Is this delamination or oilcanning ? - SailNet Community
 
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post #1 of 8 Old 09-03-2009 Thread Starter
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Is this delamination or oilcanning ?

I have just looked at a 45 foot boat built in 1979 and described as being a solid glass hull.

When I rub my hand over the hull there are some very noticeable ripples 3/16ths to 1/4 inch deep over 3 to 6 inches just under the turn of the bilge. I think they are both front to rear and top to bottom

I can not believe the boat came out of the mould like this.

Before I go to the expense of a survey does anyone know what this might be and how serious it is.

I do like the boat but I suspect something serious could be wrong.
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post #2 of 8 Old 09-04-2009
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If a boat is pulled too green from a mold it not uncommon for some weird changes in shape to occur. I've seen small FG lapstrakes with almost offset "planks" as a result of being pulled too green (ie: to early, before the resin has fully set up/cured). It can also happen when the initial layup separates from the mold and becomes able to move and adjusts to stresses as it cures. If that's the cause then you should be able to take a flexible batten and lay it over the area in contact with the hull. If the ripples are all away from the batten (the batten forming a smooth curve with the ripples as dips away) then I would initially suspect a separation when molding. Regardless of the cause, when this happens there is then the question of what to do. Simply toss several thousands of dollars of materials and time for what is basically a cosmetic problem or what?

You are right to be concerned, if it is a solid layup you can try scratching your fingernails over the area and the areas surrounding. Often separations will be detected by a distinct change in sound as the space created by the separation acts as a resonator. This works as well to detect voids in decks etc. where the vacuum bagging or whatever failed to force intimate contact between the outer layers and the core.

Since it is a solid layup you can also try trans-luminescence which is a big word simply meaning shine a light thru the hull. Damaged areas, separation, bruising and delamination will show up as darker areas. Depending upon the amount of veil coat (some boats don't even have a veil coat) you will need a powerful light and to remove the bottom paint to the plastic. Before scraping off the bottom paint I would try shining the light above the waterline to see what sort of transluminesce you get for that hull. If there is a heavy veil coat you might not get much. The navy used to require that all boats built for them in FG were layed up without gelcoat so that they could inspect the layup for bubbles, voids and unsaturated mat, roving, cloth etc all of which show up as dark or black spots or areas. Hand held million plus candlepower lights being readily available make this an easier proposition than it used to be. Also you can check with the manufacturer if they are still in business. If it was pulled green or separated from the mold and the ripples are as a result they might have a record of that (and that they had to reduce the price of the boat as a result for cosmetic reasons.)

I hope this helps. Keep us posted as to what you find.

Bests,
Wiley
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post #3 of 8 Old 09-04-2009 Thread Starter
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Thanks Wiley

That is exactly the sort of information I was looking for.

I am going to go back today and have another look at the hull myself and may see if I can find a local expert to give me an opinion.
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post #4 of 8 Old 09-04-2009
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Most probably the boat has been blocked improperly and the stresses from the improperly placed jackstands and *location of blocks under the keel* are causing the warpage of the hull.

Especially if the far aft trailing section of the keel is sitting on a 'block', the keel aft section will tend to 'rotate up' and the flat hull sections adjacent to the keel root will 'buckle'. When blocking such keels the aft block should be placed DIRECTLY under (and slightly in front of) a line running straight down from the intersection of the aft section of the keel and the hull; if the keel is blocked aft of the above location then the keel will apparently 'rotate' and hull buckling will almost certainly develop. Many boats of this era are subject to this 'blocking / jackstand' anomaly, and if properly 'reblocked' will rapidly resume their proper 'shape'. Such boats also benefit if the far front and far aft jackstands be set up a bit 'tighter' than those set amidships.

Pearsons, ODays and other similar boat designs will do this buckling if blocked improperly .... Nothing to worry about if not left too long and the FRG doesnt begin to 'creep' (permanent viscoelastic distortion).

Suggest that the hull be 'reset' properly on the jackstands so you can make a better decision.

:-)

Last edited by RichH; 09-04-2009 at 09:39 AM.
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post #5 of 8 Old 09-04-2009
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Blocked improperly, impact damage, osmotic problems in the layup...you'll probbaly need the surveyor or other professional "hands on" opinion to find out. If it is just cosmetic, no big deal. If it is structural...

Have you tried asking the owner and broker "What's this all about?" Sometimes, you'll get more than a blank stare.
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post #6 of 8 Old 09-04-2009 Thread Starter
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The broker just got a reply from the owner. The boat was peeled and gelcoated some years ago. It might just be sloppy fairing work.

Although I am not discounting improper blocking I dont think that is what is wrong. But I have never seen bad blocking ripples who am I to have an opinion.

I will get a surveyor to look at it if we decide to go further.

John
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post #7 of 8 Old 09-05-2009
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John, In retrospect that is an obvious answer. I only witnessed close up a peeling several years ago in the early 90's. Immensely obnoxious noise and the cutter head would create ripples exactly as you describe. The machine I saw was a cutter head on a articulated mechanical arm that was robotically controlled by a joystick. There was a vacuum setup but in spite of that the operators view was limited. I remember thinking that more damage than good could easily be done in moments in the hands of an unskilled operator, which is true with any power tool. And "OJT" training means some less than perfect work. The cutter was carbide and could take off gelcoat and part of the first layer of mat in one pass. Like I said the noise was very very bad and after watching once I stayed as far as possible from any such work when in the yard. Fortunately I'm retired and was when I watched the peeling and so there is no job requirement to be present. Hopefully newer better machines are doing this work but the one I saw in the early 1990s would easily produce such ripples.

Aside from cosmetic after effects (the ripples, poor fairing afterwords) did they replace any laminations removed with epoxy or vinylester layup or simply overcoat and call it good? If they can give you a date when this was done and if there has been no further blistering then the job was successful from that aspect save that it was less than beautiful. If you wanted to verify replacement of removed layup you might pull a thru hull and get a visual x-section of what was replaced.


Bests,
Wiley
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post #8 of 8 Old 09-06-2009 Thread Starter
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Thanks Wiley I think it may well be the peel and recoat job that is the problem. I suppose that if it was done a few years ago and has not yet failed there can not be much wrong with it. However there are about a dozen dime sized classic osmosis blisters at different points on the hull.

I guess I just need to bite the bullet and get a surveyor.
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