Boats and foils comparison

Sidecar

Super Anarchist
2,783
1,223
Tasmania
with lift comes drag, the teams will be playing around with nose-up vs nose down to to find the sweet spot,

View attachment 336546
Downwash is lift as well, especially when it is close to the “ground”... 

Nose down can run the risk of AoA being too negative and the underside increasingly becoming the “lifting” surface, causing a harder landing.

There are many things at play here.... interesting times.

As for the next edition of the cup, all they have to do is remove the bow restrictions and all the “boats”will become tunnel hull ground effect scows. Why else would Welbourne (who knows a thing or two about dynamic lift) choose a scow shape over a skiff shape?

.

A047BCBC-06BF-43FE-B265-8CC54DB6DEFB.jpeg

82D433AB-0B56-4B39-9EC4-111AEEDE0A7B.jpeg

 
Last edited by a moderator:

Xlot

Super Anarchist
8,678
1,121
Rome
Downwash is lift as well, especially when it is close to the “ground”... 

Nose down can run the risk of AoA being too negative and the underside increasingly becoming the “lifting” surface, causing a harder landing.
F1 cars have a flat bottom, and they use negative AoA - that they call “rake” - to increase downforce

 

Sidecar

Super Anarchist
2,783
1,223
Tasmania
Sigh. It’s not lift it’s drag ffs....
The only time a flat plate is all drag is with an AoA of 90 degrees. Up to  AoA ~ 40 degrees, a flat plate produces more lift than drag.

Otherwise many basic model planes, toy foam gliders and paper darts would not fly.

 
Last edited by a moderator:

uflux

Super Anarchist
The only time a flat plate is all drag is with an AoA of 90 degrees. Up to  AoA ~ 40 degrees, a flat plate produces more lift than drag.

Otherwise many basic model planes, toy foam gliders and paper darts would not fly.
Yes it may provide more lift than drag...But it is also produce a hell of a lot of drag. Not very efficient. Which is why a lifting boat ac yacht under these rules is nonsense 

 
Last edited by a moderator:

Sidecar

Super Anarchist
2,783
1,223
Tasmania
A sky diver doesn’t have thrust as per your other examples. I don’t really think gravity counts as thrust...Hence a sky diver is simply a controlled fall.
So is a highly efficient high aspect wing ratio glider...... It is just that one does it better than the other.

.......And AC36 won’t be a controlled fall event?

 
Last edited by a moderator:

neuronz

Anarchist
876
71
europe
Downwash is lift as well, especially when it is close to the “ground”... 

Nose down can run the risk of AoA being too negative and the underside increasingly becoming the “lifting” surface, causing a harder landing.

There are many things at play here.... interesting times.

As for the next edition of the cup, all they have to do is remove the bow restrictions and all the “boats”will become tunnel hull ground effect scows. Why else would Welbourne (who knows a thing or two about dynamic lift) choose a scow shape over a skiff shape?

.

View attachment 336551

View attachment 336552
Because it is an easy way of limiting trim and thus controlling angle of attack in absence of rake control when the boat heels?

 

neuronz

Anarchist
876
71
europe
One aspect that has not been considered in the ride height discussion yet is the necessity for the foils/struts to provide sideforce in the absence of a keel or significant Veal-heel. The vertical bit is quite short IMO, which is why I suspect that upwind boats will want to foil quite low. Downwind leeway is generally less of a concern, however, too much leeway may still affect the performance of the foils.

 

Sidecar

Super Anarchist
2,783
1,223
Tasmania
That would suggest that the boats with the lowest (relative) hinge mounts and least hull immersion/water contact could be the best performers?

 
Last edited by a moderator:

barfy

Super Anarchist
4,690
1,188
As discussed by quite a few on here previously, low ride height will allow for a higher arm position before the foil tip breaks surface. This higher arm position then vectors more lift into windward lift, controllable with the flaps. This is probably a better solution than trying to resist leeway with the arm stocks (unless low riding), as the arms are aligned along the desired vector. Right from release of the design it was obvious that these boats were going to have insane angles both upwind and downwind, making them faster around the track as GD and others have said.

 

Boink

Super Anarchist
1,589
779
That would suggest that the boats with the lowest (relative) hinge mounts and least hull immersion/water contact could be the best performers?
Whilst I understand what you are suggesting, it is way too simplistic to state what you have said in such brief terms.

The hinge point is controlled by the MWL. The relationship of this to relative surface is all about the distribution of hull sections and area of curves. This is where AM & Ineos seem to be relatively undeveloped water plane shapes. They are simplistic and straightforward in what they wanted to achieve. The Italians seem to have caught the NZ concept - but almost as if overheard, and seem unsure as to how to best implement this concept. The Kiwi's however, being the creator of the rule, have also built the most complex set of hull lines that appear to allow both nose down and slight windward heel without allowing the protrusions to either impact hard or suck the hull back down upon contact. The shape definitely has merits in terms of hull release on take off ( this being the bit the Italians did comprehend.....) And as an aside may allow lower COG by placement of heavy gear into the bustle. There would also be structural gains from the Bustle that would give useful resistance to slamming and impact loads - the oil canning that we would more readily associate with flatter panels. 

The on deck aero treatment seems most considered for Ineos with the other 3 tied in those honours. But does the Ineos hull shape allow as many modes as the Kiwi boat? Not sure, but I suspect not. Only the teams will know which of the modes are proving to be the most fruitful in terms of performance. So then expect to see B2 aggregate around the modes that they are trying to achieve most commonly. I.e. nose down, low and windward heel in flat water upwind etc. Does the Ineos deck treatment do all that it could at this point? Is the nose too broad & scow like to have anything other than hard impact upon contact, which whilst undesirable, is also somewhat inevitable. Does the finer nose of the Kiwi boat overcome this? Will control be so resolved, come Cup time, as to remove this concern entirely? 

B2's will look very different. Only then will we know how confident the designers are to double down on their selection of choices or transfer and develop a theme that was seen or inspired by another teams' boat.

 

The_Alchemist

Super Anarchist
2,626
1,428
USA
Whilst I understand what you are suggesting, it is way too simplistic to state what you have said in such brief terms.

The hinge point is controlled by the MWL. The relationship of this to relative surface is all about the distribution of hull sections and area of curves. This is where AM & Ineos seem to be relatively undeveloped water plane shapes. They are simplistic and straightforward in what they wanted to achieve. The Italians seem to have caught the NZ concept - but almost as if overheard, and seem unsure as to how to best implement this concept. The Kiwi's however, being the creator of the rule, have also built the most complex set of hull lines that appear to allow both nose down and slight windward heel without allowing the protrusions to either impact hard or suck the hull back down upon contact. The shape definitely has merits in terms of hull release on take off ( this being the bit the Italians did comprehend.....) And as an aside may allow lower COG by placement of heavy gear into the bustle. There would also be structural gains from the Bustle that would give useful resistance to slamming and impact loads - the oil canning that we would more readily associate with flatter panels. 

The on deck aero treatment seems most considered for Ineos with the other 3 tied in those honours. But does the Ineos hull shape allow as many modes as the Kiwi boat? Not sure, but I suspect not. Only the teams will know which of the modes are proving to be the most fruitful in terms of performance. So then expect to see B2 aggregate around the modes that they are trying to achieve most commonly. I.e. nose down, low and windward heel in flat water upwind etc. Does the Ineos deck treatment do all that it could at this point? Is the nose too broad & scow like to have anything other than hard impact upon contact, which whilst undesirable, is also somewhat inevitable. Does the finer nose of the Kiwi boat overcome this? Will control be so resolved, come Cup time, as to remove this concern entirely? 

B2's will look very different. Only then will we know how confident the designers are to double down on their selection of choices or transfer and develop a theme that was seen or inspired by another teams' boat.
You sure have drank the hometown kool-aid.  Every assumption you make is that the NZ design is better.  I know you want to believe they have the most advanced design, have the greatest ideas and are never wrong, but that possibly may not be the case.  You do know that a hull that doesn’t touch the water has less hydro drag than one that “bounces” off the water?

 

Lickindip

Anarchist
758
525
Auckland
I guess the US Navy should never have used the F-14 Tomcats fighter jets.  It was designed to produce about 40% of its lift from the fuselage for better survivability.  
F-14 are designed to go over Mach2, have space for 2 massive engines and a heap of armement as well as no requirement to be in contact with the ground or water to cantalever their flying ability ... extreamly useful to compare lifting bodies usefullness ay

have a crack at the below puzzle, (add your own dimensions and forces in)

if your hull is a 'lifting' (positive being up) body [orange force], then you will need to de-power your rig [blue force] earlier then any other boat who has zero lift or negative lift

You run a huge risk of the hull pivoting around the water foil in a good gust of wind

image.png

image.png

 
Top