...had a first "Anne Boleyn" maneuver last weekend footing hard with the kite.Needed to reassure myself that kinetics from the wire,in the vicinity of the rear beam , with the asymmetrical kite; creates a LIFTING effect on the leeward hull (this is the accepted dogma - right ?)....
Found a great piece of research on the U.K. Cherub (skiff or obese angel depending on paradigm) site. Wondered about its applicability to the reaching F16 ? Thoughts?

What Happens When You Set The Kite ?

Reaching is a race between the rig and the hulls. When the rig speeds ahead--kite or not--me and the hulls definitely lose. That, of course, is the noble pitching moment .

If you wish to see the lift effect in action have a look at a 12 foot skiff in flight.. They bounce across the water..

To be honest I dont believe our pole is long enough (and we should have gone masthead but thats another story) to really generate the lift one sees in the 12s. Even then you will often see skiff sailors traping off the rudder outrigger.

It all helps but wont prevent mining..

Hi Paul,
I belong the the first group you mention, who knows that putting the kite up, even in strong winds (up to 25 knots) actually helps to stabilise the boat downwind & prevent pitchpoling. I`m not the mathematical anal-yst type, so don`t ask me why. There are so many forces at play I just accept that it works.
A friend of mine has a video on 18ft skiffs in Australia, it`s of a series of races in varying wind-strengths. In one race it was blowing about 25 knots, maybe more. 90% of the fleet put in BIG pitchpoles on the bearaway round the weather mark, and only one boat flew the kite. Those that didn`t were really struggling to keep the nose up, while the boat that flew the kite was flying.
What I find on the Mozzie is that even when the nose goes under, and it does, the boat feels more "pitchpole-resistant", it doesn`t slow down as much as without the spinn, and the spinn seems to lift the bows back up, effectively saving the moment. I find that the boat has more of a tendency to get powered up very quickly & want to capsize over sideways, rather than going in nose-first, a healthy yank on the tiller stops this. What I also find is that keeping the boat flying a hull helps to keep the bows up, could be that in loading up the leeward side of the leeward hull you are using what others have referred to as dynamic lift, effectively maximising the use of the hull`s bouyancy (mathematical types please feel free to correct me here.)
My experience may be very different from yours, remember my mast is only 7,3m long so I have a lower CE in the main & spinn. (Actually my mast is in two lengths of 4m and 3,3m, but that`s another issue which I`ll raise in my next post.)

Cheers
Steve

Hey All,

Eric Poulsen and I have been corresponding with regards to his observation that the Taipan F16 seems to lift and stabilize when the Asymm. kite is set.My inability to drive the boat faster downwind proportionally to wind velocity increase , is my one frustration w/ cats when compared to my
skiff experiences...

I've revived this old thread because our rules allow latitude for innovation and I'm hoping one of you smart sailors wouldn't mind passing along your perfect solution to the diving kite conundrum ...

Here's what I think is so exciting about this research (attached)for catamaran sailors : the Cherub is a skiff who's rig (main and jib), in conjunction w/ a highly refined, planning hull , created significant lift - the cool thing is , the lift of rig and hull together still result in a net downward force as soon as the asymmetrical kite is factored in to the equation ! Our boats always sail in the displacement mode ( I'm told the 18ht has a planning hull...), and have really narrow hulls up front w/ limited bouncy ; betcha the downward force of the kite is amplified many times compared to the Cherub skiff...! This is, I suspect, why the smart designers at Stealth are willing to take a drag hit to windward (pure conjecture on my part), w/ there fixed foil rudders because they can be driven w/ impunity downhill and why the Blade has that midhull bulge (appears to sail w/ bows out of the water w/ the kite set).

The exciting part ? We've identified the problem ( the asymm. kite drives the bows down as the wind velocity increases placing limits on how fast the boats cn be sailed). So, thats the problem- who's got a solution ( No, I don't want a Cherub).

When it is honking and your bows are under a lot of pressure the best thing you can do is fly the kite and over sheet it. most punters ease sheet which moves the COE further forward: increasing the pitching effort. We run the kite in up to 30 TWS and over sheet it to hell, then we have no worries, to increase power just pop the sheet a bit. you have to match steering and sheet very carefully at this stage. The danger is that you ease sheet and become overpowered then you ease sheet again and make the problem worse... so the trick is to ease sheet until power is right, then if you get a gust you must bear down and sheet on as the power drops then ease sheet again and cycle continues. hope this makes sense.

Macca,

These are good points and I think we're doing this (also loose luff and oversheeting when it's really light to make gennaker camber favorable for apparent wind drives...).When it's windy and choppy I've also : raked the mast aft beyond recommended to lift the bow's , tensioned the retrieval line
to spill some power (i've seen 49er crews do this),wired off of the transom...

I'm just wondering if there isn't a structural/design innovation(adjustable T-foils ,adjustable hull canting,more hydrodynamic lift/planning aspect to hull,flatter gennaker cut...) someone's been considering that would allow us to
drive the boats like skiffs on the kite reaches without compromising the boats easy brilliance to wind.One never knows if one doesn't ask...

Paul

When you say "wired off the transom" do you mean back foot at the back of the hull? Most people sail like this. If your crew is able to they should have their back foot on the rudder case and their front foot actually on the transom. I know it sounds strange but you can do it and it makes a massive difference.

As for T foils etc, sure they can be done but you are better to get the technique perfect before looking at these options.

I drive my kite as Macca described. I pull the sheet tight during the puffs and sheet it out more in the lulls. Of course I've been doublehanding my boat. I found that I got very good speed downhill if not excellent speed. Furthermore I drive deep with the weather hull just skimming the surface when I can and try to stay in this groove by steering and running the main traveller simultaniously. I understand that this can only be done when doublehanded. So together we ride the puffs by sheeting in the spi sheet, sheeting out the maintraveller proportional to the amount of tiller action. The latter is so proportional that I'm even think about hooking my tiller to the travellersheet directly and sail this way singlehanded. That way I can do the same when singlehanded. The Taipan seems to react very well to this traveller/rudder/spi sheet action. You get a push every gust and ride deep till the lulls come and you head up a bit again keeping the boat powered up and waiting for the next time the afterburning fires.

I do share you feeling somewhat with respect to the boat not going proportionally faster with increasing winds. However I find that my boat under spi very quickly reaches high speeds in only little wind. Much more than I ever experiences on a skiff. After this the cat speeds up a little with increasing winds but as it already achieved a large boost at mild winds there isn't much more left. To be really honest I think this to be the better setup. I much rather have 80 % of the speed at force 3 and 100 % at force 5 or 6 than 50 % at force 3 and than double to 100 % at force 6. You got more earlier on a cat and the net result is that you are always faster (way faster) than a skiff in my opinion. In force 3 more so than in force 5 /6. I also found that I can drive my spi in conditions that I can never drive a skiff in. Typically when we have force 5/6 winds than the surface conditions is way beyond a 49-er or other skiff with wings.

I fully agree with how stable and smooth the Taipan F16 feels under a kite. One has to find the right mainsail trim and most rotation (easy to do) but after that she feels like a much larger boat. I really expected it to by much more nervous due to its short hulls but honestly I find it more smooth and relaxed that the I-18 and Tigers I have sailed in the past.

I've been aware of the Cherub calcs for a long time and I think they give the correct reading of the situation. The whole of the boat is lifted slightly while there is more net pressure on the bows. That is exactly supported by the movements of the crew on board. Under spinnaker I'm way back even more than without a spi. Ergo the bows most be loaded up more. And I agree that any angled sail must have a vertical force component = lift. THe thing here is to realize that the first (bow pressure) is the result of a moment (forces time leverages) while the last is the result of a sum of forces). These are two different things AND independent of eachother.

>>( I'm told the 18ht has a planning hull...),

Some guys will tell you anything. There is no planing or even "true wavepiercer" 18HT at this moment. There are just making things up. If anything he jav 18HT is no more than a 90's generation hullshape with a trimmed deck at the bows and sterns. The end result is consistant with this. It behaves like a 90's displacement hull with reduced bouyancy. In most cases this means "Worse".

The only true wave piercer hulls in cat land (and planing is still tentative) are Flyer A-cat, Bim XJ (a carbon copy of the flyer), Capricorn F18, Blade F16 and Blade F18. The Stealth F16 comes closest to planing of all of these. This one is actually far more planing oriented that it is wave piercer oriented. It needs to be realized that planing hulls and wave-piercer hulls are not one and the same. Wave-piercers work for different reasons and the "piercing of waves" doesn't have much to do with that as well. They perform as they do because of a different distribution of bouyancy.

As far as I'm aware the Stealth is not accepting any serious drag hit upwind. At least nothing I've seen indicates that. It actually did rather well on both courses, with its strong point being the downhill that is true. That was against Taipans. I'm not too sure if the Blade rides with it leeward bow out of the water under spinnaker, but then I have only very limited footage of it sailing under spi. I do know that it was designed to sail with it bow just in the water in nearly all conditions. It is not like the Hobie Fox or FX-one.

The solution in my opinion, if you think the bow pressure is limiting the speed, is to look at T-foils rudders first. This seems to be the most simple solution and can be fitted easily enough to any existing boat. Best would probably be to be able to actively engage the T-foils on the downwind legs. I heared somebody say that the T-foils may not be very effective upwind. And I figured that to make full use of them you need to angle them downward to provide downforce at normal hull attitude (keep wetted surface low) So my immediate thought was to have the T-foils rotate freely upwind. weathervane themselfs and to lock them into a downward angle downhill with a flick lever system. On the other hand I though that by driving deeper I can make more ground in a race and keep the boat fully under control at speed. Personally I feel no need to fiddle here.

Wouter

Macca ,

I always sail solo ( probably an issue w/ my personality)...
I think I can approximate the technique of you much venerated
aussies ( attached - but much lower on the wire) and agree far astern one foot in loop other on rear beam is the way to lift the bows...

Paul

Wouter ,

Doc and I sailed a regatta in which catamarans(about eight) and International 14's (ten or so) shared a start in conditions that Bethwaite would identify as optimally skiff favoring (flat water - windy...). Without getting too verbose the I-14's with their T-foil rudders ,optimized kits (25-30k buck boats) and really good sailors (former world champ crew , olympic 49er crew, couple PCC and national champs...), sailed away from the fleet of catamarans except for our F16s.I noticed the F16 was faster on all points of sail (we lost ground on tacks and tactics...) except the long reaches where the skiffs would foot in gusts and just accelerate away...

Observations from F16s sharing a start with skiffs:

We didn't yell as much or bang into each other at the start.

We didn't capsize as often.

We weren't lauded by the monohull sailors as superheroes.

We were faster upwind.

We were faster downwind.

We were faster reaching.

I like sailing a skiff but only as addition to cat sailing. Sailed several but latest is the 49-er skiff.

My experience is that a normal crew does best in the light conditions when compared to a cat. Control is relatively easy here and the 49-er seems to pick up speed more easily in the light stuff. Mid range it is buy buy baby and cat rule mercilessly. Hobie 16's will beat the crap out of a 49-er here. In the rough stuff the skiff is only as good as thee lightning reflexes of the crews. Cats stay ahead here because of less strainious control requirements. There is a reason why 49-er races last 20 minutes or so and nomal cat races can go on for anything between 30 to 75 minutes. Sailing the 49-er well can be bloody tiring. But a Sh!tload of fun if you are not scared to crash and burn alot.

Also the Ausies VYC ratings rate skiffs and cats to oneanother and the second fastest skiffs 49-er / I-14's are rated the same or slower than a Prindle 16/Hobie 16 (no kites on these cats) And that feels about right from my experience. The only skiff to make an impression on catsailors are the 18's. They are rated about the same as the classic Tornado's. New Tornado's beat them on all courses I'm told. And I think Macca here has done a bit of 18 hunting on his Taipan 4.9 as well.

I really like sailing the skiff doublehanded with a good crew and get that team effort going. But when it comes down to speeds and control. cats win, hand down. That is my experience after sailing both for some years.

Sadly I didn't do to much skiff sailing this year, although I had my fill of F16's. You loose some and win some they say !

Good luck,

Wouter

Amen!