What factors determine the maximum speed of a sailing dinghy?

[SailTheMoon]

But you can't beat a big and light catamaran on hydrofoils with a dinghy on hydrofoils.

Why is that? Since both boats are supported entirely by foils, why does the hull shape matter once you've reached takeoff speed and are clear of the water?

 

[westernman]

Well actually, you probably can - a cat is potentially just extra windage once foiling, albeit more stable and therefore easier to sail during the transition stage.
The SailGP use cats, but very specialist ones - but again perhaps more for stability pre foiling, and width of foil base. Americas Cup moved to monohull, but with very complex moveable ballast.
A monohull Moth with moving ballast of the sailor is probably faster than a cat would be.

If could stay airborne, fastest of all would be no hull, dropping the floats once airborne (and capsizing / sinking at end of race).

And of course kite foiling sets all the speed records - again showing big and multihull is not necessarily added speed.

You cannot get the ballast on a Moth anywhere as far from the centre line as you can on a wide catamaran.
In the end the speed is determined by the amount of power vs amount of drag.

The amount of power you can use is determined by righting moment, which is distance of your ballast/crew from the centre line. The drag is determined primarily by the weight of the entire contraption.
A lightweight, wide, multihull with foils and a large sail area should win.

 

[westernman]

Why is that? Since both boats are supported entirely by foils, why does the hull shape matter once you've reached takeoff speed and are clear of the water?

Righting moment. A cat is much wider.

 

[KevinV]

I really only intended to make the point that a planning boat needs more careful design and control as it is less stable than a boat sat in the water.

I'm not completely with you there - my old fireball was a wobbly pig of a thing until you got it on the plane - then it would settle in a groove and stay there.

 

[SailTheMoon]

Righting moment. A cat is much wider.

 

[Chiara’s slave]

Righting moment. A cat is much wider.

This is why SailGP boats can hit 60mph. A Moth, or any other mono outside the Americas cup will just blow over before it generates enough power. AC72s are very nearly as fast, but cost an order of magnitude more. Not to mention the skill set required to sail them. So not to say that no mono can ever be as quick, just that it costs a fortune, literally, and is even more difficult to control. That holds true whether you are foiling or not. You can buy a mono that can outpace a fast cat, but it will cost at least as much, probably more, and be hard to sail. The cat is hard to sail in the sense that it takes years of practice to hit the front of the fleet. But most of us can get on a Hobie at the beach, and be blasting along in fine style pretty soon.

 

[Chiara’s slave]

Just a BTW on speed. The SailGP boats are hitting a wall at 60mph. The water is boiling on their foils. The latest sailing speed attempt is not a foiling, but a planing boat.

 

[michael_w]

A master class on sailing a planing boat in heavy weather.

 

[westernman]

A master class on sailing a planing boat in heavy weather.

Needs a touch more skill than a Mirror in the same weather.

 

[oldbloke]

I'm not sure you can call it a masterclass when they all capsize.
In the twilight zone, where anything can happen! I'm not suggesting I would do any better, been there done that enough times, 49r and Boss particularly prone to diving also RSAero with the big rig

 

[Chiara’s slave]

I'm not sure you can call it a masterclass when they all capsize.
In the twilight zone, where anything can happen! I'm not suggesting I would do any better, been there done that enough times, 49r and Boss particularly prone to diving also RSAero with the big rig

That’s more a reflection of how difficult the boats are, and how tough the conditions. My performance dinghy experience has all been in cats for the last 40 years, they too have their foibles when the going gets tough. And like almost all high performing sailing boats, the big one is the bear away at the windward mark when there’s some weight in the wind. The DF920 is similar, though it would take a brave man to screw that up.

 

[westernman]

That’s more a reflection of how difficult the boats are, and how tough the conditions. My performance dinghy experience has all been in cats for the last 40 years, they too have their foibles when the going gets tough. And like almost all high performing sailing boats, the big one is the bear away at the windward mark when there’s some weight in the wind. The DF920 is similar, though it would take a brave man to screw that up.

It is called "going down the mine".
Here is an example of just that:-

 

[Skysail]

It is called "going down the mine".
Here is an example of just that:-

Early days in the 1970s James Grogono gave a talk at our sailing club. He developed a Tornado named Icarus -‘ the boat that could fly’.

When it stopped the trapeze man went round the bow and into the water - this manoeuvre they called a Maypole.

This article is of interest

Fear of flying

And this

Foiling: the history of the hydrofoiler - Yachting World

 

[westernman]

Early days in the 1970s James Grogono gave a talk at our sailing club. He developed a Tornado named Icarus -‘ the boat that could fly’.

When it stopped the trapeze man went round the bow and into the water - this manoeuvre they called a Maypole.

This article is of interest

Fear of flying

And this

Foiling: the history of the hydrofoiler - Yachting World

Been there. Done that. I am an expert in that kind of cock up.

 

[seivadnehpets]

We raced Mirrors with full sail plus spinnaker in all weathers with two very light weight kids. Only capsized 3 times in 2 very busy seasons - and one was in huge waves when other bigger boats had abandoned racing.
But a lot was about preparation and technique. Bin elastic rudder downhaul and pull rope downhaul bar tight.
Release all controls before pinning gunter (in those days) bar tight on mast, only then pull on downhaul, then outhaul then kicker.
Well mannered boat.
Later happily sailed West Eleven with family of 5 round Gulf de Morbihan.

I used to do nutty out on my own stuff, sometimes out across the Thames Estuary overnight, or out on an early tide before daylight, so I reefed the main as a precaution, but I learned that if you need to reef one sail you need to reef both. There was a good billow blowing and I tried my usual trick of steering upwind but the jib disagreed. Luckily that was in daylight.

 

[Chiara’s slave]

In the Hurricane 5.9 class, the crew would sit on the lee hull going downwind, usually facing backwards, to facilitate breathing, and to avoid ingesting raw fish. This was to enable the windward hull to fly on the run, reducing wetted surface. It had the added benefit that they couldn’t see the lee bow burying, so didn’t get scared. The procedure was known as ‘the Wild Thing’. Singing the song helped with the courage aspect.

 

[MikeBz]

I'm not sure you can call it a masterclass when they all capsize.

It’s a masterclass from the one which doesn’t capsize in those heinous conditions.

 

[MikeBz]

An RS200 hit over 19 knots in the Starcross Steamer recently:

 

[westernman]

An RS200 hit over 19 knots in the Starcross Steamer recently

Moth at 26 knots here (even if he was swimming most of the time):-

 

[MikeBz]

Moth at 26 knots here (even if he was swimming most of the time):-

The top end of the Moth fleet is doing 22-23 knots upwind and > 35 knots downwind - without capsizing!

Upwind they can choose 'high and slow' - 18-20 knots, or sail a little bit freer and do 22-23 knots or more. This really opens up the tactical options compared to slower boats as they can pull the trigger and get to a windshift or patch of pressure some distance away very quickly.