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Thread: Semiscale Footy Catboat

  1. #21
    Join Date
    Oct 2007
    Location
    Leicester, UK
    Posts
    424

    Default Re: Semiscale Footy Catboat

    Flavio,

    Nice boat, fast work and good applied science

    BUT

    What I want to know is - what colour is the dog that must sit in the well area of the cabin?
    I am also working on the concept of a holographic projected helmsman - so that he (or she) does not violate the box-top rule, but is (virtually) there like Graham's gentleman sailor on Pintail.

    Being (slightly) more serious - when sailing downwind the Gaff rig is all that you say - but a cat rig is more off-the-boat-centre than many other rigs (since the pivot point is at the LE of the sail).
    This would (it seems to me) require a little constant rudder to counter the turning pressure of the sail - so if the wind was flukey - and the pilot too slow there might be a tendency to luff up in calm moments, or zig-zag at the best.
    Not a problem (I zig-zag anyway) but the cat rig seems the least balanced of all the common types. Can I move the mast back and have a whopping bowsprit and 3 jibs, please?

    andrew

  2. #22
    Join Date
    Mar 2008
    Location
    genova, Italy
    Posts
    216

    Default dogs and downwind performances

    Andrew,

    I can understand that you are seriously concerned with the well known problem of "helmsman head box rule compliance".

    Anyway, I can reassure you that according supreme court of New York state, a wooden head can be considered as a "spar" and strictly speaking is allowed to be above top of the box.

    Zig zagging is fun.
    Straight lines are boring, and not so good even from tactical point of view ( both combat and regatta ).

    I strongly advise to zig zag both downwind as well upwind ( it seems that this way boats are able to go almost against the prevailing wind direction )

    Seriously speaking, our technical dept. is currently undergoing the final evaluation of a modified stern detail to improve coursekeeping and at same time fto be " hystorical correct" for this kind of boats

    more next time ....

    flavio

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  3. #23
    Join Date
    Mar 2008
    Location
    genova, Italy
    Posts
    216

    Default building news :

    Building is under progress :

    During lthese days I have added a keel case and a watertight mast box.

    Bottom plating has been glued yesterday evening, and during next days I hope to be able to finish the hull.

    One or two interesting things :

    topsides panels have straight line cuts... funny isn't it ?

    easier to plot
    easier to cut
    easier to add chine and deck stringers

    last but not least, years ago I have discovered - by chance - that this is a nice way to obtain beautifully faired fair 3-dimensional curves

    +++

    As I have already mentioned to Andrew, I have been thinking about a modified stern detail to improve course keeping and steering control.

    Adding an outer keel on the transom, will help to have :

    - an almost vertical rotation line for the rudder
    - rudder area moved about 10 mm aft, increasing blade area efficiency
    - a small shift to the stern of center of lateral plan

    this detail ( shown below on "pequod" a non footy model ) is in compliance to box rule ( outer keel will fit inside stern slot ) and has been succesfully tested by Bill Hagerup on his Cobra.

    And it is also hystorically correct due to the fact that has been widely used on old american sharpies.

    have a fair wind :-)

    Flavio




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  4. #24

    Default Re: building news :

    Gorgeous, Flavio! I love the little details on the pequod. Presumably the other pictures are construction photos of your little Brando?

    -Rick

  5. #25
    Join Date
    Mar 2008
    Location
    genova, Italy
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    216

    Default Brando update

    Hi Rick,

    yes you are right, 3 pictures on my previous post are showing Brando's hull, only one of them is about Pequod.

    News :

    hull shell has been finished, during next week end I am looking to add deck and other "semiscale" details : gunwales, rubstrakes, skeg and so on.

    Hull budget, seems to be promising :
    - FCU ( footy control unit ) is 195 gr, using worst case scenario ( heavy batteries, heavy receiver )
    - Hull is now around 40 gr, when finished it should be 55-60 gr
    - Final displacement, most probably, will be within the planned range ( 450 - 500 gr )

    small details have been modified here and there :

    - shorter deckhouse
    - larger rudder
    - a cockpit well will be added both to improve appereance, as well to be used as space for antenna coiled wire
    - due to a designer's small mistake, hull bottom panel is slighty broader than planned 100 mm ( in order to use a single panel of balsa )

    FCU has been preliminary tested on board the hull to check that it will be possible to stow everything on board without problems.

    Keel slot on hull bottom is now longer than needed, in order to allow small longitudinal adjstments of of keel position looking to optimize balance after sailing test.

    By the way ... I have not published hull panel drawing to be used for model building because I feel that it would be unfair to do that before testing this new design .

    Anyway, I confirm that I will do that as soon as possible.

    ... stay tuned

    Flavio

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  6. #26
    Join Date
    Mar 2008
    Location
    genova, Italy
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    216

    Default simple beauty

    Brando is growing, and I hope to enjoy first sail during next weekend.

    Building is smoothly following my very simple plans and ,as psicological booster, I am very happy to know that all boring and disgusting problems related to rc and electrical stuff have been 90% already solved using the FCU concept.

    Today I would like to write few words about the aestetical aspect of this model.

    Simple beauty "workboat style" is just a simple matter of careful design ( nice sheer, flared sections, twisted topsides ), half dozen of sticks here and there, and an additional sunday afternoon of pleasant work.

    No special skills, no cosmic tools ( sandpaper and razorknife only ) are required.

    In my mind the overall effect of these details is very impressive - see below -
    The change from a naked plain shell, to something resembling a true sharpie is evident, and I like to compare it to the difference between an arial capital such as A to same letter using garamond font A

    Last but not least a nice deck to hull joint improve both strenght and watertighness.

    Additional weight ? : between 4 and 5 gr

    Flavio

    Folgore ITA 5
    Brando ITA 14

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  7. #27
    Join Date
    Mar 2008
    Location
    genova, Italy
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    216

    Default hull almost finished

    Stern details modified , as planned, to improve course keeping and maneuverability.
    Now connection between servo and rudder should be easier due to the fact that both rotation axis are parallel.
    Arrangement has been designed to use both whipstaff method, as well the usual push-pull rod.
    Push pull is easier and simpler, but whipstaff has several technical advantages.

    Forefoot has been carefully shaped into a nice curve to connect stem to bottom.
    Most probably this is not so important from performances point of view, but without doubt, once again this is a nice addiction to a pretty look.

    A deckhouse ( or coachroof ? ) has been build together with a cockpit coaming, its sides are vertical, straight lined and at 90 angle each other to simplify building.
    The roof will be removable to install/remove the FCU block.

    Dimensions :
    Brando has been designed and built to the limit of box rule
    Max beam is 151 mm
    Lenght overall is 304 mm

    ( 1 mm of safety margin for varnish :-) )

    Weight is - so far - 64.8 gr( a well known "racing" footy built using titanium,carbon fiber, kevlar is 79 gr - empty - )
    Taking in account varnish, and missing details weight, final shell mass shoud be comparable.
    A good starting point to achieve "decent" sailing performances.

    Things to do
    varnishing
    keel and rudder
    spars sail and rigging
    final check
    sea trials


    Weather forecast for next weekend are not nice, but without doubt I am currently proceeding almost in accordance to my basic previsions.
    Sea trials are to be expected soon.


    It would be nice to release a Mk I version of plans in order to have , I hope, at least few of these model taking part to Mystic Show Footy Race
    There are no doubts about Brando compliance to the 100% wood rule :-)

    Flavio



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  8. #28
    Join Date
    Mar 2008
    Location
    genova, Italy
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    216

    Default Ultralight Brando

    Yesterday evening , I have re-read all the posts of this thread ( now almost three weeks old ) .

    Quoting Rick from his wish list : " I'm obviously not looking to win regattas, but rather have fun , cute little boat to play with on lake, and on the off chance that I ever make it to a footy event, be able to "compete" ...

    Even if I feel confident that this catboat footy will be a "decent sailer" I have been thinking about its race potential, and I have found a specific weather condition where Brando could be unbeatable.
    Hull bottom is so wide and flat that Brando should be able to stay upright without ballast keel ( yes ! ) even if in this case it would be impossible to recover from a 90 capsize.

    Making simple calculations it seems tha a light rc version of this footy should be able to have positive stability at 90 heel using about only 50 gr of lead ( 2 oz - more or less ) , kissing the water with a displacement between 250 and 300 gr only.
    Sailing in this ultralight displacement trim , it would be possible to withstand wind up to 5 or 6 kts ( not a gale, frankly speaking ) with a sail area to displacement ratio 150% higher than usual , and - in turn - an impressive speed both upwind as well downwind.

    An interesting option ( still to be confirmed on the water ! ) for very very light weather race zones ( Italy or Florida .. )

    Definetely not suited for the Bikenhead 30 kts scale storms...

    See enclosed computer screen shots : transom stern is high on waterline, and forefoot also is above static waterlevel.

    One thing more to be tested during sea trials :-)

    Flavio
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  9. #29
    Join Date
    Mar 2008
    Location
    genova, Italy
    Posts
    216

    Default balsa

    Due to very bad weather forecast for next sunday, designer, builder and skipper have agreed to postpone Brando delivery and sea trials.
    Most probably they would be happy to have only static flotation test to be carried out during weekend, in my bathroom facilities.
    Anyway even if building activities are a bit more relaxed, other small details have been added here an there.

    I hope it would not be too much out of topic to spend few words about raw balsa

    In the past I have experienced a very uncomfortable feeling discovering that, notwistanding my careful attention, few of my model hull were unbelivably twisted .
    Now, due to improved technology as well a deep experimental research, I have been able to have a better understanding of this mystery

    1 - balsa specific gravity is very very very variable
    I have found on different planks 1000 mm x 100 mm x 1.5 mm weights from 16-18 gr up to 40-42 gr
    In other words specific density change from about 100 kg/m3 up to over 250 kg/m3

    2 - wood stiffness is almost exactly related to specific density

    3 - wood properties for balsa wood are different within the same plank too ( !!! )


    Example

    I have cut first topside panel of Brando from a good, smooth and dry plank , from a good manifacturer ( Graupner ) : Its average density was about 200 kg/m3

    - first topside : 4.1 gr ( good )
    - second cut : 7.3 gr ( ! ) due to so large discrepancy I have cut a third topside
    - third cut : 5.6 gr intermediate value
    Using advanced methods ( two books, and two calibrated banana yoghurt pots ) I have done a test to check different bending of these topsides and result are very impressive - see below -

    Deflection were absolutely different.

    Conclusions,

    1 - building a model hull using very thin balsa panel, can lead to unpleasant ugly hull shapes due to unsymmetric ( port and starboard ) stiffness of various parts.

    2 - problems can be avoided using a cheap digital kitchen scales, as well making preliminary simple stiffness test ( beer cans can be used instead of yoghurt for thicker balsa :-) )


    Next time few words about rudder and keel ( I hope )

    Flavio
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  10. #30
    Join Date
    Mar 2008
    Location
    genova, Italy
    Posts
    216

    Default rudder, varnish and other things

    I am taking advantage of a lack of real deadline to "waste" time adding more decorative details, frankly speaking, absolutely useless from technical point of view :

    - A detailed companionway
    - A tapered laminated tiller
    - Few additional bright coats of varnish


    ( by the way, varnish weight is about 5 gr each coat, decreasing from first to following layers, most probably due to initial balsa adsorbtion and progressive saturation. )

    Rudder

    I have built a first rudder, may be I will do another one - slighty different -after first trials.

    Span is almost to the maximum of rule box ( 200 below top of the box )
    Chord is about 40 mm
    Thickness is 4 mm, as a compromise between low drag, and high lift

    On the leading edge there is "dent" to achieve a partial balance moving rudder area closer to pintle pivot line ( and in turn to decrease torque on the servo )

    Overall side area is about 15% larger than on my Folgore, to take care of the wild steering abits of catboats

    The nice shaped tiller will be linked by a whipstaff to an hitec HS - 55

    Blade material is poplar plywood : light, soft and inexpensive

    Pintles and gudgeons are home made using brass wire

    Next steps :

    Rudder linkage, and keel fin blade

    Flavio


    ps problems to download latest pictures today , I will try again later
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