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Seawolfflo · 04-11-2020, 01:50

So I recently made this overview of some of the major innovations in the IMOCA class boats competing in de 2020 Vendee Globe, and One interesting perspective I'm wondering about more and more:

Could we not say that, the foils, are actually kind of turning these monohulls into a type of catamaran? as, factually, the foil and keel lift the boats out of the water almost completely, leaving the boat flying on two points of contact with the water (Stabilized by the hull of course but still...). So we might say they are actually very strange looking catamarans, where we replaced the second hull with a foil.

Curious what you all think of this

?

B23iL23 · 04-11-2020, 02:07

So what would you call a trimaran with foils? What does it turn in to?

It's still a mono in my books and probably 50% of the time the hull is still in the water.

Seawolfflo · 04-11-2020, 02:23

Quote:

Originally Posted by B23iL23

So what would you call a trimaran with foils? What does it turn in to?

It's still a mono in my books and probably 50% of the time the hull is still in the water.

I think you are right but that is also exactly the point. I think the big shift between the mono hulls and multi hulls, has always been (in essence) that the multi's bring the hulls up out of the water.

I read an interesting qoute by Pip Here, speaking about Charal as it caught up with her during the last Fastnet race. And she said: "I needed to blink my eyes several times to convince myself that the boat flying by, wasn't a catamaran but a mono, as the entire ship was flying 3 feet above the water, with the nose up maybe 6 or 7 feet...".

B23iL23 · 04-11-2020, 04:46

The tech is amazing and the speeds just blow your mind. I saw them a year ago in France and they are like F1 cars. I did notice that they don't have standing headroom and why? Because at the speeds they are going if you stand up you are likely to fall and hurt yourself. These guys sail around the world mostly crouched!

They have overcome the primary limit on a displacement hull by lifting the boat out of the water but you have to wonder where it ends. What is the upper limit and will the drivers break before the boats?

Seawolfflo · 04-11-2020, 05:22

Quote:

Originally Posted by B23iL23

The tech is amazing and the speeds just blow your mind. I saw them a year ago in France and they are like F1 cars. I did notice that they don't have standing headroom and why? Because at the speeds they are going if you stand up you are likely to fall and hurt yourself. These guys sail around the world mostly crouched!

They have overcome the primary limit on a displacement hull by lifting the boat out of the water but you have to wonder where it ends. What is the upper limit and will the drivers break before the boats?

Yes

did you know that many of the IMOCA foiling drivers are now wearing body armor when they are sailing over 25 knots

. Like helmets, knee and elbow pads, back protectors etc. It's like survivor on board these boats hehe

Mag3 · 04-11-2020, 09:12

Technically yes, but i think what you're really asking is different...

boats have moved from displacemet to --> (largely) planing to --> (largely) hydrofoiling...

in my view those are three different conceptual approaches to boat design regardless of whether there is 1, 2, or 3 hulls.

Yellowtulip · 04-11-2020, 10:03

They're monohull as they only have one hull. But they're foiling monohulls, not even 'foil-assisted' applies any more. Technological progress has enabled them to fly on their foils for extended periods, though not all the time.
But they still only have one hull.

Rennsail · 04-11-2020, 10:06

Still monos in my book.

zstine · 04-11-2020, 10:46

To give the OP a break I will assume he knows 'it has 1 hull' and by definition is a mono-hull. But Perhaps what he's trying to say is that the physics is more like a catamaran. certainly the traditional righting moment due to the distance between the center of bouncy to the CG is no longer the only consideration as outboard foils create lift and the A75 has no lead keel at all... so in that sense they are becoming more like cats.. i guess..

zstine · 04-11-2020, 10:54

Quote:

Originally Posted by B23iL23

.. I did notice that they don't have standing headroom and why? Because at the speeds they are going if you stand up you are likely to fall and hurt yourself. These guys sail around the world mostly crouched!

They have overcome the primary limit on a displacement hull by lifting the boat out of the water but you have to wonder where it ends. What is the upper limit and will the drivers break before the boats?

They don't have standing head room because windage on the hull becomes a large resistance to going faster. has nothing to do with safety

The upper limit now has become cavitation of the foils... at least in the highest performance boats. I don't think the IMOCA boats are at that limit.

TeddyDiver · 04-11-2020, 11:13

Quote:

Originally Posted by Seawolfflo

So I recently made this overview of some of the major innovations in the IMOCA class boats competing in de 2020 Vendee Globe, and One interesting perspective I'm wondering about more and more:

Could we not say that, the foils, are actually kind of turning these monohulls into a type of catamaran? as, factually, the foil and keel lift the boats out of the water almost completely, leaving the boat flying on two points of contact with the water (Stabilized by the hull of course but still...). So we might say they are actually very strange looking catamarans, where we replaced the second hull with a foil.

Curious what you all think of this

?

Could we not say that, the foils, are actually turning these boats into a type of foilers (never mind the number of hulls hanging in the air)

B23iL23 · 04-11-2020, 11:22

Yes and no. They do lower the roof to streamline but even the boats without an enclosed cockpit, the crew rarely stand when in race mode. They move around on their bums.

Quote:

Originally Posted by zstine

They don't have standing head room because windage on the hull becomes a large resistance to going faster. has nothing to do with safety

The upper limit now has become cavitation of the foils... at least in the highest performance boats. I don't think the IMOCA boats are at that limit.

Dave_S · 04-11-2020, 13:33

As far as I am concerned.

It is a catamaran in function hidden in a mono's appearance. I expect NZ design team realised the hull was almost irrelevant when they were designing last season's cats. The hull is almost just mechanism for supporting the foils and the midship foils are points of righting moment which are substantially offline to the centre line of the boat and seperate to each other.

The rear foil on the rudder can now be a single because of the single hull and this will save drag. I expect there are also significant gains in drag reduction made by adjusting the angle of the arms to more closely match the righting moment with less losses and helpful when setting up for turns and tacks.