Gunboat G4 with UptiP Foils

Sorry, I can not get the video to display exactly the same frame shot at exactly the same indicted time with any consistency,...it keeps jumping around on me.

But I did view a sequence of frames that makes it appear as though the helmsman is leaning back (pulling on tiller I suppose ?) until the boat just really starts to go over.

 

You need a faster finger.

Anyways, it looks like they were either not able to dump the main or were not doing it quickly enough. The boom was still firmly at the center in that moment.

 

That is also my interpretation; for the G4 the combination of hull flying and foiling is without any safety margin.

 

G4

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I 100% disagree with that statement. It is obvious from the video that the mainsheet/traveller system did not work the way it should have either due to a crew mistake, a design fault, a mechanical installation fault or a combination of any or all these. Easily correctable and NOT RELATED to the fact that the boat is a cruiser/racer foiler.

I did a rough calculation of righting moment when level and at an angle of heel of 32 degrees based on a lightship weight of of 5950lb and a crew weight of 990 lb. The result was that the boat has 65% of the RM at 32 degrees(still flying) as it has level. This result is based on 100% lift from the lee foil.
When the lee hull first hit the water at 46 seconds in the AOH was about 45 degrees.Had they popped the main then I'll bet she would have recovered. There is no doubt she would have recovered if the main had been popped at 32 degrees.

Total RM level flying on lee foil=9615ft.lb.
Total RM @32 degrees still flying on lee foil=62197ft.lb.(65% of RM level)

 

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.

 

Yep, right after Lewis did a killer cutback at Jaws....

Ooops. Blame the painkillers.

 

Coincidentally, a day or two before the G4 fell over I was going through some old mags and came across a piece about the difficulties of mainsheet control in Formula 40s in the late '80s. Some of the F40s used hydraulics as well, but no perfect system had been found at the time.

This is not a new issue, nor apparently a solved one. Is it possible that at this size range there is no way to handle the power fast enough?

 

H, 11.5' @32 degrees. That's above the heeled center of lift of the lee foil. I'll continue to replay the video, but so far I don't see your scenario where the "boat rises on the foil, not because of speed but because the local water level drops away due to the wave profile". Do you have a time on that-I'd like to try to understand?

click for best view---

The top left picture appears to me to be the same attitude the G4 was at one point in the video where the stern appeared to be touching water when viewed from aft.

 

Mainsheet dump problems

I grew up indoctrinated about never leaving any sheet in the self tailing winch but ensuring it was in a cam cleat. Lock Crowther was very forceful about this point. I have sailed with two old salts who were friends of Lock who don't like self tailers.

That being said, on Shawn Langman's ORMA 60 there was no mainsheet cleat that I could see. In fact when driving hard the mainsheet was wrapped around the drum of the self tailer and I was to windward with the others. It was only a delivery trip but I seem to recall I couldn't even find anywhere to cleat the main apart from the drum.

The French guys know what they are doing so there must be some serious issues with dumping the mainsheet on highly loaded boats. Maybe explosive bolts in the mainsheet system! It would be interesting to talk to someone who sails these boats to tell us some of the issues.

cheers

Phil

 

Powered winch, few blocks, no self tailing? I won't have self tailers on a boat either. The problem with powered anything is the jams can get a lot worse in a hurry. Having any sail you can't dump in a hurry though is wishful thinking. I tend to handle the puffs with the main initially and keep drive going with the jib but every boat needs to be sorted on its own. Looking back at the old Rudy Choy CSK narrow racing cats they said they only thought there were a dozen people at the time who could really handle one to its potential.

I like the idea of this boat but think they should leave out the things that can't get wet and accept that there are days when it all will. I suppose they are thinking of trying to sell enough hulls to offset the mold costs but the clientele is apt to wind up in the deep. I'd want the righting package.

 

Firebird cat righting system

Firebird righting system:
https://www.youtube.com/watch?v=655COFngiQA

 

G4 cruiser/racer on foils!

From NA Doug Schickler(engineering G4):

the foot pad rocking back and forth(see video in next post) develops hydraulic pressure for a 1:2 ram in the boom. pulls in on the main sheet to tension the leech. red button between feet is to release the same ram. All at the feet of the helmsman, nobody else.

The trav (really controlling the angle of the boom to CL) is on a winch, not sure if 1:1 or 2:1. This is in the hands of a second person.

In the wipeout, both are released (too little IMHO). The ram due to the rate of flow in the ease system, the trav due to any number of things -
the thought that 1.5 m was enough
the thought that the leach would also ease
miscommunication
override
other line screw up
This system is not different that an X40 or our Kuka Light. Agree a second release adds more options. Suggested that to HC just today.


Doug Schickler
Schickler Tagliapietra Yacht Engineering
www.styacht.com
ST Yacht on Facebook & @STYacht on Twitter

"It is very easy for those of us on the sidelines to identify "fatal flaws" in others work and denigrate to taste. If, on the other hand, you assume the designers and engineers who spend thousands of hours pouring over this stuff are something other than potted plants, you may find that the world is a more interesting and nuanced place." SHC

 

G4 cruiser/racer on foils!

Foot pedals for hydraulic pressure-watch vid:
https://vimeo.com/125166258

 

I'm not even so sure that that the pressure can be relieved fast enough on those fat-headed mainsails, ...particularly on that sailing angle?

 

G4 cruiser/racer on foils!

G4 tested by Kai Concepts 4/15/15- https://www.youtube.com/watch?v=Kpeu0ic1xgE