SailNet Community banner
  • SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!

I have a new blog entry on rudders

7K views 48 replies 15 participants last post by  bobperry 
#1 ·
It's a bit different from your typical designer article on rudders but I think it's interesting.
 

Attachments

See less See more
1
#3 ·
Andrew:
Yes please. I'd appreciate that.
I tried to do that but just could not find the right buttons.

I had James Judd from The Cone up for dinner last night. He's on his way back to Oz tomorrow for some CONE racing. He is renting the apartment that my son owns behind his house.
 
#7 ·
Len:
That's interesting. I don't recall seeing tubercles on any Orcas. Maybe I'm just not looking hard enough. You don't by chance have a pic of your old pal you could post do you?

Years ago designer Dave Pedrick tried to simulate the tip of a whale fin on some of his rudders but that effort did not catch on.
 
#8 · (Edited)
Borrowing from nature

Interesting post.

The swept back fin keels and rudders drawn by C&C and William Shaw at Pearson and others in the 70s also resembled natural fins of sharks or fish (no tuburcles, though).

The even older, traditional designs before computer assisted design showed similar natural looking curves and overhangs, producing some really beautiful boats (not the rule breakers).

It appears many yacht designers have now moved away from those more natural design features to the more modern, completely vertical keels and rudders, straight sheer, and very little overhang from racing boats.
 
#9 ·
James:
I agree that the old shapes were more "organic" and sweet to the eye. But the newer shapes work better if you are after boat speed and control. The trend in production cruiser racers almost always follows what the racing classes are doing. I think its a bit like putting a spoiler on the back of your Toyota. They want to look racy.

Overhangs have dissapeared because production builders want max volume for a given LOA. I could argue that overhangs like you see in the old boats are not very effective but I'd step on toes and piss people off. Overhangs are pretty but dangling a lot of boat out in the air does not displace any water so I don't buy the argument that overhangs increase sailing length. Yes, they do when they are immersed and in many cases they can be immersed particularily in the stern. I think the argument for overhangs today has to be a subjective one. They just look great.

Give me a minute to get my sand bags piled up before you attack.
 
#10 ·
I love it when design and engineering take a cue from nature. Good stuff Bob!

I get the idea that short overhangs increase volume, speed and efficiency if done correctly, but I don't want to sail an ugly boat even if it is fast and roomy for her LOA. I need a bit of salty overhang so I have something stare back at when it's time to leave the boat and head off to work.
 
#12 ·
Kwalt:
Yes, I agree. With a wide stern you can use some overghang aft to clean up the wake and gain some sailing length so you are not dragging the transom corners. Bow overhangs have pretty much dissapeared. I think it is a mistake to lump bow and stern overhang efficiency together. I like some bow overhang on my cruising boats so I can get the ground tackle clear of the stem.
 
#14 ·
Kwalt:
I'm not seeing tubercles on the Orca dorsal fin. They don't use that fin to generate power so I'm not sure why they would have tubercles there. I think, like the Humpback, you would see them on the pec fins but I don't see them there either. Do you?

Those are some great pics.
 
#15 ·
Good stuff.

No one is making the argument for reserve buoyancy in the ends and seakindly motion any more?

What do you think about the newer open transoms for oceangoing boats?

There have always seemed to be complaints about inadequate drainage in the traditional cockpit design, plus you eliminate the need for two more through-hulls that could fail.
 
#16 ·
James:
Not sure overhangs have much to do with seakindly motion. In fact, most boats with long overhangs would have more hull rocker so they might be more inclined to hobbyhorse.

Boats with fat sterns have plenty of "reserve buoyancy" compared to pointed ended double enders.

Open transoms are the easiest to drain as you say.
 
#18 ·
Smacker:
You were thinking of "Tubercules".

Very soon my blog will be attached to a site where I will be paid for hits. I can't give out the details yet. but it is happening.

I appreciate your kind words as ever. I'm having some fun with it and the traffic is quite good.

Still got the light on for you. You must have some reason to come to Seattle.
 
#19 ·
These tubernuckle things only appear on the humpback whale. Just curious as to why, if they are desirable, they don't appear on other mammals of the seas. It appears that the humpback pectoral fins are much longer than other those on other whales, not sure if this has any impact. What do they allow the humpback to do that is different than other whales?
Or is it just that a long time ago some warty whales were ostracized from the herd and started their own group and now these warts really just serve some sort of sexual purpose, in which case they would be even more suitable for sailboats.
 
#20 ·
Z;
Good question and I don't know the answer. Clearly the Orca has none. I'm not an expert on whale physiology so I wouldn't even try to guess why the Humpback has them. But if you pressed me I might say that it has to do with the amount of power the Humpback generates from the pec fins compared to the tail. The more power put into the pecs the more likely they would be to stall especially when swimming on the surface. When swimming deep I can't see them doing anything.

Yeah, that's it.

I did read the book FLUKE. So I got that going for me.

What I do know is that the designer who came up with them for ICON, Paul Bieker, is very smart. I pay attention to everything he does. A lot of people do. I also know the warts work on ICON according to the owner.

It's all fun.
 
#22 ·
Smacker:
I'm not drinking. I'll watch you drink.
I have now gone 23 days without drinking and I think I like it. I had a big Sunday dinner with company, roast beef and baked spuds with Caesar salad and while the others drank nice wines I drank tea. Tea is really not a good drink to go with dinner. But I'm a better cook when I am not drinking. I just, from time to time, find myself reaching out for that glass of wine that isn't there. Damn!

Good news is that I have lost 14 lbs. and I am looking my old kumite weight of 197 lbs. right in the eye. Beware of angry old guys.
 
#23 ·
If you ain't drinking I ain't drinking. We'll just sip tea on the porch and be angry and old to all the passers by. I already have the black knee-high support hose with suspenders and bermuda shorts to complete the motif. This could be fun.
 
#24 ·
That's actually the standard uniform of Australian angry old farts. With the obligatory short sheeved white shirt.

"Passers by"? There are no passers by up here unless you count seagulls, seals, sealions and bald eagles. I haven't seen anyone all day. I saw the mail truck go by but all I saw was an arm out the window. One of my clients signed me up for the NRA so I get a lot of mail.

I have no problem being around drinkers. I am not judgemental although I'm going to work on that.

It's blowing about 20 with gusts to 25 or so. Not the right weather to sit on the porch.
 
#25 · (Edited)
I think we still have a lot to learn with whales and fishes in what regards hydrodynamics:

The skin of a shark is like sand paper. Why is not smooth like silk?

Well, natural selection does not make mistakes in what concerns improvements and the shark is one of the oldest spices alive, quite primitive in some ways, but in what regards fundamentals is just a very efficient animal and one of the most important things for a sharp is speed.

It skin is not soft like silk because its rough skin works better in what regards hydrodynamics and makes it faster.

"The structure of the shark's skin is made up of tooth-like elements and of tiny grooves running parallel with its body. The grooves somehow mute the development of turbulence in the water that's being dragged by the moving shark.

The water that a boat or a fish or a swimmer drags with it is one of the major reasons it takes so much energy to move through water. A dolphin also has a special skin. It's soft and compliant. It yields to your touch.

People who can do the mathematics of fluid flow, struggle to describe the action of either a shark's or a dolphin's skin. If they ever manage to do so accurately, they might be able to create artificial skins for ships -- skins that would save an enormous amount of energy and greatly reduce fuel consumption."

If you want to know more download "Passive and Active Flow Control by Swimming Fishes and Mammals" from F.E. Fish and G.V. Lauder. Just google it and you can download the full paper.

I know that experiences have been made in navy submarines (and those are top secret) and even on Americas cup boats (these ones without any conclusive result) but I dream the day I would put some anti-vegetative with a rough touch, to help to improve boat speed:D

Regards

Paulo
 
#27 · (Edited)
Bob,

I looked at van Nierop et al. and there seems to be something of a tradeoff here. They compared foils with smooth leading edges to foils with varying sizes of tubercles, but otherwise similar shapes. They found that the smooth foils had the highest coefficient of lift (Cl), but that the relationship between Cl and angle of attack had an abrupt inflection point at about 12 degrees (i.e., the foil stalled very suddenly at 12 degrees). In contrast, if tubercles were added to the leading edge the foil, the peak lift coefficient was reduced somewhat, but higher angles of attack could be used without a resultant stall. They show that a smooth foil had a peak Cl of about 1.2 at about 12 degrees, with the aforementioned precipitous drop-off in lift above 12 degrees. Their "tubercled" foils had a peak Cl as low as about 0.9, but a much flatter Cl/angle of attack curve at stall. (Note: The foils used in van Nierop et al. have tubercles along the entire leading edge, rather than just near the root of the foil, as in the pic on Bob's blog. So I suspect that the relationship between angle of attack and Cl would be a bit different for the actual boat rudder in the pic.)

Correct me if I'm misinterpreting things here, but it seems to me that a smooth foil should in theory give one the best performance, but the tubercles give the helmsman some feedback before the stall actually occurs. This would allow the helmsman better control, at the sacrifice of a bit of rudder performance.

EDIT: Changed "Cf" to "Cl" (my bad; I just reviewed a paper earlier today that was full of references to coefficient of friction, Cf; in other words, Duh)
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top