I need mathmatic or physics assistance...Originally Posted by frank durant
Can someone help me understand the relationship between theoretical hull speed and the actual sailing capacities of these yachts. We did 7.2 the other day and I thought I was getting a bad reading or something - or just one FINE sailor. Frank put my speed to shame! I understand the theoretical hull speed mathmatical calculation, but why are these boats apparently regularly far surpassing that?
Kyle
C-65 Lucky Dawg
OK OK.....please re-read my post and you'll see "the 4 1/2 knot gulf stream push had NOTHING to do with it...honest".......and if ya believe that...well......
(the speed over ground was accurate,but I was near the appex of the gulf stream sailing N with it) Having said that...these designs DO surpass hull speed often, paticularly on any kind of reach. Remember that waterline increases as the boat heels.
Last edited by frank durant; 07-13-2007 at 10:04 AM.
breaking the speed barrier
No JEALOUSEY, yeah, jist a lousey sinking feeling of will I ever make it!
Well of course I will! the wind in my thinning scalp, the sand between my toes, the frosty at a beachfront cafe.......
But we do have this thread here that came along with the past intact!! That's cool and breezey.
As to exceeding the numbers for the A/C hull....
Let me just say this: I've seen 100s of hulls on the hard at the yard where I slave dilligently on Little Gull. Numbers be damned: the Ariel hull I'm working on is THE MOST PERFECT KEEL-HULL SHAPE ever conceived. From entry to bustle it is clean and true. The rudder at the end on the keel must make the least amount of fuss thru the water than any other.
The rounded angles of the hull at the forward waterline, the break in the blige amidship, the tuck and rise of the hull leaving the waterline at the stern. Without flaw. The sculpting of the ballast keel without any bulbous. As fine a stem entry sweeping into the bottom of the keel as can be imagined. I cannot see how any better, easier, shaping of this deep underbody that becomes the rudder can be done. It's all curves with a single purpose of slipping 5500 pounds thru the water. No bumps, no flats , no wingy-thingys.
The underbody shape of the Ariel is without flaw. This is the essence of the word finesse. I haven't seen it better anywhere. Not even the folkboat. Not talking engineering, talking bout that warm feeling you get when something LOOKS right.
that gorgeous babe will let me touch her!!!
I'd guess much less fuss than a fin keel and rudder on a skeg or stand alone. When this kind of underbody turns even slightly, eddys are made, and while by definition you get lift you also get the water being glued to the boat on the other side. How much wetted surface there is in relation to weight is important in the dinghy/finkeel shape underbodies currently in fashion.
But I think the rounded, natural, fish like underbody on 338 is as near to perfection any boat of this type has even been conceived. Carl Alberg, who never let anyone mess with his lines, and I guess, with the many boats of all sizes he drew, certainly experienced a sort of swedish satori which produced the perfectly proportioned waterline and underbody on the Ariel/Commander. How often did he repeat it? Every enlightened line came together to blossom as the true nature of sailboat.
Alberg's own sailboat was C-302. Isn't that so? WHY? Did he know something we don't know?
It's beyond the measly numbers and the comfortable BS of yacht design formulas. Because that garbage can't explain why the Ariel goes faster or looks better than it's supposed to. Can they? Certain socalled inanimate objects sometimes make it over to the magical side. The Ensign? The Alberg 30? The Triton? NOPE, only the Ariel/Commander made it to this other side.
Last edited by ebb; 07-13-2007 at 02:26 PM.
Ebb, we were writing at the same time!
this is re Frank's response.
----
Right, I did read that! I'm sure you're glad you weren't going against it.
Nonetheless, 5.76 knots isn't really an accurate estimate of our hull speed. I doubt that my 7.2 is top speed. Likely "theoretical" hull speed doesn't calculate actual sailing but just the mass of a boat at rest at the waterline/sail area/water density/etc - and therefore everyone's hull speed is simply a comparable average that isn't exactly true to the real sailing of each boat.
So the question "what will she do?" stands...
I know I sound hung up on this heel and speed thingbut I am really just curious
Last edited by Lucky Dawg; 07-13-2007 at 10:54 AM. Reason: Ebb beat me to it...
Kyle
C-65 Lucky Dawg
Please...argue with Ebb..get another responce.I really like reading his 'poetry'. He writes to the extreme of his detailed boat restoration. These craft ARE beautiful..they DO sail extremely well...their motion IS great....but Ebb puts the same facts down SOOooo much better
The theory is that a displacement boat can't get over the bow wave it creates going through the water and get up on plane
Heeling the boat gives it a longer waterline and spreads the distance between the bow and stern wave, allowing greater speed
So, to answer your question, I have no idea.
I just like to look at pictures
Last edited by commanderpete; 07-13-2007 at 12:05 PM.
C'Pete - now that's a convenient angle! You can wash your hands in the drink without leaving the comfort of your tiller-side seat.
Alas, these are likely just the idle questions of a single hander... Cripes I'm out there and the ol' noggin has to occupy itself with something!
The storm clouds have given up for the afternoon - I'm going sailing
Kyle
C-65 Lucky Dawg
Please...argue with Ebb..
Au contraire! Not arguing by any stretch - throwing my ignorance at the mercy of the well informed.
Last edited by Lucky Dawg; 07-18-2007 at 08:41 PM.
Kyle
C-65 Lucky Dawg
The formula for theoretical hull speed (ths) is:
ths = SQRT(LWL) x 1.34
Therefore as the boat heels over, the LWL increases and therefore ths increses as well.
And just for the record, I am not a math major (far from it), but I found a great pearson website that had that, and other formulas, on it. Here it is.
Jack
Jack...now, heel the boat over and increase the length of the waterline(and speed) in the 4+knot gulf stream and she'll really fly
Frank... you are lucky, I have only ever had to race against the stream.
Jack
Pa-shaw
Thanks Jack for the lead to those Pearson numbers.
The number of times Bill Shaw's name is on that list shows us that Alberg's designs were the transitional datum for boats changing from wood to frp. The Ariel could have been designed for wood but while the topsides might remain the same (except for that amazing eliptical cabin front), the underbody would have had to have much less sculpting than what we have in the Ariel. Alberg designed a beautyful hybrid shape for the in-the-water part of the Ariel that may not have been surpassed by anyone since.
But Alberg's easy driven slack bilge designs were over taken by the Shaw wider beam, harder bilge, fin keel, spade rudder designs. The engineers and the techs stepped in to make lighter less wetted surface structures suited to glass and oweing little to past wood boats except that their impetus obviously came from rowing dinghies.
If you could make the keel and rudder more pliable and bendable you'd maybe get more speed, like whale shark and dolphin tails. I feel that the hard planes of modern sail dinghys actually limit speed by creating eddies. Of course we now have new generation sleds that are not really boats, but water-surface speed machines. Surfboats.
I wouldn't know, but has anyone read of a Bill Shaw sailboat exceeding its W/L rating? Well, surfing a swell, maybe.
I don't know how it goes, but engineered shapes are linear shapes to me, boxes with curves. Now if you took an ideal marine speed shape like a great white and translated that to a hull, you might have something. Might have something that relates to what Alberg came up with. Alberg's form is the SOFTEST hard form imaginable. Know what I mean? I bet that a bendy rudder/tail on an Ariel would make them go even faster. A little bendy, OK?
A good comparison of Alberg and Shaw is the Pearson Ariel and the Pearson 26. Alberg was the transitional designer - he put Pearson in the frp boat business. Shaw designed marketable leisure products for them. Not knocking it, there just is no accounting for taste.
Alberg never forgot that a boat should look like a boat.
There is a story of a transAtlantic race in which an Alberg 35 in a raging storm ended up taking all its sails off. While other boats freaked and struggled and broke things, the crew on the Alberg 35 went below and played cards while the boat lay a-hull.
You've seen this picture. A mighty storm, the whole world's coming loose, it's all gone to hell... but there's a gull bobbing UP and DOWN in the waves, waiting, maybe a bent feather, no problem.
Is the word Sea-kindly?
Last edited by ebb; 09-19-2007 at 03:32 PM.
Ebb, I agree with you... in fact I think a few modern designers agree with you as well. I just went to the Newport boat show and a couple of the "new" designs look very Alberg-ish. Soft gradual curves, few to no hard edges. The biggest difference is their use of a fin keel and spade rudder.
I asked a few of the dealers about the benefits of their "new" design. I followed up their long winded answers by asking them if they felt their boat were very similar to classic Alberg designs. All I got were confused looks and a few stammers.
Jack
Das Boot is still alive and well - I'm glad to hear you like that picture of her last year. When we get waves in Chicago, she pitches excitedly, spraying crew plentiful at times. It's part of the fun.
You lucky people in the Bay area - your season never ends. We have to start worrying about winter storage here...
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