Fitting Knees – small boat

Introduction

Transferring loads between components of a yacht /boat is really important. Its structure is stiffened up with the use of a knee which is usually wood, or metal in later boats, or a composite structure in modern boats. The knee joins the two components (for example deck and hull, hull and seat, hull and transom) together and provides a load path and structure etc.

Fitting them to a small boat, it is vital for them to fit both components and be secured for them to do their task.

As with most boat building, it is not a simple  union, usually having to match the curve of the hull and fit around other structural items like the gunwale and plank lands etc. Demonstrated in this skill is a simple process to get this right.

Procedure

The process is demonstrated in the accompanying video clips with a step-by-step guide. The conversation with the boat  builder, in this case Marcus Lewis, is unscripted and covers the technique from his experience.

  1. Take the prepared blank knee (half lapped, run through a thicknesser to get the finished siding and planed base) and place on the seat close to the required location.

  2. If necessary, make the level stick and mark the offset

  3. Using the level stick, place on the horizontal points such as top of the gunwale, make sure it is level and draw a line across the knee.

  4. Now mark the offset of the key points, top and bottom of gunwale, depth of gunwale, depth of planking, plank land and  planking at the top of the seat, plus any other items which the knee has to be cut in around.

  5. Mark the bevel of the gunwale so this can be cut later, simply lay the stick on the top of the knee, line it up with the inner gunwale edge from above. Draw along the stick to mark this.

  6. Join up all the marks.

  7. Set the bandsaw table to match the required bevel. In this example there were two cuts down the knee on this setting. Then the knee is rotated, the angle changed to match and cut.

  8. The bandsaw table is moved back so it is flat and all the horizontal lines are cut.

  9. The knee is checked in position, looking at the fit and bevel. If there are any gaps, more will be required to be trimmed of,f so scribe the new cutline with a pencil. Repeat the process in steps 7 and 8.
  10. Offer up the trimmed knee and check for fit, if necessary repeat step 9.

  11. Once happy, mark its location on the gunwale and label the top of the knee (in this case, middle seat, starboard side, forward knee).

  12. Start on the next knee.

Once all the knees have been fitted they can be shaped, cleaned up and secured in position. With this sailing dinghy, this was done with a copper nail through the gunwale and then riveted. A screw was then put through the land of the top plank, counter sunk and plugged, then fixed to the seat.

 
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Tools Required

  • Level stick (self made, straight piece of wood and a bubble from a spirit level)
  • Hammer
  • Clamp
  • Band saw with a tilting table
  • Dust extractor
  • Rule or straight edge
  • Personal Protective Equipment (PPE)
  • Pencil

Materials Required

  • Oak
  • Half lapped and glued with epoxy to make the blank knee