This is an interesting topic, when I first got my first TI back in spring 2010 (i'm on my 3rd TI now). I took it out into the normal low winds (4-8mph) around here in Sarasota, FL and it ended up being a boring ride for me in low winds. Around here it's only once in a blue moon that the winds get high enough to really get a stock TI moving. Right away I designed and made a jib and spinnaker system to add more sail area to the boat. Total sail area went up to 265 sq ft with the stock 90 sq ft main, 40 sq ft jib, and 135 sq ft asymmetric spinnaker. All the sails are fully roller furled and the boat has very similar performance characteristics to either the Weta or the Windrider 17 (it tops out at around 20mph). I have right around 2500 sailing miles on the design now with no major difficulties. I car top the boat on my Denali and am out enjoying the boat every weekend mostly around Sarasota and Key West, FL. There is nothing complex about my setup, and I have gone into great detail on this forum on how I designed and built everything on my boat. see the ultimate Tandem Island (hydrofoils,spinnaker,jib,etc)
The TI design is fine as long as a couple minor things are taken care of before adding all the extra sail. First off the bow on the TI is very weak (because of the big hatch opening so some sort of bow re-enforcement is needed. Second the main sail is mounted so far forward that unless you add a bow sprit you cannot get enough air into your front sails. The bow sprit also helps lift the bow so it no longer dives (because the angled sails help lift the bow). It works so well I was able to remove the hydrofoils, don't need them anymore.
My jib is worn out now so I've got it cut back to about 22 sq ft but it still helps a lot. I'm in the process of designing and making all new sails right now. The new main and jib sails will furlable soft wing type sails. And I will convert the G2 spinnaker to a g1 spinnaker (screacher like on the Weta). The G2 spin is still good for down wind but will be deployed from a halyard and sail bag when needed (screachers are not so hot on downwind).
By going to wing sails the side force when in a reach will be much less and I should be able to show more sail in a reach with them. I also plan to extend my AMA's 1 additional foot on each side so the boat will be 12 ft wide (vs 10), this should give me the correct flotation needed and will also raise them up a little higher.
With the current centerboard and the new rudder system there is no problems with steering, I try to trim the sails so the rudder remains neutral (less drag that way), but the boat still has a tendency to try to round up when pushing it, however I can sail much closer to the wind than most boats.
Of course the mast has to be stayed from the rear because of all the extra sails, and I had to add a small brace on the bottom of the hull at the mast base to lessen the force on that tiny 1/4 stud at the base of the mast. Also because the boat is pushing much harder and much faster the nylon sheer bolts are no longer strong enough by themselves to not sheer when you bury an AMA at 18+ mph. I have a simple rope connecting the 2 AMA's that prevents them from rattling around and possibly coming off. Once I extend the AKA bars I will add another rope to hold the AKA's straight in a Y shape like a truss. I've also been thinking about adding another tramp for the rear seat area in a triangle shape so you can hike out in the rear seat. Though I mostly solo from the front seat, there is a definite advantage to keeping as much weight as possible to the rear, unfortunately you cannot hike out from back there currently, I can run all my sails from either the front seat or the back but it's a pain to un-cleat the sail lines in the front while in the back so I may add another group of 4 Harken cleats to the rear AKA brace. As far as the tiller goes, it's not a big deal to add an extension pole with a rope loop on the end so you can steer while hike out. Total cost for all my mods (not including the gas motor) was around $300-350 bucks and I made all the stuff in my garage with just basic tools (hacksaw and drill). I have not made any changes at all in the last couple years, I just take the boat out and use it most every weekend in pretty much any conditions. If we are planning a river adventure I just leave the sail gear at home or back at our campsite. I design and build all my own sails which is not difficult if you read up on it and your wife has a nice top of the line sewing machine, as long as you do the sewing while she is at work she will be none the wiser.
I consider my boat to be unique in the way that there is no other capable 18-21 ft boat on the market @200 lbs that you can car top and rig in about 30-40 minutes, then store it in your garage. We have a camper when traveling so the hitch is already used, and live in a restricted community where no trailers are allowed to sit in your yard. We often go out with at least 3 adults on board and have gone out with 3 adults and 2 kids (5 people), I keep 6 PFD's with the boat. I have sailed around many Weta's and windrider 17's and both have to have a trailer and both take a lot longer to rig. Plus the WR 17 is over 400 lbs (it's a monster). All 3 boats are a wet ride because you are up close and personal to the water (the way I like it).
What would I suggest to Hobie to improve the TI, nothing at all, the boat is an engineering dream just as it is designed. If they wanted to offer a kit to make it into something like mine they could easily. The bow brace I made is very similar to the one Jim (Hobies chief engineer) used in EC 2011, I only added a 3 ft fiberglass pultrusion bow sprit to the brace to get the fore sails further forward and so they provide some lift for the bow and that's it. Adding a brace at the hull bottom at the base of the mast is a super simple mod, that re-enforces the mast base enough to support the additional sails (side to side bracing is sufficient from the factory).
Of course the rear stay line is important to help counteract the forward force. On my first TI I re-enforced the mast to make it stiffer, but on #'s 2 and 3 I didn't bother, I like the ability for the mast to flex to spill excess wind. I have not snapped a mast yet, and have been out in pretty bad conditions many times, as with any sailboat if you put too much sail out in bad conditions something will break, you just have to use common sense (don't put your huge spinnaker up in 25 mph winds DAH, (though I have done it in 20mph plus winds a few times). I have made no modifications to the TI hull at all, everything just plugs right onto the factory boat (the extra brace at the base of the hull is easily, removed, and the bow sprit/brace just bolts to the front AKA cross bar and is held down to the bow front by straps). I often lift the front of the boat by the bow sprit to load it onto the car. The furling mast topper is super simple and just slips onto the existing mast, and you can still put the sails up and down on the water if you come to a low bridge.
Here is my TI anchored last week down in the keys:
Here is the TI with all the sails out
And here is my TI on the car roof (going out sailing)
If I were Hobie I wouldn't change a thing, I would just start offering a kit just like they do on their other boats, they could probably use existing sails (like h16 sails). Though a screacher like on a WETA or WR17 (which they don't currently offer) would be desirable.
The kit would include:
The bolt on bow brace
Small insert to drop behind the mast base on the bottom of the hull.
Mast topper similar to mine.
A set of 1 ft longer AKA bars
rear stay line
Jib (roto furling)
and optional spinnaker (screacher preferred) roto furling
All the additional harken blocks and sail control lines (the boat already comes with all the necessary tapped holes for the additional harken hardware).
Nothing else is needed, the boat can still be used as a basic TI or as a kayak, just leave the extra rigging at home, though I have never done that, once you have it, you won't go out in the water without it. I know I'm having the time of my life with this boat and it performs flawlessly in pretty much any conditions as long as you use your common sense.
That's my wish list, I would think exactly the same could be done with an AI.
Hobie will this be ready by Xmas.