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 Post subject: Ti and AI top speeds?
PostPosted: Mon Oct 01, 2012 3:26 pm 
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What tops speeds are you guys getting on these craft under sail alone and how much was helped by surfing if it applys?

Thanks in advance!

Pete


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PostPosted: Mon Oct 01, 2012 4:50 pm 
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17 MPH is the top I've done. I can't say it won't go faster, but I'd have had problems with it at much more than that.

No surfing, just very, very strong winds preceding a thunderstorm. On a reach, the starboard Ama was completely underwater.


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PostPosted: Wed Oct 03, 2012 7:06 pm 
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I highly doubt you did 17 and have zero belief it'd go faster.

Typically they top out between 10 and 12.2 mph. Unless you were sail surfing off Maui you never hit 17mph. That's fine for a Hobie cat with well over 100 feet to 200 sq ft of sail but completely impossible for any of the Hobie sailing kayaks.

Sailing kayaks in general have often had the person thinking and bragging they were doing 20 knots. The waterline is often above the seat so it's understandable.

At anyrate with out emmemse surfing assist you didnt do 17mph.

Pete


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PostPosted: Thu Oct 04, 2012 1:49 am 
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On my AI, 10.3 mph on a broad reach with gusts in the 25-30 mph range.


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PostPosted: Thu Oct 04, 2012 8:21 am 
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That speed wasn't a guess. The Garmin GPS in the AI at the time said 17.1 MPH. Winds were gusting to 40MPH. As I said, I would have had real trouble in anything more. It was a handful as it was and I was lucky not to capsize - the center hull was coming out of the water. I do not believe I could have sustained that speed for a long period.


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PostPosted: Thu Oct 04, 2012 6:50 pm 
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Thanks for the reply guys.

I appreciate the details in the 17.1mph. I don't know anyone personally whose sailed in wind that heavy. Lol, I retract my doubt.

I wonder if it wouldn't be a neat development from Hobie if they added an add-on lifting foil to help the AMA stay on the waterline under extreme conditions. Not that it would probably need it for averege conditions. As it is I like the add-ons in the way of spray suppression skirts and such that's available. I don't sail a Hobie but I sail a kayak. Merely a Hobie fan.

Pete


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PostPosted: Fri Oct 05, 2012 12:36 pm 
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Petewp:
Let me get this straight, you posted asking people to share their top speeds, then you don't believe the results when they tell you. Why did you ask in the first place.....

We all know Tom and he is not the type to just throw stuff out there, this likely really happened to him, (most everyone carrys GPS's these days by the way).

A normal TI with a standard sail I'm pretty sure can easily run .6 of the wind speed. so in a 40mph wind .6 is 24mph. Of course as speed goes up the horsepower required to drive the displacement hull goes up exponentially. Here is a website where you can calculate the speeds yourself ( http://www.psychosnail.com/boatspeedcalculator.aspx )

Running through the formula with an 18 ft boat at 400 lbs the max speed is 12.1 knots (according to the formula)

In the example I entered it takes around .6 horsepower to propel the boat 6mph, but it take 47 hp to propel the boat 10 mph, (sail force needs to be thought of as to horsepower of course).
With the formula set to a 7 mph desired speed it takes 1.5 hp to propel the boat. I have a gas 2hp motor on my TI and the max speed in smooth water is around 7mph (I don't think I'm getting the full 2 hp into the water), but this kind of confirms the formula (at least in the limited range (below max), What it does show is the amount of horsepower required to propel a floating log past the hull speed.
So obviously the TI hull has some planing going on because I have had mine up to 18-19 mph on many occasion in under 22mph winds. That by the way was measured with GPS and not just for a few seconds. On one occasion I was sailing from Ft Desoto Island to Egmont key in open water (about 9 miles), about 4 miles was a downwind reach with the wind at around 20-22mph the wind angle was coming from around 220-230, I had all 265 sq ft of sail out and maintained 18 to 19 mph the whole distance (measured with GPS), with me and my wife aboard, as well as coolers, scuba gear and two tanks lashed to the AKA's.
Another occasion was down in key west the winds were a steady 20-23mph, Just me and wife (no coolers, scuba gear, and scuba tanks this time so we were not at max weight). The wind was again coming from around 220 deg, we maintained around 18 mph with the main and spinnaker deployed (no jib this time, as it was interfering with and collapsing the spin so I furled it). We were chasing down and following one of the big Sabago sailing cats (the Marquesa is 70 ft with one of the largest sails in south florida (according to their website), just to say hi, my wife works down there and knows alot of the crews. The run was 2-3 miles. The spin also creates a lot of lift so it helps lift the front of the hull so we plane a little better. I removed the hydrofoils from this new boat ( my 3rd TI, don't need them anymore since I added the two ft bow sprit. Next time we do a run like that I will do some video.

The formula fails at around 12mph so this is kind of telling us that the TI hull is not the same as pulling a floating log through the water (ie.. putting an outboard on a log LOL), there is some planing going on. The reason I added hydrofoils to my older TI's was specifically to get the bow out of the water at faster speeds (just so it could plane some). Part of the trick is to try to keep the weight aft (fat guy (me) in the back), and hike out so the AMA's don't bury (the nylon sheer bolts break at higher speeds (I have sheared at least 4 while underway).
With just the mainsail, trying to keep more weight aft, and hiking out (with the hydrofoils engaged on a 20 plus mph downwind reach I used to be able to do around 14 mph (measured on GPS), turn off the foils and I would slow down to around 12mph (more drag from the bow (boat goes back to a log LOL)). The foils do rob some speed, as do the mirage drives, If someone were to tape up all the mirage and scupper openings, you can likely go faster, as long as you can keep the bow and AMA's out of the water, and the rudder as neutral as possible.
I find that on a broad reach (90 deg to the wind) the tipping force is greater, and it is really difficult to keep the AMA's from burying (which slows the boat down), so a 90 deg reach is not the fastest on these boats.

Actually with my boat I get the best upwind performance with the jib. In higher winds you have full sails out and keep the boat pointed as tight as possible into the wind, be careful though, if you relax and turn away from the wind a little with that much sail out, you definately will go over, or at the very least totally bury one AMA (which slows you right down). The trick is hiking to keep the AMA out of the water. In 15 mph winds I can easily get up to 7-8 mph pointing about 20 deg off the wind with the jib, maybe 5 mph without the jib, but it's hard to get closer than 30 degrees to the wind and still maintain speed without the jib, of course with the TI you can sail straight into the wind if your willing to peddle a little, but it's not fast.
As soon as I get closer to 90 deg off the wind I have to furl the sails a little or your just dragging the AMA through the water. It seems on the TI in winds greater than 15mph you actually go faster on a reach with the sail furled a little ( a turn or two).

I suggest you have someone with real sailing experience go out with you, they can give you a lot of valuable pointers on how to read the sails, which sails to fly and when, reading winds, weight distribution, and drag. Just little things like rudders create great drag if not used correctly.
My advise if you want to get the most out of your TI, don't get too comfortable in that seat (good weight distribution helps just as it does in a Laser or Sunfish). The sail design on the AI/TI's is a really good modern boomless sail design, and can be sailed easily by someone with no sailing experience at all, but to get the most out of it requires a little sailing experience and knowledge.
Sailing Cats like the H16, etc is a different knowledgebase I can understand how frustrated a cat sailer would be in a TI or AI, but a laser or sunfish sailer would have a good time.


Hope this helps you, and you should apologize to Tom.


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PostPosted: Fri Oct 05, 2012 1:44 pm 
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Thanks but no apology is necessary. Had I included a little more information in my first post the issue would not likely have been raised.

When I first took delivery of my AI, the spring winds had just died down for the summer. So if I wanted to sail fast, I had to jump in the water whenever an afternoon thunderstorm moved through. I was worried about lightning more than anything else, and got the heck off the water the instant I could hear the thunder. But the pre-storm winds were great.

While I like to sail fast, the first time a really, really big gust caught me unaware, I nearly reconsidered. I did not think the center hull of these boats could be easily lifted out of the water. They can be. Enough wind will overcome nearly any formula. Imagine how fast you could travel if caught in a tornado!

Seriously, it is this immense power contained within nature that attracts me to sailing. My kayak buddies that have never sailed still don't have any idea what I'm talking about. They've never felt the "shove" that a strong wind gives you. As Adolf Galland was credited with saying about his first flight in an ME262 "It feels as if angels are pushing." That's how I felt the first time I got some good wind in the AI's sail.

For comparative purposes, this video shows my AI at a leisurely pace of less than 10 MPH. No problem, easy sailing.

http://www.youtube.com/watch?v=ukN04bnycrM


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PostPosted: Fri Oct 05, 2012 3:21 pm 
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Location: Auckland NZ
I have regularly done 10knots (GPS speed over ground) with a good breeze on my AI. Surfing down following waves undoubtedly does boost sailing speed for as long as you can stay on the wave face. I (believe I) actually got the boat planing for a fraction of a second on one occasion too.

Of course GPS speed over ground is not triffically accurate, especially in tidal waters, and it is sometimes difficult to keep your eye on the GPS when concentrating on all the other things and trying to peer at the screen through torrents of spray (at any kind of speed it's a wet ride !) so it is easy to miss a reading.

Putting ballast in the stern tends to increase sailing speed in my experience.

By way of comparison I have had the AI hull (as a kayak - no amas) loaded up with fishing equipment up to a maximum-speed-I-have-ever-seen of 7.5 knots (GPS speed over ground) with a following wind and tide, both paddling and pedalling and I regularly get the same boat up to 6-6.5 by surfing waves (swells, not breakers) just under pedal power. My normal pedal-powered cruising speed over relatively short distances is 4-4.5 knots which I can keep up for half an hour; for an all-day trip I would average 3.5knots including rest stops and some sailing. On the basis of these figures I do not think 10 knots is at all unreasonable for a loaded AI in favourable conditions and would expect more for a TI, so Tom's 17mph (14.8 knots) GPS s-o-g doesn't seem at all unreasonable to me.


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PostPosted: Sat Oct 06, 2012 6:14 am 
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Fusioneng,

You were flying 265 sq.ft of sail with spinnaker included and doing virtually 20mph on a TI. Moreover it wasn't a surge but a sustained speed.

And you want me to apologize to Tom and believe that you essentially put a hobie18 rig on your TI deck.

Ok, Im in awe.


We'll leave it there.


Pete


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PostPosted: Sat Nov 17, 2012 9:14 pm 
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Petewp wrote:
Thanks for the reply guys.

I appreciate the details in the 17.1mph. I don't know anyone personally whose sailed in wind that heavy. Lol, I retract my doubt.

I wonder if it wouldn't be a neat development from Hobie if they added an add-on lifting foil to help the AMA stay on the waterline under extreme conditions. Not that it would probably need it for averege conditions. As it is I like the add-ons in the way of spray suppression skirts and such that's available. I don't sail a Hobie but I sail a kayak. Merely a Hobie fan.

Pete

Actually it would be awesome for Hobie to develop a set of 6 hydrofoils that could be fitted to AIs & TIs without any drilling. Perhaps 3 lengthwise cradle configurations that hug the bow and sterns, clicks together at a "spine" running down the middle and straps to the hull and amas. Wish I had a way to build some and try it.


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PostPosted: Mon Nov 19, 2012 8:21 pm 
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Drewyaker:
Funny you should mention that, I did design a couple different sets of hydrofoils foils for my TI a couple years ago. It's actually pretty easy to do with no mods to the boat itself.
The first design I did to get the bow out of the water, and help keep my butt dry. I added little blocks to the Mirage fins (which are hydrofoils) to lock them into an 8 degree angle of attack when they are pushed up against the hull bottom, they raise the boat in the water a few inches and keeps the bow from submerging (not out of the water though). I outlined the design in the thread the ultimate Tandem Island ( viewtopic.php?f=69&t=33720 ) they only cost about a buck to make and do not interfere with the mirage drive function when not being used. This is probably not what you have in mind though.

The second set of foils I designed and built are based on a flat bottom NACA 4312 design. There are 4 foils each foil is 3 feet long x 1/2" thick and 4 inches wide. There is a lot of math involved in designing these things, but it's all pretty straight forward. The materials were about a hundred bucks (alunimum), I made everything in my garage all freehand with no tools, just a hack saw, and a power drill. Each foil is mounted to a 1/2" steel rod about 15 inches long mounted at the center of lift and sticking out one end of each foil.
What I did is tie the end of the rods to the AMA knuckles with spectra string (no mods to the boat). I then made a small plastic rib (made from a 1/4" thick polyethylene cutting board) that stands upright on the foil and holds the foil at the correct attack angle. When the foil starts to lift it pushes up, the little block hits the bottom of the AMA, and sets the foil to the correct angle of attack. I actually made the block with a fiberglass pulltrusion spring so the foil stays neutral until you hit 6-7 mph, from there the foil overcomes the torsion spring and tilts increasing the angle of attack (so the foils don't drag at low speeds). Each foil angles downward and outward at about a 10-15 degree angle (mounting the end of the rod to the AKA knuckle, the running the foil straight out under the AMA. With the 15 degree angle as the boat speeds up and lifts, part of the foil leaves the water, thus decreasing the surface area as the boat rises, so the boat will rise to a certain height at one speed, but slightly higher at higher speeds with surface area decreasing as speed goes up. The ends of the foils are held straight by spectra string tied to the bow of each AMA. To keep the foils from flopping around I held them up against the bottom of the AMA with bungy cords. When not being used you just unclip the bungy and flip the foils up on top of the AMA out of the way. I just kept them mounted to my AKA bars all the time, and only put them down when I wanted to use them. The spectra string holding the end of the rear foils was clipped to the metal padeye in the center of the AMA (for the never released jib kit).
This was actually my second design, my first design was with a float ski in front of the foil to control the angle of attack (like the Trifoiler), but the second design worked better, the floats created too much drag and didn't handle waves well.
The area I live in (South West Florida) is not too good for this type of boat, there is not enough wind 90% of the time to use them (typically under 5mph winds in the summer). Everything did work if the conditions were just right, and I could get the boat up almost out of the water (just a little bit of the tail with the rudder would be touching).
Foils are very hard to get right, and keep in mind when the hull is in the water you get drag, and you also get the drag from the foils, double drag until the hull lifts. Mine were design to raise the boat at around 8mph, getting to that magic number was the challenge.
What did I learn from the experience.... my boat has 250 sq ft of sail, but most of that is from the 135 sq ft spinnaker. Spinnakers only work downwind, and only up to the wind speed (no multipliers). With just the mainsail and jib the TI doesn't have enough sail area and the Ti's sails are not really designed to amplify (multiply) the wind. Basically if you have a hard time getting the boat over 8 mph without foils, once you put the foils down that number becomes 6mph (you lose a couple mph from the foil drag). You can't sail fast enough to raise the boat up. You would have to have a boomed mainsail probably 23 to 25 ft tall at least 155 sq ft to get enough wind power to get the boat up (according to my calculations). Because of the heeling moment from the large sail, you would need larger AMA's mounted at least 2 feet further out from the present design (12ft wide, current TI is 10 ft). Or you could go to a twin mast (like the trifoiler), which by design eliminates most of the heeling moment. The only way I couls see this working would be if you had at least a 5hp gas motor that can get you past the dead zone (over 8mph), then you might be able to maintain speed and possibly speed up once the hull lifts. I currently have a 2 hp gas motor, and it can't propel the boat fast enough to get out of the dead zone except once in a blue moon (the max my small 2hp motor will propel the boat is around 5-6 mph (without the foils), the motor is too small.
Bottom line, it requires so much re-design to the boat it is not worth attempting unless you have a big bag of money and all the time in the world. Just go out and buy a used Trifoiler if you want to play with that stuff.
Below is the spreadsheet I used to calculate my lift ( hope it comes through clear enough)
Image

Good luck
Bob


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PostPosted: Thu Dec 06, 2012 7:40 pm 
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Sold my 23 foot sailboat to buy a TI. I am an experienced sailor and after 6 years with the sailboat my max speed was 7.2 kts. Took my TI out for the second time ever fishing on Tampa Bay. Fishing sucked but winds were 12-15 kts so sailed instead. Got the TI to 8.4 kts max and averaged 5.7 kts. Cant wait to get it out in 20-25 kts of wind.


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PostPosted: Thu Dec 06, 2012 8:20 pm 
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MikeSail:
You will find with the TI that the best winds are 15-20mph, a lot of the guys in the Islands, and the Aussies don't even bother going go out if it's less. In under 8 mph winds the TI is not as fun unless you add a bunch of sail area (like I did). I have been out in 25-30mph winds but it's not all that fun unless your near a windward shore away from the big waves (waves slow the boat down a lot). The boat handles weather pretty good actually, I have no difficulty or fear taking mine out in open water (but I always have my gas motor on board just in case).
One thing you will find out in heavier winds is the full sail overpowers the boat (too much heel). If you watch your AMA's, when they bury under the water, this creates a lot of drag, it's better to furl the sail in a turn or two then hike out on the tramps you will really fly. Try to get as much weight as possible aft, this allows the hull to plane a little.
Hope this helps you
Bob


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PostPosted: Fri Dec 07, 2012 4:12 pm 
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Yea, a lot to consider if one was to actually make use of any kind of hydrofoil system. I saw hydrofoil wake boards and wondered if that could be made to work under an AI or TI. Didn't think about the 8 mph mim speed though.


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