Fred :
Most of the stuff you are describing to do, I did to my TI well over a year ago now, and have many miles on the boat now with no major issues. If you go to the Hobie forum post (The ultimate Tandem Island (hydrofoils,spinnaker,jib,etc) viewtopic.php?f=69&t=33720 it goes into great detail explaining the super simple designs which would work equally well on an AI or TI. Before making the bigger jib I used an old Hobie kayak sail for a while and it worked great ( was a little small for the TI but would be perfect for an AI). I haven't made any additional changes since then, I just use it as is, though I would like to replace the assymetric spinnaker with a bow sprit and a roller furled screacher or furlable gennaker (similar to the furling screacher on the WETA boats, I'm designing it now and have the material).
My total sail area is similar to both the WETA, and the Windrider 17, which are both nice boats. The WETA is much smaller than the TI and the WR17 is comparable in size. I'm just guessing but assume my performance to be comparable to either. However my total costs to date on the boat are around $5,200 (including the motor) I think the other boats are double and triple that cost and couldn't see myself car topping either one, or kayaking up a river in either of them.
You are correct, with more sail the bow can nose dive under water and doesn't always come back up again ( I call it nautilus mode), thats why I added the hydrofoils. But I've only nosedived a couple times, it turned out to not be as bad a problem as I thought. The boat doesn't pitchpole, it just slows down until you can get the bow up again (and you get really wet), I just turn on the hydrofoil and the bow raises back up.
The jib makes a huge difference, I simply don't understand why nobody has them. When I first got the boat I would go out in 5-8 mph winds (typical around here) and got bored pretty fast with just the mainsail putzing along at 3-4 mph and had little success going upwind much closer than 45 degrees (maybe I'm just a really bad sailer).
Many of the dive sites and Islands we go to are 5-10 miles out, I'd much rather get out there at 15-17 mph than 5-6. When the boat is loaded down with two adults and 4 scuba tanks, and gear we are right at the 600 lbs capacity, we can only get up to around 12 mph max when loaded heavy, in heavy seas the speed goes down more because the boat itself is very light. Still no match for a Hobie Cat
I don't think I would put on a jib without a roto furler or not being able to furl the mainsail. Often when I come into harbor I furl the main and come in on just the jib (better control around all the other boats). The boat will sail 5-6 mph on just the jib alone. BTW it's pretty easy to make a roto furler for the standard Hobie kayak sail from 1 1/2" PVC (plenty of postings about it on the forum). I'm also pretty sure any of the furling jibs for the H14, H16, (maybe H17, getaway) would mount right on and work very well on a TI, I would love to find a used one.
My assymetric spinnaker looks similar to the G2 gennaker rig on the northsails web site you linked. It works well anywhere 90 to 270 degrees. It's ripstop nylon , and I don't like to fly it in over 15 mph winds. My design I think lifts the bow more than a G2 gennaker would. What I don't like about my sail is it collapses at anything closer than 90 degrees and begins to flutter, I would prefer something thats good to under 70 degrees (slightly upwind, where a screacher would shine, but the screacher wouldn't be as good downwind).
If you end up adding a jib I recommend you make a bra to fit over the bow (like shown on my post) made from nylon strapping, It's tied to the AKA crossbar (strongest point on any boat), so the bow of the boat doesn't take all the sail load. I'm pretty sure if you tie your jib to the lifting lug you would eventually tear it off. There are no changes to my boat itself currently. The original hull was replaced a while ago (torn scupper holes) and I didn't fill the replacement hull bow with epoxy (didn't need it). There are no holes drilled or modification to the boat itself (Hypocritic oath, no changes to the boat itself, just like doctors LOL)
I only made these mods for my own purposes and don't recommend anyone modify their boat unless they really know what they are doing, and willing to take the risks involved.
On your followup pic, it's my opinion that the jib is too close to the mainsail and will fowl the air going over the mainsail, I think having the bottom of the jib sail as far forward as possible keeps clear air around the mainsail (that's why I'm thinking about adding a bow sprit, to get my genaker another foot further forward in cleaner air). Hope this helps
Bob
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