Looking for advice on Keel repair...

[NahanniV]

I have been chasing leaks into my bilge for the last three seasons. First season I thought it was the leaky stuffing box but repairing that did not dry the bilge. Second season I found leaks in the connections between my water tanks, but after fixing them the bilge was still wet. This season with the help for a borescope I found that the water was coming from under the floor pan possibly near the base of the mast compression post. We also noticed that the leak was worse when sailing hard and stopped when rigging tension was eased.

Exposing the suspected area was quite a chore. Had to remove: the mast, compression post, salon table, floor, and fuel tank to get to it.

[NahanniV]

The mild steel compression post base was badly corroded from being continually wet.

But I could not see where the water had been coming from.

So, I put the compression post back in. The marina manager was not too keen on re-stepping my mast so I made up a jig to supply the compression:

[NahanniV]

Bingo !

The leak was coming from the front edge of the keel and trickling down to the bilge area. I had to cut some inspection holes to see it.

[NahanniV]

Got hauled out.

Nothing was easily visible from the outside, so I asked the guy pressure washing the bottom to give that area an aggressive spray. That showed up two small cracks. Sanding off the bottom paint revealed them plainly:

[NahanniV]

Cutting away some bad laminate on the inside revealed more of the cracks.
Some of the laminate (roving) seemed to have been never properly laid, it was just laying over the "V" of the keel, hard, but not attached, as if it was unable to conform to the sharp bend or the keel.

Also, I noticed some red filler or possibly paint in the crack.

[NahanniV]

The boat has previously had its underwater gel-coat removed. There is a layer of white filler over the whole underwater surface. Sanding away the white filler revealed the cracks from the outside.

Nothing that looked like laminate was removed, only what I would call filler.

The cracking seems to be less than two inches long (some of the pics are closeups).

[Don C L]

Personally I'd re-design and build a new base for the mast after a bunch of glass work on the hull. That part of the hull/keel is obviously not designed and/or built to take the compression forces which can be as much as the displacement of the boat. I'd probably be thinking of some kind of stainless frame to spread the load out over more of the hull capable of handling it. I wonder if other Finnsailer owners have seen something similar. There are a bunch of folks on here very familiar with repairs like this, I hope they chime in!

[OceanSeaSpray]

Well, you have a cracked fibreglass hull. You are going to have to grind the glass back to a taper on each side of the crack over a fair distance, dry the laminate really well and lay some new woven roving over the area.
Use epoxy resin (much stronger bond to the old laminate and new reinforcing) and rebuild the laminate. Start with the shorter pieces of cloth and keep overlapping outwards until you are done. You cannot use any chopped strand mat at all with epoxy.
If you can glass from inside (it looks like it), then also do that and build it up from "flat" on each side of the crack.

Add an epoxy underwater filler over the entire repair area as it is just setting (still tacky) and then sand/fair later once cured. Don't cut into the new glass when you sand. Heat the entire repaired area to about 50degC for a few hours about a week after completing the repair to post-cure it and reach maximum strength. Don't put any load on it at all before then.

[NahanniV]

Originally Posted by Don C L

Personally I'd re-design and build a new base for the mast after a bunch of glass work on the hull. That part of the hull/keel is obviously not designed and/or built to take the compression forces which can be as much as the displacement of the boat. I'd probably be thinking of some kind of stainless frame to spread the load out over more of the hull capable of handling it. I wonder if other Finnsailer owners have seen something similar. There are a bunch of folks on here very familiar with repairs like this, I hope they chime in!

Certainly I will replace the compression post base. I was surprised to see that it was steel. It looked bad, but there was actually quite a bit of it left after I cleaned it up; A bit of rust expands a lot. I'm thinking of replacing it with a base made up out of a composite material like G-10 or Phenolic.

It was interesting that the survey said:
"Mast Compression:Compression is absorbed from the deck stepped main mast through a wooden post secured over a re enforced floor integral to the hull liner. There is no sign of fracture or stress overload."
Obviously the surveyor did not really look at it.

I was thinking that the crack and leak, was probably just poorly repaired collision damage.

[OceanSeaSpray]

This type of damage arises from mast compression and insufficient strength. You would never see that due to a collision. By pulling up on the forestay and backstay while pushing down on the mast step, you are effectively trying to break the hull in half, all the time.

High compression, slamming can cause cracking like that. The compression loads should be transferred into the floors first, not directly into the hull, so they are better spread out. Make sure the mast step design can achieve this. Nothing wrong with steel, it is strong, resists fatigue well, cheap and easy to work with. You can encapsulate it in epoxy and glass if you want, or galvanise it, or do both.

[NahanniV]

Originally Posted by OceanSeaSpray

... The compression loads should be transferred into the floors first, not directly into the hull, so they are better spread out. Make sure the mast step design can achieve this. Nothing wrong with steel, it is strong, resists fatigue well, cheap and easy to work with. You can encapsulate it in epoxy and glass if you want, or galvanise it, or do both.

The compression post base bears on the floor pan which is bonded to the top of the encapsulated ballast at that point (see attached). Wouldn't the ballast transfer the force to a large area of the hull ? Not sure how I could improve this ?

This crack has been there for a long time. As I was sanding to reveal it crumbly filler fell out of it.

No, nothing wrong with steel, the original lasted 35years. But I am not a welder or machinist, don't know where to get it galvanized, so making it out of a sheet of composite will be less expensive and completely corrosion proof.

Cheers,
JM.

[jimbunyard]

If I'm understanding your pictures, the transverse crack that is letting in the water is about 3 feet forward of the compression post base. If that is correct, I agree that the keel had an abrupt encounter with something immovable, and was not repaired adequately. I think the repair approach outlined above is pretty good, on the inside I would only remove enough glass to get to well saturated material, taper it well, and put in layers to equal 1.5 to 2 times the hull thickness in that area. On the outside you're kinda limited by fairing requirements, but I'd try and grind enough off to get at least a couple of layers of biaxial on, well feathered in.

It looks like the compression post step sits directly on the keel. That is good if it is so. If you want to replace the existing one with G10 or phenolic, and make it removable, I think you might have rigidity and strength issues. If you want to build it in permanently, probably not so much, but it will need to be well thought out.

Alternatively, you could just copy the original in aluminum, stainless, monel, or even just plain steel (the one you have doesn't look that bad), and not have to re-engineer anything at all....

[NahanniV]

Originally Posted by OceanSeaSpray

.... lay some new woven roving over the area.....

Do you think I will be able to get the woven roving to conform to the shape of the keel in this area ? Or, do you mean smaller pieces ?

Cheers,
JM.

[OceanSeaSpray]

Originally Posted by NahanniV

Do you think I will be able to get the woven roving to conform to the shape of the keel in this area ? Or, do you mean smaller pieces ?

Cheers,
JM.

Yes you should. It will follow shapes up to a point by "twisting" it a bit out of axis, try draping it dry first. Also choose its weight so it remains pliable. 450gsm is quite easy to mould into place, 600gsm starts to spring back quite a bit if you try to go around a small radius.
Always wet the surface and lay dry glass. Always try to get the resin to come through from underneath before adding more from the top, so you get a strong, glass-rich laminate. Paint over with resin after the last ply so your laminate doesn't try to "go dry" as it cures.

If you experience issues with glass lifting, as you don't need to worry about letting solvents out with epoxy, you can cover your repair with a piece of cellophane (the one that tears clean without zero stretch, the epoxy won't stick to it) after you have finished and stuff rags and a weight on top (inside) if needed to hold the glass down in the corner. Outside you can tape the cellophane tight over the repair. Only do this if you have to.

Your GA drawing is quite good. Since you are in fact pushing down onto the ballast, you are not going to be able to spread the load much more than that. The problem is around tensile strength in the hull itself, so build it up on the inside.

[pcmm]

Originally Posted by NahanniV

Do you think I will be able to get the woven roving to conform to the shape of the keel in this area ? Or, do you mean smaller pieces ?

Cheers,
JM.

I would avoid using woven roving as without mat as it creates a resin rich laminate which is not what you want. Use 1708 biaxial for this. its 2 layers of unidirectional fibers with an epoxy compatible mat all stitched together. Much stronger than roving, and takes curves much better. its thinner so will take more layers but will be far stronger in the end.

laminates are much easier to work with if you build up the patch on a work table saturate it and then place the patch on the hull, just like putting up wall paper.

This method works for me:

https://www.youtube.com/watch?v=6N7YMr6E564