To some extend we already know the difference of this due to the experience with the various F16 who basically all went from low aspect boards to higher aspect boards (but not very high aspect).

In the light and strong winds there is no noticeable difference that can be solely attributed to the daggerboards. I personally would also add unstable conditions to this, significant waves and gusts. In the medium wind conditions the higher aspect boards seem to do slightly better (roughly 7 to 13 knots). The largest benefit of higher aspect boards is that you can raise them a little without totally losing pointing or drive. With the low aspect F16 boards this is an issue and thus the reason why these low aspect boards are always kept fully down just as with the Tornado. On the F16's it is especially important to be able to raise your boards as when you are sailing 1-up you really do want to have less board area in the water then the 2-up version.

With respect to hurting yourself on the trailing egde. The older F16 boards all had a rectangular crosssection in the top halve of the board. Here the trailing edge is 20 mm thick and that hurt a whole lot less then a sharp trailing edge. Sadly, this is more work to make and therefor alot of boards makers just forget about this issue. The newer F16 daggerboards try to compromise on this by cutting away the trailing edge on the top 1/3 of the board. This thickens the trailing where you can hit it. The jury is still out on that however.

In the sailing and tuning seminar that Greg Goodall held at the F16 Global Challenge last august he discussed the issue of raising boards at some length. He said that experience to this point had shown them that leaving the boards all the way down even on spinnaker legs was the fastest. He doesn't pull the boards up unless he has to do so on the upwind leg and basically keeps them were they are for the whole race.

Basically high aspects boards are a performance refinement rather then a performance improvement. As such their effect is relatively small. I personally belong to the camp that believes that an aspect ratio anywhere between 3 and 4 is enough. Old Taipan boards had ratio of 1.85 which is indeed low, and modern F18's have ratio's of 4.5 to 5.5. The efficiency is also a strongly non-linear behaviour, meaning that going from ratio 2 to ratio 4 will create some benefit X but going higher again to say ratio 6 will not nearly have as much benefit. I think the rule of thumb I derive for the boards some years ago was that with each increase in aspect ratio by 1 point you would win 2/3 of the efficiency of the former step (but I'll have to check that). Example :

difference efficiency going from aspect ratio 1 to 2 = say 1 ; total = 1
difference efficiency going from aspect ratio 2 to 3 = 0.67 ; total = 1.67
difference efficiency going from aspect ratio 3 to 4 = 0.44 ; total = 2.11
difference efficiency going from aspect ratio 4 to 5 = 0.29 ; total = 2.40
difference efficiency going from aspect ratio 5 to 6 = 0.18 ; total = 2.69

As can clearly be seen after aspect ratio 4 the difference in almost negligiable. Of course the drawback of high aspect boards is that they become increasinly sensitive and it will be hard to make them stiff enough. All these factors need to be balanced to one another. And here we find the reason to favour aspect ratio between 3 and 4.

I hope this is clear enough for most readers here.

Wouter