America’s Cup - ETNZ launches 1st AC75 (new)

[jmh2002]

These propeller related posts are a huge derail of this thread.

Let's try to stay on topic please - America’s Cup - ETNZ launches 1st AC75

[cal40john]

Originally Posted by jmh2002

These propeller related posts are a huge derail of this thread.

Let's try to stay on topic please - America’s Cup - ETNZ launches 1st AC75

Keeping a thread on track 100 posts in?

OK, is the anchor on ETNZ carbon fiber? Would that work better as a Danforth or a Rocna design?

[CassidyNZ]

Originally Posted by MicHughV

...I notice their boat also sports foils on the rudder..makes sense to me.....it would appear to be quite a feat to balance a 75' boat on just one immersed foil...nice to have that " extra" leg in the water at the stern to help control pitching.

All the foiling boats in the AC have foiling rudders going back to San Francisco in 2013 and Bermuda in 2017 and includes all the AC72’s revealed so far. The foiling rudder is fundamental to the balancing act that maintains level flight. Riding on just one foil in the water would be challenging indeed.

[AKA-None]

Originally Posted by jmh2002

In the right context I'm all for the 'practical is beautiful' and 'fast is beautiful' type of thinking sometimes. So all I can say is that Team UK's boat better be damn fast for me to start thinking about liking how it looks...!



Yes, those were my exact first thoughts too! Hopefully the designers have some other intentions...

Actually I’m wondering if they are taking some lessons from F1. Maybe they see a possibility of lift up front and this is an effort to reduce that?

[a64pilot]

Originally Posted by AKA-None

Actually I’m wondering if they are taking some lessons from F1. Maybe they see a possibility of lift up front and this is an effort to reduce that?

I would think it’s an aerodynamic feature, but don’t understand how.
I would not at all think they are trying to create downforce, I would assume either lift creation or the minimization or drag is what they are attempting, assumption is minimization of drag, or possibly now that I think of it, stability, my guess is stability.

I think as someone else said, these hulls maybe ought to be thought of as fuselages at least as much as they are hulls. Surely they will evolve into a lifting body shape I would expect as the designs mature.

Even though it’s an old design, it’s my understanding that the fuselage on the F-16 generates more lift than the wings do. I can’t prove that though it was something I was told.

[StuM]

Originally Posted by MicHughV

...regarding the drag of a spinning propellor vs. a fixed propellor...I was told by an experienced navy helicopter pilot, that a helicopter pilot can still exert some control over a helicopter with a failed engine but spinning blades vs. blades that don't rotate at all...
off course, helicopter blades are long and narrow vs. the more stubby one's of a boat's prop..but I would imagine the same theory would apply...
a spinning tree leaf also falls much slower than a non spinning leaf, so there must be some theory behind this phenonima..maybe wiser heads can provide a better answer...

Auto-rotation in a helicopter is an entirely different situation.
Essentially, you "feather" the blades so that the downward motion through the air gets them rotating as fast as possible. Then when you get close to the ground, you "flare" the blades, dramatically increasing vertical drag and slowing your rate of descent to something survivable.


Spinning leaves/seeds again use aerodynamics. The offset centre of gravity causes the leaf to rotate horizontally, causing airflow over the leaf, especially a low pressure vortex above the leaf which provides lift.


Neither of these are situations applicable to a fixed propellor spinning in water. Physics and empirical studies both tell us the same thing consistently. Locking a fixed boat prop when sailing will increase drag.

[MicHughV]

..I agree that we have gone off topic....in that regard I want to bring it back...I will start by mentioning that the graphics and color scheme of the Brit boat sucks..seriously....I don't see the union jack anywhere. This boat is going to be plastered all over international TV and countless internet sites...is this the best the Brits can do....stiff upper lip and all that...where is the mojo I ask?? An a/c boat needs a little zip...sum fire..a little in your face bravado...y'know....some artistic smack talk...some swagger...c'mon....gimme a paint brush and sum paint...I can fix that !!

[MicHughV]

...to get back on topic....these a/c boats are all " foilers"...hull shape must by definition play only a supporting role !!!....ie, an attachment point for the foils..it''s all about the foils....get up on on foils and stay on the foils...beyond that, everything else is academic....the hulls provide little in the speed department...they are a platform for the crew, the mast and sails and the foils..for all intents and purposes the hull could be a log canoe..or a plastic box....
.....the foils require some hydraulic or mechanical assistance...in this regard the hull is of some use..I think we are missing the boat here....it's all about the foils..it's clear that there are different approaches to foil design...and how to maneuver or articulate them...
...I think all the a/c boats will employ the latest and best sail technology, cordage and other such materials, but at the end of that day it's going to be all about the foils.

[tp12]

The scow bow on the UK boat should go a long way to stopping the bow from digging in and that shape looks like it'll shed water quickly.

Really looking forward to seeing these sailed in anger. Some pretty cool tech in these boats, bring em on I say!

[CassidyNZ]

Originally Posted by MicHughV

....the hulls provide little in the speed department...they are a platform for the crew, the mast and sails and the foils..for all intents and purposes the hull could be a log canoe..or a plastic box....

Except that whilst it is a platform for the crew, it also needs to ensure safety, security, a place where relief from huge forces of wind, spray can be found. The following differences have become evident:

- ETNZ - deep wells in which crew can hunker down out of the wind/spray which at 50kn of boat speed will be formidable. Just extend your arm full length out of the car window at 90km/hr and see how tiring it gets after a few minutes. Coincidentally it also contributes to reduced air drag.

- GGYC - wells exist but not so deep, crew exposed to wind while standing and grinding, same elements of fatigue seemingly inescapable, less air drag reduction.

- INEOS - beam on protection for those rare moments when wind will come from the beam, otherwise a low profile foredeck ensures that wind and water is funnelled straight into the crew, coupled with what looks like a series of cheese cutters supporting the slab sides for when the boat nose-dives (and the chances are, it will).

These opinions are totally mine and not based on anything other than the observations made from pictures on assorted media. As always, I could be totally wrong and there may be heated/climate controlled bunks in the apparently less hospitable designs

[StuM]

Originally Posted by MicHughV

...to get back on topic....these a/c boats are all " foilers"...hull shape must by definition play only a supporting role !!!....ie, an attachment point for the foils..it''s all about the foils....get up on on foils and stay on the foils...beyond that, everything else is academic....the hulls provide little in the speed department...they are a platform for the crew, the mast and sails and the foils..for all intents and purposes the hull could be a log canoe..or a plastic box....

If the designers are smart, the hulls will also provide aerodynamic lift, stability and "ground effect" lift.

[jmh2002]

Yes that has already been mentioned in earlier posts. American Magic's hull design is especially considered to be making use of the ground effect.

[jmh2002]

Originally Posted by MicHughV

...to get back on topic....these a/c boats are all " foilers"...hull shape must by definition play only a supporting role !!!....ie, an attachment point for the foils..it''s all about the foils....get up on on foils and stay on the foils...beyond that, everything else is academic....the hulls provide little in the speed department...they are a platform for the crew, the mast and sails and the foils..for all intents and purposes the hull could be a log canoe..or a plastic box...

Everyone (even so called yachting journalists included) keeps saying things like this as 100% fact (or nonsense, a plastic box...?) yet are seemingly mostly failing to notice, realise, mention (or understand) that both TNZ and Luna Rossa have specifically designed hulls with features that are also meant to be a benefit while the boat is NOT flying.

They may be wrong of course but clearly they think that this may be beneficial. So much so that their entire hull is designed around this possibility...

Most of these points have been covered earlier in the thread and may well be worth re-reading to gain a better understanding.

And of course not to mention CassidyNZ's valid points about the hull's other purposes, also already well covered earlier in the thread.

Although American Magic's hull 'looks' more 'aero', they appear to have paid less attention to the cockpit, crew, and mainsail end plate. Team GB's crew looks even more exposed.

Whilst by comparison TNZ's crew appear to sit lower in the boat, and even the wheel and helm position looks quite a bit lower too.

So I don't think bold statements in any one direction are useful (and I already see some bold but perhaps not quite totally thought through posts...).

But I would say that the Hauraki Gulf has vastly more 'all round' conditions than Bermuda, and TNZ and Luna Rossa's boats look to be more all rounders, capable of performing in multiple different conditions.

On the other hand American Magic and Team GB's hulls seem to be much more narrow focused.

As for the scow type hull, well, they better hope they are flying because any time they are in the water they look incredibly slowed down by all that wetted surface (see a video that I posted earlier on Page 2 of American Magic Foiling, Gybing, and Parking... http://www.cruisersforum.com/forums/...ml#post2977637)

As I also mentioned earlier, TNZ's hull seems to be able to operate in what I am calling 'semi-displacement mode' which I speculated may be helpful at multiple different moments.

Let's see if that ends proving to be useful or not.

[jmh2002]

PS: did I really just call a 75ft state of the art foiling monohull an 'all rounder' ?

[tp12]

Originally Posted by jmh2002

As for the scow type hull, well, they better hope they are flying because any time they are in the water they look incredibly slowed down by all that wetted surface (see a video that I posted earlier on Page 2 of American Magic Foiling, Gybing, and Parking... http://www.cruisersforum.com/f...-ne...ml#post2977637)

Regarding the scow bow's wetted area, that's what it looks like, sure, but only if they're perfectly flat.

Some good discussion here:
https://www.boatdesign.net/threads/s...ing-bow.58219/