Yrvind

Discussion in 'All Things Boats & Boating' started by Manie B, Aug 16, 2011.

  1. Manie B
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    Manie B Senior Member

    Moe Joe I fully agree with you on the "swim platform"

    I had a good look at that 3D drawing that Michael Tatschl had made and that drawing clearly indicates that the swim platform is now becoming a hull extension.

    Plain and simple that is not a ten foot boat anymore.
    My problem with the new extension is that an "add on" of this magnitude points to inadequate planning.
    When you sit down and spend months drawing and planning a new adventure you must get your ideas down properly, and not "add on" because "add on's" have a history of becoming abortions.

    I am still profoundly impressed with this whole adventure and love the work Sven does but the "hull extension" is not in the spirit of AIT

    I include photos of what I call a swim platform.
     

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  2. Angélique
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    Angélique aka Angel (only by name)

    Yes, it would have been much stronger if the buoyancy box extension was built as an integral part of the hull. Sven builds very strong but in the small chance the seas smashes the swim platform and buoyancy boxes off he loses the rudders and the hull might be severely damaged by the broken out attachment points . . . :(

    P.S.

    I think this is Sven's explanation: ‘‘ I will take advantage of the (10') rule ’’

    But is this still a 10' boat . . :confused:
     
  3. Angélique
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    Angélique aka Angel (only by name)

    Four of them looks to be cats and have most of the swim platform within the hull length.

    The swim platform here looks a bit high to be comfortable and has a folding ladder which in up position is not accessible from the water which is bad for a solo MOB.

    [​IMG]

    Alternative is the swim platform just above the waterline with a cut-out for the rudder and with hinge points attached to the hull for folding up vertical against the stern and lowered + hoisted by a rope on the corners, operated from the hatch. That way the platform has less horizontal surface exposed to smashing seas and if build with steps it is still useable to climb up in vertical position in the unfortunate event of an MOB. To be able to rescue yourself as MOB requires of course to be on the leash when more than head and shoulders are out of the hatch otherwise steps will be of no use . . . :eek:
     
  4. shantyboat
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    shantyboat Junior Member

    Ten Feet

    I was surprised when I saw the 3d model. The swim step being integrated into the bottom of the hull like that makes it a boat that is no longer ten feet, imho. My opinion for what it is worth. Either way, I'd love to follow the journey of that amazing little boat. Bryan http://shantyboatliving.com
     
  5. sharpii2
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    sharpii2 Senior Member

    I looked at the latest drawing on Sven's web page.

    His is clearly not a ten foot boat.

    The so called swim platform is really a fore and aft sponson that lengthens the boat to around 13 ft.

    It is clearly faired into the bottom of the boat and, even if it is completely free flooding, it extends the waterline by close to a third.

    According to the original Around-In-Ten rules, IIRC, any part of the boat that extends past ten feet must be quickly removable. I don't recall it saying that it had to be above the LWL (rudders would then have to be included). And "quickly removable" was never specified by any set amount of time.

    With my "Football" concept (see attachment), I assumed rudders and bowsprits would be counted as quickly removable.

    That being said, The length extension of the "Yrvin 10" will almost certainly improve its seaworthiness. It acts as a long, fat skeg, which extends well past the hull, which will resist broaching much more effectively than simply lengthening the hull another three feet.

    If it is free flooding, and I assume it is, it can act as a very effective dampener against pitch poling, as it provides little buoyancy for its bulk.
    Seeing how well it seems to be connected to the hull, I think there is far less of a likelihood of the boat losing its rudders from it than from the transom of the main hull itself.

    Even though his boat most likely will never be counted as a ten footer, it could still break records as the smallest boat to do a non stop, one stop, or even two stop voyage around the world.
     

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  6. Angélique
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    Angélique aka Angel (only by name)

    Many thanks to Sven for answering our concerns, much appreciated [​IMG]
     
  7. sharpii2
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    sharpii2 Senior Member

    I think a sea going version already exists. Someone has an ocean going sharpie that has them. He even had some posts in the sailboat section.

    If the hull itself is deep and flat sided enough (like most ocean going sailing ships), it acts as a crude keel itself (See attachment below).

    Chine runners merely increase the effective depth of this hull, the same way end plates and winglets increase the effective span of a wing.

    To make this system more weatherly, Matt leydon set up a weather helm
    then threw on a large, deep rudder.

    In that case, it was really the rudder, not the hull, that was providing the lift to windward.

    This, by the way can be done (and has been done, in some parts of the world) with a much shallower hull.

    The advantage of this system is that no centerboard slot is needed, nor are pesky, often hard to get to (on high sided boats) leeboards.

    This is probably the main reason Matt uses this system.
     

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  8. Angélique
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    Angélique aka Angel (only by name)

    Above quote is from post #139 on page 10 of this thread, to read it in context of the surrounding posts there . . :)

    Forgot that one when I wrote it, your description sounds like Hogfish Maximus of Chris Morejohn . . . ? ?

    Her chine runners are very well visible in these haulout pictures, here some sailing pics . . :cool:

    More info:
    Chris Morejohn -- on Blogspot --

    Gallery of Christopher Morejohn -- on Picasa --

    Hogfish Maximus -- thread on the sailboat section -- post #69 is in the quote below --

    Profile -- on Boatdesign.net --

    2th link in the quote doesn't work for me at the moment, the rest still works fine.

    P.S. - - Fixed broken link, works OK now.
     
  9. Angélique
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    Angélique aka Angel (only by name)

  10. sharpii2
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    sharpii2 Senior Member

    Yup. That's the one.
     
  11. Angélique
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    Angélique aka Angel (only by name)

    :D :D . . . So, who will post the solution here . . . :D :D
    :) :) :) - - Thanks Sven [​IMG] - - :) :) :)
    P.S.
    At least we should have some interest on the hour they borrow during summertime . . ;)
     
  12. Angélique
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    Angélique aka Angel (only by name)

    Just learned on the Hogfish Maximus thread (post #111) that besides chine runners she also has a daggerboard for leeway resistance.
     
  13. sharpii2
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    sharpii2 Senior Member

    He also states, somewhere in that thread, that the main use of that board is to induce heeling.

    IIRC, he retracts the board, once the boat has heeled, then relies on the chine runners themselves for leeway resistance.

    Apparently, without the board, he can't get the boat to heel over far enough on its own. At least under certain conditions.

    Perhaps his chine runners aren't big enough. They do seem proportionately smaller than those on PARADOX.

    Here's a concept that takes chine runners to the furthest extreme ;)

    I might build a model just to see if it would work.
     

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  14. Angélique
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    Angélique aka Angel (only by name)

    If I interpreted the drawing right the hull looks like the Sea Shadow stealth ship if we extend her sides underwater and close the gap between the hulls . . ? ?

     

  15. sharpii2
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    sharpii2 Senior Member

    Thanks for the pictures, Angelique.

    Interesting comparison.

    The warship posted has its sides flaired in to deflect radar upward, instead of back to its source, IIRC.

    The purpose in my drawing is to is to deflect water the same way.

    As the boat begins its close reach, about the closest thing to a tack it can probably get, The hull starts to crab, pushing water aside on its lee side. With more standard flair sides, some of the water is pushed aside and some goes under the chine. The more extreme the flair is, the more true this is.

    With the reverse flair, its easier for the water to climb the side a bit than it is for it to sneak under the chine. This means the boat shoves more water aside and, reactions being equal and opposite, the boat is shoved to windward that much more.

    IMHO, long, shallow keels work differently than short deep ones. The latter work very much like airplane wings, with the windward side providing most of the lift (About 2/3). With long, shallow keels, the situation is reversed. Most of the lift comes from the lee side, as it is easier for water to sneak under the bottom of the keel and form whorls, from the lee side, than it is for it follow the windward side.

    Area for area, the short, deep keel is vastly superior to the long shallow one, when it comes to upwind performance.

    That being said, they do have their short comings.

    Chief among them is added draft. Though retractable versions can be used, they all add a certain amount of complexity and inconvenience.

    Of secondary concern. Because they are so effective, they offer the temptation to trim their area to an absolute minimum. With an attentive helmsman and/or ideal conditions, this is not a problem. But with a less than attentive one and rough conditions, such a keel is likely to stall and lose much of its lift. The higher Aspect Ratio (AR) it is, the more this is true. It can take a very small change in angle of attack for this to happen.

    Long, shallow keels, though they provide relatively poor lift, provide quite reliable lift.

    They can also actually sail in shallower water than a retractable deep keel can.

    This is the source of my fascination with them.

    Naturally, they offer a temptation of their own.

    The temptation is to give the keel less and less responsibility for windward lift and to give the hull itself more and more. If the hull is boxy and deep enough, the keel can theoretically be done away with completely (See first attachment).

    In the age of sail, this was quite common for larger ships, which had to restrict their draft, so they could get into port. Usually, a generous skeg and cut water were added and faired into the hull itself.

    In another thread, I proposed a scow with a long keel under it (see second attachment). The theory is the keel will provide some of the lift and the straight sided hull would provide the rest. This boat was supposed to sail in a very shallow lake, with a typical depth of one to one and a half meters. The boat can heel significantly without its sailing draft increasing. In effect, it is really a twin keel boat.

    The reverse flair scow is, IMHO, an interesting thought experiment.

    It would be class legal in the new class I'm working on creating, and may be quite seaworthy, if its weight distribution is correct. A wave hitting its side would have a harder time capsizing it or even knocking it off course, as the lee side would tend to dig in and the wave would tend to climb up the windward side, rather than push the boat over.

    The negatives, however, are significant.

    As the boat is loaded down, its water plane diminishes. This subtracts from initial stability significantly. So, if water got on board, the free surface effect could be even more disastrous.

    I took a straight sided scow, I drew on my ancient "Plyboats" program, and sloped the sides inward at the top at about a 1 to 3, run over raise, ratio. I raised the waterline to compensate for lost displacement.

    At 15 deg. of heel, the program said the sloped side version had more than 1/3 less righting moment.

    Still an interesting idea, eh.
     

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