Many boats have Teak & Holly floorboards ( 5 mm teak and holly with 9 mm ply backing ) fastened to the boat structure with number 8 countersunk SS screws. Over the years, the teak and holly top surface shows the dings and wear of age, plus the screw fasteners have enlarged the countersunk holes, and some fasteners have stripped the thread in the securing “fiberglass” structure underneath.
The floorboards in this photo are 25 years old, are from a CS 33, and they show the effects of much use, but they remain structurally sound. No need to replace but a bit of surface sanding and a light coat of varnish on all surfaces and they remain very serviceable. To further improve the appearance, the ugly screw countersinks in the wood were lined with brass inserts (countersunk washers). The section of floorboard in the left of the photo has the countersink well worn and the floorboard in the right of the photo shows the up-grade method and parts.
The brad point drill shown is a quality HSS 7/16 diameter drill used to counterbore all existing mounting holes ( the CS33 has 52 ) to a depth of .160 to allow the number 10 countersunk washers to sit flush or just below the floorboard surface. Care is needed here to centre the counterbores in the existing holes and to control the depth: a drill press is a must. Then bed the brass countersunk washers in place with epoxy glue. After the glue has set, drill through each brass washer with a 13/64 drill to clean out the hole to insure clearance for the number 10 screws that will now be used to secure the flooboards. Note this screw size may be one size larger than the original and that is an advantage as many of the holes at the boat-attach points may be partially stripped after floorboard removals and re-assemblies over the years. For re-assembly, number 10 flat head brass screws look best but they are normally slot driven and best installed by hand: one blister is allowed. However, the battery-powered driver is much more convenient and recessed flat head SS screws will fill the bill. Both options are shown in the photo.
The brad point HSS drill and the number 10 brass countersunk washers are available from Lee Valley and the number 10 screws of your choice are best purchased in a box of 100 from a fastener supply house.
by Ed Sulis