Hello Home Foundry People! I am redoing a 400 pound / 180kg cast iron keel/centerboard mechanism on my 21' / 6.4m sailboat. It does not seem to be in too bad shape but I will not know until is is removed from the boat. Does the group have recommendations for paint for refinishing this? I have heard that coal tar epoxy is a good base layer. I have also heard about treating the bare metal with a phosphate. If the process becomes too involved I could loose time sailing this season so I will be thinking about that too. Hiring out sandblasting is a thought but last quote I got was pretty high so I bought some wire wheels and paint removal disks to use at home. Boat is dry on trailer most days and normally only splashed in fresh water. Thanks for the input!
I would guess the part of the board you can't see is in the same condition as the part you can see.. not that bad.. Once you get the boat off the trailer and at least as high as it is on the trailer, the fun starts.. The good news is once you unbolt it, it will fall out.. The bad news is once you unbolt it, it will fall out.. You're gonna need a transmission jack,or something like that, to lower it and put it back.. A job like this could keep you from sleeping..
True, true. I got in a set of jack stands that should allow me to lift the boat to remove the trailer to remove the keel. A transmission jack or ATV jack would be perfect for the keel. I have a really good floor jack and was thinking of taking it apart (centerboard from keel stub) so I am only handling 200# at a time.
Hot dip galvanizing and bolted on sacrifical anodes would be my choice if cost is no object. Phosphoric acid in water will also remove the rust if strong enough and won't leave chlorides behind to restart the rust process like hydrochloric acid does. A cold galvanize zinc rich paint would slow down future corrosion but may need a tougher coating over it for abrasion resistance.
I've had a lot of experience taking boats off trailers and putting them on stands for repair and gel coating. For the center stand a couple 12" 2x4s and a piece of carpet to increase the load bearing surface and spread the weight evenly.. I've never taken a sailboat off a trailer. mostly 24'-30' powerboats.. And a 40' house boat.. only needed one of those to cure me of doing house boats. Power boats are easy, the transoms are clear on each side to slide a stand under, while on the trailer. We lowered the front of the trailers, place the rear stands, big L shaped stands, about4"x24" loading surface.. When you lift the front of the trailer the weight of the back of the boat transfers to the stands. We used a hoist to lift the front of the boat and pull the trailer out. You're going to need 3 really good balance points before you get under it. For some reason, every time you look up at the bottom of that boat, you'll remember how heavy it is.. Fredo
Mark, thanks. I am hoping that being in fresh water and on a trailer most of the time means that it hasn't been attacked too bad galvanically . Fresh water would be aluminum anodes versus zinc, right? Fredo, thanks. A hoist for the front would save 2 or 3 re-blockings on the front stand. I have a heavy basketball pole next to the boat, the thought of making it into a derrick or crane crossed my mind...Yes, I will be thinking about that 1800 pounds / 820 kg overhead. The stern has a bit of lift and a wineglass shape to it so I'll need to be careful with it. The front will have a bit that can notch into a stand.
I've got zero experience with aluminium anodes but I see it's on the opposite side to zinc with iron in the middle so you'd think the iron would corrode and protect the aluminium. On a related note my 20 year old aluminium step ladder sheared a few rusty steel rivets this morning when I used it: the aluminium was untouched but the fasteners and rivets had lost their zinc and were rusty enough to fail. Edit: the Standard electrode potential is not the same as the galvanic series, according to the galvanic series, aluminium and zinc are less noble than steel or cast iron and will protect them.
https://anodeshack.com/how-to-choose-the-correct-type-of-boat-anode Cliff notes for recreational boat anodes: zinc for salt water, aluminum for brackish, and magnesium for fresh water.
Is the goal to have the boat look good on the trailer or to prevent failure of the keel due to corrosion? If the concerns are aesthetic and budget is not unlimited, wire brushing followed by cold-galvanizing paint and then (Maybe)a finish coat or two. If concerns are purely functional, just leave it as is. That cast iron is very resistant to corrosion (that is why sewer pipes are commonly made from it) and will last for about 200 years sitting in the water or 1000 years on the trailer. Paint the boat hull deep red below the waterline and no one will notice. ;-) Denis
Transmission jack is what you need. Used one with some welded up jigs for my brothers keel. Having the adjustment of the transmission jack really helps when it is time to put things back in place. For the rust consider a small pool* made with a plastic liner, filled with water/caustic (or just plain old baking soda) and use a battery charger and a sacrificial steel anode. Rust removal - electrolysis * a shallow hole in the ground or just some 4x4s laid on the ground lined with the plastic.
What do we do with the rusty centerboard...so early in the evening? Removing the trailer, pivot bolt, and centerboard was relatively uneventful and the pieces do not look so bad. The red stands are bearing the weight, the sawhorses happen to fit underneath. New bolts/washers/locknuts ordered and received along with some wire wheels and paint removing disks. Thinking it might be a good time to change the wire to the winch as well. I can see you point about the transmission jack Shoe, the centerboard was possible with a simple jack with the cable still on the one end. The stub keel will be more awkward, especially going back up covered in sealing goop as I try to align 8 bolts without dinging the threads... I'll take a look at the link, thanks.
Parts are power washed and a test of sanding media is showing the poly-carbide disks as a winner between effort expended and paint removed and metal left undisturbed. The wire wheels are 'bouncy' and the flap disk is too aggressive and the big sander disk is slow. One possible finish path is clean metal, epoxy, and finish paint, with the epoxy wet-rubbed into the metal (read that as being effective, maybe at West System?) Another is phosphoric acid treatment and paint. Are all the phosphoric acid based 'rust busters' more or less the same or is there a clear winner like Ospho? A third is a clean or rusty metal primer or etching primer and finish paint. The poly-carbide disk (lower left, purple lines) is leaving pretty clean metal so wondering if the phosphoric acid is overkill? I appreciate the previous comments, thanks!
Phosphoric will get into the pits that mechanical cleaning can't reach, so it's good to finish the cleaning with it. I've found phosphoric acid at much above 5% will remove the rust rather than convert it and in the tropics would need rinsing and a hit with WD40 or it'll develop an orange dusting of rust before it's had time to dry....possibly a hot air gun would minimize it by drying faster. A commercial sandblaster would make short work of it but you have to get it there first.
Thanks Mark. Blasting would be nice, I used to work in a shop with sandblasting and painting equipment, this would have been an easy home project there... I took the purple wheel attached with a proper spindle nut and went after the face that mates to the boat and the side shown above. I did not time it but I want to say it was less than 1/2 hour and a single 4$ wheel to get those two sections done. At this rate I will have about stripped the parts before I could have driven to and from the sandblaster's shop. The slot is going to suffer more from not being blasted... From the smell, a previous owner or the boatbuilder may have coated it with polyester resin. The wooden rudder was also painted with resin. I ended up sanding that down to wood to repair and refinish (resin came off easily) and per the advice from my fiberglass supplier, coated the wood with epoxy and then a durable alkyd enamel aka 'tractor' paint.
