A tenth of a knot, eh? . . Well now, that's worth trying. Could equal many boat lengths at the finish of a race . . .
A tenth of a knot, eh? . . Well now, that's worth trying. Could equal many boat lengths at the finish of a race . . .
LOL - Bill, I knew you would say that.
I really don't think you'd see near that much of an increase. Probably it would be more like a couple 1/100ths. (Which might still be a boat or so...)
Kurt - Ariel #422 Katie Marie
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sailFar.net
Small boats, long distances...
One design racing is soo competitive that if something will add to boat speed, no matter how slight, it's worth adopting. Hell, a 1/100 of knot would be worth it.
This photo posted on page 6 of Ebb's photo gallery. The design is taken from Alberg's lines drawing of the Ariel/Commander hull. It was likely added at one of the later drawing modification dates.
The rudder shape is similar to what is seen in mid 1960's and later heavy displacement designs. My guess is that it is more efficient and has less drag, but is not a pretty
Last edited by Bill; 02-28-2005 at 04:20 PM.
Hmmm... sounds like we need some more scientific way of proving this theory. Perhaps the association should sponsor a grant for me to make 2 (or more?) rudders. One perfectly flat, another with a certain taper. Observations will be made in various conditions i.e. wind speed, points of sailing, etc. Someone nuetral on the topic will verify the data and ensure the data taker(s) are reasonably sober. Thoughts???
Plywood too thin and the can too large.
Can see by quick History search we all had this words befor.
Yam gonna chord mah rudder, keeping it passably strate offen the keel awhile, not too much, and kinda fe e e el that mother in nice slow curves to the tip. No big letter chords, just pure technigue! This konsellation-style rudder lends itsel to shapely turns top to bottom.
There be no flat surfaces on ANY creature in the sea.
Y'all have in the A/C bottom the nicest curves there on any boat what has ever floated on water, it's almost criminal how animal that underwater shape IS. Personally can't abide that ear shaped appendage, jist naturally lean to that tip of a fin that wags there. Carl put that finny rudder on all subsequent designs of his, I believe. I know, I know, have to watch these emotions.
Last edited by ebb; 02-28-2005 at 06:54 PM.
From the peanut gallery: during my time spent on the ComPac site, when I was thinking I would be happy with a trailer sailer like the CP16 perhaps, one of the mods for this boat which reportedly had fantastic results, was changing from the stock aluminum flat rudder to a fiberglass rudder with a foiled shape: less vibration and more responsive tiller were some of the improvements reported.
A BIG difference I suppose is that the CP16 is not full keeled and has a detached rudder...
Ted Brewer
Someone asked for an expert opinion on rudders. Ted Brewer, well known yacht designer, wrote an article on rudders for the Sept/Oct 2002 edition of Good Old Boat magazine.* Here is what he had to say about keel-hung rudders, amongst other things.
"Many older boats, such as the Folkboats, Albergs . . .and similar classics are full-keel designs with the rudder hung on the aft end of the keel. Keel-hung rudders are traditional and can be one of two types: outboard rudders, with the rudder mounted on the transom or on the stern of a double-ender, or inboard rudders, with the rudder stock emerging through a rudder port in the hull. The latter is more efficient when the boat is well heeled and the rudder is put hard over as it is less likely to ventilate (suck air down the low-pressure side) and so lose lift and steering ability.
The difference in the two types is not critical to the average cruising skipper though, and thousands of outboard-rudder yachts have made long and successful voyages . . .
The profile of older-style, keel-hung rudders was generally almost a half-circle on the trailing edge, or shaped like half a heart. Tank testing in the late 1950's and early 1960's showed that the better shape was to have the rudder squared off at the bottom, parallel to the waterline." [Karl’s added rudder in the lines drawing fits the picture.]
"As well, the top of the inboard rudder should be carried very close to the hull so the gap between the rudder and the hull is as small as possible. Less than a quarter-inch is desirable, and the thickness of a well-worn dime is better yet. Tests have shown that a gap of even a half-inch can reduce rudder efficiency by almost 10 percent due to ventilation. It will also increase resistance by several percent due to crossflow across the top of the rudder from the high- to the low-pressure side."
Ted then goes into a discussion of spade rudders that includes foil thickness based on NACA calculations. In explaining the popularity of spade rudders, he writes, "The spade gives the best combination of minimal drag combined with maximum lift and turning moment for its area."
[*Brewer, Ted, Rudders, skegs, and spades . . ., Good Old Boat 26, vol. 5, no. 5, September/October, 2002, pp 22-25]
Interesting.
I wonder how you would fill the gap between the top of the rudder and the hull (and still be able to lift the rudder out if needed).
Something like rubber weatherstripping perhaps.
Last edited by commanderpete; 03-01-2005 at 06:46 AM.
I plan on using something sacrificial, like "good stuff" foam, shaped to the right size and clearance, then covered with a layer of F/G.
Or a strip of balsa wood.
-km
aka, "sell out"
S/V Beyond the Sea
C&C 35 mkIII
crazy ole ebb, he will have the top of the rudder flat (spelt p h l a t, not rounded) and have there a piece of wood like teak that is screwed in from the top - by swinging the rudder to one side and using a short driver or the small rightangle 12v.
And the top of the fairing piece on top of the rudder is also flat, exactly matching the V-SHAPE on the boat that is over top of the rudder. If you want to get technical.
The two holes thru the filler piece are oversize but countersunk so no threads of the screws engage it, just the flat heads. Top of rudder is drilt proper for screws. IMCO this is a fairing piece not requiring an act of congress to hold it on. IMCCO you want it not sacrificial, but rubber might be good, if you plan on going aground. Talk this out.
I would use bedding compound, NOT POLY. This filler/fairing piece will keep the rudder from coming out of the shoe until the rudder is put way over. You have to be able to lift the rudder out of the shoe to pull maintenance. And to put it back in again. So you don't want anything permanent on the top. When messing around with the rudder it would be more convenient to take the fairing piece off until work is finished.
Embedding a pair of C'pete's barrelnuts in the top of the rudder with corresponding machine screws holding the fairing piece on would be too high end for an Ariel.
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See cleats like those on your rudder on Tritons that come into the yard. Seems to me if you are looking for super hydrodynamic flowsure patterning why in hell put the cleats on cattywonkus? Those bars should be horizontal, somewhat closer to the stream of water passing over the hull. If two aren't enuf, put on three, or four, but on a waterline. Picky picky, sorry
Some might consider gluing on some hypolon flaps off the keel that would overlap the rudder, because that round rudder shaft there behind that squared off keel is creating vortexes that are slowing you down, too.
Last edited by ebb; 03-01-2005 at 04:37 PM.
Well, what about when you have a little bit of rudder angle? BAM! gap up on top again. Put a big ol' 'bump' on the bottm of the hull around the rudder tube that is flat on the bottom so the top of the rudder and the hull never wander away from each other? Trim the sails so the rudder remains dead center? Never look at the knot meter, instead focus on forming tan lines? (imagine CPete'esque photo attched here)
Good point there Tony. We'll leave it to the engineers. You should go sailing with Willie.
I'm gonna keep riding my old rudder until it decides to fall off.
The original shape certainly does work. I've never had the boat do an uncontrolled round-up no matter how far she heeled over.
Last edited by commanderpete; 03-01-2005 at 08:45 AM.
Besides, if you did change the shape you would need a new PHRF certificateOriginally Posted by commanderpete
That damn rudder is probably preventing me from bringing home the silver.
One time the Commitee Boat didn't even wait for me to finish. They just pulled anchor, went home and gave me a DNF.
The Indignity!
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