28' sail cat

Discussion in 'Multihulls' started by mihari, Sep 4, 2009.

  1. boat fan
    Joined: Sep 2008
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    boat fan Senior Member

    Hey ....we all have to start somewhere.

    On the whole this group is quite accomodating and helpful.

    Some are very experienced and knowledgable , but don`t bother helping any newbies. ( Pity )

    Don`t worry too much about the attitude , don`t take anything too personal either.

    Terhohalme is right about anyone starting out on designing though ...you have to do a lot of reading , the more the better. It takes time. :)


    Some people here are quite rude .When you get responses expressed like THIS .... it really pis**s me off .....
    " net etiquette " ...sadly lacking with some :mad:

    A small minority here also think their " knowledge " is "precious " .....best to just ignore those .......:D


    When you look at some designers offerings ( and these are just a few examples ) you realize that the cost of their plans are such a bargain.

    Kohler ( K designs )

    Richard Woods

    Mike Waller

    Bob Oram Etc......... Etc.......

    These guys also SAIL their boats , lots of experience and if you build to their PROVEN designs , ...You get a good boat without the risk of building a boat with major flaws that you or I could have overlooked.
     
  2. boat fan
    Joined: Sep 2008
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    boat fan Senior Member


    Be careful here mihari .

    If you have a powerful boat ( meaning a rig that generates a lot of power in relation to the overall displacement of the boat ) it can catch you out.

    In a previous post I mentioned " stuffing " my Nacra , (back when I raced that boat we referred to pitchpolling as "stuffing it " :D )

    That can happen in relatively smooth flat water.We used to look for the " darkies " on the surface...you see darker patches on the water`s surface caused by small ripples ...(areas of high pressure air) .The idea being that you search out the " darkies " and sail from one to another and get more lift and acceleration and boat speed.( We found one alright ....:D )

    Those high pressure areas can be difficult to see and you can inadvertently sail right into one , next thing you know you are screaming along with the leeward bow doing its best to bury itself as the boat accelerates. If the sheets are cleated .... over you go .This can happen weather you are on a race boat or not. If you are unlucky and have conditions of short steep seas ( not necessarily high ) the problem can compound. There are numerous other scenarios that can lead to pitchpoling.( Long hulls are NICE !!!!!!!!!)

    Watch right near the end ::D



    http://www.youtube.com/watch?v=BnTWclNSfKI&feature=related

    Results of "Stuffing it " below....:D
     

    Attached Files:

  3. mihari
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    mihari Junior Member

    Being a windsurfer at heart, I do appreciate speed and fighting with the wind. But I will leave that to windsurfing. I don't plan to take my cat anywhere near extreme conditions.
     
  4. Pat Ross
    Joined: Jul 2006
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    Location: Florida

    Pat Ross Corinthian 41 Tri #12

  5. mihari
    Joined: Sep 2009
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    mihari Junior Member

    Hi to all that followed this thread... Sorry I had not posted in such a long time... It is just that I have been spending most of my free time sailing (unfortunately not in a cat), and some pondering, doodling, and all the usual stuff a designer wannabe does.

    I really like the idea of having knuckles on my cat. I will definitely have them. I was wondering if anybody thinks that this construction method of a rounded knuckle that I came up with, might be viable. I think it might be quicker than strip planking. The Idea is to make a one sided mold for foam to be purred in, then poor and fair the foam to desired shape, glass it on free side, remove mold, and glass on molded side.

    Has it been done before? Does anyone think it might work?
     

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  6. boat fan
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    boat fan Senior Member

    Hello Mihari.

    There are easier ways......

    Derek Kelsall makes a flat molding for a radius deck edge.

    You could apply this to a plywood build too.
    That edge could be glassed onto the plywood panel while lying flat .
    Would stiffen the panel a little , but if the radius is not too large ,
    you will still be able to get it to bend enough , so it should work ok.

    Personally if I was building with sheet material , and wanted a knuckle ,
    I would do it with sheet material ( developed ) on the inside of the hull.
    Much easier.

    Check out Derek Kelsall , KSS.....

    Hope this is helpful. :)
    [​IMG]

    Meanwhile on the main table a deck edge radius is being made by wrapping fiber glass cloth, about 100 degrees of arc, around a length of plastic pipe and applying the resin manually. The two inch tube has been covered with brown parcel tape to provide an easy release.

    [​IMG]
    The electric scissors make light work of trimming the glass to the deck edge radius batten. the glass should cover the face of the batten, but its best with no excess above the batten.

    [​IMG]
    Back to preparing to make the deck edge radius batten. This is the good old fashioned sticky, smelly, hand laminating job.

    [​IMG]
    Back to the deck edge radius. More of the sticky stuff. This is only done once or twice for most boats, but it does need care to get it right. An arc of chopped strand-mat glass has been laminated onto the 2 inch tube and allowed to cure. 90 degrees of the same has been laminated into a steel angle. The batten we are making needs these two to be brought together with the space between full of that micro balloon mix. i e - a right angle with an arc set in it. The steel angle has been set on supports to hold it with open angle upwards. The mix is being applied, with tube sitting ready to drop into place.

    [​IMG]
    Trimming up the deck edge radius batten is a dusty job. Note masks and the shop vac taking away most of the dust. The main trim is done by setting the grinder, with cutting wheel, on a block which sets the level and sliding along the table. The table has so many other uses, we wonder how boat builders can work without long tables.
     
  7. sabahcat
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    sabahcat Senior Member

    ^^ Great if you have a small boat and want a tiny radius made from solid glass ^^
     
  8. Elmo
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    Elmo Junior Member

    It does not have to be tiny.......
     
  9. sabahcat
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    sabahcat Senior Member

    Really?

    How much glass and resin will it take to do a radius of say 120mm that has the same strength as say 16 mm Light Timber core and 600 gsm db in and out? (this is the radius and layup on my boat)

    Answer me that and then tell me if the weight time taken and cost of material to make a solid radiused deck edge of that size is a viable option in comparison.
     
  10. sabahcat
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    sabahcat Senior Member

    Have you any additional evidence to support this theory?

    I would suggest the fwd beam wasn't attached with sufficient strength.
     
  11. Elmo
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    Elmo Junior Member


    Really ?

    Firstly, light timber core will be lighter, no doubt.
    I don`t see any comments that disputed that.

    Secondly, that deck edge could just as well be laid up over that pipe former
    with foam core strips and glass.
    Or slightly thinner timber strip core and glass.Or duflex and glass.

    I don`t know the exact strength characteristics of 120mm that has the same strength as say 16 mm Light Timber core and 600 gsm db in and out.
    Do you ? Does it matter ? Hardly.

    I also dispute saying that it needs to be " solid ". An inside lamination of glass would be sufficiently strong to overlay with core.
    Going that way would only be marginally easier, if any.
    Now tell me that it could not be done.

    On a 28 ft cat that radius would not need to be "tiny" at all.
     
  12. sabahcat
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    sabahcat Senior Member

    Correct me if I'm wrong but isn't that the whole methodology of the Kelsall hull to deck radius build?
     
  13. Elmo
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    Elmo Junior Member



    Yes it is.

    And furthermore , Mr Kelsall does not seem to mind the extra weight either.

    In fact , he uses them on his large cats too.

    I also happen to like his boats .

    I was answering your concern about weight.( strip it.)

    What`s your point ?
     
  14. sabahcat
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    sabahcat Senior Member

    Pretty obvious I would have thought

    I said it's not really suitable for large radius's due to the amount of resin and glass used, therefore needs to be a small radius to be affective.

    You disagreed and said large radius's can be done, but then changed the way it could be done to the method that I already said (strip plank, 600 in and out) which is not the way it is being done in the pics I referred to.

    This is not kelsals method .

    Therefore, using kelsals method is not really cost effective for larger hull to deck radius's

    Which is what I said originally.
     

  15. mihari
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    mihari Junior Member

    OK guys do not argue over this. We all agree that any section that replaces the spacing material between the structural material with epoxy is heavier and more expensive.

    The method I described above might actually not be quicker nor cheaper than foam strip planking. What kind of foam would I use? I guess the stuff that comes in the spray bottles with the long nozzles, used in construction to fill gaps is not good enough, because of the elasticity of the dried foam. A chem engineer was telling me that I can get foam with just about any properties that I want. Is there a preferred foam? Would it be anything close to the stuff they use for insulation on walkable building roof tops (a favored brand here is roof-mate)?
    http://building.dow.com/europe/uk/proddata/styrofoam/roofmate-slx.htm
     
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