Moth on Foils: 35.9 knots(41.29 mph)

  • Thread starter Thread starter Doug Lord
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Moth on Foils!

In the video I saw the wand was working normally. It doesn't matter where the wand is necessarily-it matters where the flap is. You can't possibly be suggesting that a foil with full up flap is not going to dive?
 
Doug Lord said:
In the video I saw the wand was working normally. It doesn't matter where the wand is necessarily-it matters where the flap is. You can't possibly be suggesting the a foil with full up flap is not going to dive?
Click to expand...

Apparently you're of the opinion that Moths nose dive because the flap comes up when the wand comes clear of the water creating a downforce. That is wrong. Provided the main foil stays full immersed and doesn't ventilate (i.e. air from the surface reduces it's lift), Moths don't nose dive (they may still crash by stuffing the bow into the back of a wave, but that's a different story).

The flap on current production Moths, going back to Bladerider and Prowler days, does not create down force.

The above is another example of the wand fully forward, clear of the water, and the boat not nose diving, yet again disproving your theory.

You still have not found anyone to support it.
 
If the flap doesn't go up when the wand goes forward the boat won't dive. A wand system won't control altitude without the facility of having downforce* available. You can't control altitude with a wand if the foil only lifts in one direction. On the Rave, Osprey and my boats the mainfoil is set up with a +2.5 degree angle of incidence. Wand controlled flap movement is -20 degrees up, +30 degrees down. These boats use some downforce for maximum righting moment but downforce is essential for the wand to be able to control altitude. A wand system won't work without being able to generate downforce.
* the absence of vertical lift, negative lift

http://www.teknologika.com/mothblog/wp-content/uploads/2009/10/Magic-Wands.pdf

A) From the PDF above:
The Flick-off
This will aggressively add more-flap up, and may even cause the foil to stall, crashing the
boat back down again. This is an option, not a necessarily recommendation, as there are
some circumstances where this setup may be horrible. In an aggressive, steep chop for
example the boat could porpoise up and down with every wave peak and trough as the
wand flicks-off, then the boat drops, then the wand re-engages, then the boat rises again,
then as you pass the next trough the wand will flick off again. The reason this shouldnʼt be
used with a bent wand is because a it can get caught around the bow.

B) Rohan Veal:

“Recently we have been removing the hump and cutting up the bottom/back edge of the
centreboard about 2mm so the flap can come up more (hence have more negative lift
when the boat gets too high), but the problem with that is that the wand can travel a lot
further forward now and consequently the boat bounces up and down a lot when the wand
gets pulled past vertical at full height and then gets gets pushed back 90 degrees when
the boat comes back down. [Changing] the gearing [will] stop this problem you can easily
remove the bell crank and cut about 4mm off the top (with a grinder), but you will need a
5mm tap to clean up the thread after it is done. This should increase the speed of travel of
the push rod running down the centreboard and move the flap faster, and not make the
wand flick forward so much.” - Rohan Veal 3rd January 2008
 
I thought the wand had been in the water, but a Barracuda had bitten the end off.....;)


Ref Chris Rashley's comments in one of the vids.....
 
We're not discussing a Rave or any other type of boat, we're talking about Moths. This started because you asserted that all those nosediving Moth crashes were due to the flap coming up, not the main foil ventilating.

If everything I and others have posted can't convince you, then you're a hopeless cause.

To say the absence of lift is downforce is disingenuous, that's called "weight". When talking about hydrofoils, downforce is a positive force downward created by flow over the foil. When I have time I'll do an experiment to see if a stock Bladerider foil actually creates downforce with the flap fully up, it will be interesting. Perhaps I'll even have some video.

But even if it does, it won't prove that the crashes were due to the flap coming up. If it was, I'd have had a zillion more crashes than I've had.

Maybe one day you'll get close enough to a Moth in the flesh to see how wrong you are, but I'm not holding my breath.

Great timing, yet another wand clear of the water shot with no crash. Oh, and the wand–on–a–sprit setup doesn't go past vertical because to do so would break the class rules, so the flap is max up when the wand is vertical. Also watch the video at about 1:09.
 

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Moth on Foils!

You didn't even read what Bruce or Rohan said-it's not a question whether or not the Moth foil develops downforce-it is a fact backed by those guys-and anyone who really knows how a wand works. In fact, Bruce describes exactly what happened to the Moth in the original video in "flick-off". You can ignore the facts but they won't go away.
To say that a wand can control altitude w/o using downforce is just ridiculous.
 
I read that years ago, the PDF is on my hard drive. Just because I didn't mention it doesn't mean I haven't read it. I ignored it because none of it supports your statements.

Bruce doesn't say the foil develops downforce, so you get no support there. I've never seen a Moth "crash back down" because the flap caused the foil to stall. If a Bladerider flap goes that far up it will weaken the Sika hinge and cause it to fail very quickly (but it doesn't as it's limited by the strut, as it is on all production Moths). Maybe some home made flaps can do that, or production foils that have been poorly customised. I've had the flap rip off the back of the foil (I have video if you want to see it) and yes, I "crashed back down" very quickly but it was not a nose dive. I didn't even capsize, which isn't boast of my sailing skills, just a fact that the event was surprising but nothing like a classic nose dive (of which I've had quite a few).

Rohan mentions "negative lift", not downforce, which is exactly what happens: the net lift is less than the weight of the boat and crew so it goes down. Not rocket science. Not the foil developing downforce.

Meanwhile, you conveniently ignore yet more video evidence of a non–crashing Moth with the wand fully forward.

Why don't you contact Bruce (he's still quite active on SA) and ask him? Or PhilS? Or any of the many Mothies who post on SA?
 
Moth on Foils!

Like I said: you can ignore the facts but they won't go away.

This is classic: "negative lift, not downforce" !!! How absurd can you get?
 
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