RS Aero - No Speed Hum

Have you noticed that there is no speed hum with an Aero?

This is Peter Barton's reply to one of my recent questions about the RS Aero.  Peter looks after the RS Aero out of the UK, and usually manages to get back to me over night. There is a 10 hour time difference between Australia and the UK.  

This time I was following up an question posted in this blog from the Tijuana Taxi.

Tijuana TaxiMay 20, 2017 at 9:06 PM

Great Blog Nick, well done on 2nd at the Nat's as well. One thing you didn't mention about the foils was the trailing edge, the designers have made this a mitre. When I first test sailed one I thought this had been filed to remove some dings, but on receiving my own boat the mitred edges were still present. I am pretty sure RS have not made mention of this in previous literature but my thoughts are by creating a laminar flow away from the rudder, cavitation is avoided and the boat steers even more effectively downwind than the Laser. I would be interested in your or anyone else's thoughts on this.

Hi Nick, Yes, that looked wrong to me initially too! I checked with Alex at RS who confirmed that the main reason is to stop/reduce the humming of the foils, it allows a cleaner re-attachment of flow, otherwise you get cavitation down the trailing edge which can cause the humming sound.

Peter

Have you noticed that there is no speed hum with an Aero?

I tried to take a photo of the edge of my Aero centre boat, but my iPhone camera could not get it the edge in  focus, so here a shot of an Aero board next to an ageing Laser board.  Apart from having a clever trailing edge, they simply look so much nicer.  And there is no rattle or hum.

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The Laser's five basic design flaws

When you compare the 2013 designed RS Aero with the 1969 designed Laser it is easy now to see the Laser's five basic design flaws.

Three are due to the technology and materials limitations of the day, namely the Laser hull weight, the Laser hull shape and foils.

But why did designers, Bruce Kirby and Ian Bruce, chose a sail plan that required block to block sheeting at the transom?

Setting a low boom  also required a cockpit inset into the boat so low it cannot self drain. Centre sheeting and self draining cockpits were common in Moth designs in the 1960's and its hard to explain why the Laser ended up with such a poor configuration.

The Laser was unlucky to end up with a hull weight of 59kg as just 5 years later Ian Bruce and Frank Bethwaite produced the 68kg (fully rigged) Taser using Fiberglass sandwich foam. This substantially larger boat two person boat carries 11.5m2 sail and planes upwind.

In 2013 RS produced the Aero with a hull weight of 30kg

The Kirby's foresight was the was the unstayed mast that simply slotted into a hole in the deck. Comprised of two pieces aluminium tubing it made easy work of rigging, storage and transport. The approach now perfected further by the Aero and the WASZP.

Images:

1.  Bruce Kirby's doodle on a yellow legal pad. The tear sheet from this pad later became what we called the “million dollar doodle.”

2. 1960's Australian Moth with centre sheeting and self draining cockpit

3.  The WASZP with no stays, good when dismounting at 20 knots.


Read more about the history of the Laser design in Kirby's own words.
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Laser Dinghy And The One Design Dilemma

The dilemma for all sailing classes is how to stay relevant with new modern materials and design. One design classes are particularly caught in a bind.

This is ILCA Executive Secretary, Eric Faust explaining the International Laser Class Association policy.

“ILCA’s policy regarding the introduction of new equipment is that it should always have the same characteristics as the existing equipment and that the new equipment should not give a performance advantage when raced alongside existing equipment,”

In reality this is impossible to achieve. It is a pretence and indeed an absurd idea that one can use new materials and design and make them perform the same (as badly) as the old materials and design. One can only imagine the internal politics at the ILCA and the process to resolve this impossible situation and this is reflected in the time taken, around 10 years, for the ILCA to introduce a better full rig sail.

The old full rig sail was made from a 1970's cloth that distorted out of shape after one regatta and a dozen or so practice sessions. The sails short life span was made worse by contemporary super vang/cunningham techniques. So in the real world we have had a classic arms race. The one design principle gone with cashed up sailors gaining the advantage as only they could afford the necessary supply of new sails. 

With new sail cloth and new design, the new sail was always going to be better than the old sail. Straight out of the bag better, and as a more durable sail it was going to stay better for longer. So it was impossible for it to "have the same characteristics as the existing equipment and ..... not give a performance advantage when raced alongside existing equipment,”

Nonetheless the ILCA stuck to its policy. Clive Humphris, the ILCA Technical Officer.

"The main objective of the design project for the Mark II was to create a sail with equal performance to the existing sail, but with better durability. We worked very hard to ensure that the Mark II was not a faster sail and wouldn't make all the existing sails obsolete overnight.'

Notwithstanding their efforts to make a slower sail, the new MK II sail turned out to be noticeable better than the old sail, upwind faster and higher. Boats with the old sail were simply pinched off in the first 100 metres. At my Laser club, we all converted to the new sail within three months of its introduction. There was no point even using the old sail as a training sail, it felt and performed differently.

Single handed dinghy sailing is a close competition, loosing just a half a dozen boat lengths on the first beat can be the difference to being in to the leading group or the last group for the rest of the race. It would have been better for the ILCA to design the best MK II sail it could, because we were all going to buy it anyway.

The introduction of the composite carbon top section is a similar story. Years in development, delayed by internal ILCA politics and legal cases, the new top section has just become available. The old aluminium top section was ok in 1970 but it bent easily and broke after a few seasons. The new top section has again been designed to have the same characteristics as the old aluminium sections, but hopefully it won't break or bend. So for just for safety reasons alone everyone should buy one. Of course they are not really comparable because if they don't have permanent bends like the old one, if they are as stiff as the good aluminium sections, they are not, for most sailors, the same.

For me there was inevitable conclusion, observing the introduction of the new MK II sail and carbon top section, the process, the delays and design compromises. It simply demonstrated that the Laser would always be stuck in the past, there were too many issues to fix and even the simple ones would not be fixed properly. It was time to take the big leap solve all the design and materials issues in one hit and go to a new modern class. Laser dinghy farewell.

Read more about Laser rake variations Steve Cockerill.

Comparing Laser and Aero Foils

Aero Rudder

The first thing you notice when going from a Laser to an Aero is how responsive the boat is to the rudder and how light the rudder feels.

Upwind there is hardly any pressure on the tiller. Holding the tiller on a Laser upwind in a breeze puts real tension in the steering arm, there is significant weather helm, a big contributor to fore arm muscle strain.

Both boats need a lot of sheeting and this is hard on the sheeting arm. The Aero having a light helm gives one arm a break on each tack.

The Aero foils certainly look more efficient, the modern materials help and it is interesting to compare them.

The Laser rudder has a defined rake which is the cause the strong weather helm feel upwind. The Aero rudder is almost vertical.

Laser rudder

Both rudders probably have the same braking effect. When the two rudders are placed over each other they appear to have a similar surface area. The Aero rudder is longer and deeper in the water and has minimal rake which accounts for light weather helm feel.

The Aero rudder is very effective at steering while the Laser rudder lacks bite off the wind and down wind.

Downwind the Aero rudder actually works and the boat can be steered under rig adding to stability in 20+ knot runs.  The Aeros flat wide hull at the back also adds considerable stability.

Laser and Aero centre boards

Comparing the two centre boards, the Laser board seems to be a little larger, but not as deep in the water because it is raked back. The Aero centre board is deployed vertically and is skinnier and deeper.

On the water the Aero centre board is significantly better. There no vibration or humming when on plane, the board is properly fitted in its slot and does not ride up like the Laser board.

Aero rudder over Laser rudder

There is a trap to the Aero's more effective rudder and its light feel. Dinghy's are slowed by using the rudder, it acts as a brake.

Greater care has to be taken when using the rudder on the Aero,  it works so well to turn the boat it is tempting to over use it.  It is worth remembering Steve Cockerill's advice about using weight and sheeting to help steer.

Upwind on the in light/moderate breeze I hold the tiller extension as lightly as possible. This gives feedback to keep the boat flat just near the point where it is past flat and the balance changes to a lee helm.

The light hull weight means you have to scoot in and out a lot in puffy conditions. Fortunately the shape of the deck facilitates this, but more on this feature in future posts.