Cracked front of keel - now what?

MagicalArmchair

MagicalArmchair

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I have been doing the unenviable job of removing my rusted mast truss from Triola.

http://www.ybw.com/forums/showthread.php?434586-Mast-truss-extraction-from-solid-Polyester-Resin

The force of the rusting truss expanding encased in the polyester resin coupled with the removal process has split the front of the keel and she was taking a dribble of water!! (which is the end game for this problem, and a problem our good friend and fellow forumite michael_w experienced first hand)

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Normally with repairs, I would create a 12:1 bevel, and cut out 2 layers of fibreglass per mm of original layup using West system epoxy - but by jove, the hull is an inch thick here, that would mean to repair this one inch crack would mean creating a bevel of 24 inches in diameter and around 40 layers of fabric plus fairing epoxy on top. Is there an easier way? Grind back with a demel and fill with epoxy and colloidal silica? That just sounds like a recipe for it to pop out half way across the channel. :(

Edit: Looking at an old post on here, I found a broken link from VicS to what I think was this document: http://www.bluemoment.com/downloads/grp_repair_manual.pdf. This offers an alternative to a bonkers 24 inch hole in the front of my keel:

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A better idea?
 
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If it's non-structural (and in that position it probably is), then I'd be tempted just to grind back to the undamaged substrate, leaving a keying surface on both sides of the crack, clean up, then refill with more of the same. A coat of antifoul and Bob's yer ...
 
It's a structural area but the good news is that you have plenty of space in there so just widen up the crack ,fill up with epoxy and the thickener of your choice and then apply a thick layer of glass or better yet carbon fiber with epoxy spanning the whole area generously. On the outside grind down enough to apply a few layers of the same . Make it rather wide .
 
Thanks all. Mike, I've had a look through all the West System documentation (including here http://www.westsystem.com/ss/assets/HowTo-Publications/Fiberglass-Boat-Repair-and-Maintenance.pdf), and they seem to advocate the 12:1 bevel everywhere that breaks me out in a cold sweat. Its interesting your Ballad had the same damage area when your truss failed, it shows I caught this just in time and that it could have been the death of Triola had I left it out of sight and out of mind.

I like the idea of 30boats of top and tailing the repair with GRP/Carbon Fibre:

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That will keep the repair size down and stop me having to grind out the 12:1 bevel (Effectively destroying the front of the keel in the process). I'm seeking some advice directly from Wests technical team at Wessex resins (I know they will say 12:1...). I'll also ask EC Fibreglass (they will say go talk to a boat builder :)). Any other suggestions?
 
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MagicalArmchair said:
Thanks all. Mike, I've had a look through all the West System documentation (including here http://www.westsystem.com/ss/assets/HowTo-Publications/Fiberglass-Boat-Repair-and-Maintenance.pdf), and they seem to advocate the 12:1 bevel everywhere that breaks me out in a cold sweat. Its interesting your Ballad had the same damage area when your truss failed, it shows I caught this just in time and that it could have been the death of Triola had I left it out of sight and out of mind.

I like the idea of 30boats of top and tailing the repair with GRP/Carbon Fibre:

rbRvThk.png


That will keep the repair size down and stop me having to grind out the 12:1 bevel (Effectively destroying the front of the keel in the process). I'm seeking some advice directly from Wests technical team at Wessex resins (I know they will say 12:1...). I'll also ask EC Fibreglass (they will say go talk to a boat builder :)). Any other suggestions?
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In my vue due to the particular shape of the affected area what you really need is a shoe that will take the compression stresses and at the same time keep the sides of the boat from spalying out.For this it must be very rigid hence the suggestion for carbon fiber and epoxy and also be very strongly connected to the sides.Epoxy over a wide area will achieve that.You can make it as thick as you want and then build the mast step accordingly.I would make it integral with the repair.
On the ouside the repair won't need to be as strong because the interior repair will relieve the bottom laminate of the compression stresses so just connect the two sides of the crack with a few layers of heavy roving or carbon fiber with epoxy.
 
Mark,
You could try posting on this problem on the East Coast Forum. Whilst I appreciate it's a PBO type of question, Javelin of the Southwold Boat Yard who is very much a hands on type of guy, posts on there, and may be tempted to offer some advice if he has a solution.

Good Luck, Ballads are lovely boats.

John
 
Thanks 30boat, taking the shape of the area into account will be key - and as you say, what is on the inside of the boat is what will matter in that area. As well as the area that is 'holed' I need to look up and down the whole front of the keel to make sure it hasn't been weakened further down. I may as well strengthen that up at the same time regardless.

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Thanks John, I will post on the East Coast Forum and see if I get a bite from Javelin. And thank you for your kind words, yes she is a wonderful boat: fast, spacious, forgiving, seaworthy and pretty, so worth the work in the short term.
 
Just one small thing.It is better to start with a small piece of laminate and then increase the area as you add on layers.This way each new layer grips on the base laminate instead of all of them relying on the adhesion of one layer.
 
Thanks 30boat, interesting that West recommend the opposite, starting with the largest piece first and working back to the smallest (and that's the way I've done repairs in the past).

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Cut an appropriate number of pieces of fiberglass fabric the same shape as the hole. The first
piece should match the outside edge of the bevel, with subsequent pieces gradually getting
smaller. The final layer should match the inside edge of the bevel. The combined thickness of
the layers should be slightly thinner than the original panel to allow for shaping and fairing
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From here: http://www.westsystem.com/ss/assets/HowTo-Publications/Fiberglass-Boat-Repair-and-Maintenance.pdf
 
I should imagine once its all a single bonded entity it makes little difference :) Thanks for your assistance 30Boat, I'll go with the 'top and tail' with thickened epoxy as the sandwich filling option to limit the size of the repair whilst keeping the strength up.

I have had a response from West saying they have sent my repair suggestion to their technical chaps to see if its viable.
 
MagicalArmchair said:
I should imagine once its all a single bonded entity it makes little difference :) Thanks for your assistance 30Boat, I'll go with the 'top and tail' with thickened epoxy as the sandwich filling option to limit the size of the repair whilst keeping the strength up.

I have had a response from West saying they have sent my repair suggestion to their technical chaps to see if its viable.
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Please post the results here.It will be interesting for us to see how it went. Good luck.
 
Wessex resins (West systems rep) called me to discuss my email and we had a lengthy chat about the repair, which he had followed up with a detailed email full of cracking instructions. What a great company, David was an hour was on the phone to me with useful, practical, real world advice, they will be getting my business going forward.

The upshot of the advice is below (I think, awaiting confirmation from them my layers vs depth is correct - I normally factor 2 layers of fibreglass per mm):

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I will post a full write up once I have completed the repair. On Wessex Resins recommendation, due to the structural nature of the repair, I will be getting a marine surveyor in to oversee, sanity check and document the repair for the ships papers (Alf Cackett of http://www.marinesurveyorskent.co.uk/ who is a great and professional chap.).
 
Just a few comments. The 24 to 1 chamfer is obviously designed for repairing thin GRP which might be expected to flex. Not nearly so necessary for heavier structure. If you can get access to inside of the cracked area then yes apply layers of cloth with epoxy after grinding down to clean laminate. If you can't get access to the inside then you have to make do with a repair on the outside. I would suggest grinding the front face of the keel then back on each side to give an area of grip. A bit above and below the crack. People have suggested carbon fibre for this repair but actually kevlar is far better for this role. It is flexible to easily take the curve of the front of the keel. (more flexible than glass) but has huge tensile strength so that if it has a decent length of grip down each side of the keel it can hold the keel together across the crack. Carbon has somewhat better tensile strength than glass but it's real value is in stiffness. Good for the finished job but not when going around corners. One problem with kevlar is that being so tough it is hard to cut with scissors. Try sharpening your scissors and bending the blades to increase overlap. Use lots of layers as with glass.
I don't think you need to go top vaccuum for the repair but just using cling wrap and masking tape over the runny resin will help to hold it all in place.
good luck olewill

PS re the people who advocate for a patch putting the biggest patch on first. Surely that means that the smaller patches put on later must press the first larger patch into a concave to get it into the hole and get a flat surface at the end. It also means that only the large patch is attached to the chamfer all subsequent patches adhering to the large one. Far better is to put the small patch into the hole first followed by larger and larger so that each patch is flat and overlapping to the substrate. It seems so obvious to me perhaps I am missing something.
 
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William_H said:
Far better is to put the small patch into the hole first followed by larger and larger so that each patch is flat and overlapping to the substrate. It seems so obvious to me perhaps I am missing something.
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Have to say, I'd agree with that. I've always done my own work like that, and I've certainly seen quite big repairs requiring Lloyd's certification done that way.
 
I have looked at Mark's hull and I am 99% certain of the cause of this problem. The hull was moulded in two parts and then joined together. The encapsulated keel is too thin and wrongly shaped with the keel wider and thicker at the base than the top for a single piece moulding (unless the mould was in many pieces). Also the thin aft tip of the keel is pointed and could never be easily made as one piece, the same applied at the aft end of the skeg. There is a rough join on the bow just under the forestay tang, again something a single peice hull would not have, The really impressive evidence is there is a feint crack down the centre line of the transom. Surprisingly a joined hull was quite a common production method 40 to 50 years ago. Mark has stated that his hull is about 25mm thick, which again suggests it could have been moulded in two halves to about 12mm thick and then reinforced internally for the balance. I would expect most, if not all, of the lay up was made using a chop strand gun, rather than chopped strand rovings.

So the agressive work to remove the rusting mast truss has opened up the original joint which would have only be reinforced internally. This will make the repair far easier as opening up the crack and sealing with epoxy, along with an internal and external laminate will certainly do and excellent repair.
 
Thanks all, and thanks for having a look Roger (wish I could get down there on a day like today and crack on, earning the pennies somewhat gets in the way). Yes, you are spot on, she was made in two halves. It'll be interesting what my surveyor says over the weekend also.

The chaps at Wessex Resins gave a very good summary:

Hello Mark

Very good to talk to you about your proposals for your repair to your Albin Ballad.

Firstly let me state as I mentioned we are not a company of engineers, marine surveyors or composite designers and we would strongly suggest that you employ such services for on site advice on a critical structural repair such as the one you propose.

We would suggest reading our Fibreglass Boat Repair and Maintenance manual you can download from our website.

Good sound repairs to Glass Fibre reinforced Polyester (GRP) structures are quite feasible using epoxy, in fact the secondary bond characteristics of an epoxy are far better than any other resin system available.

The steps we suggest you should follow are.

Assessment of the damaged area and the extent to which this should be repaired, a Marine surveyor may be able to help here, but the extent of the damage may not be apparent until preparation by grinding is conducted.

Choosing the correct materials Epoxy will provide the very best resin choice due to its adhesion to suitably prepared surfaces and its structural strength within a laminate. Multi axial glass fabric such as 450g biaxial fabric is unsurpassed in its strength when combined with epoxy for GRP repairs.

Joint or Repair design is fundamental to good results, it is simply inadequate to fill a fracture in GRP by opening it up slightly and filling it, this is just like a butt joint and does not provide enough surface area to support stress loading. Damaged GRP should be ground back to a strong broad taper, enhancing the available contact surface area. It should be thought of as a scarf joint rather than a butt joint. We advocate a bevel of a minimum 12 times the material thickness.

Preparation should be scrupulous, with surfaces clean, dry and well abraded. GRP should be ground back to expose good sound fibre, micro cracking of the existing polyester resin may become apparent as the grinding process proceeds, grinding should be conducted as deep as is required beyond any cracking crazing or fracturing. All materials should be to hand with glass fabric already cut from patterns and including personal protection such as nitrile gloves.

Conducting the repair by priming the prepared GRP surface with mixed epoxy. Filling small voids or discrepancies with epoxy thickened with 406 Colloidal Silica, ensures a continuous contact when laminating. On large areas each layer should be wet out individually with epoxy, never building up thicker than 3mm at a time to avoid exotherm. The layer with the largest area should be laminated first this provides the maximum continuous fibre of any layer. The use of peel ply will help with complicated or lengthy repairs that cannot be conducted in a working day.

There are just a couple of details worth mentioning on your repair Mark .

The external fracture could spread fore and aft as well due to the split moulded manufacturing of the boat, this needs further investigation by grinding before proceeding. The fracture itself needs grinding to a broad taper before filling with epoxy mixed with our 406 colloidal silica and 402 milled glass fibre blend combined, using the 2 step bonding method above. After this has been conducted a broad spread of laminate should be introduced at a bevel of 12:1 minimum.

Your proposal for an additional epoxy/glass floor in way of the keel trunk and to support the aft end of the new stainless steel fabricated mast foot is sound, just make sure there is a good spread of laminate either side.

You should inspect closely and repair if necessary the bulkhead bonding in way of the original mast foot.

You should grind deeply into sound laminate on the existing interior hull and introduce a broad spread of new laminate.

Bed the new stainless steel mast foot on thickened epoxy, our 404 high density filler provides maximum compressive strength when mixed with the epoxy.

I hope this helps you make the right decisions.
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They suggested against using carbon fibre as it is too rigid. Epoxy and resin gives 4%, as does Polyester and resin, so it is more compatible and sympathetic with the original structure, carbon fibre only gives 2%.
 
MagicalArmchair said:
Thanks all, and thanks for having a look Roger (wish I could get down there on a day like today and crack on, earning the pennies somewhat gets in the way). Yes, you are spot on, she was made in two halves. It'll be interesting what my surveyor says over the weekend also.

The chaps at Wessex Resins gave a very good summary:



They suggested against using carbon fibre as it is too rigid. Epoxy and resin gives 4%, as does Polyester and resin, so it is more compatible and sympathetic with the original structure, carbon fibre only gives 2%.
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Good advice there.I feel they are being cautions which is understandable. I see the point of carbon fiber being too rigid so multiaxial glass will be more suitable and also cheaper. The need for grinding until sound laminate is found is unquestionable. I would try to make sure that the laminate used to bond the two halves of the hull was removed entirely.
The things you can do with epoxy and glass , or carbon fiber, are amazing. I cracked the underside of my P Bracket a few years ago while extracting a stubborn cutlass bearing. Instead of replacing it I cleaned it and the area around on the hull and wrapped it up in carbon fiber and epoxy. I made the whole thing tight by stretching a rubber band made from an inner tube while curing which pushed out all the air and excess resin. The result hardly needed any fairing and is still going strong.
 
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