Crack in hull bottom

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Yoramy
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Crack in hull bottom

Post by Yoramy » Wed Jul 04, 2018 12:20 am

There's a crack in the hull below the stuffing box. This area which is approx 40 cm deep by 15 cm wide bilge, fw of the stuffing box is holding the stuffing box dripwater has probably been full of water for many years. It had multiple gelcoat-deep small blisters, without acid.
Boat was scraped and dried for the past 7 months. A lot of work was done including on thru hulls and the stuffing box, boat repainted and launched yesterday. A leak was visible immediately at the bottom of that small deep bilge, under the the point where the shaft enters the stuffing box. Water was coming in at a slow rate and somehow it became slower throughout the day as the bilge was dried and the leak isolated
The boat was relifted the next day and some 25-30 cm long cracks were visible on both sides of the hull below the shaft, dripping bilge water out from a single point.

Without removing the shaft, access to this area on the inside is very limited. I can just touch the bilge bottom with my finger tips. There are just a few cm between the hull and the shaft and less between the hull and the stuffing box.

Would resin and fiber repair - dry, grind, sand, lay wet diagonal fabric - on the outside alone be sufficient to restore structural strength and stop water?
How far around the cracks should the repair extend?

The cracks were not there before the boat was put on the crane straps to be lowered back to the water and they appeared exactly below the aft strap. I have scraped, sanded and painted this area extensively and would have noticed them, however this section of the hull felt and sounded thinner, with light coming through, and small blisters. The boat was left on the straps for the weekend with all that weight on a now dry, compromised area of GRP.

How should this fix be done so the straps do not crack it again. I believe this is not a high stress area when sailing.
Image

Westerly Conway ketch 1979

Your input is appreciated!
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Jolly Roger
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Re: Crack in hull bottom

Post by Jolly Roger » Wed Jul 04, 2018 1:26 pm

This looks far worse than it actually is. I would suspect the glass mat was not fully whetted out and compacted when your hull was laid up.

This repair can be done completely from the outside. You will get the best repair using epoxy rather than ordinary resin. Read this guide from West Epoxy for detailed advice. https://westsysteminternational.com/ima ... ersion.pdf

First you will need to drill a small hole (3 to 4 mm diameter) through the end of the crack, this will stop it cracking further. You will need to grind away a large area, but not completely through the hull. You will need to remove about 10 to 12 mm from the cracked area and to fair this out by about 30cm length wise outside the cracked area and up the sides and on to the turn of the hull. Once the hull has been washed to remove any dust and dried, then cleaned with acetone, you can start the repair. First fill any crack remaining and the holes you drilled with epoxy mixed with a filler like West 406 Colloidal Silica. Then it is time to start laying up graduated pieces of 300gsm woven mat. Start with a piece that just covers the cracked area, increasing in size with each layer. Each layer should be whetted out before being laid on the hull and covered with Peel Ply fabric to ensure you get no wax bloom to stop the bonding of the next layer. You should have about 6 to 8 layers of mat to complete the repair. Final fairing can be done using epoxy with 409 Microspheres as this is easy to sand. It may be wise to add a couple of formers or epoxy ribs into the inside of the hull for additional support - dependent on the space between the prop shaft and the hull.

You can get all of the materials (and advice) from Cornwall Fibreglass Supplies or East Coast Fibreglass Supplies
https://www.cfsnet.co.uk/acatalog/CFS_C ... TEM_3.html
https://www.ecfibreglasssupplies.co.uk/ ... poxy-resin
Roger
Concerto Fulmar FR38
Photos at http://s1294.photobucket.com/user/Conce ... 2/library/

Yoramy
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Re: Crack in hull bottom

Post by Yoramy » Wed Jul 04, 2018 10:21 pm

Hello Roger and thank you for the reply
Indeed the photo makes it look much worse than it is. However, I have today started widening the cracks and removing any loose material and there was much of it. I found two layers of glass at the bottom of that bilge working from the outside. And these layers were no longer attached to each other. It seems the top one was poured after the external was formed. Unfortunately some of this glass could be easily removed with my fingers. Then eventually I went through inside, with ease. I removed all the dark, crispy, separated or soft glass. I now have a hole of about 20 cm long and 2-4 cm high, instead of these cracks. There was no choice. The bad glass had to go if any fix was to be properly done.now there's just a few mm of dark glass on the aft end of this hole. The layers I mentioned, at this stage of the excavation are not a single mass, yet are hard to separate. I'm reluctant to continue and excavate as this may reduce the upcoming repair strength, and the hole is big enough already...and the loose stuff is gone.
I would like to do the repair from the outside only but not sure if it will provide enough strength.
I'm considering creating a mold of resin or epoxy with fabric ( which?), then when dry press itnwith supports against the hull from outside after laying fabric and resin or epoxy on the outside of the hull.

It is repairable I hope to a good level of strength. Once repaired the boat will be lifted on its keel, not on a strap pressing some 5-6 tons over a 6 by 25 cm just- repaired bilge bottom. The cause of this is clear to me - a weakened area, full of water for decades, then dried, scraped, primed, sealed and painted, then the press of the strap for a whole weekend.

Your input is highly appreciated
here are some images
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Jolly Roger
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Re: Crack in hull bottom

Post by Jolly Roger » Wed Jul 04, 2018 10:51 pm

The bottom of the hull at this point is not that structural as the sides of this area are the structural part to help stop the hull from flexing along the center line.

If the existing layers of layup are showing delamination, then inject some epoxy resin to secure them. Try to find how high it goes up the hull and then drill several small holes through the outer layer, but not right through. Then use an epoxy putty to seal the exposed crack. Use a syringe to inject the epoxy in the holes until no more can be injected.

Opening up the crack is not a problem, but just makes the first layer of repair a bit more difficult to bond to the hull. The Peel Ply taped to the hull should be sufficient to hold it whilst it sets.

Try to build up a thickness of layup nearly equal to the original hull to allow for final filling. This whole area will be stronger than the original layup as epoxy is stronger than resin.

The advice given on the YBW thread is slightly mixed and shows the cautious nature of many boat owners. Just consider what you would have done if you were in a far flung port abroad with no internet access.
Roger
Concerto Fulmar FR38
Photos at http://s1294.photobucket.com/user/Conce ... 2/library/

Yoramy
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Re: Crack in hull bottom

Post by Yoramy » Thu Jul 05, 2018 9:21 am

Thank you Roger
The existing delamination is only on the bottom of the bilge, not up the hull from inside so I wonder if any holes should be drilled and injected with epoxy.. The top glass layer at the bottom of this bilge seems to have been poured on top of the external hull layers. There is actually no space between that top delaminating layer and the bottom one. Yet if I push a sharp tool in between them, the top layer can be slightly lifted with some effort. So there is no space to inject anything there.
I don't think I can get a hold of real peel ply here in South Portugal. Stuff is really difficult to get here in shops. Is there an alternative to peel ply?

Iwould rather use epoxy but from what I understand, epoxy would not bind well with fiberglass fabric?

I'm thinking of laying up a first full size (160x50 cm) piece of fabric on the whole area I've now grinder to the laminate, have it round the hull from top of starboard to top of Port. However gravity will pull the materials down unless I get it thickened, and even colloidal silica is nearly impossible to get here. They use talcum powder here, which I understand tends to take water over time. How can I solve that dripping and sagging problem which would likely appear as the wet materials are laid up from the outside?

Then I could lay a second tried and fourth layer on the outside. Is it better to wait for each layer to dry up before I lay the next one?

Then I want to start on the inside, and with the limited access there, either pour epoxy into the depression created by the outside new skin and existing cavity of the hole, or add fabric to it, although maneuvering wet fabric down there is extremely difficult as I have learned when I rebuilt recently the small bulkhead holding the stuffing box and the Stern tube flange in that bilge.

An alternative is to build wet layers of fabric and resin in the shape of the hole, away from the hull. Then insert it into the hole from the outside, add a large layer of wet fabric on top of it rounding the hull side to side, and somehow (how?) hold it in place as it dries, then add more layers, cut to the full size of the grinder area.

Unfortunately the ybw thread did not produce any tangible suggestions so far, in contrary to this thread

In a far away port with no Internet access, I would probably start laying up from the outside with any available materials, then add whatever can be added from the inside, and set sail.

Thank you, your input is very helpful

Jolly Roger
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Re: Crack in hull bottom

Post by Jolly Roger » Thu Jul 05, 2018 8:58 pm

Yoramy wrote:
Thu Jul 05, 2018 9:21 am
The top glass layer at the bottom of this bilge seems to have been poured on top of the external hull layers. There is actually no space between that top delaminating layer and the bottom one. Yet if I push a sharp tool in between them, the top layer can be slightly lifted with some effort. So there is no space to inject anything there.
If you can lift the top layer, then there is space for some epoxy. Just inject as much epoxy as you can get in, any excess will squeeze out. Any extra bonding is worthwhile to achieve.

You need powder bonded mat. This is the reason.
"Necessarily the individual strands of glass that make up the mat need something to bind them together. In conventional emulsion bound CSM the binder is broken down by the polyester or vinylester resin it is designed to be laminated with. However, the binder used in conventional CSM is not broken down by epoxy resin meaning the individual strands all stay together in their original mat making the CSM impossible to laminate with properly. 'Powder Bound' fibreglass matting (CSM) is designed for use as chopped strand mat for epoxy resin, using a powder based binder that does not need to be broken down in the same way as emulsion bound mat, making it essential for use when laminating with epoxy resin, either making a mould or a part."

Peel Ply is used to pull the excess resin through it and peel it off the surface as it removes the excess epoxy along with the wax surface that forms. There alternatives for Peel Ply and Mr Google suggests polyester dress liner fabric or Rip Stop nylon.

With regard to the first layer of mat, you can fit it externally and support it with the Peel Ply or the alternative. Tape both top edges to the hull and if need be use some cardboard for extra support. The Peel Ply and cardboard will be thrown away


The West epoxy guide suggests this wet method for laminating.

By working with small quantities of epoxy, it is possible to work at a comfortable pace over quite large areas to be reinforced.

1. Prepare the surface for bonding as discussed in surface preparation (page 10).
2. Pre-fit and trim the cloth to size. Roll the cloth neatly so that it may be conveniently rolled back into position later.
3. Roll a heavy coat of epoxy on the surface.
4. Unroll the glass cloth into position over the wet epoxy. Surface tension will hold most cloths in position. (If applying the cloth vertically or overhead, it is possible to wait until the epoxy becomes a little tacky). Work out wrinkles by lifting the edge of the cloth and smoothing from the centre with a gloved hand or a squeegee/spreader. If cutting a pleat or notch in the cloth, lay it flat on a curve or corner, make the cut with sharp scissors and temporarily overlap the edges.
5. Any areas of cloth which appear to be dry, (white in appearance) apply more epoxy with a foam roller.
6. Remove the excess epoxy with a squeegee, using long overlapping strokes of uniform pressure. The object is to remove the excess epoxy that may allow the cloth to “float off” the surface but avoid creating dry spots by exerting too much pressure on the squeegee. Excess epoxy appears as a shiny area while a properly wet out surface appears evenly transparent with a smooth cloth texture. Subsequent coats of epoxy will fill the weave of the cloth.

Hope all of this explains how to progress now.
Roger
Concerto Fulmar FR38
Photos at http://s1294.photobucket.com/user/Conce ... 2/library/

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