Conference unifix::sailing

>>>    a Pearson 19 which has a very thin fiberglass hull.  It is so thin
>>>    that I have a good deal of surface cracks at the beam running towards
>>>    the stern.
    
The key is to figure out if it's boat flexing that is causing structural 
cracks, or merely the gelcoat crazing (which reflects minute local stresses 
right at the very surface -- quite common, and having more to do with the 
physical properties of the gelcoat resin & hardener than the design itself.)

So these may just be superficial gelcoat flaws.  If minor and well above the
waterline, they may not be worth the trouble of repair -- at this stage, 
anyway.

If they are on the outside surface, your repair (if you decide to do it) 
probably should also be on the outside.  

Forget carbon fiber.  Expensive, hard to work with, and the benefits won't 
outweigh costs and hassle on a Pearson 19.  Besides, unless it's a 
structural problem, adding frame strength just adds weight.  Unless 
designed, engineered and installed carefully, new frames ("ribs") may just 
provide new "hard" spots for stress to accumulate -- it may add to you 
woes down the road, not cope with them.

You've heard it before in this file:  To be sure(r), hire a qualified 
surveyor.  He'll give you the straight skinny, suggest repair strategies 
if appropriate, and probably charge less than botching a single repair.  
Plus (if you go for a complete survey) he'll look at everything and give 
you a full picture, paying attention to interacting factors.

J.

Call the factory and ask for their advice. This is even cheaper than a
surveyor! And many times they have knowledge that the surveyor has no
access to. (E.g. they might have this problem on many 19's...)

It would be useful to know what caused the overstress. I presume this is
a trailerable boat. Does it sit on the trailer properly? If not, the boat
may be undergoing stresses on the trailer that it would never experience in
the water.

--RS

    The cracks may not be related to the thickness of the construction.
    I have these on my boats but most of them have occurred at known
    impact points.  The bottom of the interclub dinghy has many from
    years of beach landings.  The cracking is superficial and has not
    to my knowledge been the source of leaking.  Where it's been bad
    enough to actually cause the gelcoat to chip away, I've used the
    gelcoat repair kits or Marine Tex to patch the affected area with
    good results.  
    
    When I first bought the interclub I saw the cracks and, in a panic,
    called a boatyard for advice.  "Forget it, they all do it" they
    told me in a less than respectful tone.  I fixed them anyway.  After
    the first few collisions and beach landings, I realized the yard
    had been right.
    
    Thiness and softness don't always go together and neither is
    necessarily bad.  Press on the bottom of a Laser hull, even a new
    one, with both hands.  It's surprising how much flex there is. 
    But that's the way they're built.  Lack of stiffness may be more
    disconcerting than it is unsafe unless the softness is extreme.
    If any of the following occur, your boat may be a candidate for
    some reinforcement:
    
    	Inability to maintain shroud tension.
    	Noticeable hull twisting in waves.
    	Creaking noises coming from the centerboard or keel.
    	Cracking at knees, bulkheads, and other areas intended to be
    	reinforcement points.
    	Noticeable flexing in the hull under body weight.
    
    If builder says to put in another layer of glass, it probably needs
    it.  I'd suggest mat or roving for bulk.  Carbon fiber and other
    directionally woven cloths are probably wasted for this application.
    Take an experienced person out sailing for a diagnosis.  If
    reinforcement is needed, I'd go with the simplest solution first.
    You can get creative with additional knees, stringers, fillets,
    grids, etc later.
    
    - gene

RE: "softness" of the hull,

Some flexing of fiberglass is quite often desirable, as it allows local 
stresses to be transferred to a progressively larger area.  Stiffness 
can creates hard spots, which can cause failure at the nearest adjacent
weak point before spreading the load effectively. 

SORTA OFF THE POINT, BUT INTERESTING:  As an example of this, on a recent
flight I happened to sit next to a Qantas 747 pilot (he was deadheading),
and we enjoyed a couple hours discussion about some of that plane's design
features.  Besides the rather amazing fact that fully fueled a
trans-Pacific 747 weighs over one million pounds (!), he said he'd seen a
film of Boeing testing a 747 wing to failure.  With the gear tied down, an
upwards point load was applied to each wingtip region; failure finally
occurred when the wing was *32 feet* above horizontal, at several times
the maximum airframe loading required.  Obviously sailboat hulls aren't
engineered are carefully as airplane wings, but the effectiveness of using 
the materials properties and load distribution through flexing is the same. 

;-),   J.

    Thank you for the great suggestions!  Before I bought the boat it
    was sitting on a trailer.  I do not trailer the boat, it stays in
    a slip.  The reason for sending this reply is the crack got so bad
    on one side that a piece of the fiberglass actually chipped off
    just above the waterline.
    
    The boat actually leaked after a good day of sailing.  Being a previous
    wood boat owner I am always sensitive to water in the hull.  I have
    a habit of checking for water before leaving and when I get back
    in.  
    
    Upon discovering the leak I used the Fiberglass repair kit and it
    worked well.  Pearson recommended laying sheets inside the hull.
    The survey is a good idea.  Thanks for all your suggestions and
    comments.
    
    Jim