Drag reduction

[PeterF]

Hi all, I'm new here but I've been a background member for some time.
As well as boats, I'm also interested in aircraft, and I've recently been reading a discussion on another forum about some radical methods of drag reduction for aircraft. I've been wondering if they could they be transferred to the marine world?
http://www.oshkosh365.org/ok365_Disc...id=3339&page=1
It's a lot of reading, but there are some interesting concepts - natural laminar flow, non planar airfoils, span efficiency and wake immersed propulsion etc.
Obviously sailboats need to be just as efficient on both tacks, but there might be a way to apply the principles - especially with the increase of solid wing sails. Powerboats too.

[tunnels]

Originally Posted by PeterF

Hi all, I'm new here but I've been a background member for some time.
As well as boats, I'm also interested in aircraft, and I've recently been reading a discussion on another forum about some radical methods of drag reduction for aircraft. I've been wondering if they could they be transferred to the marine world?
http://www.oshkosh365.org/ok365_Disc...id=3339&page=1
It's a lot of reading, but there are some interesting concepts - natural laminar flow, non planar airfoils, span efficiency and wake immersed propulsion etc.
Obviously sailboats need to be just as efficient on both tacks, but there might be a way to apply the principles - especially with the increase of wing sails. Powerboats too.

With planes the same principle dont apply in most cases . boats have this thing called water to cntend with , its much harder and more dense that air so there we have hydrodynamics to consider !! if you get up enough speed and make your boat fly then you are smoken and crossed over into aerodynamics and immediatly into something else called surface effect !! Now we have things called Tunnel boats that go fast and do fly!! but not quite Just on the borderline !!,
Some do get airborne but thats unintentional and there no controls built in a boat for that!, so the usually out come is they crash in a screaming heap with lots spray and bits of boat everywhere . Need to watch F1 tunnels racing .

[Petros]

PeterF,

I have worked in the past in aerodynamics and yes there are a lot of similar principles than can be used to improve sailboat performance, and in some racing classes (where allowed) they do. The response by Tunnels above is not completely true (and a typical response from sailboat owners who usually do not know much about aerodynamics), the principles can be applied to the underwater surfaces (i.e. hull, keel and rudder) with great benefit in terms of performance, though sometimes at the sacrifice of ride comfort, so they are often used in racing applications only. And you will have to trust me on this, many basic concepts of aerodynamics are NOT intuitively obvious, that is why most peoples ideas about it are incorrect.

Aerodynamic drag reduction can also be applied to all above waterline surfaces as well, but the improvement will be small since the air speeds are relatively small compared to aircraft (or even road cars). In a race every advantage helps, but you also have practical considerations, and the racing class rules. A fully cantilevered mast, without all the cable stays and spreaders, will reduce drag and improve airflow over the sail surface (sails generate lift to drive the boat, so cleaning it up means less drag and more thrust), but it would drive weight of the rigging way up, and raise the cost of the mast drastically. The class rules are the single biggest road block to better sailboat designs, they limit what the boat will look like. Because of this the improvements in the many class of sailboats have only been in materials sciences, with only minor incremental gains in everything else. The few unlimited classes tend to have very different looking kind of boats, that are very practical for anything other than racing.

There is another practical consideration in non-racing boats, that is most customers of sailboats want their boats to look "traditional", not like a aircraft hull on its side with a wing instead of a sail. No matter the improvement, if you can not sell it, it has no practical matter. there have been lots of innovations in wings sails, but I do not think any have been commercial success.

Since virtually all of sailing is either sport or recreation, there is no commercial advantage to improve the designs. Since radically different designs can not be raced in most classes, and would not be popular recreational sailboats, there is not much of a market for them. There is no industry pressure to produce better designs. Most buyers want their sailboat to look like a sailboat, only a very few eccentrics would want their sailboat to look like a winged space ship, not much of a market to justify the development costs.

I thought about building a dingy or small cat to test out a variable camber wing sail I want to experiment with, but I do not see any real market for such an invention. It is just a hobby, other than perhaps trying to use the concept to set a new speed sailing record, it has no real application. And I do not see any commercial benefit to be the one to sail fastest on a short closed coarse. You get your name on a list in a web site, than what?

BTW, after skimming the EAA forum you posted above, most of those people do not know what they are talking about either. So do not take what any of them say as gospel, it is just another case of the blind leading the blind. They think copying laminar flow shapes will improve performance on their aircraft, they are not just wasting their time, but will likely get killed. Those specialized shapes may have gains in very limited speed ranges (Reynolds numbers), and only if the surface are kept clean and polished (kind of hard to do on a sailboat for any length of time). When specially developed laminar flow shapes are used in a non-laminar flow environment, their performance is even worse than conventional shapes, and can have very unpredictable properties (which is what can kill people in an aircraft). ON a sailboat the advantages would be very small, or nonexistent if the surfaces are not kept clean.

So there you have it. That is the reason you do not see a lot of innovation in sailboat design. For all practical purposes, the commercial development of the sailboat stopped after the invention of viable internal combustion engines. It is cheaper and more cost effective to get your passengers or cargo to port by burning diesel fuel than to use sails. So the only development in sailboats have been for sport or recreation, and a rich mans sport at that.

[PeterF]

Ok, that makes sense. I thought there must be some reason why practically all sail boats look identical!