Centre Case leaks

 Fresh water, if left to lie in a wooden boat will cause rot to occur, mainly in three places

1. Along the logs of the centre case, which is basically the lowest place in the boat if the trailer is level.
2. Around the lower transom area, occurring if the trailer has been tilted.
3. Around the area bounded by the back of the cabin bulkhead, seat and coaming (I suspect that the coaming on your boat will be out along the gunwales.)

 Centre board leak. In early boats, the centre case ply stopped at the keelson, (F) and leakage was prevented by putting a filler such as Bostick and tensioning the bolts along the logs. Over the years the bolts loosen, and the old style filler cracks, so in comes the water.

In repairing this, it is important to remember that the water should be stopped from the outside, otherwise, it will still penetrate the wood and cause rot.

1. Thoroughly clean the area around the centre case inside and see if there are any obvious cracks and evidence of dry rot. If there is dry rot, the rotten wood should be scraped out and then the area treated with Everdure, a 2 part epoxy that soaks into the affected area and seals it, then filled with PlastiBond.
2.  Then try nipping the bolts up a bit. Firstly clear the paint off them and work the nut loose a turn or so. Then tighten
3.  Drop the boat off the trailer and roll it on to its side – not as hard as it seems.

 The centreboard will need to be removed. This is done by opening the plates on either side of the log and pushing the pin out. Be sure to firstly swing the board out. Again, thoroughly inspect the area.

It is a fairly sure bet that the leak is occurring where the logs/ply and keelson join, about 50mm inside and hard to see and get at. The area needs to be roughed up with a rasp, including the back of the centre case, and a layer of 50mm glass tape put in. Not so easy, and a tooth-brush is probably the best way to spread the resin before and after laying the tape. Give it plenty of resin. You will have to turn the boat to do the other side.

If there is evidence of cracks along the keel area, clean back to timber and put glass tape along it.

From the Building Guide:-

Centre Case

An optional method of building centre case is to extend sides through to bottom of boat.

Make sides from 1800 x 1200 x 12 ply. Cut to 2 off 1800 x 600. Position logs on sides using uncut edge of ply as top.

Mark shape of sides as shown in sketch.

• Position logs from dimensions shown on plan
•  Sawn edge
• Allow case side to come to edge of logs

Mark positions of log to side screws to clear retaining bolts. Clamp logs to sides and drill screw holes. Remove clamps clean chips away, glue and screw together. A pump action screw driver, or two people should be used to get the 40 screws driven before the glue sets. Use a piece of scrap timber same length as case logs and mark position of the 40 screws. Have screws in same position in both sides. The end spacers are cut and positioned as shown in sketch. A packing block can be used to fill the gap between the extension of the case logs. This fills in a cavity that is almost impossible to paint. The end spacers are glued and screwed to one side. Both sides are brought together and temporarily screwed. Bore hole for plate pivot pin. Fibre-glassing the inside of the centre case is the best method of protection. Unscrew sides and fibreglass both sides keeping faces of spacers and mating face on other side clear of resin. Use a heavy resin coat this will give added protection. The pivot hole can be bored slightly large and a liberal coating of resin applied to inside of hole.

This will prevent water soaking into inside of ply sides and case logs.

To assemble centre case glue face of spacers and mating face on ply. Use a bead of epoxy putty along the internal join at edge of fibre glass. This will form a water tight seal when case is assembled.

Wooden block

Resin in enlarged hole

Fitting Centre Case to Hull

From inside of hull mark on centre line of keelson the position of ends of centre case protrusion below case logs. Drill holes through keel-son from these points. From these holes on top of hull mark shape of slot required to accept centre case. Use a circular saw in an electric drill to saw along these marks. A hand saw can be worked through from saw cut and the sides of slot cut through for their full length. Drill through ends and remove centre piece. Rasp ends square. Remove diagonal brace from building stock and frame spreaders and mounting cleats from frames 3 & 4. Remove piece connecting halves of frame 4.

Bring centre case up through building stocks and up to slot. Rasp slot until case will fit through and prop in position with boards across building stock.

Use the piece of timber with the case-log to side screws and centre case retaining bolt positions marked on, to mark position of bolt holes on outside of hull.

With centre case held square and firm bolt holes can be drilled. Start off with a 7m drill in electric drill and drill as deep as you can. Continue with brace and bit. For remaining holes bit can be driven through using a shifting spanner on tapered tang of bit. These will be the holes along side the centre case ply that protrudes the most This method is rather crude but is reasonably quick when a drill with an extended shank is not available. Remove centre case and clear away chips. Counter bore holes in Keelson to accept heads of bolts and bevel inside edges of centre case slot.

Centre case bolts - these can be made from brass, bronze or stainless steel rod. Use threaded rod or thread your own. Use a lock nut for head of bolt, thread rod to depth of nut, wind nut on tight and peen rod flush with nut. Use washers under heads. Run a fillet of caulking compound around centre case between under side of logs and side extension, place case in position, drive bolts through and tighten firmly.

Sydney builders claim that the practice of fitting, bolting and gluing the centre board case prior to planking saves work and reduces the risk of leakage. They also advocate the use of 8 - 6 dia bolts made from threaded stainless steel rod, in lieu of the 12 y 6 dia bolts shown on plan. Oversize washers prevent the heads pulling through the soft timber. Fit remaining keel timbers as shown on plan. A straight grained hard wood will give best service here. Use 25 wide timbers beside centre case protrusion, gluing and screwing into both keelson and centre case sides. Mark curve on timbers as shown in sketch.

Thinnest section required

hold pencil over spacing block and move along hull.

Alternative method of fitting centre case

1. Set up frames, transom and stem.
2. Fit keelson to frames and stem with temporary screws.
3. Temporarily fit fin-case to-keelson making sure it butts against frame 3.     It will also be necessary to cut away a section of frame spreaders 3 and 4 to clear top of fin-case. Spreader depth should be reduced to a maximum of 32 with a strong timber or ply strengthening plate bolted around cut-away section.       A hole will be required for the string line which will be threaded through.          Alternatively a metal plate could be used, this would not need to protrude beyond frame spreader.
4. Plane bottom of fin-case to exact curve of keelson, check for squareness. Use 150mm `G' Clamps for temporarily securing to keelson.
5. Mark out and cut slot in keelson.
6. Mark out and drill bolt holes through case logs and keelson, 4 - 6rnn stainless steel bolts each side is all that is necessary. Counter-bore heads in keelson below flush.
7. Use Epoxy glue and tighten bolts.
8. Fit and glue second keelson.
9. Fit chines and stringers.
10. Fair keelson, chines and stringers.
11. Fit transom ply.
12.  Fit planking.

Fair centre case keel timbers into aft keel timber filling gaps with scrap. Cut taper on aft keel timber, bottom edge and face of taper can be faired down to 25 minim width with a 12 radius.  Bolt aft timber as shown on plan (make your own bolts) 75nm brass screws can also be driven into this timber from inside of hull.