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 Post subject: Centerboard Rehab
PostPosted: 03 May 2021 08:40 
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Tactictian

Joined: 06 Aug 2020 09:02
Posts: 142
Sharing some pics and description of what I did to my CB. First time it was removed. Ever. I shared bolt pics in another thread. Five of the six removed intact. One was so corroded that half of it is still in the keel and I could not remove it try as I might with extractor bits. Working upside down doesn't help!

Here were the issues:
1) Corroded bracket bolts
2) Lower padeye bolt not tapped straight into board
3) Stuck padeye bolts
4) Corroded bracket
5) 40 years worth of paint on the board
6) Cracked aft seam where two-piece mold was glued together
7) Lots of gelcoat cracks and nicks
Cool Ground down tip from dragging on the bottom
9) Very thick and brittle trailing edge - not optimal

Pressed for time with other boat projects I gave the board to my buddy Barney who operates a boat building business from his basement building full cored racing Albacores (Hapco Marine). He's also an engineer. Here's basically how we solved the issues:

1) The one corroded bracket bolt could not be removed. I drilled an adjacent hole as far as I could into the keel. There must be stainless bedded up inside there because I could not easily drill more than 3/4". I filled the hole with high density filler and tapped. I figure that 5 of 6 new 5/16" bolts (316 stainless) plus one smaller 5/16" bolt will be good enough. Far less was holding the board in place previously. I may tackle the corroded bolt at a later date.
2) Barney drilled, filled, then re-drilled and tapped a new bolt hole into the board. This new hole is not solidly through the steel bedded in the board laminate. How the factory couldn't drill this straight is beyond me! Seems to be a problem for others.
3) Original padeye bolts were tough to remove. Had to apply heat and file a deeper slot into the screw head, then apply amply torque.
4) I had my shop welder clean and lay new beads on my bracket.
5) I sanded the old paint off which took hours. One nice surprise was the gelcoat was in excellent condition other than some chips on the surface from voids.
6) Barney ground, filled and glassed the aft seam
7) All gelcoat voids were picked, sanded, filled, and faired.
Cool Barney used milled fiver and epoxy to fix the tip. Should be very resistant to wear now.
9) I wanted a better performing board and a tough trailing edge. Barney extended the trailing edge about 1" (yes, there is room in the trunk) with multiple layers of glass. The edge is now about 1/8" thick and very very strong. The extra area plus sharper trailing edge should provide better windward performance.

I also repaired the damaged front of the trunk at the bottom by grinding away the damaged glass (very thick in this area), adding a few layers of new tape, cutting the curve for the board leading edge, and fairing.

Barney applied a few coats of Interlux 2-part epoxy primer then three coats of Pettit Vivid bottom paint and burnished. He did an awesome job. Looking forward to getting this thing in the boat which is a whole other affair!


Attachments:
File comment: Delivered in custom cradle
T37 CB Repair 8.jpg
T37 CB Repair 8.jpg [ 698.25 KB | Viewed 0 times ]
File comment: Board hung for painting
T37 CB Repair 7.jpg
T37 CB Repair 7.jpg [ 126.11 KB | Viewed 0 times ]
File comment: New trailing edge ready for final shaping
T37 CB Repair 4.jpg
T37 CB Repair 4.jpg [ 229.94 KB | Viewed 0 times ]
File comment: New glass layers laminated
T37 CB Repair 2.jpg
T37 CB Repair 2.jpg [ 219.11 KB | Viewed 0 times ]
File comment: Scarfed trailing edge for new glass
T37 CB Repair 1.jpg
T37 CB Repair 1.jpg [ 80.66 KB | Viewed 0 times ]
File comment: tons of gelcoat cracks repaired
T37 CB Repair 9.jpg
T37 CB Repair 9.jpg [ 986.74 KB | Viewed 0 times ]
File comment: Bolt hole anything but plumb!
T37 CB Repair 5.jpg
T37 CB Repair 5.jpg [ 931.06 KB | Viewed 0 times ]
File comment: Ground down the side of the board of the stuck bolt to see what might be the issue
T37 CB Repair 10.jpg
T37 CB Repair 10.jpg [ 357.03 KB | Viewed 0 times ]
 
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 Post subject: Re: Centerboard Rehab
PostPosted: 03 May 2021 11:31 
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Tactictian

Joined: 16 Mar 2007 16:10
Posts: 143
Wow!
Excellent CB rebuild.
I need to either rebuild or replace my CB one of these days.
Now that you have gone thru the rebuild process, would you recommend to others, or replacement?
I think Tartan charges around $3k for a new CB.

Cheers,
Nick
S/V Angela Mia
Hull #336
Lake Superior.


 
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 Post subject: Re: Centerboard Rehab
PostPosted: 03 May 2021 11:50 
Offline
Tactictian

Joined: 06 Aug 2020 09:02
Posts: 142
NP336 wrote:
Wow!
Excellent CB rebuild.
I need to either rebuild or replace my CB one of these days.
Now that you have gone thru the rebuild process, would you recommend to others, or replacement?
I think Tartan charges around $3k for a new CB.

Cheers,
Nick
S/V Angela Mia
Hull #336
Lake Superior.


I would recommend having a boat builder friend who will do the work for some good scotch! I think that it depends on how you value your time. If this is "fun" work for you, then a worthy project so long as the board isn't compromised. Mine was generally solid and not as bad as some of the others I've seen posted on the forums. Some of the projects were on the hull and bracket so those you need to do yourself or pay someone to do them. It also depends on how far you want to take this. We didn't have the time for a proper foil profile fairing job with templates. The actual shape of the board is not too bad and we took offsets and plotted. Shape is pretty much a basic NACA 00 section. The longer cord and sharper trailing edge change a little but not much. I think the extra area and sharper edge will be a performance boost. Having a nice smooth foil will definitely help! So, it's worth it if you like to muck with such things and not worth it if you don't. If your board has been neglected and/or not checked, you should at least take the time to do so.


 
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 Post subject: Re: Centerboard Rehab
PostPosted: 03 May 2021 11:59 
Offline
Skipper

Joined: 09 Aug 2017 15:35
Posts: 725
Location: Maine/USVI
My board was fine, a little paint stripper and some serious sanding and she came out like new. Padeye good. But the hinge plate system for the board to hull attachment - do you have photos of yours? I still have a piece of a bolt up in there where someone went to a smaller size bolt and tapped into a broken off bolt to repair. My board draws up and is tight against the port side of the centerboard trunk. To the point where if I drop it sometimes it won't come out on it's own. It's close, but sticks ever so slightly. All I can figure is whenever the repair was done to the hinge assembly it's off a tiny bit favoring the port side. Anyone else have this issue?


 
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 Post subject: Re: Centerboard Rehab
PostPosted: 03 May 2021 20:39 
Offline
Tactictian

Joined: 06 Aug 2020 09:02
Posts: 142
Before and after weld touch ups


Attachments:
File comment: After new welds
20210309_150849.jpg
20210309_150849.jpg [ 4.41 MB | Viewed 0 times ]
20210306_101045.jpg
20210306_101045.jpg [ 3.97 MB | Viewed 0 times ]
 
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 Post subject: Re: Centerboard Rehab
PostPosted: 04 May 2021 08:29 
Offline
Skipper

Joined: 09 Aug 2017 15:35
Posts: 725
Location: Maine/USVI
So your board now stays centered, goes up and down clear? I'm going to take mine apart again before I launch and see if I can tweak it at all. It looked like someone grounded ever so slightly once and might have somehow tweaked it to port. The distal end of the board is far enough from the hinge plates that if it's off a tiny bit, the end of the board can get out of square to the trunk. How sloppy are the threads on the bolt that your centerboard hangs on? For as much use as these boards actually see, I'd still like to be able to make a couple degrees better to wind on occasion if desired.


 
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 Post subject: Re: Centerboard Rehab
PostPosted: 04 May 2021 08:52 
Offline
Tactictian

Joined: 06 Aug 2020 09:02
Posts: 142
Maineiac wrote:
So your board now stays centered, goes up and down clear? I'm going to take mine apart again before I launch and see if I can tweak it at all. It looked like someone grounded ever so slightly once and might have somehow tweaked it to port. The distal end of the board is far enough from the hinge plates that if it's off a tiny bit, the end of the board can get out of square to the trunk. How sloppy are the threads on the bolt that your centerboard hangs on? For as much use as these boards actually see, I'd still like to be able to make a couple degrees better to wind on occasion if desired.


I have never detected an issue with the board going up or down incorrectly. I suppose if the pin got bent it would operate off-axis. Threads are not sloppy as far as I can tell and the head of the board is rectangular in cross section so it should go up in the right plane but with some slop due to clearances.

If you want better pointing, the board is a good place to start but I bet the sails and how you trim them have a lot to do with it. Bottom line is that this boat will naturally take on a lot of leeway because that's what is required to produce the lift for force balance. I would not be surprised if we have 6 degrees on each tack, widening your tacking angle by 12 degrees off what you see on the compass. We should be able to point with most modern moderate shoal keel boats. An adjustable backstay is also critical to genoa shape.


 
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 Post subject: Re: Centerboard Rehab
PostPosted: 05 May 2021 06:14 
Offline
Skipper

Joined: 09 Aug 2017 15:35
Posts: 725
Location: Maine/USVI
Everything on my centerboard assembly looks almost new. It was a freshwater boat most of it's life. But there was a tiny indication of a scrape on the centerboard hinge and the forward trunk from a grounding, and the threads are a little sloppy on the hinge pin. Since there was a bolt tapped into an older (larger) bolt into the trunk, there was obviously a repair.

I guess before I launch I'll pull the hinge out again and see if THAT is square. If the "repair" involved completely re-drilling the trunk holes, maybe they got it off by a couple degrees to port. It goes up, but there's just enough friction on the aft end of the board that causes it to stick sometimes. Not the end of the world, but any gain to windward is useful. I raced my Pearson 10M in the Caribbean 10+ years ago, and while I may never race the Tartan (famous last words when Foxy starts in on me for the "Classics Regatta") I'm sure that couple of degrees will always be in the back of my mind.

Focus now is getting in and getting gone. Same thing with the Dyer 29 lobster boat once I get the reman Cummins into it. Everything (hopefully) goes on the sinking boat in Newport for delivery to St. Thomas in November.


 
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