After 6 months experimenting, I think I am now at my final configuration which allows me to sail with the main boom parallel on all rigs.  Through my whole dinghy sailing career I wanted to sail with the main boom parallel to the deck.  It looks right and usually fast.  Mast rake is up to 2 degrees and my challenge was getting a fin in the right position to work with this rig.  

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The goal was to sail with a perfectly balanced boat with a hint of lee helm so when I am looking for wind shifts, the boat is sailing as fast as it can upwind.  With the previous weather helm I had tended to lose speed when I looked up the course.

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I am using a Craig Smith fin with a Robot bulb. 

 

Fin

Leading edge of top of fin to line perpendicular from bow (excluding the bumper).  500mm (measured parallel to the waterline).  I have since moved this to 515mm (23/11/2024) to try and get the boat to drive off the jib instead of trying to luff up all the time.

Fin leading edge is exactly 88 degrees (now 90 degrees as I moved the top of the fin back) to waterline (tiny rake)  I had got this to vertical but the boat was not quite balanced right.

Bulb angle to waterline 2 degrees.  Bottom of bulb is 2mm above max draft

Hull to top of bulb down leading edge of fin.  330mm

Bow to tip of fin where it enters bulb 640mm.

C of G of bulb is 5mm forward of leading edge of fin

 

Fin weight.  I can't give you the exact weight but it is lighter than anything I have seen.

 

Rudder

Depth of rudder 220.  Very thin chord but no experience of stalling.  I have since tried this down.  Shortened the rudder by 15mm and trimmed 5mm off the back

 

Rig

Top of boom band to step 135mm

A rig mast rake  1040  (bow behind bumper to 900 mm mark on mast measured from top of foredeck.)

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My next step is to work up a set of sails for open water.  More on that as the summer progresses assuming we eventually get summer weather.

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In the build up to the worlds I settled on Sailboat RC sails and went for the max depth A Rig sails which I have to say have delivered good speed.  I change the mast prebend a little bit and moved it further down the mast which made a significant difference in mast stiffness to the point I had to rake the spreaders back a few degrees more.  The blog covers events at the worlds

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The only niggle with the boat this year was i the fin is still too far forward as I still get occasional weather helm and this can slow the boat in waves in a breeze so I am working on moving the top back (See above comments in brackets) but leaving the bulb in the same position