Ferro Boat Reinforcement

[Azymuth]

I am planning on painting epoxy on my ferro hull below the water line.
I am also thinking about sheathing the underwater area with 2 layers of 600 gm double bias knitted rovings to ensure the thickness of the epoxy and add abrasion resistance to the hull. Perhaps even adding some resistance to point loading? Also perhaps making future repairs easier?

I have drilled test holes to check the armature - 6mm steel rods every 50mm longitudinally and 6mm rods every 100mm diagonally. 4 layers of hex mesh both sides although I did notice that the mesh is occasionally a bit rusty and seems a bit light. The cement is very hard and dark grey and about 22mm thick. The boat is a 35ft Samson of around 10 tons.

Comments please - Is the strength of the ferro so great that the additional strength of the sheathing is likely to be neglible?

[Simes]

We run a Ferro Schooner (Talisman of Fambridge) in UK waters. Assuming that you hull has been well laid and plastered you probably do not need to sheath it. Talisman is 32 years of age this year and upon have the hull surveyed this year we were delighted with the general condition of the hull. In the past I have always liked the idea of load sharing for spot loads on the hulls under water areas, I still like the idea now but with a decent ferro hull it is less important.

From a point of absolute safety and security, if I were to run Talisman upon a reef is a few grams of GRP / Epoxy going to make that much difference? If so . . . then have at it.

With Talisman there are many other areas that I need to address first.

Bon Hiver,

Simes

[Borealis]

I have a 1977 cement hull, launched '80. The cement is very hard. i am currently hauled out and doing minor touch ups to the hull. The previous owner had a disastrous situation where his anchor chain jumped the roller and the seas caused the chain to saw through the cement at the bow, luckily he caught it before it reached the waterline. If it was FRG the boat would have sunk, but he used mat/glass to make the repair. I discovered it whe I was scraping , grinding, sanding for new paint. I am not impressed at some points where the mat didn't bond well and i was able to scrape it off in sheets, however, in other places the mat adhered to the cement excellently and I can grind at it and it stays put. My conclusion from my findings is that the resin needs to be thick and have excellent adhesion to the substrate or else the mat will absorb the resin and create a weak bond. FOr repairs to my hull I only have to worry about 2 types of material, steel and cement. Adding a couple layers of mat and thick resin adds to the materials that you must consider for repairs. My cement hull is not going to break. All that being said I do think that glassing over a rough cement hull may give it a smoother finish but would be a lot of work. I like to grind my cement deficiencies until any rust stain is gone, open the area a bit so the spots dry and epoxy will fill the void. Sand, fair, paint. You mentioned 'abrasion resistance to the hull'. Your glass mat will likely abrade whereas your cement substrate will not. Now you have a fiberglass repair to make.

[Borealis]

Another point I forgot to mention. If there is any moisture in the cement then it must come out someplace and if that is between the cement hull and glass mat layer then now you have a blistering and delaminating problem, just as you would see in glass over plywood.