Here is a shot of the forward pivot end of the steel centerboard (="centerplate", = "plate") from below. I read that rust expands upto about 8 times the thickness of the steel it consumes, not a good situation in the center-case where there must be a snug fit of the plates pivot cheeks in the centercase.
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| Center-plate rusted and stuck |
To get the center-plate moving i attached to tips of a pair of vicegrips to the aft end of the plate. Then used a large screw driver (on a wood block) for leverage and thankfully the plate moved down about 1 cm with a crunchy rusty sound. Thanks to the investigator forum for this idea.
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| The center-plate emerges from its trap!! |
Once enough plate was exposed, a C-clamp was attached as a lever point on the plate. It was much stronger than the vice-grips.
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| C-clamp for more leverage power. |
Then there was room for more leverage power with a small crow bar. The clamp was moved up a bit too.
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| Small crowbar |
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| Lifting wire emerging |
When further room was gained a large crowbar took over. A fair bit of force was required to shift the plate.
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| Large crowbar |
I dug a small trench in the ground under the plate to get further plate swing room. Then worked the plate up and down for awhile to hopefully free it up. In retrospect this step could be skipped and would have to be anyway if you have a concrete floor. I found that removing the forward ends pivot bolt has the most effect on freeing a rusted stuck center-plate.
The pivot bolt is located inside the cabin, below the floor boards. Once these were clear the top of the center-case could be seen in the keels bilges.
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| The bilges and centercase below floor board level. Red arrow indicates position of the center-plate pivot bolt. |
The pivot bolt was fibreglassed in during the original construction over 30 years ago. Just a small lump is apparent where the bolt is hidden.
So i removed the fibreglass with a wood chizel. In retrospect i would have just taken just the top of the bump off first then pared the rest away until the compression washer was exposed..
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| Chizelling bump off |
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| Exposed pivot bolt nut |
I did the same on the other side of the centercase, removed the fibreglass bump there too. Once the pivot bolt was loosened, the centerplate became allot easier to pull up and push down (by grabbing it on the outside) Again with the learnings of hindsight, one of the first jobs would be to loosen the pivot bolt prior to using the vice grips to pull the plate down.
The pivot bolt came out easily, barely a slight tap of a hammer needed. It was a little bit bent but the stainless bolt had held up well.
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| Pivot bolt |
With the increased freedom of movement the plate began to drop at the front end. The yellow packing pads began to emerge first.
A rust removing tools were tried as the board freed up. Some suggestions were try a slate cutter, machete, heavy hacksaw blade, even an old wood saw. I found that an old hardened piece of thin spring steel was the best tool. I hate to say this but, then i noticed it looked like a rusted old ruler, when the rust was brushed back i discovered it was a John Ramon and sons ruler made in Birmingham England. Graces guide indicates it must be older than 1963 when the company changed name. Hardly a scratch on it, they probably don't make them like that any more.! I think i picked it up with some other old rusty tools in a garage sale decades ago.
Finally with a metallic clang the plate fell out. It was a good sight to see and I was very relieved that it eventually came out.
As suspected nearly all the rust was centered around the pivot hole and cheeks at the foward end of the plate.
The 2mm thick side packers had imbibed allot of rust too, they were made out of laminex sheet or something similar. They were unfit for service.
The lift wire hard eye was swaged to the aft end of the plate. So it had to be cut up with an angle grinder to take the plate away.
The pivot bush is about 17 mm diameter with a 10 mm bolt hole.
The center-plate at only 90 cm long is relatively small for a yact this size, this is because the shoal draft keel does allot of the job in reducing leeway (side-drift) when sailing. The plate makes all the difference going to windward and more as I later found out.
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| Center plate is out. |
The decision on how to proceed next was made. Other Investigators had done
1) Hot dip galvanize the existing mild steel plate
2) Fabricate an Aluminium plate
3) Fabricate a stainless steel plate
4) Have no plate at all (It was discovered by one owner!)
Number 1 - was probably the cheapest option, it lasted 25 to 35 years this time, its weight exactly as designed.
Number 2 - is lighter maybe the design likes the heavier plate and lower COG? What about electrolysis and the least noble metal (aluminium)? its still being tested
Number 3 - Expensive but very good!
Number 4 - Sailing performance would be ordinary and helm balance - trim affected
So decided on option No 1 - Re-galvanize.
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