bellying sail glider.jpg

    I'm still concerned that I'm sure I've seen twice as many different self-setting rigs on TV documantaries than there appear to be on the whole WWW - that can't be right can it?

    Thanks.

    PS. have a look at this soft gaff wing https://www.wharram.com/site/how-we-...m-wingsail-rig
    PPS. I might consider linking two sails on two masts with a push rod - if I can kick the push rod off in emergencies - I will have to do those model tests before I get any handle on how bad getting backwinded might be.

  5. #75
    Join Date
    Dec 2011
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    North East England
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    Default Re: Inflatable Proa

    Thought the different sail angles are a nuisance I am sure the sail and tail will eventually find a point of balance. This will cause more drag but I am sure it will work. That said I have only ever seen the self trimming sails using ridged wing sails which don’t twist.


    I still think your bigger challenges are

    1. eliminating friction to make the whole rig pivot freely. This is not just a case of having good bearings but also centre of gravity in line with the bearings.
    2. having the true centre of effort also in line with the pivot in all conditions. This will only be achievable by experimenting and any adjustments will effect the centre of gravity above
    3. developing enough force from the trim tab either big area of a long way from the sail



    I think you have reached the point that the design has be done with models. Just scraps of wood and card no more than 12 inches big will be fine. I learned the hard way that things that look fantastic on paper won’t work. Ideas develop much quicker and with better results in model form


    Not sure what you’re searching for but I put into google
    ‘Self trimming sails’ and found lots of good stuff.


    https://youtu.be/62GTpuC5a1Q


    http://www.sailwings.net/article.html


    https://pdfs.semanticscholar.org/52c...282.1525152716


    Anyway good luck and keep enjoying what you are doing.

  6. #76
    Join Date
    Mar 2018
    Location
    London, England, UK
    Posts
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    Default Re: Inflatable Proa

    Thanks Tink,

    Sorry to be so late replying, but family birthdays came first and the blitzkrieg summer of "The Year Without a Spring" was killing my seedlings so they came second.

    I will be taking your advice on using small models for the rig - I need to find the most compact way to self-set a soft Delta wingsail - I'm still hoping to fit two on a very small kayak! Scaling down a rig throws up few problems (though as you pointed out, friction doesn't show well).

    However, when it comes to testing whole-boat handling the square-cube curse was so strong at 1/6 scale that I won't try that again. Setting 1/216 on momentum and static stability moments against 1/36 on sail area heeling/pitching moments was just crazy.

    Since it's a 10' boat I think I can manage 1/3 scale for final tests - which will make momentum effects much more 'real'. Incidentally when under sail the full size one has a name: "Cursory Empiricist" in honour of the late, great Ian M Banks' characters-who-are-starships. I still call 'it' a she - some proa rules are made to be broken.

    I agree that there's enough self-set stuff out there to be getting on with, but there's a lot less than I hoped - especially images that would help me get a better feel & more holistic grip on the whole issue. Other people have commented on how little there is - apparently Randy (Sizzor) Smyth's wingsail went into a patent-pending blackout, not sure if it is out yet.

    An interesting post on the Hobie forum by 'fusioneng' (whose other posts are absolutely solid) suggests that sailmakers and many of their big customers have always done their best to play down 'soft wings' - the makers may be happy they use more sailcloth but their old machines aren't capable of handling a novel 'cut' (Wharram's soft gaffwing suffered endless delays from this)...

    I also feel paranoia creeping in when I remember how sniffy & snarky the 'experts' were in the 60s when wingsails appeared - prompting endless bad press from the hacks utterly reliant on them for both copy and advertising revenue. I was a keen teen (just) aero-modeller at the time & it looked really suspicious - but I was still put off trying the new ideas on my land yacht models.

    Google searches throw up so much commerce and clickbait that you need to dig very deep, but it is now possible to find some pretty good science in papers from the 60s showing wings did work then, and clearly demonstrated all the advantages we can see now.

    I suspect that if the America's Cup hadn't gone multi-hull we'd still be getting a drip-feed of technology - probably very like what's currently dripping into windsurf sails. For a spell I worked as a buyer in top-end IT, so I'm very familiar with how big cartels use 'the drip' to maximize (and stabilise) their profits.

    Funny that, the new AC75s are now trying to 'sell' us computers to go with soft wings - two drips linked as a couple make a merry dance, but it's just another way to get us to pay much more for massively diminishing returns while taking our eye off the benefits of the happy medium.

    Regards.

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