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Old 20-04-2015, 12:32   #91
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Re: Gunboats Full Foiling G4 Cruiser/Racer

I got a hold of some additional video about the capsize and have now uploaded it for everyone

https://vimeo.com/125490884
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Old 20-04-2015, 12:59   #92
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Re: Gunboats Full Foiling G4 Cruiser/Racer

LMAO!
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Old 20-04-2015, 15:57   #93
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Re: Gunboats Full Foiling G4 Cruiser/Racer

New basic nav instrument needed in the cockpit... an altimeter.
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Old 21-04-2015, 05:32   #94
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Re: Gunboats Full Foiling G4 Cruiser/Racer

I see another potential problem as far as the "cruisability" In my home waters those foils would be incrusted with barnacles in one week. Might be able to get a hard coating to stay on like Copper Coat though.
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Old 21-04-2015, 16:16   #95
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Re: Gunboats Full Foiling G4 Cruiser/Racer

Quote:
Originally Posted by colemj View Post
I don't know how much more experience the crew could have been - they were professional racers. The helmsman, Mischa Heemskerk is an A-cat world champion, so he knows a thing or two about sailing a foiling catamaran. These weren't mom and pop cruisers having a go at it.

BTW, bearing off in a multihull at those speeds is a very dangerous thing - and certainly won't depower it (until it is upside down). Likewise, dumping power when on foils is another really bad idea.

I'm guessing you have not sailed fast multihulls, let alone foiling ones?

Mark
Just reading thru this subject thread and felt that maybe a slight correction is needed here. Contrary to our engrained tendencies to turn upwind in most serious situations, turning off-wind was what was needed here.
There are some pretty good discussions starting on this page:
Gunboat G4 with UptiP Foils - Page 7 - Boat Design Forums
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Old 21-04-2015, 16:24   #96
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Analizing Film Clip

Quote:
Originally Posted by SailFastTri View Post
I disagree with you on this Mark. Bearing off was the thing to do, the only thing that would have kept them upright at that moment, but the video shows that they rounded up, thereby increasing apparent wind, they didn't dump the main, and based on observing the rudders it appears they didn't even attempt to turn downwind until 0:47 in that "wipeout" Vimeo video -- and by that time they were already going over.

BTW I'm not a seasoned racer, nor have I sailed a foiling cat. But have been sailing performance cruising tris since 2001 and made enough mistakes to spot crew errors.
I think these 2 posting agree with you,....and it does appear as though there was an effort by the helmsman to turn downwind
Gunboat G4 with UptiP Foils - Page 8 - Boat Design Forums
Gunboat G4 with UptiP Foils - Page 8 - Boat Design Forums
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Old 21-04-2015, 16:27   #97
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Re: Gunboats Full Foiling G4 Cruiser/Racer

This was an really good analysis...
Quote:
Originally Posted by hump101 View Post
Doug, what VCG are you using for this calc? My calc is based on VCG being 4m above the foil, about at bridgedeck level, and the foil centre of lift being 1.5m inboard from the extreme beam. I've ignored TCG effects of crew. This gives vanishing stability at 32 degrees when on the foils, and 63 degrees when on the hull.

It's worth noting that the boat doesn't seem to be able to foil at this angle, as it comes off the foil at 22 degrees, before any sheets are released, so beyond 22 degrees the hull is in the water, and the stability correspondingly increases. However, the effect of dropping off the foil increases the heel angle from 22 degrees to 34 degrees in just 2 seconds (43 to 45 seconds in the video). The rotational inertia created by this rapid angular acceleration, combined with the main still drawing with increased AWA, is greater than the residual stability, even with the hull in the water. The gennaker was dumped at 45 seconds, so good response from the crew, but not enough residual stability so too late.

The helmsman has the steering over to turn downwind at this point, so the correct manoeuvre was attempted, but the boat did not respond to the helm, I suspect due to the starboard rudder (only one in the water) was in the hole created by the foil diving into the water. At 48 seconds the helm is over to turn upwind, I'm not sure if this is an attempt to re-engage the rudder, or if they are falling at this point. At 49 seconds the boat is near to its static stability limit, and there is no way back.

One interesting aspect is seeing the effect of the combination of foil geometry, wave geometry, and heel angle. We've seen these foils operate in relatively flat water (SF) with the AC72's, and as they rise due to speed they side slip and stabilise, typically heeling to windward as they slip, in a self-stabilising manner. However, in this case the boat rises on the foil, not due to speed, but because the local water level drops away due to the wave profile. The boat immediately drops, and hence rotates to leeward. As it rotates, the increased immersion of the foil is offset by the increasing angle of the lifting surface, and hence the foil is unable to recover lift, but even if it could, the angle is such that the lift component from the foil is too far inboard, so isn't helping.

Without wanting to be negative, I would suggest that the G4 is showing the limitations of the J foil arrangement when combined with a relatively narrow, high VCG vessel when flying, and waves with amplitude around half the beam. With so little residual stability they will need to sail as flat as possible in future, reducing sail when necessary to ensure they still have control as wave size increases. They can open the limits out a bit with automated foil control, but there are inherent limits to what can be achieved with the same basic geometry.

Alternatively they could just keep driving it like they stole it, and allowing us all to learn so much more. It is a brilliant boat, but it has confirmed what my calculations have been telling me for my boat, so I'll be using a different geometry, and processing the heave signal to include roll and pitch before feeding into the foil control.
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