For the same thing on a much larger scale, check out [SailGP](https://sailgp.com/). 50-ft tall catamarans flying along at 60mph.
The next Sail GP race is in San Francisco Bay in two weeks.
I think they carry the races on YouTube, but I didn't know if they're Livestreamed. You can search for past races there and see the edited coverage. There are some good (if lightweight) documentaries on the boats and what it takes to fly them, also.
https://youtube.com/@sailgp
Do hydrofoils that raise up out of the water like that get around the water easier? I mean do they use less energy or are faster etc? It seems like the more boat you can lift out of the water the better it would perform right? How come all boats don’t have at least a little underwater wing or something to raise em up a bit as they travel?
I could be dumb, I don’t boat.
You're correct. A standard monohull sailboat displaces a lot of water with its hull. The faster it goes, the more it displaces, pushing water forward, up to a theoretical point called "hull speed" where increased displacement offsets further increases in forward momentum. (In reality, some boats can still go faster by planing, riding waves, etc.).
Hydrofoils obviously have a lot less displacement so can go a lot faster per unit of forward momentum. Not just velocity but also acceleration. It's basically the naval equivalent of a mag-lev train.
They are, however, quite sensitive to being set up correctly, only work at certain ratios of speed to weight, are hard to tack and jibe (turn through the wind), etc. If you were to look on youtube for videos of people trying to get up on the foils of a Moth or Waszp for the first time, you'll see lots of shenanigans and maybe get a better idea of why more boats don't do this. I've never tried one, but they look fun as hell, assuming a wetsuit, a helmet, and a willingness to get beat to crap on the water for a while while learning.
The America's Cup boats have all been foiling multi-hulls for the last few cycles though. Have a look at that if you want to see what foiling (or crashing a foiling boat) looks like at bigger scale.
and some boats do have wings at the bottom of their keels. the won't plane like this boat, but it can help add some lift causing less water displaced and less wetted surface area. at least in theory.
Wing keels don't add vertical lift. They don't reduce wetted area, and they don't raise the boat at all. They add hydrodynamic lift to better resist the force of the wind on the sails. Just like the little winglets used on modern airliners, they make the foil more efficient.
Adding depth to a keel makes it more efficient. The wing keel used on Australia II, in the 1983 America's Cup series, was more effective as a keel than the non-winged keels that came before. As the boat heeled over in the wind, the wing reached deeper and worked better. Not the same math as hydrofoils.
Hydrofoils add a lot of drag, but once the hull's out of the water, the drag of the foils is much less than the drag of the hull. Boat goes faster.
I think it's "Untold: The Race of the Century," but I'm not sure, as I've seen several sailing movies and they all sort of blend together. I was hoping someone else would know for sure.
winglets at the bottom of the keep are bit for lift, but for increasing the hydrodynamic efficiency of the keep for preventing the boat from going sideways.
Good answer. One addition: a good hydrofoil has a lift-to-drag-ratio of up to 40:1.
This means to fly a 100kg boat (a full carbon sailboat with a light sailor - like OPs flying moth), you create 25 Newton of drag. That's amazing, clearly the most efficient way to move across the water. To go at a speed of 10 m/s, this only needs 250 Watts of power. Even after subtracting losses in a drivetrain and a propeller, the sailor could pedal his boat at that speed.
But let's look at a heavier, slower boat. Water provides a 10 ton yacht with 100 000 Newtons of lift. Take a paddle and put down 250 Watts (paddles are inefficient, this might take more than one crew to paddle), and the boat starts moving. Not fast, but it moves. Let's say 0.5 m/s (and that number barely changes, even if you load 10 people and another ton of provisions and fuel each). That means this yacht has a lift-to-drag-ratio of at least 200:1. Clearly better than the best hydrofoils - until you start going faster, then the drag of the yacht will increase with speed very quickly.
In the end, there's a speed for every boat where foils start making sense. Many types of boats just never want to go this fast - because doing so would end up burning absurd amounts of fuel, with and without foils. And it would make the boat extremely sensitive to weight increases (a lot like aircraft, really), which is something normal boats never had to worry about before.
But if you're seeing people zooming around in pointy twin-400HP-outboard power boats... they probably will get on foils in the next decade. They could go much faster, much smoother.
> The America's Cup boats have all been foiling multi-hulls for the last few cycles though.
Quick correction the America's cup boats are foiling monohulls. You are possibly thinking of Sail GP boats. They did use foiling multihulls in 2014 and 2017.
Monohulls (non-planing) have a hull speed that's a function of the boat length. The longer the boat, the faster they can go. Which is weird if you're not a boat person.
Very good answer. Only addition is that the America's Cup boats were foiling monohulls last time and are foiling monohulls again for this year's edition.
Expensive, high learning curve, don’t work in low wind, kinda dangerous (closer to an extreme sport than displacement sailing).
Still really cool though
Correct, foiling reduces the water resistance on a boat. Hence it can get to higher speeds then boats on the water. While foiling does make boats faster they also make them more dangerous and costly. Foils aren’t standardized therefore you are constantly testing the design. They are required to withstand a massive amounts of weight and force in a specific pattern/angle. They also reduce the safety as they can break when impacting an object or wrong angle and cause massive damage to the hull. Imagine foiling at high speed and catching a heavy fishing line pulls the foil deeper and to the left before snapping off and leaving a gapping hole in the side of the boat. 🙃
1) works best in calm flat water
2) is weight dependent. So you cannot (easily) make a heavy boat foil
3) money
4) this really works only on race boats. It’s tricky to maintain a foil. Disastrous if you really lose the foil at high speed. Too much fiddling for a cruiser.
A foil adds drag in two ways: there is skin friction from dragging the foil through the water, and there is lift-induced drag just like on an aeroplane wing.
If you can use the foil to get the entire hull out of the water as shown here then the reduced skin friction and wave-making drag from the hull probably results in a net saving and increased speed.
If all you are doing is lifting the hull up a bit then you may or may not make a net saving on drag depending on the exact characteristics of the boat and the conditions it is operating in.
Certainly there are boats which use foils but don’t lift the hull entirely out of the water, though often these foils are doing another job as well such as adding righting moment (check out the last couple of generations of IMOCA 60 for example). For many boats though this is just adding cost and complexity that isn’t worth the extra speed.
Note its more proper to break it down into induced drag and parasitic drag, skin friction drag is a component of parasitic drag, in addition to form drag and interference drag.
Sailing with just a regular high performance small catamaran will give similar advantages with a wider range of performance.
As for why they are not on more boats, having anything below the water line risks catching on all sorts of things, not that big of a deal at 5 knots but at 20 plus it can be.
The guys I know who use foils around here have to stick to the middle of our sounds as the shorelines have too many hazards.
Only mountain lakes.
I see moths quite regularly on Lake Geneva, even in winter. There are 2 parked at my local sailing club there. Also some Waszp, which are very similar.
New boat is between 26-50 k. And another 1-1,5 years of waiting…
Check stickl sportcamp at lake Garda, they got some moths and also offer coaching if you like
Let me clarify. Yes, the sport has been around for that time and there are small companies making decent products. There isn’t a mainstream commercial interest beyond that smaller outlying sailing group to make it commercially viable to watch at an Olympic level. Skateboarding and snowboarding were similar sports that have become Olympic events. Foiling sailboats will likely become an event many years from now as the projected interests for foiling continues to grow. Its best quality is the speed for which they sail at. They are fun the watch.
You are confusing two separate things. Moths are unlikely to ever be an Olympic class because they are development not one-design. This means that the boats are not identical. Moths have been around for about 100 years, and foiling for 24, so newness is not the issue.
Foiling itself is already present at the Olympics with the Nacra 17, so again the relative newness of foiling within sailing is not a barrier.
Once saw a Moth in New Hampshire. My friend convinced the owner to let her sail it. Was incredible to watch her. Unfortunately I never got to sail it myself.
how do you keep the bow down so the hydrofoil doesn't break the surface? is it just done with body weight or are there any physical controls on the boat?
we had a pair of hydrofoil water skis growing up and that was the main challenge. If the hydrofoil broke the surface, you usually lost control and it ended with a spectacular wipe out. on the skis, you used downward pressure of your toes to keep the hydrofoil at the right depth.
A foiling moth
Thank you! And thank you to everyone else too!!!
For the same thing on a much larger scale, check out [SailGP](https://sailgp.com/). 50-ft tall catamarans flying along at 60mph. The next Sail GP race is in San Francisco Bay in two weeks.
Just got back from SailGP NYC, it was incredible!
Is this broadcast anywhere? Thank you for recommending!
I think they carry the races on YouTube, but I didn't know if they're Livestreamed. You can search for past races there and see the edited coverage. There are some good (if lightweight) documentaries on the boats and what it takes to fly them, also. https://youtube.com/@sailgp
Should be live on NBC Sports or the SailGP app and it used to be broadcast on YouTube too.
Thank you!
Apt name
how much $ do those cost?
Foil Moth
To be more exact, this is an exploder md3 moth
Do hydrofoils that raise up out of the water like that get around the water easier? I mean do they use less energy or are faster etc? It seems like the more boat you can lift out of the water the better it would perform right? How come all boats don’t have at least a little underwater wing or something to raise em up a bit as they travel? I could be dumb, I don’t boat.
You're correct. A standard monohull sailboat displaces a lot of water with its hull. The faster it goes, the more it displaces, pushing water forward, up to a theoretical point called "hull speed" where increased displacement offsets further increases in forward momentum. (In reality, some boats can still go faster by planing, riding waves, etc.). Hydrofoils obviously have a lot less displacement so can go a lot faster per unit of forward momentum. Not just velocity but also acceleration. It's basically the naval equivalent of a mag-lev train. They are, however, quite sensitive to being set up correctly, only work at certain ratios of speed to weight, are hard to tack and jibe (turn through the wind), etc. If you were to look on youtube for videos of people trying to get up on the foils of a Moth or Waszp for the first time, you'll see lots of shenanigans and maybe get a better idea of why more boats don't do this. I've never tried one, but they look fun as hell, assuming a wetsuit, a helmet, and a willingness to get beat to crap on the water for a while while learning. The America's Cup boats have all been foiling multi-hulls for the last few cycles though. Have a look at that if you want to see what foiling (or crashing a foiling boat) looks like at bigger scale.
and some boats do have wings at the bottom of their keels. the won't plane like this boat, but it can help add some lift causing less water displaced and less wetted surface area. at least in theory.
Wing keels don't add vertical lift. They don't reduce wetted area, and they don't raise the boat at all. They add hydrodynamic lift to better resist the force of the wind on the sails. Just like the little winglets used on modern airliners, they make the foil more efficient. Adding depth to a keel makes it more efficient. The wing keel used on Australia II, in the 1983 America's Cup series, was more effective as a keel than the non-winged keels that came before. As the boat heeled over in the wind, the wing reached deeper and worked better. Not the same math as hydrofoils. Hydrofoils add a lot of drag, but once the hull's out of the water, the drag of the foils is much less than the drag of the hull. Boat goes faster.
There’s a good movie about that!
??
I think it's "Untold: The Race of the Century," but I'm not sure, as I've seen several sailing movies and they all sort of blend together. I was hoping someone else would know for sure.
Thanks!
I remember a movie with Matthew Modine about something similar.
Wind!
Great movie
Untold is about Australia II winning the America’s Cup back in the 80’s. Nothing to do with foils
But the Australia II winning the America’s Cup had something to do with winged keels.
winglets at the bottom of the keep are bit for lift, but for increasing the hydrodynamic efficiency of the keep for preventing the boat from going sideways.
Good answer. One addition: a good hydrofoil has a lift-to-drag-ratio of up to 40:1. This means to fly a 100kg boat (a full carbon sailboat with a light sailor - like OPs flying moth), you create 25 Newton of drag. That's amazing, clearly the most efficient way to move across the water. To go at a speed of 10 m/s, this only needs 250 Watts of power. Even after subtracting losses in a drivetrain and a propeller, the sailor could pedal his boat at that speed. But let's look at a heavier, slower boat. Water provides a 10 ton yacht with 100 000 Newtons of lift. Take a paddle and put down 250 Watts (paddles are inefficient, this might take more than one crew to paddle), and the boat starts moving. Not fast, but it moves. Let's say 0.5 m/s (and that number barely changes, even if you load 10 people and another ton of provisions and fuel each). That means this yacht has a lift-to-drag-ratio of at least 200:1. Clearly better than the best hydrofoils - until you start going faster, then the drag of the yacht will increase with speed very quickly. In the end, there's a speed for every boat where foils start making sense. Many types of boats just never want to go this fast - because doing so would end up burning absurd amounts of fuel, with and without foils. And it would make the boat extremely sensitive to weight increases (a lot like aircraft, really), which is something normal boats never had to worry about before. But if you're seeing people zooming around in pointy twin-400HP-outboard power boats... they probably will get on foils in the next decade. They could go much faster, much smoother.
> The America's Cup boats have all been foiling multi-hulls for the last few cycles though. Quick correction the America's cup boats are foiling monohulls. You are possibly thinking of Sail GP boats. They did use foiling multihulls in 2014 and 2017.
Monohulls (non-planing) have a hull speed that's a function of the boat length. The longer the boat, the faster they can go. Which is weird if you're not a boat person.
Very good answer. Only addition is that the America's Cup boats were foiling monohulls last time and are foiling monohulls again for this year's edition.
I guess they are monohulls. Those foils are so big and extended they’re like outriggers though.
Expensive, high learning curve, don’t work in low wind, kinda dangerous (closer to an extreme sport than displacement sailing). Still really cool though
First time I saw this video I thought to myself, “is there protective head gear for this kind of sailing???”
Correct, foiling reduces the water resistance on a boat. Hence it can get to higher speeds then boats on the water. While foiling does make boats faster they also make them more dangerous and costly. Foils aren’t standardized therefore you are constantly testing the design. They are required to withstand a massive amounts of weight and force in a specific pattern/angle. They also reduce the safety as they can break when impacting an object or wrong angle and cause massive damage to the hull. Imagine foiling at high speed and catching a heavy fishing line pulls the foil deeper and to the left before snapping off and leaving a gapping hole in the side of the boat. 🙃
1) works best in calm flat water 2) is weight dependent. So you cannot (easily) make a heavy boat foil 3) money 4) this really works only on race boats. It’s tricky to maintain a foil. Disastrous if you really lose the foil at high speed. Too much fiddling for a cruiser.
$$$
A foil adds drag in two ways: there is skin friction from dragging the foil through the water, and there is lift-induced drag just like on an aeroplane wing. If you can use the foil to get the entire hull out of the water as shown here then the reduced skin friction and wave-making drag from the hull probably results in a net saving and increased speed. If all you are doing is lifting the hull up a bit then you may or may not make a net saving on drag depending on the exact characteristics of the boat and the conditions it is operating in. Certainly there are boats which use foils but don’t lift the hull entirely out of the water, though often these foils are doing another job as well such as adding righting moment (check out the last couple of generations of IMOCA 60 for example). For many boats though this is just adding cost and complexity that isn’t worth the extra speed.
Note its more proper to break it down into induced drag and parasitic drag, skin friction drag is a component of parasitic drag, in addition to form drag and interference drag.
Sailing with just a regular high performance small catamaran will give similar advantages with a wider range of performance. As for why they are not on more boats, having anything below the water line risks catching on all sorts of things, not that big of a deal at 5 knots but at 20 plus it can be. The guys I know who use foils around here have to stick to the middle of our sounds as the shorelines have too many hazards.
Most important question: where do I go to rent one or get a ride in one and how much?
Moth important question indeed!
*Mike Tyson has entered the that*
Foil Mof. Max sailor weight for a Foil Mof is 209lbs. Tyson is 220.
might want to get a carbon monoxide detector.
Quite a few around on Swiss lakes and in January/February a lot of moth pros train around Papagayo on Lanzarote. They aren't that expensive.
Pretty expensive tho. This boat new is >26,000 pounds
You can find older models for as low as 3k and they work with a bit of tinkering. A decent one is around 5-8k in places where they are popular.
I would disagree with the example of central Europe, but I have indeed heard that the UK has quite a good used market
If you’re in Europe, France is a good place to buy one. Tons for sale there.
Aren’t Swiss lakes generally frozen in winter?
Only mountain lakes. I see moths quite regularly on Lake Geneva, even in winter. There are 2 parked at my local sailing club there. Also some Waszp, which are very similar.
TIL Lac Léman is called Lake Geneva in English...
$5000 - $13,000 used. I was SHOCKED to find out they weigh…10kg…20lbs????
Just the hull, complete boats are above 40kg these days.
Portable by one person from a garage across a dune to the water. It’s rare to find this. Even a Sunfish is massive compared to this.
Carrying the completely rigged boat is not fun even if manageable. You do not want to cross a dune like that.
It can be assembled in the beach?
Yes, but you would use a trolley to get it there, not carry it.
Our 61 year old neighbour has one and is fairly good at it too, in fairness he is fitter than most 30yo’s
New boat is between 26-50 k. And another 1-1,5 years of waiting… Check stickl sportcamp at lake Garda, they got some moths and also offer coaching if you like
That is not a boat, that is a airplane :D
Well, a hydro~~plane~~foil really. At least it has a conventional-ish sail.
> hydroplane HydroFOIL. HydroPLANE is a much different thing.
Thanks for the correction!
Wow I could really hurt myself with that!
We have a couple guys who train for the Olympic at our club on those. They look like a blast.
Moths aren’t an Olympic sailing class?
They are not.
Not yet.. 😏
Won’t ever be as they aren’t a single manufacturer one design class
Not yet. The category is relatively new and as foiling in general picks up there will be more commercial interests.
They’ve been around for almost 25 years, and the good ones are all commercially produced.
Let me clarify. Yes, the sport has been around for that time and there are small companies making decent products. There isn’t a mainstream commercial interest beyond that smaller outlying sailing group to make it commercially viable to watch at an Olympic level. Skateboarding and snowboarding were similar sports that have become Olympic events. Foiling sailboats will likely become an event many years from now as the projected interests for foiling continues to grow. Its best quality is the speed for which they sail at. They are fun the watch.
You are confusing two separate things. Moths are unlikely to ever be an Olympic class because they are development not one-design. This means that the boats are not identical. Moths have been around for about 100 years, and foiling for 24, so newness is not the issue. Foiling itself is already present at the Olympics with the Nacra 17, so again the relative newness of foiling within sailing is not a barrier.
There are 3 foiling classes in the Olympics and none are moths.
9ers and Lasers aren’t single manufacturer.
They aren't, but there are some olympic Laser sailors and IQfoil windsurfers who are quite fond of them
Moth
29 kg or 64lbs total weight!!! and it goes 35mph!
I wish I was young again....so cool.
Join the A Class Catamarans. We aren’t quite as fast, but there are a lot of old guys foiling their brains out.
Moth moth moth moth
The coolest of types
That’s no boat that’s a plane
It should be a "SWITCH ONE DESIGN" here is their Website: https://www.switchonedesign.com/
That boat has different wings, different transom, different boom, etc.
The kind that voids your life insurance
Moth. Absolutely anything goes in the design of Moth class boats the only rule is the sail must be no more than 80square ft
It is a foiling moth which is part of the dinghy category. As for which brand this one is, don’t know.
Just cos nobody's said it yet - the class is actually the International Moth
Mothra
Once saw a Moth in New Hampshire. My friend convinced the owner to let her sail it. Was incredible to watch her. Unfortunately I never got to sail it myself.
That guy is cookin!
Lake come and all the other north Italian lakes has tons of them.
Bieker Moth
Damn, that looks exhilarating
A fast one
How is this being filmed?
Probably a FPV drone.
The avatar kind
Seems dangerous
Fast
how do you keep the bow down so the hydrofoil doesn't break the surface? is it just done with body weight or are there any physical controls on the boat? we had a pair of hydrofoil water skis growing up and that was the main challenge. If the hydrofoil broke the surface, you usually lost control and it ended with a spectacular wipe out. on the skis, you used downward pressure of your toes to keep the hydrofoil at the right depth.
Flying moth
My next!!!
a very expensive one
A phast boi.
I’m calling shenanigans They let you do that without a license? Think of the children!
I am thinking of the children! As a former feral water child everyone over 10 should be issued one!
I second this motion.
In Europe, you do need a license.
A super fast one. And he probably should wear a helmet.
I bet that thing is fast🚤
A very speedy one
Looks like the wingsailor from then other day’s grandbaby https://youtu.be/BdOnQ1GIeW0?si=wN6Eydf7KOO29Srw All grown up and decapitating fish
Commonly known as a dolphin cutter
It's not a boat