Opinions on this newbie amateur daysailer

Discussion in 'Boat Design' started by Murdock, Oct 20, 2006.

  1. Murdock
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    Murdock Junior Member

    Thanks a lot for your answers,
    got another couple of questions, on my preliminary structural calculations got this results, which I have not anything to compare with to check.
    A fiberglass & resin privider, gave me this parameters:
    Fiberglas cloth #600 Roving + Poliester resin 450 centipoise density on a 50%-50% basis
    Tensile strenght 45.000psi
    Tensile modulus 2:500.000 psi
    Flexural strenght 65.000psi
    Flexural modulus 3:000.000psi

    aplying this parameters, got some flexibility results I'm not sure it's allowability.
    5cm torsion deformation on hull seems to be too much for the resin flexibility?
     

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  2. Murdock
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    Murdock Junior Member

    Some more fresh meat for the pot...
     

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  3. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Regarding cost and weight and durability (polyester boats get soft), have you considered plywood, for example 6mm okume with 300g of glass?

    At the stern, have you considered a partial transom or a cross beam at the top? It will make the boat much stiffer (re your calcs on deformation) and you can fasten the rudder with a better "arm".
     
  4. wet feet
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    wet feet Senior Member

    An impressive amount of work has been going on.Frame shapes determined,components nested for best use of sheet material and size of working table determined.I am a little curious about the 4.606 by 1.4 component near the bottom right hand corner of the layout.It might be the expanded surface shape of the hull but I would have serious doubts about the possibility of a hull shape of this type having a developable surface.The radiused chine would be a major challenge.I would understand the uses of a representation of the surface as an aid to calculating weight.Can we have an outline of the next few steps in the process?
     
  5. Murdock
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    Murdock Junior Member

    Thank you all for your comments,
    Raggi_Thor, considered as an option a plywood hull, but on a similar cost basis think would be more age-proof a resin hull.
    On the stern considerations, at this stage still thinking on an open end, no transom, maybe the option would be a beam for stiffness (by the way, the master section deformation calculated was the third from back).

    Wet feet: that weird section is an approximation of the developed surface, surely not the real thing, but an approximation at the sole effect of estimating roving lenght & resin consumption. my construction idea is not using any plywood on the hull, all sections/reinforcements will be done on multiple roving #600 + resin (as much layers of roving as of final calculations needed) hand or cnc cutted (that's the paper plot sections for)

    At this stage, I'm still convinced on the need of a positive mold (cnc cutted sections + some concrete/plaster) because there is not available here any adequate marine grade plywood, also probably would be abbandoned the vacuum infusion idea, the only resin available here is polyester or isoftalic (30min is not enough for infusion & at 450centipoise density makes a need of about 10hp 0.9bar pump).finally, as it is a flammable, non transportable by public systems, the product can't be acquired from any near country.
     
  6. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    I think you are doing a great job :)

    If you don't use vacuum, will you have more polyester?
    Maybe 35% glass and 65% polyester?
     
  7. Murdock
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    Murdock Junior Member

    Raggi_Thor: If you don't use vacuum, will you have more polyester?
    Maybe 35% glass and 65% polyester?

    I would like mostly to use vacuum infusion, but it frightens me a bit the possible resulting disaster of using some inadequate timed resin or too high viscosity for the pump capacity. (have not find still enough info on styrene monomer dillution for decreasing density versus final catalyzing time and final resistance to calm me down)
    by the way, 35%/65% is that the common ratio? a resin provider here gave me an excel sheet, on which he stated 50%-50%, but surely he has not any experience on hull glassing... most of his sellings are related to automobile industry...
    will check it next month when glassing the hull. by now, I'm finishing with all models for cnc cutting next week.
    Attached a couple more drawings on what I'm thinking the cnc routing & the molds might ressemble. (hope the Devil's tail won't interfere the plans:) )
    again, thanks a lot for your support
    Murdock
     

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  8. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    I think 50/50 is a bit optimistic, maybe possible with biaxial cloth or woven rowing, but not with csm.

    1/3 of glass and 2/3 of polyester is an old rule of thumb.
     
  9. Murdock
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    Murdock Junior Member

    well guys, think drawing time is ended, let's begin second stage...
    attached a comparative excel with diferent cost alternatives in relation with building method and (last but not least) final estimated weight of hull.
    at first sight, strip planking (#3) seems to be the simplest & cheaper building method, but weight scares me a bit. (still convinced the plaster mold gives the better cost/weight compromise)
    opinions please?
    Murdock
     

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  10. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    With strip planking you don't need gelcoat, BUT you should use epoxy instead of polyester...It's more expensive, but it keeps the water out.
    With a 300g biaxial cloth set in epoxy on both side the wood core can be quite thin. What have you used to et 46.31kg?

    I think that the 90 kg total weight with polyester could easily be 110 if you are not very careful.
     
  11. wet feet
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    wet feet Senior Member

    I think before too much more work and especially before beginning construction,it would be a good idea to incorporate a bit more displacement.An earlier post mentions a displacement of 285Kg including crew and the design has a displacement of 181Kg according to the version of Freeship that I opened it with.These figures nedd to be brought closer together before embarking on the effort and expense of building.How about building a scale model in order to identify and deal with the challenges?
     
  12. Murdock
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    Murdock Junior Member

    Raggi_Thor:
    What have you used to et 46.31kg? an aproximation, 4.50m lenght x 2.10m developed beam x 5mm thickness ply @ 700kg/m3 average wood density x 2 (hull + cockpit) x 70% of the total plywood plank area. (remember the "weird development sections" on post #17)
    I think that the 90 kg total weight with polyester could easily be 110 if you are not very careful. I'm conscious about it... still thinking that a resin hull over a concrete mold gives me some more "margins" for decision on where to use just one biaxial cloth or multiple clothes, as a way to save weight

    wet feet:
    Maybe on a bigger hull, the displacement vs the total hull+crew weight can be of vital importance, but on this type of hull (correct me if I'm wrong) as soon as the wind puffs on the sails, as the thing "jumps" it will begin planning over surface, discharging all water that could be on the basin/cockpit.
    (i.e. on a windsurf table, displacement-guy's weight, is irrelevant?)
    I remember on my early days at the sailing school, sailing on a ply hull of about 3.00mts called a Penguin (used to think it was a class on the 70's) when sailed by a crew of two, you had to be extremely careful to balance your weight, because it tends to capsize, or sink by aft untill sail loads, and begin planning.
    Remember, the main use for this thing, will be beach-fun, even some training, hardly some regatta, (maybe an open source class can be created on future? as moth did? all info is available for free to anyone, just ask for it). If it becomes a problem, a semi-transom attached might keep us dry.

    Murdock

    by the way, seen this hull photos over the net, same considerations about displacement? :D
    (don't misunderstand me, I love this kind of design)
     

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  13. Raggi_Thor
    Joined: Jan 2004
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    Raggi_Thor Nav.arch/Designer/Builder

    I exported your (very nice) Freeship model to IGES and opened it in Rhino.
    The outer skin has an area of 5.77 m2.
    6mm Okoume weighs less than 3kg/m2, 2.8 to 2.9kg has been my measures.
    2x300g biaxial glass + equal amount of epoxy is 1.2kg/m2.
    That's a total of 4kg/m2.

    6m2 x 4kg/m2 = 24 kg for the outer skin.
    The inner skin is probably smaller, say 20kg.
    Then, whats the area of all your frames and other internal structure?

    We built the Backman 18 with 8mm pine strips in the bottom, 6mm Okoume in the topsides and 8mm in the deck and cockpit. The complete hull is 150kg.
     
  14. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Gaussian curvature, Green=0
     

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  15. Raggi_Thor
    Joined: Jan 2004
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    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    Minimum radius, Red=0.1m and smaller, Blue=0.4m and larger.

    You can probaly skin this hulll with two large panels on each side and for example strip planking in the radius chine.
     

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