Reduction of strength due to delamination

Discussion in 'Boat Design' started by Mr. Curious, May 17, 2010.

  1. Mr. Curious
    Joined: May 2010
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    Mr. Curious New Member

    A 37" sailboat from a famous Swedish boatyard has a extensive delamination in the entire hull. The delamination has been determined by ultrasonic testing and also by inspecting a small circular part taken out of the hull.

    Total hull thickness is 12 mm and the delamination is located approx. 4.5 mm from the outer surface of the hull.

    Is it possible to roughly estimate the reduction of strength in the hull due to this delamination?

    Reference to literature or other web locations regarding this type of defects is also appreciated!
     
  2. messabout
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    messabout Senior Member

    S.W.A.G. (scientific wild assed guess) Probably not reduce impact strength much, but might reduce torsional strength by a signifigant amount. Can you determine the extent of delamination such as the length and width of the separation or separations?
     
  3. gonzo
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    gonzo Senior Member

    The hull is not safe.
     
  4. messabout
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    messabout Senior Member

    Gonzo does not mince words.

    If delamination covers very much of the boat, then I would hasten to agree. I suggest that you get some opinions by a qualified marine surveyor who can examine the boat first hand. That may cost a bit of money but it is better than chancing a disaster.

    It may not be much consolation, but yours is not the first boat to "come unglued".

    Hope for the best.
     
  5. marshmat
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    marshmat Senior Member

    I concur with Gonzo.

    To elaborate further: The delamination is about a third of the way through the hull; instead of a 12 mm thick panel, you have a 4.5 and a 7.5 mm panel that are, in essence, acting separately. The former case is about three times stiffer than the latter case. The damaged hull will flex far too much, and this will greatly accelerate its deterioration and increase its vulnerability to catastrophic damage.
     
  6. apex1

    apex1 Guest

    That boat is gone...........
     
  7. dskira

    dskira Previous Member

    Just to be very mean and gossipy: the name of the yard?
    I will tell nobody :D
    Daniel
     
  8. tunnels

    tunnels Previous Member

    It could be a magnificent REDO job !! if some one has the nouse and skills and got it cheap !!!:confused:
    As long as the inner skin is reasonably thick enought ,being a totall delamination would be a blessing and save hours of grinding . :p
    Did a cat once where the builders had used corematt in the bottom of the hulls it simply came apart from end to end both hulls so did a nice cut , grind and reshape or the sharp edges to take the bond of the new glass and simply rebuilt from in inner skins back towards the outside !! same as male moulding and if you make a nice job of the layers of glass you wont end up with to much fairing . !!If this is a yachts hull simply ending up with a reasonly good thickness of csm on the last layers and peel ply the outside and use wide laminating rollers and you could get a pretty good fair finish , then disc sand with a large disc pad grinder back into the csm and a generous layer of fairing compound and long board it from end to end all over and you could get a boat better than the original !!
    Look at the possitive side of whats in from of you !!:D :p


    If we never made mistakes how would we ever learn ????
     
  9. tunnels

    tunnels Previous Member

    Reference to literature or other web locations regarding this type of defects is also appreciated!

    Dont want to know the company just what was the constuction ?? what is it made from (glass lay up )and how was it made (what kind of core and how was it built ?)hand laminated, resin infusion etc etc ??. This is a interesting subject and not something that should be pushed under the carpet , Lots to learn so dont be shy and hold nothing back This what talking about things like this in this enviroment is all about !!:D
     
  10. Mr. Curious
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    Mr. Curious New Member

    I´m not the owner - just interested in the case.

    Posting a detailed description of the construction taken from http://www.hallberg-rassy.com/


    Standard Specification
    Hull and Deck
    Laminate construction of hull: white isophtalic gelcoat and isophtalic polyester is used. Hand lay-up method, insu*lated above water line with Divinycell PVC-foam against heat and cold. Integrated rubbing strake with brass strip. Blue decorative band in gelcoat. Under the mast support there is a metal beam cast into the hull stiffener. Strong under floor reinforcements, bonded with composite. Lead keel with reinforcement bolted on with fifteen stainless steel bolts. The stainless steel rudder shaft is carefully mounted with two self aligning bearings for low friction in all situations. Strong engine foundations of GRP for effective sound insulation. Deck and coachroof areas and also cockpit are of sandwich con*struction, solid in parts, laminated to the hull.
     
  11. Fanie
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    Fanie Fanie

    Could a medium be pressurised into the lamination to bond the inner and outer ? Why not. Many of the silicone similar bonds offer extreme strengths and may save the day.

    On the build I would say it's rather poor that something like this should happen. I don't see how anyone can stop and complete a hull later on. Layers should go wet on wet.
     
  12. Joe Petrich
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    Joe Petrich Designer

    How far forward and aft, up and down is the delaminated area? Square ft (m) of area affected? If the surrounding glass is sound (hard to know for sure) and the area is fairly small, say 1-2 sq ft it should be repairable. The bigger the area the worse off you will be. If it is a small area it may be caused by local contamination during lay-up (someone sweated on the glass and failed to clean it up for example) or a local lapse in getting the air out of the laminate with the roller. Larger areas may mean a bad batch of resin or another problem, basically not good.
     
  13. marshmat
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    marshmat Senior Member

    Original post said entire hull (so probably not the entire hull, but a significant percentage of it at least).... I agree, a couple of square feet ought to be repairable, but not delamination over a significant fraction of the total hull. Since the OP said it's at roughly constant depth, that suggests (to me) either a bad batch of resin, or a break of a few days during layup without proper protection or surface preparation when work resumed. Of course, all we have to go on is what the OP has written here...
     
  14. Joe Petrich
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    Joe Petrich Designer

    OK, re-read the first post. If what he said is true it's toast. Of course with enough money anything is possible. Agree with you on possible causes. You have to be careful when laying up. You don't want any secondary bonds in the hull laminate.
     

  15. tunnels

    tunnels Previous Member

    I am only guessing on this . The greatest causes of delamination are the density of the foam core is not high enough and this is really common 1!
    The bonding of the core to the outer skin , pressed into wet glass not vac bagged . Using Sheets that are not perfirated is a major , Even perfirated sheets need a few more holes to suck the resin through ,as well if they are have not had the bonding surface primed with a generous coat of resin .The issue of how much vac to use is something very few people know about as well . If you suck it as tight as you can you stand to have a thin under cured layer of resin and glass between the core and the hard skin .Not enough vac and the core wont conform to the shape of the hull and large areas wont be stuck with totall unbonded areas . Or the vac released to early and the core pulls away from the gelled resin slightly .
    Bonding into a layer of wet glass looks easy but like all things there are tell tail signs to look for and simply does the crew know exactly what they are doing like im talking 110% every one working on the job .To bond a whole side of a boat in one hit you have to be well rehursed with the complete operation from the time you cut the first sheet till you clean up when its finished . Using a core bond is another whole lot of simular issues to and it takes a really exsperianced crew to get a large area down and stuck properly . Weather can play a big part in all these operations so unless you have lots of know how with the materilas you are using you could have a hard time .
    Yacht hulls are quite differant to work on than power boat hulls !! The method for the core is simular but the materials used can be a lot differant .
    Theres a lot of other things that can and do contirbute to delamination as well But choice of core material and poor workmanship combined and you have a disaster in the making !!
    :D
     
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