Boats and foils comparison

[Tornado-Cat]

We have 4 very different boats, which will be the best option ?



View attachment ETNZ-sail-Live-Sail-Die6.webp

 

[Tornado-Cat]

Different foils too.

 

[Rasputin22]

Whoever had the best bullets! 

 

[RobG]

Different foils too.

View attachment 324868

Rocket pods? Maybe to help with flow at the tips of the flaps? But then why only on the bottom?

T joints on the bulb look dirty, shouldn't they be filleted?

 

[Sailbydate]

So, I see a shit load of drag going on, on two of the foil versions above.

The torpedoes 'may' be more stable - but are they faster? Not likely.

 

[Tornado-Cat]

So, I see a shit load of drag going on, on two of the foil versions above.

The torpedoes 'may' be more stable - but are they faster? Not likely.

We don't know whether the torpedo is for better hydro drag or to play with the mass within the rule.

 

[Boybland]

I think we need both new boats with the rig up before we can really have this conversation in full.

But I actually think the answer lies in the weather on any given day, ETNZ really look to have targetted the light stuff hard and I feel AM are at the other end with LR somewhere in between, although those foil pods are just odd and don't even look real, are we sure they are not just for show!

 

[Tornado-Cat]

I think we need both new boats with the rig up before we can really have this conversation in full.

But I actually think the answer lies in the weather on any given day, ETNZ really look to have targetted the light stuff hard and I feel AM are at the other end with LR somewhere in between, although those foil pods are just odd and don't even look real, are we sure they are not just for show!

For the pleasure of speculation, if I was willing to foils as soon as possible, I would chose:

- Orca for flat water

- Sardine for little chops

- Flipper for waves

Now, at speed and foiling, I think I would prefer the Orca hoping to get a small air cushion between hull and water.

 

[Horn Rock]

I would prefer the Orca hoping to get a small air cushion between hull and water.

I think you're naive to think there will be any sort of ground effects or hovercraft like effects for Defiant. Their shape is purely conceived for minimal drag through the air whilst up on the foils. It's going to go splat when she comes down off the foils, and be way more sticky with her large wetted area than the other two. In marginal conditions Defiant will be the last boat to rise, and the worst performer in any contact with a chop.

To me, Te Aihe still looks the most advanced design of the three we've seen so far.

 

[buckdouger]

Rocket pods? Maybe to help with flow at the tips of the flaps? But then why only on the bottom?

T joints on the bulb look dirty, shouldn't they be filleted?

I think the answer is no. You want maximum space for flow to pass between or you accelerate the flow and increase cavitation issues. 

 

[buckdouger]

We don't know whether the torpedo is for better hydro drag or to play with the mass within the rule.

I think it is for drag. The rule definitions seem to preclude the pod from inclusion in the mass modification calc, or at best an interpretation is required. Someone posted they felt the definitions section where this argument logically derives is normative, but the rule does not state that it is normative, and I don't think we can assume. 

 

[darth reapius]

I'll throw my thought out there...

Bulb foils are the high speed foils, non-bulb foils are the low speed foils.

Think of it like moth foils, heavy air foils are far smaller in surface area and wouldn't have room for ballast, therefor the weight is distributed in a bulb at the joint.

Light air foils are far larger in surface area and have the volume inside to spread out the ballast internally without the bulb.

Sheer size of the foils is a dead-give-away to me, TNZ's foils appear to be 4x the area of both LR and AM and of a thicker cord. 

If I have some time I will model them up, just need some good front/rear/side images of all sets to get even mildly accurate shapes and volumes etc.

 

[Horn Rock]

Bulb foils are the high speed foils, non-bulb foils are the low speed foils.

I think you could be right. Te Aihe's foils definitely look to have more surface area. More lift for lower wind ranges. What are the rules for foil changes in the cup match? 

 

[Tornado-Cat]

I think you're naive to think there will be any sort of ground effects or hovercraft like effects.

That is what I thought at the beginning, we tried concave with sailboards years ago and it did not work. However these boats will sail over 40 kts, have you put your hand outside of a car at 80 km per hour ? it lifts, and the boat is a bit more larger than a hand. I don't say the boat won't crash, I think a few cm of air cushion above water can make the difference. Remains to be seen though.

 

[buckdouger]

I think you could be right. Te Aihe's foils definitely look to have more surface area. More lift for lower wind ranges. What are the rules for foil changes in the cup match? 

I think this is broadly right darth reapius, except that in addition to high-speed low-speed the tradeoff between takeoff speed and top speed is a factor too that teams have to weigh, looking at their predicted modes around the race course in different scenarios. 

 

[The_Alchemist]

Let me throw out another idea about the torpedo or bulb foils in use by AM and LR.  When these boats are foiling, the foils will be just below the surface of the water.  The torpedo/bulb could give some bulbous bow effect or be similar to a swath hull.  As such, it may reduce the drag of the foil arm in the water.  I suspect that the foil arm may not be long enough to get the same wave cancelation effect, but at the speeds these boats will be going it may be a factor.  Add that to the versatility of "foil modifications" with the 80/20 rule, improved control of the RM (weight in one spot) and some possible super cavitation effects.   And to think, I haven't been drinking...

 

[Horn Rock]

have you put your hand outside of a car at 80 km per hour ? it lifts,

To really get lift (like a wing) the underside would need to be dead flat to generate pressure differential. Their hull is still quite round which leads me to believe it's more about drag reduction than lift. Also, at speed they're getting enough lift from the foils, so lift generated by the hull would not seem necessary.

 

[Horn Rock]

what if the flatness of Defiant's hull is meant for windward-heel touch downs?

Kinda like doing an edge touch? Interesting idea, but from what we've seen these boats seem to come down with a flat attitude. There does seem to be some heel - either way - whilst flying, but yeah, coming down with a significant heel might lead to some unintended consequences - as in capsizes - as well as requiring  very precise control between the main, helm and foils.

 

[RobG]

I think it is for drag. The rule definitions seem to preclude the pod from inclusion in the mass modification calc, or at best an interpretation is required. 

Definitions aren't normative when there is a rule that is explicit. Rule 13.2 (c) defines the bulb as part of the "foil wing":

13.2 For the purposes of Rules 5 and 10:
(a) a foil does not include the metal foil arm head, fasteners attaching the foil arm head to the foil arm, any foil arm drum, or any other components inside the hull IGES that are disconnected from a foil when it is removed from the yacht;
(b) except for parts of foil systems, any material that does not move relative to a foil flap must be part of that foil flap; and
(c) except for the foil arm stock, foil flaps and foil systems, any material within the region described in Rule 13.4 must be part of the foil wing.

Where rule 5 is "Component limits and modifications" and figure 13.1 associated with Rule 13.4 includes essentially everything beyond the end of the arm that isn't explicitly excluded by 13.2 (i.e. the flaps and foil systems) as part of the foil.

I don't know how the change allowance is applied though. Can any of the 6 "foil wings" be modified by up to 20% mass? In that case, those with a bulb can effectively have 12 wings if they remanufacture their 6 existing foils into 6 new foils.