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Wet Sanding 101

From time to time a boat may need to have its wet sanded finish renewed so that the superior speed facilitated by the boundary layer can be realized.  Here’s how it is done:

  • Place boat upside down with full access to wet sanded area. (Avoid slings if possible as they will block your “flow”.)
  • Place masking tape along the water line to avoid scratching any area not to be wet sanded.
  • Take a bottle of water (great if you have a hose), spray the bottom of the hull and wipe entire boat with towel.
  • Wait and watch for areas where the water dries first – these are the areas that will need retouching (areas that stay wet show that it is still “holding” the water in the scratches).
  • Take 600-grit (what we use in the shop) or even 1000 grit wet sand paper (gray) and fold into ¼ sheet.  Fold so that the sandy side doesn’t scratch itself.  Fold it over a flexible sanding block.  It is best not to use sandpaper over bare hands as they will have high spots.  (In the shop we use a Soft Block flexible sanding block by Motor Guard – generally available where marine or automotive paints are sold.)
  • Wet the area that needs attention: It is best to establish a quadrant that is about 3 feet wide (you want to be able to apply a consistent level of pressure so don’t go too wide)
  • Place gray side onto hull at outside edge of area to be sanded; start at the top.
  • Hold paper with one palm down and other hand applying pressure on top.
  • Stroke the boat in a parallel line.  (Imagine stroking a scared horse to calm it down.); shift body to keep weight behind hands.  One stroke across then move down.
  • Keep everything (hull and sandpaper) wet.
  • Change paper often (unfold sheet and refold; don’t reuse once you have used; probably one ¼ sheet per section or two). If area is very long you can consider one pass the whole length.

NB Most wear will be in the first few feet of the bow.  This is the most important area as this is what “cuts” through the water.  If the boat is to be stored outside for an extended period of time, coating the wet sanded area of the boat with dish washing detergent will help prevent any buildup of dirt such as tree sap, bird droppings, etc.

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