Steve,

Another great post!

You said:
>> Don`t know the I-17R, but have seen it on the Inter web-site, nice boat. I don`t know it`s specs, I presume it`s a bit heavier than Taipan / F16, or you wouldn`t be asking.

Here's a comparion of I17R vs Taipan F16:

(Most I17R data taken from performance web site, Taipan data is approximate based on AHPC's data for T4.9 on it's web site and my estimating changes for the F16 version)

I17R:

Length = 17' 5"
Width = 8' 2.5"
Mast = 30' 4"
Main = 170 sf
Weight = 335 lbs (my estimate from ISAF; some claim it's only 315)
Righting/heeling moment ratio of: 116
(my calculation - main only, crew wt 170 lbs on trap)

Taipan F16

Length = 16' 2.5"
Width = 8' 2.5 "
Mast = 28'
Main = 157.5 sf
Weight(*) = 230 lbs
Righting/heeling moment ratio of: 115
(my calculation - main only, crew wt 170 lbs on trap)

If I've got the data close and done the calculations right the mathematical basis for their stability is nearly identical but the greater mass of the I17R might allow it be get through chop better in ligher winds but the Taipan would do better accelerating in gusts. Still, this is math and theory; practical testing is more important. Steve, I appreciate your taking a stab at an I17R vs Taipan 4.9/F16 comparison but you are disadvantaged in not having had the opportunity to sail them both. So, to reiterate the question: anyone else been lucky enough to sail them both and compare (and under what wind/wave conditions)?

Regarding high aspect sails with less chord you said:
>> Don`t think we should be studying your sailplan under "hydrodynamics" unless you want to know how it behaves while submerged ! Aerodynamically you`re correct though . High aspect wings on aircraft with less chord are more efficient at producing lift than low aspect, but are more sensitive to angle of attack & are easier to stall (detach airflow).

You mean you don't routinely sail your cat inverted to check out the hydrodynamic efficiency of the sails? Maybe that explains the difference in sailing philosophy between US sailors and you ozzies!
Thanks for the explanation and confirmation my instinct was right.

You also said:
>> They also produce LESS lift than low aspect sails AT LOWER SPEEDS, however their higher efficiency compensates for this, so a low aspect sail will feel more powerful, but have the power closer to the boat, where you want it in high winds, while a high aspect sail will generate more lift higher up, making it better suited to lighter winds. That`s why it`s important to have your rig set up so that the top of the main twists off in strong wind, to depower the top of the rig & allow the lower half to produce the power, thereby staying upright.

Great input. The issue you raise with twisting the top of the main for higher winds is critical, I agree (same in windsurfing). This raises another whole topic which I feel is important as well: mast stiffness. It is my believe that most US masts tend to be quite stiff, which can make it harder to twist off the main with the downhaul interactively from the trap or tramp (without damaging the sail). This may be less of a problem with longer masts than shorter ones. It seems with these really stiff masts, prebend is the only way to adjust twist easily but it obviously doesn't let you do that dynamically. I don't know how how stiff the I17R mast is since it's fairly long and carbon fiber, but I believe that most Hobie aluminum masts are very stiff. Anyone have input on the I17R's mast stiffness and if it's easy to control sail shape and twist easily via downhaul?

Regarding comparing Taipan and Mosquito:
I really enjoyed your comparison as well as your superimposed diagram! You raise an interesting option: I would think that the standard Taipan sails would do quite well in light and medium wind (even for a non-expert) but might become challenging (for non-experts) in higher winds for the reasons you described. It would seem reasonable then to get a second main made specifically for higher wind conditions (obviously for recreational use and not for racing) which looks more like a Mosquito sail (less area up top, smaller overall sf, maybe slightly flatter draft) - this would make a lively Taipan more controllable in a big blow wouldn't you think? If someone did that, do you think a Taipan would tolerate the 28-30 kt winds that the mosquito can take (obviously assuming the sailor has the skills to take a Mosquito out in those conditions)?

You also said:
>> If you`re sailing in high wind & waves a lot, I`d pick the longer boat, even if it`s a bit heavier. I do have a problem if it`s 50% heavier though, I think there`s a fine balance between all design elements which either make a boat a pleasure, or a pig.

So my final question to you is: Sounds like you were leaning to the I17R for higher wind/waves given its 1 ft longer hull and 100 lbs heavier weight (46% heavier). But don't forget it has a 2' 4" taller mast and 12.5 sf larger main. Obviously a smaller main could be put on either. Given the above, any change in which you think would be better?

Thanks again for the great input,

Jerry