Fiberglass Scantling for Hurricane in Selway Fisher Micro 8

Discussion in 'Sailboats' started by mtumut, Apr 1, 2016.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    The "hurricane" in the topic heading tells me it is not to be taken seriously, or encouraged in any way. It is a fantasy, and should remain one.
     
  2. TANSL
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    TANSL Senior Member

    To be more precise about design categories :
    A. OCEAN: Designed for extended voyages where conditions may exceed wind force 8 (Beaufort scale) and significant wave heights of 4 m and above but excluding abnormal conditions, and vessels largely self-sufficient.
    B. OFFSHORE: Designed for offshore voyages where conditions up to, and including, wind force 8 and significant wave heights up to, and including, 4 m may be experienced.
    C. INSHORE: Designed for voyages in coastal waters, large bays, estuaries, lakes and rivers where conditions up to, and including, wind force 6 and significant wave heights up to, and including, 2 m may be experienced.
    D. SHELTERED WATERS: Designed for voyages on sheltered coastal waters, small bays, small lakes, rivers and canals when conditions up to, and including, wind force 4 and significant wave heights up to, and including, 0,3 m may be experienced, with occasional waves of 0,5 m maximum height, for example from passing vessels.
     
  3. upchurchmr
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    upchurchmr Senior Member

    Tansl,

    Did you make those up yourself?
    Who else couldn't have come up with the same list.
    What does this list imply, if anything?
     
  4. Jamie Kennedy
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    Jamie Kennedy Senior Member

    All very good and valid points. Thank you.
     
  5. Rumars
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    Rumars Senior Member

    Tansl is quoting the "Directive 94/25/EC of the European Parliament and of the Council of 16 June 1994 on the approximation of the laws, regulations and administrative provisions of the Member States relating to recreational craft" Annex I part 1. Complete consolidated text at http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:01994L0025-20130101

    There are ISO-EN standards aplying to different parts of the boat to be respected in design and construction in order to be compliant and get a CE marking so you can sell the boat in Europe.

    You are "strongly discouraged" to sail a cat. D boat offshore but it is not forbidden. The design category is an indication for the buyer as for what normal opperating conditions the boat was designed for.

    Back to the OPs question I think the problem for converting from plywood to monolithic glass is weight. The smaller the boat the bigger the problem. The dry weight for the Micro 8 is given as 500kg out of wich 250kg is ballast. So you are left with 250kg overall and in a "no plywood, no core boat" that is not much. The Micro 8 requires 15 sheets of 6mm ply, 3x9mm and 3x12mm. I quote the designers webpage "the hull skin consists of several layers of ply to produce a very tough hull." I do not think one can replicate the boat as designed in glass without creating a semi-submergible.
     
  6. TANSL
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    TANSL Senior Member

    Rumars has perfectly answered your innocent questions.
    Any designer who must comply with any rules to design his boat knows that one of the first things he should define is the design category of his boat. So yes, many people are interested in that list.
    Cheers
     
  7. Westel
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    Westel Senior Member

    Nice "touch down"........on the wrong side of the field :D:D:D LOL !!!
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    I'm pretty sure the OP has moved on to new adventures, this one is now passé.
     
  9. TANSL
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    TANSL Senior Member

    Three days ago that mtumut has forgotten us. But we can continue talking about our stuff, right ?. In addition, knowing that the OP is no longer interested in his thread gives us some freedom of action.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    His Antarctic DIY sail-drone was much more interesting than the hurricane-defying 8 footer. Not to mention much less dangerous. Matter of fact, the former would make a great doco, if it were not so devilishly difficult to do.
     
  11. Jamie Kennedy
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    Jamie Kennedy Senior Member

    Good information here. Without using some sort of core, you would need roughly 3 times the weight in fibreglass to match the thickness, but perhaps only twice the weight to match the panel stiffness, and perhaps the same weight to match the tensile and compressive strengths, not that they matter much. The critical one is panel stiffness. I think we can agree that increasing the hull weight from 250kg to 500kg is not an option. Still, it seems reasonable that this boat could be built in fiberglass, even without using expensive core materials. Options might include:
    1. fiberglass stiffeners
    2. expandable foam floatation that also provides some panel support
    3. using a lighter fibre material like hemp as a coremat type middle layer

    But I agree that all of these would pretty much require a redesign, and the third one would required some research and testing.

    From what I understand it will still never be a Category A,B, or perhaps even C because of the way they determine those classifications. I am not certain, but I doubt that even a Contessa 26 would make category A, on technicalities like righting moment, even though it is likely a more capable boat, properly fitted, than many larger designs that make category A. Correct me if I am wrong but the categories determine righting moment in absolute terms rather that relative terms, unnaturally favouring larger boats.

    EDIT: I stand corrected. The righting moment isn't in absolute terms. The categories do favour larger boats, but not necessarily in an un-natural way. There still might be a case for singlehanded or shorthanded sailing to choose a proven and well fitted category B over a larger more difficult to handle and maintain category A, but the categories are still very useful. I am curious though, whether a Contessa 26 or Folkboat makes the grade of B, or if they only make C, even when fitted for ocean crossings.
     
  12. TANSL
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    TANSL Senior Member

    When working with a sandwich panel, not only the total thickness must contemplate but the thickness of the outer and inner layers must be checked and what is called the "effective thicness" average distance among medium parts of plies. Not comparable therefore the total thickness of the sandwich and the total thickness of a "normal" panel. The core material does not cooperate much to flexural resistance but getting the distance to the neutral axis of the outer/inner layers is greater, so that the first moment of the area for ​​these layers is greater.
    The categories of design not only depend on the boat's righting arm. It has also a lot to do with, for example, downflooding points, downflooding angles, resistance to waves and wind ... Regarding the scantlings, when calculating the design pressures, category introduces a factor whose value varies from 0.4 to category "D" to the value 1 for the category "A". No one factor that directly relates the length and design category.
    These are two more complicated issues than it appears at first sight.
     
  13. Jamie Kennedy
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    Jamie Kennedy Senior Member

    Some of the advantages of smaller boats which I think these categories do not take into account:
    1. Smaller boats are more difficult to design to avoid rollovers, but are easier to design to survive rollovers.
    2. Smaller boats, like insects, can be stronger relative to their size, and this can be used to make them inherently unsinkable, such that downflooding becomes a non-issue because the water has no place to go, that space already taken up with foam floatation, freshwater containers, or other containers filled with food and other gear. Sleeping and shelter quarters can be above waterline.
    3. Smaller boats have rigs that are easier to handle, and can be short and light enough to make feasible to reduce in storm condition, such as a gunter rig, and even to carry spares.

    I don't think the extremely short record breakers, under 14 feet, have taken full advantage of these possibilities. In fact, I think they are too short to take full advantage of them, because they become so slow that they need more food. On the other hand boats like the 18 foot Drascombe lugger that Webb Chiles sailed across the Pacific, Indian, and Mediterranean; and the modified 19 foot daysailer that Ant Stewart sailed around the world were perhaps too open for extreme conditions. I think there is still a lot of room for improvement in the 14 foot to 20 foot range. Sven Yrvind seem to have gone back in this direction, although I think he compromises too much on strength at the expense of speed, and the ability to go to windward. I think something half way between Ant Stewart's approach and Sven Yrvind's present project would be most promising, in a design somewhere between 14 feet and 20 feet. I think it could also be beachable, which would provide some important options for survivability. As far as being able to scrape over coral reefs in a breaking sea, that would be pretty extreme. Yrvind's current project seems to be the most capable so far in that regard, but I still something that can sail to windward up to gale conditions is just as important, if not more important. As far as food and fresh water requirements, payload requirements, I think for solo expeditions it should be be possible to carry only 100 pounds of dry food for 100 days, and I think with the ability to catch or make freshwater I don't think more that 100 pounds of fresh water needs to be carried at any given time. So with only 400 pounds of payload including the solo sailor and his clothing, I think these boats can be built a lot lighter, less than a ton in total displacement including the payload. Perhaps as low as 1200 pounds total for a 14 foot boat, 1600 pounds total for a 20 foot boat. Those weights include 200 pound skipper, 200 pounds food and water, 200 pounds gear and spares. So 600 pound boat including rigging for the 14 footer, and 1000 pounds for the 20 footer. The question of ballast comes into play. I think even for the 14 footer some is required for some self-righting capability. I think it is desirable to be able to sail outside in a moderate breeze, even on a trapeze as Ant Stewart did. However, it is also desirable to be able to hunker down and survive rollovers in extreme conditions, perhaps repeatedly, without the crew having to go outside of the hull. Being able to shift crew weight from one side to the other while upside down to assist the keel ballast, plus perhaps more sheer to get some volume on the ends when capsized, and less freeboard in the middle, and perhaps a small area of cockpit which can flood and then self drain. I think these can provide self-righting capability without having to go to high solid ballast ratios, which in turn allows the boat and rig to be smaller, more dinghy like, relying on crew weight and shiftable ballast weight for sailing in less that storm conditions.

    Anyhow, the categories aren't really intended for this type of craft, any more than they are intended for lifeboats or life rafts or ocean rowing boats, but there is certainly a long tradition of sailing and surviving, and sometimes perishing, on oceans in open boats.
     
  14. TANSL
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    TANSL Senior Member

    You have your opinions, I guess based on your own experience, and although I do not share, I'm not going to argue. What I have to say is that the paragraph I have selected from your post is not correct at all. All entities that are dedicated to say how they should be designed, engineered, any floating device, requires that, as one of the main data, the device design category to be defined.
     

  15. Jamie Kennedy
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    Jamie Kennedy Senior Member

    This reminds me of Dennis Conner's remarking that applying Lloyd's Rules to the America's Cup was like applying the Federal Motor Vehicle Safety Standards to Formula One. It is reasonable to believe that the safest design for a single handed ocean crossing would not necessarily comply with Categories A or B, or even C, and of course doesn't have to. It's like comparing apples to orangutans.
     
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