To scarf or not to scarf

Discussion in 'Boat Design' started by lazerus, Nov 26, 2008.

  1. lazerus
    Joined: Oct 2008
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    lazerus Junior Member

    That is the Question.Well the latest question.:)
    The boat I am going to build (in about 4 weeks now) calls for two layers of 3/8" mdo ply over a first layer of 3/4"x2" fir edge glued.Would I get any strength benefit by scarfing the plywood edges or the joints of the fir planks at least enough to make the extra work worth it?
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    In a word yes, but the real question might be, "is it necessary for this additional strength?"

    With multiple layers of material, you can stagger butt joints and eliminate leak potential. Scarffing will make individual planks seem as one continuous piece, but again is this necessary.

    An inch and a half of hull planking is fairly substantial, meaning a healthy size project. What is the boat and what do the plans suggest?
     
  3. lazerus
    Joined: Oct 2008
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    lazerus Junior Member

    Here it is:cool:
    The designer admits its overbuilt.At first it was designed for 1 1/2" fir,plywood is an optional build and as I understand strong enough on its own.The 3/4x 2" fir is to help keep the hull stay fair when putting on unscarffed plywood.Cheaper and its easier than adjusting the blueprints for the change in hull thickness that ply allows.Quicker than scarfing too.
    Yes The first post was badly worded
     

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  4. Bob E
    Joined: Jul 2008
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    Bob E some day

    I don't know about the rest of you but I'm going to be doing a whole lot of scarfing tomorrow. Have a great Thanksgiving all of you fellow yanks.

    Bob
     
  5. Manie B
    Joined: Sep 2006
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    Manie B Senior Member

    Lazarus this may help a bit

    i did scarf joints on my build and i lined the pieces up by drilling 3 holes right thru both panels and then inserted 8mm dowel sticks before epoxy. My scarfs were 8 to 1 some 6 to 1

    it works well - strong and accurate

    but is a lot of work

    i now got a cheap router and started playing with step joints - to me its a WHOLE LOT quicker easier faster and accurate

    i router to half the thickness of the plywood and 3x thickness in width so on 9mm ply the step is 4.5mm deep x 27mm wide

    my hulls are now scarfed joints but all my decks and tops will be stepped joints
     

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  6. Loveofsea
    Joined: Jan 2007
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    Loveofsea New Member

    Scarf every chance you get!

    I built a 19ft skiff using the principles of aircraft construction rather than traditional boatbuilding design. Specifically, as FEW structural components as possible, each part being as big as it could possibly be...

    Scarf splice to make all components 'one piece' then assmeble as few pieces as possible--(avoid butt joints!)

    the less seam area, the greater the structural integrity.

    When building aircraft, they go to extraordinary expense to use the biggest structural components as possible. one example i like to give is that we use wing stringers that are 90ft long. We could easily avoid the cost of transporting stringers at an oversized length by splicing the 5/16" X 2" X 2" angles together, but the result can never match a single piece....

    "Every piece as big as it can be--as few pieces as possible..."
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    That a Buehler design, which means the scantlings are twice (or more) what they need to be. Frankly, if I were you, I'd use Geer's book and redo the whole set of scantlings, with a 10% higher fudge factor (Geer's book already produces a "healthy" set of scantlings as written), just to be on the hefty side and toss the remaining weight savings into ballast, which on that boat would be likely in the low 20% bracket as designed. You'd save a bunch of money on unnecessary materials and the increased ballast/displacement ratio will help considerably, holding that slack bilged double ender upright.

    Let me guess, he suggests an 8" or bigger keel timber, 4" thick floors, 2x6" frames on 24" centers (or closer),1" thick gussets on each side of the frames, 2x4 stringers, double 2x6 chine logs, 1.5" solid lumber planking or three layers of 1/2" plywood for the planking, sawn 2x8 deck beams with the decking being the same as the hull planking.

    Sweet God, that's way over kill. You can use it as an ice breaker during polar excursions.

    If you're going to have a 17 to 18 ton boat and pay for the materials in it, wouldn't you like a fairly high percentage to be in ballast. By this I mean there is a direct correlation between the displacement of a boat and it's cost (and effort) to build. With a 20% ballast to displacement ratio (this boat is likely in this range, possibly lower) you're hanging the remaining 80% of the boat's structure by hand. If the scantlings were redone, still producing a strong, hefty boat, but with say a 40% ballast ratio, now you only have to build 60%, which is a big savings in effort. Yep, you still have to buy and install the ballast, but this is a one shot deal, not multiple tasks and assemblies.

    I like George, but that old German is a bit anal about over building and under canvassing his sailboats. Check the SA/D on the design and compare this to your expected sailing area and average conditions. It's very probable you'll want to increase the sail area substantially. Some quick math with 1,000 sq. ft. of sail and a 17.5 ton boat, the SA/D is 14.9, which is pretty low, especially for light air or coastal work. In the trade winds this will be fine, but how often will you be sailing the trades.
     
  8. lazerus
    Joined: Oct 2008
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    lazerus Junior Member

    Actually The trade winds will fill the sails quite a bit.some of the destinations are going to be NewZeland australia the phillappines the carrrabean Holland...you get the Idea.It will be sailing constantly and I intend to cross many oceans.
    Once the boat is built I retire.My sister in ST Kitts and her hubby own a house in Bassiterre and well goodbye snow.
     
  9. Tad
    Joined: Mar 2002
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    Location: Flattop Islands

    Tad Boat Designer

    Properly scarfed and bonded joints will produce a far superior hull, but it will not be easy to accomplish. I assume you are expected to clamp the ply to the inner (first) layer with screws or ring nails? Scarfing full sheets of ply in place on the hull will not go well for a small crew, much screwing around trying to get a good fit up in the air. Alternatively you could scarf on a table, but you'll need a big crew to handle a sheet of 3/8" ply 42' long! Yes it can be done, no it's not fun...

    Why not just buy this boat....http://www.yachtworld.com/core/listing/boatFullDetails.jsp?boat_id=1503239&ybw=&units=Feet&currency=USD&access=Public&listing_id=11864&url=
    She's only a dozen years old and all she needs is a new bottom. Been for sale for a number of years, they'll probably take less than half the asking.
     
  10. Boston

    Boston Previous Member

    Par
    I loved the post
    some funny stuff there

    I think Buehler designs that way cause he is considering using basic framing lumber from the local yard
    nothing fancy like white oak frames
    or mahogany cabins
    just low grade pine for cheep cheep cheep
    the scantlings kinda make up for the inconsistencies in the material

    laughed my *** off at

    as for scarf joints
    they are the bomb when it comes to strength
    a but joint doesnt even come close
    Tad's comments are right on the money
    and Loveofsea made some good comparisons as well
    thing about chine forms no one ever mentions is that the line of the chine is vulnerable to leaking and damage and tends to be a week point in the plan
    overbuilding that area is a good idea
    but being heavy above the line isnt
    cielings, carlins, cabins and the like should be strong but light
    bellow the line build a tank
    it may come in handy some day
    but being top heavy reduces your stability in a pinch
    my two cents
    B
     
  11. lazerus
    Joined: Oct 2008
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    lazerus Junior Member

    Sure just give me a hundred grand and ill by it of course it might take 15 or so to give it the new bottom.At 64 feet it is to big to solo and ill need a captains ticket. (sry for the sarcasm but Used boat means used problems)
    There is no doubt in my mind that each of you have raised a valid point
    but consider my needs for a boat.First and foremost seaworthy,it must be as seaworthy a design as possible and still be able to be built for as little as possible tough enough to stand 20-30 years of hard use in the south pacific and points beyond.I have no plans beyond living on it and sailing.A wind too strong to put up canvas in means a sea anchor and a cup of coffee.
     
  12. Boston

    Boston Previous Member

    I know the feeling
    Im thinkin Ted Brewer's Sophia Christina as my first choice
    but its a hundred for materials
    40 just for the hull and thats not lead either
    just wood and glue

    I feel your pain mate

    far winds and clear sailing
    B
     
  13. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    Laz...

    Not trying to give you a hard time, only sharing some hard won experience. Building new with no money is a long hard road. Realize that you'll spend 8000 hours roughing out the 42' above. That is just construction time, finding materials is extra.

    There are thousands of boats for sale cheap right now, no buyers to be found. Name your price, many are being given away. There's another Buehler (40+') on cragslist seattle for $6500.00 complete! The engine (good perkins) is worth more than that.

    Yes, after 2009 all pleasure boat skippers in Canada must have a valid operators permit. Size of the boat does not matter.
     
  14. Boston

    Boston Previous Member

    my father
    his father
    and his father before him would rise from there graves and throttle me if I bought instead of build
    but
    I can salvage
    I think
    Ill let you know if I see any poltergeists

    ( good point Tad just Ive been wanting to build and retire for a while now )
    ( its the building part that lends so much satisfaction and peace of mind to the hole show so its hard to have economic realities thrown in )
    ( but appreciated none the less )

    hey folks
    go read my thread titled "the great race"
     

  15. lazerus
    Joined: Oct 2008
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    Location: Vancouver

    lazerus Junior Member

    I suppose I should mention my budget allows for $500 a month
     
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