Centerboard restoration and refit

The restoration began with knocking out the old plastic pivot bushing at the workbench, keeping it and other pivot bolt parts together so measurements could be taken to replace the entire pivot unit assembly.

The rust was removed, mostly with a power wire brush on a 5" grinder and 9" angle grinder with cutting wheel.

One thing that surprised me was the completely square edges on the 12mm thick centerplate. These looked very un-hydrodynamic so i set to it with the 9" grinder to reshape the forward and trailing edges into semblances of a parabolic foil shape to improve sailing performance.

There, that's starting to look better! A final bit of rust converter acid  to neutralise the deeper pits. The hot dip galvanising plant recommended some paint stripper to make sure no remnant paint remained anywhere as cold gal won't stick to paint etc.

A pic of what the center-case slot looks like without the plate, its a hardly-ever seen (let alone maintained) part of a trailer yacht, its either under water or on the trailer near the ground with rollers and steel beams all around it which prevent easy access to it.

The center plate of the 18 foot Teria is a similar size to the daggerboard of the 8 foot long Fatty knees dinghy. The Teria has a shoal draft fixed keel that makes up about 75% of the yachts lateral resistance, the center-plate is about 25% of the lateral resistance. The Fatty knees has only a 1" deep rub-keel and small skeg so it's dagger board does most of the work.

The pivot assembly was re-built from scratch. A stainless 10mm diameter bolt and the remains of the 3 bushes were taken around town to see what could be done. I started at the marine chanders, went to a power boat chandlers and they knew of an engineering firm just down the street - Arndt Engineering.. In luck, they had refitted yacht rudder shaft assemblies. The callipers were taken out, centerplate and pivot bolt bits were left with them, they made the bushes on a lathe with white polyacetate? a tough hard wearing plastic suitable for marine immersion for a very reasonable fee. They drilled out the pivot hole a bit and allowed for some clearance after the cold gal was on. The center bush was slightly larger than the original which made it thicker walled and stronger.

The center plate went to the galvanizing plant, it weighed around 20 kg which was just under the 25 kg minimum lot weight. So paid $55 for the plate's acid bath and hot dip in the molten zinc vat. The going rate for hot dip galvanizing at the Bohle plant is $2 / kg. Due to a long work Que it took a week to get done but it was worth the wait, it sure did look like new.

Back at the boat yard cheek pads were fabricated and fitted. I bought 2 mm black polyethylene? plastic sheet (aka chopping board plastic - is a bit slippery) at Northern Plastics. Cut round circles 270 mm in diameter with a 20mm hole in the middle.

The plate was refitted with the help of a friend. Mike got the pivot bolt in while i lifted the plate up. Some pencil marking and a strong torch helped align it. Afterwards it was apparent that the 4 mm packing was not enough the plate was too loose in the case and wobbled about. So i dropped it out and added a third 2 mm spacer.

This time i got it in solo and allot easier. The plates 20 kg weight was held up by the trolley jack below, when up in the case there's almost no fore and aft play so the pin aligned with the hole far more easily. This time, with  6 mm of plastic packing, the board fit snugly with no sideways movement.

The benefits of a "deco" floor, dug a small trench for centerplate to lower into.

Note: Decomposed granite "Deco" is an economical material often used for car driveways up here. It can be spread out like soil, but after being compacted (by cars wheels) sets hard. However it still remains workable, it can be added to or even dug through (eg to lay a pipe). It's great on the expanding clay soils we have, as it never cracks up like concrete. In the open, grass will grow over it. Under a roof it's resistant to grass and weeds, i just spray the few that do sprout.

The pivot bolt assembly got bedded down with liberal amounts of silicone sealant to prevent leaking.

Pivot bolt nut and washers inside the bilge area. The high compression plastic washers spreads load out while having a little "give" 

To refit the lift wire i bought a 3.2 mm swaging tool. It looks like a pair of bolt cutters but with a different business end that crimps the swage tight around the wire.
This time the eye was not integral with the plates lug, it was attached with a screw pin shackle instead, so future maintenance (possibly by some new owner?) will hopefully not require the purchase of an expensive swaging tool!

Lift wire now shackled to center-plate for easy plate removal.

Everything together - the plate worked well. Rising up into it's case with a haul on the lift rope in the cockpit. Lowering down by letting it out. I marked the lift rope with 2 positions, 1/2 raised and 3/4 raised. The system is simple, no purchase block and tackles required, just a pipe for the lift rope-wire, exit sheave and horn cleat.

Centerboard removal

Before this whole operation i had a good go at removing rust from the centercase slot while the boat was on the trailer. Various narrow implements were used to chip away at the mess but it still remained stuck. 

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. 

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.

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.

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.

Small crowbar

Lifting wire emerging

When further room was gained a large crowbar took over. A fair bit of force was required to shift the plate.

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. 

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..

Chizelling bump off

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.

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. 

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. 

Trailer removal and Blocking-up the hull

Some maintenance to center-board and trailer needed to be done - The centerboard was rusted into it's case and the trailer rollers and side pads were not letting the boat slide off as they should.

So the Teria had to be blocked up and have the trailer removed to work on these issues.

The Investigator forum had some good posts - It can be done at home in the driveway and another boat was done in a fully kitted out automotive shed with lifting slings - Gantries etc. Some owners enlisted a bunch of mates to hold the hull up to get it off the trailer. My method leaned more towards the at home method with modifications and the added benefit of a shed structure around it.

Teria was towed to my boat building shed out in the country. It houses my home-built Wylo 2 yacht hull , for full story see wyloyard. Over the last few years i extended the shed roof area, the west extension was originally  intended as the yachts' woodworking-spar workshop but now it was just right for use as a trailer boat repair shed.

In the wylo yard shed extension

The trailer removal began by lowering the front of the trailer to the ground.

This raises the stern up high and a 44 gallon drum with old car tyre and tarp padding was pushed under the transom.

Next i secured the hull  with strong ropes. This was to prevent Teria's  hull toppling over sideways. The ropes went through the u-bolt chainplates on deck. Two ropes went horizontally to shed posts to prevent side tipping. Two very strong ropes went up subvertically to the shed roof and could, in theory, hold the entire hull up in the unlikely scenario of the support stands failing or tipping out while i was under the hull.

More secure ropes were setup down aft to prevent the hull moving foward as the trailer was extracted..

Then the front of the trailer was jacked up again. This made the transom press down on the drum aft and the boat started to lift off the trailer. I did the lift-off because because need as much height under the keel as possible in order to remove the centerboard later, also the trailer was badly fitted and the hull was resting too heavily on the side pads, almost stuck there. 

Keel lifts off aft rollers

Hull lifts off aft side pads

The safety ropes were re-tightened to remove slack caused by the lift. 

To pull the trailer out, a come along winch was setup between the Ute towbar and trailer ball. 

As the trailer moved foward a car stand and car jack went under the aft keel. Hardwood blocks are used to protect the fibre-glass keel and to support or raise jacks and stands.

Hardwood side legs could now be fitted under the gunwales to further prevent the hull falling over.  (Allot of secondhand hardwoods from old wrecked houses up here. Bought my railway sleepers a long time ago from Queensland railways yards)

As the front of the keel emerged, the car jack was moved forward and a second car stand went under the front end of the keel. The two cars stands are placed so the centerboard case slot is exposed between them. The boat was jacked up level, stands adjusted to height and trailer pulled out for maintenance in my case.

NB. In boats with good trailers, a safer way to go is to leave the trailer in place to help hold up the fore-keel and stabilize the boat. Blocks should go under the back end of trailer, its brakes on and wheels chocked.

Rex inspects the job

I put a steel workhorse under the fore keel to further support the boat.With side legs and support ropes adjusted i was confident to go under the 900 kg hull without worry.

Chain plates maintenance

The suspected u-bolt chain plate was unbolted below decks and the fitting tapped upwards. One arm of the u-bolt had snapped off. (Fortunately the remaining side held , bending a little bit. The  mast and entire rig are held up by these deck u-bolts)

Rust stain seeping out on deck was a tell-tale sign that was not noticed before the failure.

The original chain-plate u-bolt had been fitted for over 30 years. It's a good idea to unbolt and inspect these about every 10 years or when rust stains are seen.

A closer look at the damaged indicates that crevice corrosion had taken place, and work-hardening-micro-cracking had occurred allowing salt water in to corrode the stainless steel (in fiberglass deck).

The intact side was also badly corroded.

The investigator 563 class web-forum revealed that this is a common problem in 30 plus year old boats, it has also happened in Compass Careel 18s which have a similar chain-plate system and baots are also reaching this age.

I replaced the chain-plates on both sides with high quality Ronstan 8 mm u-bolts, the same specs as the originals.

The replacement is 8mm rod throughout with small lugs to hold the deck plate in place. The original had 10 mm rod above deck and 8 mm threaded rod below deck, would this size difference contribute to metal fatigue at the deck line?

These fitted nicely into the original through deck holes. Below decks a 12 mm block of timber distributes the load. Clear silicon was used to seal the holes.

The new u-bolt also has a load distribution plate below deck. The original had two washers instead.

The rigging screws shacked above the chain plate were closely inspected. One 6 mm rigging-screw was obviously bent and another had a hairline crack in the toggle, so these were removed.

Hairline crack and rust stain on rigging toggle, a potential failure point.

The replacements are much heavier and twice as strong, 8 mm rigging screws which were fitted to hold the upper shrouds. The two remaining 6 mm rigging screws now hold the lower shrouds to the chain-plates.

8 mm rigging screw (front) is far stronger than the original 6 mm one (back) it replaced. The new chain-plate u-bolt should last another 10-20 years before replacement maintenance is required.

The inner rigging screws should eventually be replaced, the original design is still produced but need to be ordered in.

Will keep an eye on the old rigging for any sign of potential failure. Rust stains are areas to watch for cracks or frayed wires etc. The rigging wires age is not known but it does look younger than the original chain-plates.