Quick building strategies

Discussion in 'Multihulls' started by simon, Oct 17, 2007.

  1. doug kay
    Joined: Oct 2007
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    doug kay Junior Member

    I built a 9 metre ground effect and all the bulkheads were epoxied in using a wood flour mix. It withstood Wima in Ft. Lauderdale when 180 Knot odd wind gusts were recorded, my hulls are of cedar strip and after the hardback was set up the two hulls were ready for faring after 9 weeks or about 325 hours. Cedar strip hulls are enormously strong and light and have the advantage of not needing painting. The trick is to prevent the strips from springing, keep them exactly in line and fair this cuts down the fairing time and effort. If I get a any abrasions I simply mix a bit of wood flour and epoxy then sand it, no paint matching, just a touch up with epoxy.
     
  2. captainjsw
    Joined: Sep 2005
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    Location: Perth Western Australia

    captainjsw Junior Member

    Yeah not sure Andrew and have never seen any data. To be honest the time involved taping bulkheads and furniture panels is quite small - I would say a day at most - get your bulkheads in position and the glass tape ready or fibreglass lengths cut, mix your epoxy and what ever filler you want to use or is recommended. Apply the filler and turn it into a nice shape with your favourate curved scraper. Then before the filler has gone totally hard apply the resin and then the glass tape. Jobs Jobbed. If the filler is still soft the additional resin applied smooths out any unevenness. Move on to the next one. Furniture tape can be very light weight and should be. Same proceedure. Filler - say Qcells, resin and lightweight tape - on to the next panel - That was Easy. Check out my site
    http://www.johnwatson.net.au
     
  3. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    Taping is good too

    Hello AndrewK

    I do not want to open a can of worms because no multis tape all the small pieces of furniture in but I do not think omitting the glass tape on all of the furniture and especially the structural parts is a good idea.

    Glass and glue are strong but in different ways. Strength as a concept is a can of worms - that is why engineers have to go to uni. Glass gives the structure toughness that glue alone cannot. For example I regularly glue things to the shed floor with epoxy dabs. They stick well and hold onto the floor tenaciously but I can break them with a quick tap with a mallet.

    Epoxy is strong but brittle - glass is strong and tough. When you glass an epoxy cove you increase the toughness of the joint dramatically. Try and rip apart a piece of boat that has a glassed cove - it will be a real struggle.

    There is scuttlebutt that a cat builder has decided that glass is unnecessary and hasn't used any in his cat. It will be interesting to see how he goes.

    cheers

    Phil Thompson
     
  4. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Interesting idea. Thinking about it, I could be convinced. The bulkheads and furniture would normally all be in compression, unless the whole boat filled up with water, and then a bit of filleting wouldnt count for much.
    Glues or epoxys are only good for compressive strength, and if thats all that is required, then it sounds good.
    Mind you, I am doing watertight bulkheads in a canoe, where I will need the strength of a fillet with glass, in case big feet or a rush of water put shear pressures on the joints. The same would apply for strategic internal watertight bulkheads I would expect.
     
  5. simon
    Joined: May 2002
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    simon Senior Member

    John,

    thanks to everyone for the interesting input.

    captainjsw: nice site. I would be interested to know more about your current project and what you have learned from your first, technical speaking.

    Does anyone have experience with the building process in aluminium.

    In an other thread there has been mentioned that someone built a Tim Mumby 48' design in a year. Anyone knows more about this case?

    Apparently Owen Eston is building 43' aluminium hulls in around 3 months time with little outside help

    I know that aluminium is relatively heavy and just used for larger cats. I sailed on a 48' Tim Mumby and was impressed by the performance.

    Advantages of aluminium construction:
    - no molds needed
    - no paint on topside
    - lot can be precut
    - relative low price of material

    Disadvantage:
    - good and experienced welder needed
    - insulation adds extra weight and work
    - interior lining needed

    Simon
     
  6. AndrewK
    Joined: Mar 2007
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    AndrewK Senior Member

    Simon,
    Owen Easton does a great job, 12 months ago $75K and 6 months of your own time working alongside Owen bought you a 43ft Aluminium cat at the lock up stage. No internal furniture.
     
  7. AndrewK
    Joined: Mar 2007
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    AndrewK Senior Member

    No glass tapes???

    Captainjsw; nice site, will have a further look.

    I follow the same procedure as you do with the addition of peel ply at the end. I am working on my second boat at the moment and certainly will take much longer than a day to tape all of the glued and coved panels.
    Also there is huge amount of tape that goes into a 12m catamaran, certainly not an insignificant amount of weight to be saved if not necessary.

    Personaly I am very inerested to see real test data showing how much additional strength & toughnes tape adds to a join. I would guess that a reasonable sized cove contributes the greater proportion of the joint strength than the glass. But could be wrong.

    One downside of omitting the glass tape would be a reduction in stress transition.
     
  8. Alan M.
    Joined: Jan 2006
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    Location: Queensland

    Alan M. Senior Member

    I would tape the bulkheads and the larger furniture parts in Andrew. I've had joins which were just glued break due to brittleness, whereas the same join, reglued and taped, is massively strong.
     
  9. AndrewK
    Joined: Mar 2007
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    AndrewK Senior Member

    Alan,
    Are you refering to the chine panel joins that cracked during the hull rollover?

    I have a couple of friends that heve been building composite boats for a long time and both think that we are all wasting time taping everything. But both continue to do so as they do not want to take a risk with their insurance.
    Both have had experiances where they glued in panels and later decided to shift them and almost destroyed the boats in the process of removing them.
     
  10. Alan M.
    Joined: Jan 2006
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    Alan M. Senior Member

    None of the chine panel joins cracked, Andrew. They were all taped on the inside.

    I was referring to a horizontal brace on top of a seat back, that runs the length of the galley. It had glue fillets only on it, which would probably have been fine, except that when I was sanding the saloon roof, I overbalanced and put some weight on it, the brace flexed slightly and the glue immediately cracked. I ground off the glue and re-glued and taped the join, and now I can stand on that brace if I like. (Although it was never intended to be stood on.)

    Another area, which was always intended to be taped, was where the rear gussets from the cockpit roof meet the side decks. I had glued them and was planning to tape them both, but ran out of time and resin after only getting one taped - so I left the other till the next day. Well it didn't get done for the next couple of days, and I was always avoiding that side deck, using the side that was taped, until one time I forgot, and put about half my weight on the deck of the untaped side - the glue fillet immediately snapped. By comparison, on the side that was taped, you could jump up and down on the deck with no issue, as you can on both sides now they are taped.
     
  11. captainjsw
    Joined: Sep 2005
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    captainjsw Junior Member

    I am going to tape everything that is structural, my view is that the bulkheads and panels are not just in compression, when you are sailing the boat is flexing, just about glued only anything will crack in time. Well maybe a day to tape things is a bit on the light side - thats just me though, I always think things can be done as fast as I can think them, which of course is not the case. I do agree though watch the weight, a fair bit can be added without care, like only tape one side of the furniture etc, and use real light tape. One example I can give is that in a couple of places (on my current boat) - where I only glued ply a hairline crack appeared after a couple of years, now the bulkhead is secured top and bottom so structurally fine but the simple flexing of the panels causes the hard glue line to fail - I've since ground out the glue and added a small fillet of glass tape - nice messy job in a fitted out and painted boat.

    Cheers John
     

  12. doug kay
    Joined: Oct 2007
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    doug kay Junior Member

    Yes I agree with the tape being needed because of the brittleness of epoxy, I also drill holes around the perimeter of the bulkheads etc. and push glass strands through and then soak them in resin this helps the bonding to the hull.
     
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