Keel repair

Please also cross-reference to the FAQ entry on Rudder and Skeg Repairs as there is information in that FAQ entry which is equally relevant to Keel Repairs.

Here is a 2021 article on Keel & Skeg Repairs that was collated in 2021:

download article as pdf (version without photos, 127kb)

download article as pdf (version with photos, 20mb)

– photo gallery associated with repair of #086, “Stella”, formerly “Jack Iron”

– photo gallery associated with repair of #135, “Petit Chantier”, formerly “Necessity”

– photo gallery associated with repair of #174, “Anakena”


The entries below were collated up until 2019.

I am seeking information to assist a keel sole repair: (A) What material is the sole of the keel and how has it been joined with the rest of the hull? (B) What is the best strategy for repair, especially: what should I use to fill a cavity? Background: When we surveyed my Corbin, we noticed damage to the sole of the keel. No information was available as to the type of damage or when it happened, but by the looks of it this may be many years old grounding damage. I have attached two images: (1) an overview showing the crack at the leading edge and the “cavity” at the stern See Pic 1: Overview and a close-up of the stern damage See Pic 2: Closeup. Forward, I think the crack around the edge suggests that the sole was not laid up with the hull but cast separately. Aft, probing with a screwdriver dislodged a few walnut-size chunks of material, almost like gravel, and this left the white spot that is visible in the photo. No fibers are apparent at that spot. Since this was pre-purchase, we refrained from probing more vigorously. Boris S. (#131, Two Crows, previously Phoenix).

a. I have one of the early Corbins and I’m still building it. Nearly finished though. The Corbins were laid up in two longitudinal halves. Then the two halves were lifted together and glassed on the inside to form a single structure. In my understanding there were no old or new hulls. There was but a single hull mold from which all the Corbins were made. There was, however, a fire at the factory which destroyed the deck molds . So today you will see two configurations , for example, of the pilothouse, the old and the new. Since the hull is one piece there is no separate keel. You will not find a line where the keel attaches to the hull. No keel bolts or anything like that. The ballast is internal. It was placed in the bilge from the inside of the hull. It was glassed in place and covered over with fiberglass. In looking at the photograph of the underside of the keel I believe I can see the line down the middle where the two halves of the hull were put together. This would mean that I am looking at fiberglass, with the gelcoat having the barnacle growth attached. No problem here. Some epoxy or acrylic filler material should solve the problem. If, however, I am looking at exposed lead, and I’m suggesting this because I don’t see a radius where the side of the keel turns to the underside, then you will need to glass the underside of the keel. In reviewing your note i find that I failed to address the issue of the walnut size chunks you’ve extracted. This has me puzzled. I don’t believe this is fiberglass. Is this lead that has been in touch with salt water and it’s corrosive effects? If so how extensive is it? Until you’ve made a determination on these issues it’s pretty hard to suggest a solution. Sincerely, Richard Bakker= , s/v no name yet. (subsequently #008, Stingray).

b. The keel and the hull were built and laminated together, and so is the bottom of the keel. The center of the hull, including the keel, had additional layers put in and in order to do so, and since the back end of the keel is so narrow, we had to fill the aft end with putty (about 2 feet). Additional layers were then put in. Therefore, the aft end of the keel is not structural and is considered sacrificial. Consequently, when damaged, you only need to fill the damaged part with putty and cover the repair with a couple of layers of fiberglass. The bottom should be repaired using alternating layers of 24 ounce woven roving and 1.5 ounce mat, starting laminations with mat. There are many layers on the bottom and you only need to replace whatever was damaged. But, putting too much is better protection for future groundings (I know, I know, you never ground…). Personally, I would put a minimum of 10 layers of alternating mat and roving and finish with 2 layers of mat. At 1/32 of an inch each you should have 1/4 to 3/8 of an inch thick. The more, the better. Hope the above will be of some help, and have a wonderful day. Marius Corbin

c. I’m assuming that the photos you provided are of the bottom of the keel… Perhaps Marius can elaborate further on the building process, but it appears to me that after the hull is removed from the mold, the keel void is liberally lined with a filler before the lead keel is dropped in. The yellowish-orange stuff at the centre of the keel damage is probably the filler, and I’m guessing that whatever caused the damage knocked out a bit of the filler. To repair the voids you will need to fill with a resin/filler mix – you could even use finely chopped fiberglass to thicken the resin. Since you will be filling something upside-down, there will be a tendency for the filler to spill out. Get some heavy cardboard and shape it so it can catch the filler and keep it in the hole. To do this you may have to clamp the cardboard in place across the vertical sides of the keel, so the cross section of the cardboard is a U. Put a plastic drop cloth on the inside of the cardboard and you will have no problems removing it after the filler has cured! Obviously you must sand the surface of the repair area and clean it so everything bonds well. Once the filler has cured, grind down the vertical sides of the keel to about 12 inches above the bottom of the keel. Clean with acetone and cut fiberglass cloth to complete the repair. The cloth should be: (1). a piece just wide enough to span the horizontal bottom of the keel, (2). a piece that covers the bottom of the keel and goes 3 inches up either side, (3). a piece that covers the bottom and goes 6 inches up, (4). a piece that covers the bottom and goes 9 inches up, (5) a piece that covers the bottom and goes 12 inches up. This will give a solid repair and roughly 8 – 10 mm of glass on the bottom of the keel. Use biaxial /chopped strand fiberglass and epoxy resin. To finish you will need an epoxy filler like Interlux’s interfill 830 lightweight epoxy filler (it is good stuff, I have used it a lot) then sand until fair, and coat with one more coat of epoxy resin. Sand lightly and reapply primer and bottom paint. Charlie G. (#066, Pinguescence).

d. As far as I know, the layup for the keel was poured resin to set the first lead ballast into and then many layers of matt and roving between the 4 layers of lead ballast topped off with a final 14 layers of matt and roving at the turn of the bilge. The keel itself was laid up as an integral part of the hull. If Phoenix has a “shoe” attached to the foot of the keel it was a previous owners modification. Hope this helps. Jeremy P.

e. It looks to me, from the pictures, that someone has cut the fibreglass cover off the bottom to the entire keel. Corbin hulls were laid up as an encapsulated keel which would be filled from the inside. Normally the keel enclosure would be filled with lead although I have also heard of concrete being used at times. It also looks to me as if this keel is filled with concrete. However I could be wrong and misinterpreting the photo. Take a chisel to it and see what comes out. My advice would be to ensure this keel is well dried out and have that fiberglass reinstalled. This needs to be done properly with the right amount of layers which Marius can comment on. Boris, if you don’t have much experience with this I would suggest you engage someone with experience in fireglass repairs. Left unprepared it will certainly lead to serious delimitation of the keel enclosure…especially in freezing winter climates such as Toronto. Jack V (#189, Tangaroa V)

f. The following comments are from a beginner in fiberglass work, although I have made one repair to the bottom of my keel. I was able to enlarge Pic 1 by clicking on it. The sides of the keel, at the top of the pic, looked normal and the forward half of the bottom looked normal, but the aft half of the bottom with the cavities looked awful and your comment about being able to remove walnut size chunks that looked like concrete aggregate causes me to be concerned. Here is a pic that may be helpful, Scaled view of Corbin profile. Sorry that it is sideways. When I click on the view it enlarges. It shows, to scale, where the putty is in the keel and where the lead ballast is. Note that the lead is immediately above the bottom layers of fiberglass. I would follow Marius Corbin’s advice and strengthen that part of the bottom that appears weak and crumbly. Lester H. (#010, Insouciance).

g. Two weeks ago our Corbin was about to be put back in the water after being on the hard for 9 months, during which she had her topsides repainted, when a yard worker noted water dripping from the keel. It transpired that a previous owner had hit the bottom and the repair was to put a fibreglass ‘patch’ over the damage; over the years water had got in behind the patch and up into the keel! The repair involved chipping out the resin until there was no water, leaving a hole about the size of a walking boot. A gallon of acetone was then used to ensure all dampness was removed. Then two gallons of resin, four gallons of thinner and three yards of fibreglass were applied. This took two guys two days lying on their backs with our #173 “Antic” waiting in the slings! Hope this gives you some idea of what has top be done. Regards, Matt E.

h. [Ed, 2019: My understanding is it was ultimately concluded that a previous owner of #131 had sawn approximately half a foot right off the whole length of the keel at some time, to reduce the draught, leaving the bare lead exposed, without making any attempt to seal it back up. It was of course repaired and rebuilt when it was discovered on this change of ownership. DS]

Category: HULL and DECK