Adding larger fin

Question
I am considering to add  a Bic 293D ( 205 lts)to my Tabou Rocket 145 to extend my sailing to subplaning and serious upwind for which the Tabou is poorly suited due to its lack of a centerboard when winds fall below 15 knts.
Somebody told me that the Bic, although a beginner board, dramatically increases its performance beyond sub-planing and a beginner's needs, if we replace the standard 36 cm fin with a larger one, possibly a 48 cm or even larger.
Since I am sailing most of the time in under 15 knts winds, both by necessity and choice, I'd be using a 7.5 or even an 8.5 sail most of the time. ( I weigh 80 kg)
I was wondering if you have any comments or suggestions about the right fin size.  Ideally, I'd go for  as large as possible a fin to get the best upwind performance, but I wouldn't want to run into other problems. What are the implications of having too large a fin ?

Also, I was thinking of getting a rigging tool, because I've seen pro's  downhauling the sail  much more beyond what I can do by hand ,but, judging by the ease with which the rigging tool  can bend the mast, I wouldn't want to unwittingly apply too much tension and break the it ( I have a Viper 75% carbon mast). Is it a real risk?

I'd like to have your suggestions on both issues.

Thank you

Franco

Answer
Hey Franco,

The Bic 293D is a beginner board due to the daggerboard. But, it is also considered a very good intermediate/advanced board for light winds so should work well for your light wind days.

As for the size fin for a 7.5-8.5 sail, a 48-50cm should work fine for your size. About the only problem with using a fin that is too large is that it will cause too much lift for the conditions. With too much lift, cavitation can occur which will result in a spin out. The other problem is the fin wants to tilt to a horizontal plane which causes the board to rail and becomes hard to control. A 48-50cm fin should not be a problem in light winds. If you get to the point where this size fin becomes a problem, conditions will probably be at a point that you should consider rigging down.

Using a rigging tool is good for folks riding racing sails. They usually have 4 or more cambers and are very stiff sails. They are also using a high performance mast that is designed for race sails and are usually stiffer that recreational masts.

For most recreational sails (ie; freeride, two or less cambers, wave sails), a rigging tool is usually not necessary to get proper downhaul. Also, when adding more downhaul to a sail, to put too much downhaul on will just make the sail too floppy and hard to control. If a sailor needs to spill that much wind, then it is time to rig down to a smaller sail. For most masts, it would take way more power that most of us have to downhaul a sail enough to break a mast. Masts are designed to bend to shape the sail. If you use one of the types of downhaul tools below, you will never have to worry about breaking your mast.

Here are a couple of handheld tools that work well for most recreational sails. If you feel you need a bit more leverage, go for the two handed model.

http://www.windance.com/chinook-c-123.html

Hope this helps.
Keep on sailing,
Windlover