Building station moulds

In this post I will try to describe how I built the moulds for the hull.

First off what are stations?  Stations are simply divisions of the hull at even intervals drawn in by the designer.  If you were to look at the profile (side view) of the boat they would show as a vertical line that slices through the hull.  The full size lofting shows a cross section at each station which becomes the shape of the moulds that the hull well be formed around.  Imagine a loaf of bread, if you were to remove every second slice and leave the remaining you would still have a full image of the loaf despite the spaces inbetween.

In the case of the Rhode's Wherry there are 5 stations and they are spaced 20" apart.  With some overhang beyond the first and last station, the boat as designed measures about 10'6".  However, going on the designers advice, I will create a 12' boat by simply multiplying the spacing by a factor of 1.14.

Here's what I did:

1) First for each mould I made two halves. 

• Multiple pieces were joined by roughly figuring out an angle and joining the ends with pocket hole screws. 
• Keep in mind that at this point the outer edge is oversize.



Rough mould halves.  The material is spruce 2X6 that has been planed 1" thick

 2) Next I transfered the outer edge from the lofting to the wood. 
Here's a cool trick I learned:

• Take a ring nail and grind off half of the head (see pics). 
• Lay the nails flat side down spaced evenly along the line you want to capture. 
• Press the wood down onto the nails with enough pressure to sink the sharp nailheads into the wood.
• Bend a thin wood batten through the points and trace the resulting line.  (bending a wood strip results in a curve without dips and humps refered to as fair). 

Nails following one of the station moulds.  Note that the plan only shows half of each mould.

View of what the nails should look like after grinding

The nails stick into the wood allowing you to trace the line

3)  Next I cut out the mould halves and joined them.

• I screwed both halves together during cutting and sanding to make a perfect mirror image
• I used a bandsaw to cut outside the line and a belt sander to fine tune precisely.
• I joined the bottom with screws and stapled plywood gussets over each joint to add strength.
• Lastly, I added a batten along the top and extra bracing to the larger moulds.

Checking the outer edge after sanding, accuracy is very important here!



This is one saucy lookin' mould



These moulds are closer to the center of the hull and required some extra bracing

One final thought: 

Each of the moulds have a flat piece at the top (bottom in the pictures), these are strategically placed.  Since I will be building the hull upside down I extend the mould ends to meet a specific reference point on the drawing.  What this means is that when I flip the moulds upside down and space them on a flat platform the heights will be correct without shimming or leveling (I hope).

Vocabulary Lesson:

Here's some boatbuilding terms for ya'll:

Sheer line: The upper most line of the hull in profile.  Also visible as the outer line in top view.

Fair curve:  A fair curve has no dips or humps.  Builders rely on bending wooden battens and their eye to check for fairness.  As I learned, this is why lofting is still done by hand as opposed to on a computer.