Wind Gusts: AI Turns Into the Wind, Loss of Rudder Control…

That would be extremely difficult. I doubt that you could move the mast at all. Moving the center of lateral resistance further to the rear would be simple just as I explained above.[/quote]



It is not my theory and it is not a theory at all, it is basic physics. Just read any book on basic sailing principles, there are dozens of them out there. They all say exactly the same thing. It can also be found dozens of places on the web. Just Google sailboat balance. Most of them use pictures to describe this simple principle. Here is an example: http://www.sailingusa.info/sailboat_balance.htm



Again, you don't need to move anything forward on the AI, just move the center of lateral resistance slightly further back as I describe in my earlier post. And it would not cause the boat to nose down any more than it already does. All sailing vessels nose down slightly because the center of force is above the water line. Simply balancing the boat does not exaggerate this principle. If you ever owned a sailboat with a motor then you had to notice that it tends to up under power and to nose down under sail.



This is correct but your wording is wrong. The center of force, or center of effort as most call it, is on the sail, not on the hull. It is true that the center of effort is furthers back when you are sailing close hauled. But it only moves slightly forward if you ease the sheet out. Of course this principle has little effect if you are running downwind.

Note: On larger boats in very rough weather a slight weather helm is desired to prevent accidental jibe. But on the AI you are not worried about accidental jibe. There is no boom to whack you in the head.

Ron P.

Good informative post Darwinian...still being a simple pirate I will still remove some lateral resistance under the waterline....Pirate

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Master of the galleon 'Pirates Lot'

Then I guess the best answer is that we all buy the 2-man AI in Jan.

The prototypes seem to have the mast even farther forward as a percent of the boats length.

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Hobie Island Sailing since 2006

Are there any pictures of the finished 2 seater available for viewing yet? I am considering placing an order for one, but don't want to commit until I see one.

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Either lead, follow, or get the hell out of the way!

I just did some measurements and calculations with my AI sail to try to find the center of effort. This was difficult because the sail is not a true triangle. However after making allowances for that I gave it my best try. I came up with 33 inches behind the center of the mast. I was not interest in the center vertically.

To my amazement this turned out to be the exact horizontal center of the kayak, or 30 inches behind the center of the forward crossbar. The bad news was that this is about 6 inches aft of the center of the daggerboard. So, close hauled, you will still have a very slight weather helm even with the mirage drive removed.

Folding the daggerboard back pushes the center of lateral resistance back about 9 inches. This would give you an almost undetectable lee helm if you are sailing close hauled. And if you let the sheet out a lot you can still pull the daggerboard back to vertical and still be balanced. You would have the best of all possible worlds. The design of this sailing kayak is perfect if you remove the mirage drive for sailing.

Of course if the mirage drive is still in this throws a monkey wrench into everything. You will still be unbalanced with a strong weather helm and will nose into the wind with every wind gust.

Ron Patterson

This product is to be released around the first of the year (2010). No info is yet published.

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Matt Miller
Former - Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA
(Retired 11/7/2022)

Here are a couple of comments from another amateur boat designer.

Bad news? The enclosed link explains with much more credibility and clarity than I could, why sailboats should always have some weather helm designed into the boat for performance and safety reasons:
http://www.boatus.com/goodoldboat/Helm_balance.asp
This applies to all sailboats, large and small, mono and multi-hull.

The daggerboard certainly influences the CLP but does not constitute it. The hulls and rudder are significantly in the equation. Therefore, the effect of rotating the daggerboard is a bit smaller than what you might think, though still influential. Remember also, the more it rotates back the less efficient it becomes, just like an airplane flying with its wings folded back against the fuselage (in subsonic flight) -- the lift / drag ratio deteriorates quickly.

On the contrary, the contribution of the Mirage Drive on weather helm is not that great and IMO tends to add stability to the helm overall the same way a longer keel would.

What Roadrunner said....Pirate

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Master of the galleon 'Pirates Lot'

This is a very interesting topic! I hadn't realised just how complex it can be. It is starting to make sense thanks to the excellent link posted by RR .

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Either lead, follow, or get the hell out of the way!

Excellent reference Roadrunner!

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Hobie Island Sailing since 2006

Remove the mirage drive in a strong wind and you gain a couple of knots of speed. Drag from the drive is removed and drag from the weather helm is removed. I know, I have tried it several times. The difference is amazing. Just try it.

And you are simply wrong about it not having that great an effect on the weather helm. How many posts on this list have you read about people complaining about the AI turning into the wind and not responding to the rudder in strong winds. I was constantly having that problem myself. When I started removing the mirage drive when sailing I have never had that problem since and the boat responds beautifully to the rudder every time regardless of the strength of the wind.

And if you are having that problem, and you probably are, I just told you how to fix it without reefing the sail.

RonPatterson

Ron, thanks for the tip. I'll have to give it a try!

Thanks, I think you will be surprised at the results. But be sure to tether the drive before stowing it. They have been lost overboard. That could be expensive.

Ron P.

Tried out the AI in strongish, gusty, winds today (15 gusting 25 knots). I tried with the Mirage drive in and out, daggerboard up and down , reefed and unreefed. With regards to the M-Drive, to be honest, it didn't appear to make much difference what I did when the big gusts came when running close to the wind. When a little broader to the wind and on downwind runs, it felt cleaner through the water with the daggerboard up (back) and drive removed and plug in the hole. This was ok, but I failed to successfully tack every time and ended up having to paddle the AI round to complete the tack. The best compromise was to run with the drive in and I felt it did best with them at approx 45 degrees and with the daggerboard down upwind and up downwind. I got the best performance with the sailed reefed back to the start of the H in the Hobie word Logo. This gave me a manageable, quick performance that didn't overpower the rudder too badly. I was hitting 9 knots and staying with RS Fevas, Wayfarers, X Boats and several reasonably quick dinghies. (mainly because they were getting overpowered to the point of capsize unless they headed up or dumped the main!

The unbelievable thing was the amount of water that went over me today, in one sustained gust, I literally had trouble breathing due to the massive barrage of water hitting my face and upper body! The water was quite choppy with waves about 3' tall +- . There was a constant wash of water crashing off the mast and crossbars which then made a wind propelled spray as well. I have never sailed anything as wet as the AI! I am seriously wondering whether to fit a windscreen to deflect some of this in windy conditions? I know it will give loads of windage, but to be honest it spent so long with its bow and amas buried, I honestly don't think it would make any difference.

There was a couple of occasions where the gust was strong enough to lift the windward amas and bury the leeward fully under water. I believe that if it had had tramps fitted, it wouldn't have taken much more wind lifting the tramp coupled with a wave tripping it up as well to make me twitchy. Sitting in the middle probably gives an exaggerated sensation.

All in all a great days fun!

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Either lead, follow, or get the hell out of the way!

Rockraider, at the risk of being repetitious - get a sprayshield!

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