Have restored a 1962-built 32 ft. wooden cabin motor-cruiser from the waterline up and now need to go the reverse direction.
The underwater hull is double-planked as follows:
- Outside planking is longitudinal planks 1.5 cm thick, probably AMAZON CEDAR (looks like mahogany but isnīt).
- Inside planking is cross-wise of 0.5 cm thickness.
- Canvas in between the planking
A dozen so bungs over the fasteners holding the outside planks to the frames have popped off.
The fasteners under these bungs also appear to be corroded - screw heads greatly diminished. Fasteners seem to be BRASS.
Also, neeed to recaulk the hull especially the seam between the keel and the adjacent plank.
And also replace planks if necessary.
1. Do I need to REMOVE the old fasteners and in their place, insert new ones a size or two greater in diameter ? Or is it acceptable to just install new fasteners leaving the old ones put ? What special techniques / tools are available for removing old screws, which incidentally must be a painstaking process ?
2. What is the best material for underwater hull fasteners, BRASS, SILICON BRONZE, MONEL or STAINLESS ? Does the choice depend on the material of the existing fasteners (BRASS) and if these will be left in place or replaced ?
3. While installing fasteners in new holes , is it necessary to first pump in (the void)polyurethane sealant and then only, introduce the new fastener ? If old screws are removed and new ones screwed in place, is it better to fill the void with a mix of epoxi + wood powder, wait till it dries and then drill again and install the new screws ?
4. Instead of replacing planks with the same wood, could I use BRAZILIAN IPĘ ( a yellowish, hard wood currently sold in the US for garden decking) which is the closest thing to TEAK in terms of durability ? In case the canvas gets tattered, replace with a new piece of canvas or apply a generous amount of polyurethane sealant between planks ?
5. Have read recently that POLYURETHANE caulking applied over cotton/wicking driven into seams, peels off with oil that seeps out in oil-spill-prone areas such as the keel. Some recommend drenching the wicking in primer before slamming it down the seams and painting over with several coats of primer. Could an epoxi-based primer be used and would it survive attack from oil-spills ? Can good old-fashioned tar be also used as an alternative ?
Must do everything right so will not need to redo in the near future.
Rio de Janeiro, BRAZIL