View Full Version : Centerboard Trunk/Bottom Paint Theory
07-10-2006, 01:51 PM
I have a 1959 Amphibicon in need of a Centerboard Trunk rebuild. I have been pondering this question since I got the boat, but now with the rebuild looming, I am forced to make a decision about it: Do you coat the interior of the CB trunk with bottom paint?
This boat is spending most of her time on a trailer, with most of her sailing in fresh water, but we do have long range plans for a several-weeks' vacation in salt water to the Keys, and I am trying to find a berth were she can stay in the (fresh) water at all times.
The top portion of the trunk is Oak, and does not appear to have been painted on the inside, as far as I can tell. Perhaps this is why all this wood has rotted out? The centerboard itself is Teak, and is in great condition except for a slight warp. This has bottom paint only on the portion that sticks down out of the keel.
Other than a few repairs, almost nothing on this boat is epoxied or glassed. My intention is to keep it that way unless someone offers a compelling reason to change it.
My first batch of questions:
1.) Do I need bottom paint inside the CB trunk? or is it somehow exempt from growing nasties up in there? (it is strangely quite clean in there, though maybe simply from a good cleaning when she was pulled out last?)
2.) If I do need it, what bottom paint is going to work best in there for the longest time? I have good access to all surfaces in there right now, and I really don't want to go to the trouble to open this all up any more often than I need to.
3.) Originally, I think thCB trunk was white oak. Live oak may be more easily found around here than white, and I've heard it is fairly comparable. Any thoughts on one versus the other? What about teak, since it obviously survives so well down there? (Though I suppose a few pieces of 3" x 12" x 8'-0" teak would cost more than my whole boat...)
Secondly, the bottom half of the centerboard trunk is actually a slot in the cast-iron keel weight. It seems to be a recurring headache with this design that the keel weight rusts, and therefore swells against the CB, binding it up. Obviously, much contortion combined with much grinding is in my near future, but what can I do long term? Once I get it operating smoothly, I want it to stay that way as long as I can. So far, most people I have talked to have told me not to worry about cleaning up the keel weight any more than necessary, as no one sees it when it's in the water. I've got plenty of rust right now blistering the current paint, however.
Therefore, my second batch of questions:
1.) How much do I need to protect that cast iron? Will it rust away over time? Especially in salt water? Or will it be ok because it does not have access to air under water. (There will never be anything so vulgar as shore power on (or, for the most part, near) this boat, so galvanic action should not be too extreme).
2.) If I do need to be concerned with this rust, do I have to remove it all, or is there an encapsulation product that actually works? (I have used many automotive "rust-encapsulating" paints that were brought to their knees by a single Michigan winter.)
Lastly, what bottom paint(s) would you recommend for this boat for a Central Florida climate? As I mentioned she'll see a lot of trailer time, she'll get a permanent fresh-water berth if I can find one, but she'll also spend periods of up to two weeks in salt. The keel & deadwood are oak, CB is teak, hull is cedar, rudder is glassed/epoxied, the keel weight is rusty cast iron, and a lot of these features are going to have to be completely stripped and started fresh, if it makes a difference.
I've got fresh Brightsides up top, and I am eyeing up Petit's Easypoxy for the hull above the water line, since they have the perfect shade of maroon, if THAT matters. The bottom paint will need to be black or at least black-ish.
Thank you for sharing your thoughts and opinions on these matters with me... I knew I was getting in over my head with this glorious old girl, but why do something worthwhile only half way?
07-10-2006, 03:14 PM
Can't answer most of your questions, but can address a few.
First, replace the iron CB weight with lead. I'm assuming from your description that the CB is teak with an inset plate (?) of cast iron?
As long as the CB weight isn't a shoe or shaped edge-piece, just remove it and replace with lead. Here's my oak rudder with a sheet of 1/4" lead being epoxied into the hole created with a router set just slightly deeper than 1/4".
If you can't find sheet lead, and aren't into melting wheelweights or fishing weights, just buy lead shot pellets and dump them into the hole with epoxy -- you'll need more than you think, so find someone who reloads and either has extra lead pellets or who can take any leftover from you.
My boat is trailered all the time, never spending more than 3 days in the water (fresh, brackish or salt) at a time. I painted the inside of the CB case and the CB with marine enamel, then waxed it with pastewax for abrasion resistance (sorta).
For trailerable boats, don't use ablative bottom paint -- I did and it comes off on the bunks, rollers, hands -- you name it. It also comes off when you beach the boat, and my landings sometimes look as if I'd crushed a fish with all the red haze in the water...
07-10-2006, 03:19 PM
It might matter a great deal; dark maroon is going to be a hard color to keep on any wooden hull in a tropical climate.
I'm a bit confused though. You say she'll be in permanant moorage in fresh water, then indicate she'll spend most of her time on a trailer.:confused:
Alot of trailer time complicates the selection; not my strongest suit , but a trailer boat can live without bottom paint entirely, and probably should. I second Thorne's comment about ablative bottom paint and trailer boats. If she stays in the water though, I'd think a decent ablative formulated for warm water should be the answer on the bottom paint side.
My preference is to paint or coat everything I can reach. I believe many others will feel the same.
07-10-2006, 03:56 PM
Looking at the Amphibicon website, it seems that the CB weight is a shoe or end-piece.
You might consider doing without the shoe, or having an endplate fabbed up from Stainless Steel. Then use lead for the weight.
I'd be REAL tempted to replace the CB, CB case, and anything else as long as I have that part of the boat accessible. It is a critical part of a sailboat, and failure can result in anything from having to motor back to sinking. Wood is cheap in comparison!
07-11-2006, 12:00 PM
Perhaps I should clarify a few things about this boat:
1.) She is on a trailer now and for the near future. I am, however, looking for a slip for her and would like to plan for the eventuality that I actually find one that doesn't cost a fortune. Or I may follow through on my threat to build her a soaking pond in the side yard.
2.) Even if she does live on the trailer, she will be doing trips of sufficient duration (several days to a couple weeks) that I'll need something specialized for below-the-waterline use. Maybe growth of nasties isn't too big a deal for that time frame, but I wouldn't want to put topside paint down there for example, only to have it slough off part way through the trip.
3.) I see you visited the Amphicon site, but for others who are not familiar with this boat, it's a bit bigger than your average trailer-sailer. She's 26' long and weighs 6000#. She pulls 2'-4" draft with CB up and 4'-0" with it down.
4.) There are two weights involved: one is the keel weight that the CB passes through, and the other is a shoe on the CB itself. Both are cast-iron I believe.
5.) The shoe wraps around from the leading to bottom to trailing edges of the CB. Not quite so easy to replace and stay true to the original design as the inset panel method you show above, but I suppose it could be done.
6.) I don't forsee replacing the keel weight, as it is a somewhat complicated casting, and it would take a heck of a lot of lead shot to match the 1200 - 1500# mass that she currently has in iron.
I have heard people mention "hard" bottom paints for trailerable boats? Has anybody used any of these? Are these simply permanent under-water color? or do they also retard slime growth?
I've looked through my photos to see if I have any good shots that would be useful here, but unfortunately, I don't yet. I'll try to get some in the next couple of days.
Thanks for the input so far...
07-11-2006, 02:19 PM
Why not just replace the existing CB with a steel one?
It is commonly done, so hopefully someone nearby will know how to fab the steel, add weights to it if necessary, coat it, and build CB cases and pivot pins for it.
07-11-2006, 06:40 PM
Trinidad is the hard bottom paint with which I have some familiarity. There are others. Interlux makes a line of these as well, but you can start here:
The nickle tour is that ablatives are the usual sailboat (and displacement power boat) paints. These paints slough off; soft paints in other words. However, they don't do well out of the water, and tend to flake and rub off in big chunks in the event.
For planing hulls (and trailer boats) a sloughing paint is undesireable for the intuitive reasons; it removes itself from the scene in a hurry. Hence, the hard paints are more useful in the application. Most wooden boats, I think, and certainly most discussed in these pages, benefit from ablatives if they are kept in the water, or, if they see water occasionally, don't require bottom paint at all. The exceptions would be the runabouts and fast cruisers, where bottom paint must be hard enough to endure either at speed or on the trailer.
I suspect you might get specific recommendations as to which paint would fare best in your region from the local ACBS chapter, as their boats, like yours, are on and off trailers. Thus it might pay to see if a Florida chapter of the ACBS might have a few gents who could guide you in an anti-fouling paint choice that works for your application and where you are planning to cruise.
07-12-2006, 06:22 AM
The cast iron is structural and makes the CB case last longer. For an extreme example, my old Alden 43' schooner Goblin was a slight varient from the Goody and Stevens Alden 43's in that she was designed for a lone cast iron keel that housed the CB slot. Goblin was lost in Hurricane Bob but during her time, she was the only CB Alden schooner of her vintage. All the G&S schooners had been keeled over.
The secret to keeping cast iron happy is red lead. Lots of red lead. Pound and chip (not grind) the rust off. If it's really pitted maybe fair it up with thickened epoxy. And red lead the bejezus out of it. That will insulate the iron from the copper in the bottom paint.
When yhou rebuild the CB case, prime the inside with red lead and the paint with bottom paint for moralle purposes as th at't the last chance you have to get in there. Most of the CB case if above the water and does not really need bottom paint but it's a dank and stagnent place. Any poisons left in there will do some good.
My new (to me) catboat Marmalade has an iron board which works find as catboats don't sail at much heel anyway, but in general a well build wooden board is better. When weighted to just sink, it's so much easier to raise and lower, but mostly it won't bend and take that bend. On Goblin I more than once took the ground heeled rail under on a hard beat. This is just the sort of event that bends a metal board. The impact on the board is lateral and the board is already held firmly by the press of the water. But with Goblin's 60+ year old oak with iron drifts board, we could feel the board deflect on ghrounding and then feel her wiggle her buttocks as the board straightened out. Really kind of cool.
Make your board happy, keep the iron keel, and buy lots of red lead from Kirby Paint.
By the way, stainless is way over-rated and good old real cast iron (not steel) is under-rated for marine use. Cast iron rusts only a finite amount and then the rust is protective. Looks horrid as rust takes up about ten times as much space as iron, but what's under is likely sound. Chip the rust off and you'll see. There are some pretty cool primers and barrior coats around and if you get to shiney metal they could be worth it, but in the normal real world it's hard to beat red lead that's maintained each year. SS is neat stuff but when it fails it tends to be without good warning. I love SS shackles and such but they are all way over-strength. SS is nice for rigging, especially jib stays that take some wear, but rarely lasts more than 20 or 30 years. Iron stays need maintenance but if they get that there is no know end to their life cycle. The oldest in continuous use are a bit over 100 years. Some luxury yachts that have SS anchor chains but their owners are simply fools who don't anchor anyway.
07-12-2006, 09:08 AM
Ian, I agree with most of your suggestions, and certainly defer to your experience in these matters. Red lead is the fix, and Kirby's is a great source.
**However** (isn't there always at least one however?) I wasn't suggesting replacing the iron slot-keel (what he calls keel-weight) at all, just replacing the iron shoe on the end of the wooden CB that swings thru this slot.
The problems that he and other owners of this boat have is that, as you say, "rust takes up about ten times as much space as iron" -- and that increased size of the iron shoe on the end of the CB causes it to jam in the wooden CB case.
So, I suggest that he remove the iron shoe to solve this problem.
If he just wants to replace the lost weight, he can add a lead insert to the CB (see Lead in Rudder thread). If he wants metal at the end of the CB, he can fab one up out of SS, bronze, brass, or whatever metal **won't rust** and jam the board.
To have both weight and impact resistance, he might be better off adding lead inserts, and forming a shoe/edge on the bottom of the CB with a few layers of marine ply bent and epoxied together, pinned or attached with long bronze screws to the CB. That should give him both the weight and "skid-plate" elements that were provided by the iron shoe, but eliminate the rust-jamming-CB-slot problem.
Remember this boat is mostly trailered, spending some long periods in the water. Unless he leaves the CB down to eliminate rolling at anchor, most of the CB will be out of the water most of the life of the boat.
07-12-2006, 02:42 PM
Hey, this is great information, guys. I really appreciate it.
Just a note of correction... twice up there, people have said that the CB will be out of the water when anchored long term, except during use. This is not true, though I don't think it changes any of the advice that anybody has offered so far.
The waterline is a few inches above the cabin floor. The CB trunk is *entirely* below the cabin floor. Therefore, if the boat is in the water, so is the entire CB and Trunk. One raises and lowers the CB via a cable that is fed down through the steel dining room table post that is anchored to the top of the CB trunk (therefore, the bottom few inches of the table post are full of water, too! It's a bit disconcerting to think about it that way, but it works just fine.)
It sounds like we are reaching a consensus that yes, I should paint the inside of the CB trunk, even though it may be 20 years before it gets done (thoroughly) again? Seems like a hard-type bottom paint would be the way to go in there for abrasion resistance.
I understand the use of red lead to insulate the cast iron electrically... Is this stuff as nasty to work with as I think it is? Would a few layers of epoxy over the iron do the same thing? Either way, how clean a surface will I need to make this last? You say to chip, not grind, but I doubt that I could get a pitted surface completely free of rust without grinding the pits completely out?
Did I see a recommendation to coat the entire interior of the CB trunk with red lead, too? (under the hard bottom paint, I presume?)
Thanks so much for the advice!
07-12-2006, 04:14 PM
I've used Kirby's red lead and it isn't bad to work with at all -- just like oil-based paint, only you may want to dispose of the brushes and can differently.
Red lead is the original "stop rust" primer -- ask anyone who was in the Navy 30+ years ago...
It also works great as a primer for wood, which can be painted over with most good paints -- I think oil-based marine paints are best. I painted the interior of my CB case with red lead, ditto for the bottom planks both top and bottom.
Epoxy would just flake off with the surface rust, so something that inhibits rust like red lead is much better for iron. One of the contributors to the Wooden Boat publication _Planking & Fastening_ strongly recommends painting ALL parts of ALL (non-varnished) wood in boats with red lead to reduce decay and bind paint well.
07-17-2006, 08:30 AM
Ok, here are some of the promised pictures of my keel situation
This first picture shows the cast iron keel weight. Here, I've just begun to lift the hull off of it after removing the nuts from the keel bolts. The area above it (peeling to blue) is oak. This outside layer is ugly, but is pretty sound. It's the inner layer that is rotten. See below.
Here's the trailing edge of the cast iron weight. Oops. Guess I'll be replacing some of that oak deadwood, too. Note the part above there (peeling to red) is cedar. It provides a small bilge area that everything drains toward for efficient bilge pump usage.
This is the center board itself, after hoisting it up into the cabin. It seems to be in good shape, except for the rusty shoe. I don't think it's laminated. I think it's solid. When was the last time you saw a piece of teak that size?!
This shot is peering down into the CB trunk. Inside surface doesn't look to ever have been treated with anything, but it's so aged, it is hard to tell. Note the interior surface of the cast iron keel weight in the bottom of the slot. Looks pretty gruesome at this point.
This is where it all started... with a leak from the CB trunk behind this rib. When I pulled the lid off the trunk, this side of the trunk just splintered like a dried out sponge. No wonder there was water coming in! Note the fiberglass seam "repair" at these garboard seams. Is there a way to peel this up and separate this from the wood? If I can't I'm going to have to cut through it, then cut through the strip-planking edge nails in the garboard seam to drop the CB trunk out. All the while keeping the edge on the first plank neat and tidy. This would be easier if the fiberglass was gone first. Any ideas?
Here's another question: I am trying to extract the keel bolts from this mess as gently as I can, seeing as how I am removing the most substantial piece of framework in the whole boat. The bolts are set in what looks like the same white goop that sealed the CB trunk lid down (for their entire length which varies up to about 16"), as you can see in the last picture. I don't know what it is, but it is tenacious! Is there any way to soften this stuff? Ie, if I were to heat the bolts, would I be able to get them out easier? Or would I just set fire to my boat? Anybody know any good tricks here?
Also, as an aside to this, who knows a good paint stripper? I've been using Nature's Best or somesuch thing that came highly recommended from Jamestown Distributors to strip & revarnish some bright work, but it just doesn't seem work very well... at least on this particular varnish. The last 20% just doesn't want to come off. Letting it set for an hour, several hours, overnight... it doesn't seem to matter. The last bits of varnish just never seem to soften.
Thanks for all the help and moral support!
07-17-2006, 09:04 AM
Get yourself a heat gun and forget the chem strippers. Its faster and less of a pain the neck.
07-18-2006, 09:28 AM
I learned the following 35-years ago as an Apprentice Shipwright. I thik it still applies.
Yes, paint the inside of the trunk with bottom paint as well as the entire centerboard. Drop the board and renew the paint each time you paint the bottom. Since you keep the boat out of the water regularly, choose a bottom paint that is still effective (some loose potency when left out of the water). Protect the paint so it doesn't get worn off as the centerboard is raised and lowered.
The key to maintaining an iron keel is paint prep. First flush the iron with fresh water to remove salt. Sandblast it until 'near-white condition'. Immediately prime it with the primer recommended by the paint manufacturer. Off coarse choose a paint specifically developed for ferrous metal. Bottom paint goes on top of the paint for ferrous metal.
Protect the metal from abrasion from the sliding centerboard or sand bottom.
Finally, always inspect the paint when you haul and repair any scratches.
Iron treated as above can last 10-20 years before serious re-work is required. If prep is poor it won't even last 6-months.
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