Cast Iron Keel

[Guest]

I have never been able to get the keel of my Albin as smooth as I would like. I think it was factory finished with epoxy tar, but there were many hollows and rough areas. Every few years rust would bleed through, and although I filled some of the imperfections with epoxy I could never get it up to racing smoothness.
The time has come to take drastic measures, and I intend to cut it back to bare metal and start from there to get a really smooth faired finish. Can anyone suggest what products to use to prime, fill the imperfections and put on a smooth finish that will last. The boat will be out of doors, but electricity is available. Completion time middle of April. I have heard of what the Americans call longboarding to get a smoothly curved profile. Can these be purchased with ready to use abrasive surface, or is it a matter of fixing an adhesive strip to a length of timber?
Any suggestions appreciated.

 

[chippie]

Welcome to the forum, I like the name of your boat.
The thing to remember with painting is that it is a system. The paint companies provide a wealth of information on the best products for any particular job.
As I am on the other side of the world from you, I dont know if longboards are available commercially or not. It is not too hard to make one by selecting a piece of timber and screwing on a couple of shaped pieces for handles and using a contact adhesive to glue the abrasive of your choice onto it. A bit of experimentation will give you a good idea of the dimensions that suit you. It would be a good idea to radius the ends of the board so that the ends of the sandpaper are up from the working surface and dont catch. After trying the longboard out you might find that making several is a good approach, so your work isnt slowed down too much when the abrasive becomes clogged. I have found it difficult to make an effective clamping device for the sandpaper _hence the glue.
If you take the keel back to bare metal You could possibly use micro balloons in epoxy to fair it depending on how big the imperfections are.
The paint companies should be able to give advice regarding removal of the existing coatings.


Cheers.

 

[30boat]

You should also use a random orbital sander.After rebuilding it I faired the rudder on my boat to a perfect finish with nothing but my trusty Elu sander.It still meant a lot of work though,but still a lot less than it would be if I had used a longboard.

 

[oldsaltoz]

G’day Norman.
I did my cast iron keel a few years ago and it still looks great. I hope this helps.
You can get a smooth finish on your cast iron keel that will last for many years but it’s not a walk in the park.
First you need to talk to a local paint supplier and get hold of some Industrial quality paints, you will need a zinc primer, possibly an inter coat and a top coat, all paints should be the same as that used on steel piles under jetty’s; note the thickness of the zinc is critical, too thin and it won’t work, too thick may cause mud cracking and will increase the cost, so purchase a paint comb, a simple device that looks like a very small tin comb, it has a set of slots, when pulled through the wet paint it will indicate the thickness, cost about 50p.
I recommend sand blasting the keel, grinding it too slow and the cast will rust as you go (cast iron starts rusting as soon as the air gets to it) so you need to get some cover on it within minutes of cleaning. After blasting and applying the zinc coat by brush, roller or spray let it dry out; see manufacturers guide lines. You can now give it a light sanding with grit about 125. Now apply a mix of epoxy resin and micro balloons over the whole keel filling the low areas, I used an old straight backed saw blade (teeth removed) it follows the curves well; let this go off for at least 24 hours. Before sanding, wash it down with fresh water and a kitchen scourer, till the water no longer beads, this will indicate all contamination is removed, and will not be rubbed in when sanding. To get that smooth finish you need a long board (Better described as a torture board) you can make from a strip of 3-ply ply wood, make it about 850mm long and 20mm less than the width of the sand paper you plan to use, make 2 blocks about 30mm square, secure the sand paper by laying the paper flat, grit down, place the ply strip on top and pull one end over and secure it under the block by screwing 2 countersink head screws through the sand paper, ply and into the block, do the same on the other end; it helps if you pre drill the ply and blocks, make sure the screw heads do not stick out above the sand paper.
The trick to getting a uniform finish is to slide the board from side to side with a stroke at least 300mm long in a figure of 8 motion, don’t press too hard, let the paper do the work, keep as much of the grit in contact with the keel as practical, the board will bend and control the shape depending on pressure. Constantly check that you are not sanding any zinc coating off, if you do, replace the zinc and then apply more resin and balloons after it has cured.
You may have to do this a couple of times (Or more) to achieve the results you require. Then your ready to apply a final coat or two of epoxy resin then your topcoat. When that’s fully cured you can look into applying some antifouling

Avagoodweekend or2 Old Salt OZ……

 

[Strathglass]

The important thing is - as stated above - more so in this country than down under. Find someone who can shot blast it and get them to immediately ( within minutes not hours )epoxy coat it otherwise it will rust. The valleys can then be filled with an underwater filler and smoothed off.
On another tack to make your long sanding board you will need.
1- 5" wide strips of 9mm ply, 4 feet long.
2- 2 handles per board, 5"x3"x1"
3- Rolls of 5" wide metal oxide paper 40/200 grit
4- A stapler
5- 4 2" c/s screws

Fix the handles about 6" from each end of the board making sure that the screws are well countersunk. Cut the carburundum paper to a length of 54" then fix it symetrically to the board and fold the ends over the board using the stapler to fix it to the handle side of the board at the ends only. You can then use it.
The length of the board, thickness of ply and grade of grit can be varied to suit the task. I have made them up to 8 feet long when flatening dinghy hulls and I have sometimes but not always used double sided tape.
The finish on the foils can make a dramatic effect on boat speed and is well worth the effort. I have previously spent many hours working on an E Boat keel.

 

[Guest]

Thanks for all the replies. A bit of work ahead. Can anyone suggest a good brand of elbow-grease?