Saturday, April 26, 2014

RS Aero Spotlight: Hull



Here is the first of what I expect will be a series of videos from RS Sailing about different aspects of the RS Aero design. This one is about the hull.

I'm not a boat designer so I don't totally understand all the implications of some of the technical details discussed here. Perhaps some of my more expert readers can weigh in on such questions as….

Does a long chine really make the boat extremely stable on all points of sailing? And what do they mean by stability? It's easy to steer it in a straight line or it's hard to capsize it?

Does the fact that a heavier person won't have much more wetted surface than a light person mean that the boat will be almost as fast in light airs for a heavy sailor? Especially considering he might well be sailing with a larger sail?

Did I hear Jo right? The chine "peels the spray off" which "reduces the spray drag on the topsides"? I had never heard of spray drag on topsides before. Is that a euphemism for "waves smashing into the sailor's head is not fast"? Does this mean it will be a drier ride than a Laser?

What's the significance of that point about planing with the bow high "keeps a very safe manner of sailing for all skills"? It won't capsize very easily on a reach? The bow won't dig into the waves downwind?

Spot any other interesting features about the boat?

Any idea where this video was shot?


19 comments:

Bursledon Blogger said...

I get the chine and the wetted surface, but with modern CAD what did they do for 3 years - sit around trying to make their minds up?

Baydog said...

UK?

Tillerman said...

Good point BB. But can CAD simulate how a boat will actually perform in different wind speeds and wave conditions? I would rather buy a boat that has had several years of trials and improvements rather than one straight off some designer's CAD program.

Good guess Baydog. Whatever gave you that idea? I think it's definitely east of the Mississippi (in-joke.) Can anyone else be more specific?

O Docker said...


It must be a drier ride than the Laser if it doesn't capsize as much.

Tillerman said...

Baydog's humor must be drier than O Docker's if he uses fewer words.

torrid said...

Very effective marketing video.

Baydog said...

Rutland Sailing Club?

Chris Partridge said...

Looks like at least two locations. Jo Richards has the chimney of Fawley power station behind him, so it was probably filmed at Lee on the Solent. Several of the action shots are definitely at Hayling Island Sailing Club.

Tillerman said...

Ahah. A little local knowledge helps. I'm going with Chris's answers.

Sam Chapin said...

You will love it. Nice stable plane. Tillerwoman can even carry it up the beach for you

Tillerman said...

True Sam. She's a keeper.

Anonymous said...

So £4870 but not trolley? Sounds familiar.

R

Tillerman said...

You can get a trolley (or a dolly as we call it in the US) for the Aero. I think I will need one, in spite of all the macho photos and video of it being carried by one guy. But yes, that is not included in the quoted launch price for the boat.

Tweezerman said...

The hull looks to be (when looking at the photos) a modified wedge with the max waterline beam shoved towards the transom (the more modern way of looking for better hi-wind speed). The key to this program is not so much the hull as the very light weight (60 lbs less than the Laser) and a modern rig which will be much easier to depower using cunningham and vang.

Full length chines do not guarantee stability in and of itself, it is how they are combined with section shape - in this case it looks very flat, which is, of course, stable. One of my Classic Moths had full length chines on a narrow V'd shape and I didn't notice the chines adding anything to the stability.

Having chines cut down spray drag when planing is true but you have to balance this against increased drag from cross-flow upwind when the boat is making leeway. The Laser does a good job of cutting down the spray that reaches the helmsman with thatt massive turned down gunwhale (but the Laser is low freeboard and it becomes a fire-hose when things really light up).

The claim that moving buoyancy aft (which is typical of a wedge type hull) making the hull safer by raising the bow seems to me marketing malarkey. When the skipper is 3X the hull weight, it is where the skipper sits that makes the most difference, a wedge shape should support the skippers weight further aft - which keeps the bow up.

When I look at photos of the hull, there are a couple of question marks (all yacht design is compromise) but the RS group has done their homework. Best to wait for the on-the-water consensus when there are more Aero's out there among the sailing population

Tillerman said...

Thanks Tweezerman for those insights. That's exactly the kind of expert opinion I was looking for.

Could you expand on that point about "increased drag from cross-flow upwind when the boat is making leeway." I really don't understand what you are getting at there.

Tweezerman said...

All sailing hulls make leeway, in otherwards as they go forward, they also go sideways some (this is how we get the daggerboard to work - it needs some angle of attack to produce lift), a sideways drift somewhere in the neighborhood of 3-4 degrees (some more than others, the Sunfish has more leeway than the Laser). This means the water flow is not coming directly from the stem but somewhat across the hull. A chine that is near the waterline now becomes a bump which the waterflow has to cross, hence some added resistance. Designers will argue back and forth the significance of this - some believing it adds measurable resistance, some - not so much. I think with the RS Aero, the much greater efficiency of the modern rig much outweighs any harm the chines may be doing upwind.

Conversely the benefit of having chines peel off water spray really only comes into play when there is a really fast reach - conditions that are not that prevalent during the summer winds on the East Coast (at least in the Chesapeake, or the lakes).

Tweezerman said...

I should clarify that leeway applies when sailing upwind.

Tillerman said...

OK. I think I understand now. Thanks very much Tweezerman.

Chris Williams said...

I was wondering if the chine would in fact *improve* upwind performance by reducing sideways drift in the same way a "hard" rail on windsurfer is supposed to (as compared to a "soft" rail).

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