Grid system repair

[svHyLyte]

The yacht’s hull is solid, hand-laid, glass reinforced with an epoxy bonded partial hull liner extending roughly two feet above the bilges that was installed while the hull remained in the mold and still “green” to ensure a chemical as well as adhesive bond. The liner is comprised of a grid system designed to reinforce and stiffen the hull, particularly adjacent to the keel; mast-base; and where chain-plate loads are transferred into the hull. The liner keeps locker bottoms isolated from wet bilges and, during manufacturing, ensured the exact positioning of bulkheads. Before installation, the liner is partially cut-away between "ribs", and the resulting edge flanges tabbed to the hull with layers of bi-axial glass. This technique retains the strength added by the liner yet allows near full access to the inner skin of the hull. Penetrations along the undersides of the "ribs" for hoses, wiring et al are akin to penetrations in the webs of structural beams and of no consequence to the function of the sections.

Having "run aground", the keel would have attempted to rotate down and away from the from the keelson at the leading edge of the keel root, forward, and up and into the hull at the trailing edge. The keel bolts--16 or so--would have prevented separation of the keel from the hull hence the yacht accordingly rotated forward and down immersing the forward sections of the hull and raising the aft sections until the energy consumed matched the energy required to bring the yacht's forward motion to a halt.

The resulting torque introduced into the hull beneath the structural grid would have actually introduced transverse compression in the top of the ribs ribs forward of the centroid of the keel--hence the edges of the "cracks" in the forward ribs would likely show an upward ridge along the length of the cracks, while the ribs aft of the centroid would have been bowed upward, placing the top faces of the ribs in tension and cracks there would merely be "lines". The the corners of the intersections of the fore'n aft stringers and transverse ribs would have been likewise compressed or tensioned showing similar characteristics.

Despite the surface cracks, so long as the ribs/stringers did not separate from the hull--and the photos reveal no evidence of that--hull integrity would not have been compromised and the cracks would merely be cosmetic so long as they are merely surface cracks. One can determine that by releasing the tension on the shrouds and fore and back stays, relieving the tension on the yacht's hull and probing the cracks with a very thin probe. (Knowing the construct of the yachts, however, I doubt one will be able to insert a probe deeper than the depth of the gel-coat covering the ribs.) So long as the actual glass fibers in the section have not ruptured you have no issue other than cosmetic--which I suspect is the case. Merely clean up the glass, remove a very small area around the cracks--and I do mean small, no more than the thickness of the gel coat as you do not want to cut through the glass fibers, and full the cracks with Marinetex. If any of the glass fibers have ruptured, you'll want to remove the surface of the ribs to only the depth of the rupture along the tops and sides of the ribs and "splint" them by building up layers of biaxiel glass length-wise across the line of the cracks. This repair is actually better done while the yacht's afloat than on the hard as the yacht's weight is distributed and supported over the entire water plane rather than concentrated on the keel which will cause some distortion of the shape of the hull. If you do not have skills with glass, hire someone that does. Note, however, I doubt the foregoing will be necessary.

FWIW...

PS: It would be wise to clean up your bilge. Grime makes it very difficult to see what may have happened to a yacht's hull during a grounding and it makes a yacht smell bad.

[davidpm]

Originally Posted by svHyLyte

This technique retains the strength added by the liner yet allows near full access to the inner skin of the hull. Penetrations along the undersides of the "ribs" for hoses, wiring et al are akin to penetrations in the webs of structural beams and of no consequence to the function of the sections.

Despite the surface cracks, so long as the ribs/stringers did not separate from the hull--and the photos reveal no evidence of that--hull integrity would not have been compromised and the cracks would merely be cosmetic so long as they are merely surface cracks.

You certainly seem to know your boats. Are you a builder or surveyor?
Not sure I under stand the first paragraph above. "allows near full access to the inner skin of the hull" It seems to me that the inner skin of the hull is covered by the liner. I suppose you could say there is access for snaking hoses.

So you are not worried about any potential damage to the hull just aft of the keel where it apparently got pushed up and is deflected now while on stands.
I'm concerned about delamination of interior layers in that section or maybe even of the inside of the hull which is covered by the liner.

I like your answer better though.

[svHyLyte]

Originally Posted by davidpm

You certainly seem to know your boats. Are you a builder or surveyor?
Not sure I under stand the first paragraph above. "allows near full access to the inner skin of the hull" It seems to me that the inner skin of the hull is covered by the liner. I suppose you could say there is access for snaking hoses.

So you are not worried about any potential damage to the hull just aft of the keel where it apparently got pushed up and is deflected now while on stands.
I'm concerned about delamination of interior layers in that section or maybe even of the inside of the hull which is covered by the liner.

I like your answer better though.

David—

I am neither a builder nor a surveyor, although I did stay at a Holiday Inn Express the night before I answered your post….

Beyond the foregoing, I am a semi-retired Structural Engineer which does give one some insight into how structural systems operate. And, I own a Beneteau First 42, as does a close friend of mine—who does happen to be a surveyor—and because of that we have made a close study of Beneteau Yachts including on-going correspondence with German Frers, the designer of the First 42 and other Beneteau’s as well as discussion with the technical staff at Beneteau’s Headquarters and Ferenc Mate’s research on Beneteau yachts which are prominently featured in his book “The World’s Best Sail Boats”. (The foregoing was the basis of a piece I penned on the First series of yachts for a magazine a few years ago.)

N’any case, my earlier comments were predicated on the impression that you were merely concerned about apparent cracking in the lateral and transverse members of the grid system in the hull liner. Perhaps you mentioned the “indentation” in the hull on the aft end of the keel but if so, I missed it. A persistent concave indentation in the hull abaft the keel indicates that the grounding was hard enough to have rotated the back of the keel up and into the hull far enough to have exceeded the elastic limits of the hull. If so, the bond between the liner and the hull probably ruptured for some length and the glass fibers along the inner surface of the hull will have—probably did—ruptured. With that, the hull would not be able to recover its original shape as it would with strains within the elastic limits of the material. Given that, I suggest a detailed inspection of the yacht by a knowledgeable surveyor and/or marine engineer (and likely a call to your insurer). I would expect such investigation to include cutting a hole through the hull liner above the area of the “indentation” to determine the extent of the separation of the liner and fracturing of the keelson. I suspect that although the hull skin may be intact, the keelson may have ruptured with the broken edges bearing against one another, preventing the recovery of the hull-shape. Unfortunately, proper repairs will require that the rig and keel of the yacht be removed and the hull be supported on for’n aft rails, similar to the bunk-boards on a trailer, to relieve any stress on the hull during the repair efforts.

I’m sorry that the foregoing is not the relatively simple repairs I described earlier but, evidently, your grounding was much more serious than I first assumed. Unfortunately, one cannot simply ignore the damage as groundings are inevitable and while the water-tight integrity of the hull may not now be compromised, the weakness in the hull would certainly risk a catastrophic failure of the hull with the next grounding.

FWIW…

[davidpm]

Originally Posted by svHyLyte

David—
Perhaps you mentioned the “indentation” in the hull on the aft end of the keel but if so, I missed it. A persistent concave indentation in the hull abaft the keel indicates that the grounding was hard enough to have rotated the back of the keel up and into the hull far enough to have exceeded the elastic limits of the hull.

Thanks for the explanation, makes perfect sense.
Would you take a look please at the two pictures in the first post of this thread.
I actually missed it the first time I looked as the concave effect is very subtle.
Probably only a 5/15" inch or so.

That being said I would have guessed that the design shape would have been at least 1/4" convex. If that is right then the full deflection is 1/2" which might be significant.
Then again maybe their is some normal deflection with the weight of boat sitting on the keel.

What are your thoughts?

[svHyLyte]

Originally Posted by davidpm

Thanks for the explanation, makes perfect sense.
Would you take a look please at the two pictures in the first post of this thread.
I actually missed it the first time I looked as the concave effect is very subtle.
Probably only a 5/15" inch or so.

That being said I would have guessed that the design shape would have been at least 1/4" convex. If that is right then the full deflection is 1/2" which might be significant.
Then again maybe their is some normal deflection with the weight of boat sitting on the keel.

What are your thoughts?

David—

Relying upon an all but anonymous technical consult via the internet is likely not the ideal way to go with your situation. Never-the-less, if the apparent hollow that seems to appear above the straight edge of the tape measure in the photograph below is the distortion you refer to, I suspect that is merely a consequence of the concentration of the yacht’s weight on the keel alone, which was likely blocked slightly bow up when she was hauled out. The yacht’s hull is/was designed to carry it’s weight distributed over the immersed water plane, not concentrated in a relatively small area around the keel as it is when out of the water:



You will be able to ascertain with situation more effectively with the yacht in slings and some, if not all, of it’s weight lifted off the keel. Also, you might call BeneteauUSA and discuss the issue with one of their technical guys. You can start with Ward or Todd at 843-629-5300. Either of them can refer you to one of the technical/engineering staff whom I suspect will second my original thoughts on the matter (‘tho’ perhaps not) but offer you rather more valuable advice than I.

FWIW…

[mitiempo]

David

In the past few months 2 different Beneteaus - a 331 and a 40 - locally have hit rocks and the damage was extensive in the floor grid area although it did not look bad outside. The 331 repair was about 28k and the 40 repair was about 40k.

Get a good surveyor, possibly recommended by your insurance company, and with a proper survey you will know what is needed to repair the damage.

[davidpm]

Thanks for your comments. I'm using this as a learning example. I was able to get pictures but the insurance is held by others so they are handling the final disposition.

I did talk to the yard manager and he has not finished his estimate yet. He is thinking that he should drop the keel to check to see if their is any damage around the keel bolt holes.

By the looks of the keel boat heads they will have to be broken to be removed.
How are keel bolts replaced once they are broken in a steel keel?

I'm familiar with catalina lead keels where they just drill a hole and screw in a giant lag screw but what do they do in iron?

[hellosailor]

david, what you are calling the keel bolt heads, aren't those conventional hexagonal NUTS that are simply screwed onto the actual keel bolts?

If they are nuts, a nutcracker or penetrant (like PBlaster) and a torque amplifier (Spinal Tap joke, turn the amp up to "11") should spin them off or crack them off.

If the bolt actually has a hexagonal head on it, then it is some type of lag bolt or threaded bolt (Beneteau style, a bolt maybe 4-6" long) and again, penetrant to soak in, maybe a carefully used torch to encourage them, and turn the torque amplifier up to "11".

If they are hex-headed bolts and they snap off, you're looking at options like a cobalt drill and retapping. OR, quite seriously, drop the keel, clean the joint out surgically clean, rebed the keel in 3M 5200 when you jack it back up and give it a week to cure. It will be permanently attached, no bolts needed any more.

Remember, these days combat aircraft are glued together. The trick is, good prep and the right glue.

[CalebD]

David,
Can you lower the bow a tad and raise up the stern Jack stands a bit to see if the 'hollow', or deformity comes out? (Assuming boat is on Jack stands).
If you can't get the 'hollow' to disappear by shifting the weight around a bit with the Jack stands then it is time to call in the French Army as suggested above.

[SloopJonB]

Originally Posted by davidpm

By the looks of the keel boat heads they will have to be broken to be removed.
How are keel bolts replaced once they are broken in a steel keel?

I'm familiar with catalina lead keels where they just drill a hole and screw in a giant lag screw but what do they do in iron?

Keel "bolts" in an iron keel are actually studs threaded into the keel. To repair them you simply remove them, chase the threads in the keel to clean them up and thread new studs in.

Much simpler than the same job in a lead keel.