Foil sections, reducing labour and wood but increase efficiency

Storerboats Dinghy Building and Sailing Wiki > Storerboats Wiki > Foils - Centreboards, Leeboards and Rudders > Foil sections, reducing labour and wood but increase efficiency

The advantages of the method I use in my plans are that the foil section was developed after an extensive computer search for an optimum section for boats where the class rules require a flat section and only shaping near the nose and trailing edge of the foil required by the class rules.   The research was done by Neil Pollock in the late 80s.

The aim of such rules was to make foilmaking simpler and cheaper.  However they are often very restrictive.  But what if we take the basic idea and push it as far as it will go toward a more conventional full foil.  There are huge payoffs in buildability and accuracy.

These foils appear in racing classes like the Mirror Dinghy, the Sabre.  Or classes that have a very wide but thin board Australian Sharpie.

It loses a little performance (I’ll recoup that in a moment by showing how accuracy is way above what you can achieve short of CNC cutting) by being a bit thinner because of a flat between the nose and tail sections. The nose and tail sections fair into the flat section perfectly.  The chord to thickness is at the bottom end of the effective ratios used by racing sailors.  The next photos shows two foils just epoxied ready to be block sanded and varnished (or painted)



1/ I’ve made lots of foils but whether an NACAxx or NACAxx-xxx or Eppler or GAW the darn things always roll around as you make them, meaning the second side is always second rate. This method with the flat means the board sits flat on the workbench no matter what and the workbench itself becomes the reference for the templates. So the foils are WAY more accurate than any full section foil + lots of extra efficiency

2/ because of the flat section in the middle the foil can be simply tapered any way you like by just making the foil narrower towards the bottom. The same nose and tail templates can folow the curved edges until they touch.  To taper a full foil is an awful process, as you have to make templates for different widths and guestimate the curvature between them. This method is much easier + a bit more extra efficiency – building effort

Making efficient foils for sailboats the easy way.  Rudder centreboard leeboard

3/ The slightly thinner shape of the foil reduces the quantity of timber needed dramatically reducing cost – cost but it is still within the range of normal foil thicknesses, just at the bottom end. And foiil area is independent of thickness allowing both of them to be independent variables allowing a further path for optimisation. -cost -building time

4/ The amount of wood needing to be removed is much less because of the thinner profile and the requirement that only the leading and trailing edges be shaped. +ease -time

6/ because the whole method is defined and carefully expained step by step in the plans it cuts the labour and heartaching that people go through to make an inferior foil. this is such an easy way to make a nice one. -worry -wasted time

The world needs more Neil Pollocks!

The foil making method is shown on the OzRacer site here … you should see how one of these little nondescrept box boats goes to windward!  Good foils plus the stability to hold up very big sails – which we originally put on as a joke to be startled to find they work.

Note that a full section foil is more efficient for sailing IF is very accurately shaped, but this is not readily achieved in terms of the above problems and the lack of information in most plans.

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