What made Pilot Cutter so fast? Just rumors?

[NewAlexandria]

Originally Posted by Don C L

Have you read "Sail Performance" by Marchaj? I highly recommend it. I think you'll enjoy it. It may have all the math you are looking for to help you.

I'm like 20 pages away from ordering that book. I left it for the end.

[TrentePieds]

NewAlexandria:

What, PRECISELY, are you hoping to achieve with your posts on this forum?

It should be clear to you, now that we are eighty-odd posts into it, that no-one is buying your arguments or lending credence to your singular point of view. So if you are hoping to teach us something new and wonderful, something totally overlooked by naval architects and practical seafarers for centuries, it clearly isn't working. You will need a new and better approach to teaching to achieve such a goal.

If your hope is to learn something from us that you may put towards the realization of a dream you have, then that, clearly, isn't working either. You will need a better approach to learning.

In my teaching days I had frequent need, given that the world is what it is, to put two maxims before my students: 1) "You cannot listen while you are speaking" and 2) "You cannot learn while you are objecting"

I for one should be most happy to give you a second hearing AFTER you have built your craft and sailed it from, shall we say, the Daugavgrivas breakwater to, shall we say, the Kolkas breakwater? Should it suit you better, I will, of course, accept as "proof of concept" a voyage across Dublin Bay rather than across the Gulf of Riga.

Until that adventure is behind you, and you have shown us irrefutably that it is, please don't be surprised if people with real experience of voyaging under sail are quite dismissive of what you have to say.

Veiksmi :-)

TrentePieds

[NewAlexandria]

You say we are 80 pages in. True, and no one mathematically or logically was able to disprove anything or even tried to. I would really enjoy and respect someone that actually tied. Every counter argument was totally off in terms of physics and logic. More, it showed total lack of understanding the subject and lack of reading carefully what I even write.

I'm not selling anything, and you should not be buying. This could become the biggest thread on the forum eventually if I follow through. And if I ever figure this out, I could develop software that would build optimal displacement sailboat automatically down to the size of every wire. All for free, open source. Anybody would be able to build one using a simple number: Water Line Length.

I enjoy my single point of view, and I would worry otherwise. If this is some kind of reedit echo chamber and you don't like the thread, you can delete it. I mean no harm to anyone's point of view.

[Bowdrie]

Originally Posted by NewAlexandria

And if I ever figure this out, I could develop software that would build optimal displacement sailboat automatically down to the size of every wire. All for free, open source. Anybody would be able to build one using a simple number: Water Line Length.

In the "old days", (before fiberglass allowed true mass production,) yachts were generally owned by those who had lots of money and free time and the boats were all different and from a multitude of designers.
What we call "Cruising" today was quite different back then. In those days a yachtsman might take his family/guests on a "cruise" along the New England coast for a few days, real "Voyaging" or living aboard was relatively uncommon.
So anyway, theirs's an old saying, "When two boats get together you have a race".
Sailors/designers quickly figured out that to win races the hull had to be designed to optimize up-wind sailing, that's the main factor needed to win on a triangular course.
About a 100 years ago David Taylor figured out that for every S/L ratio there is an optimum Prismatic Coefficient.
Since boats going up-wind are by definition moving at low S/L ratios designers moved towards hull forms/shapes that had a PC that was more-or-less matched to the S/L ratio of the boat going to windward in a wind strength where the boat could carry a full main and a working jib, (~100%).
Way back in the beginning of this thread you compared a Channel Cutter with a W32, and had questions about their differences?
Well, it's not just about WL, DL, SA/D, SA/wetted surface, or some others, the value of PC tells a lot about what point of sail the boat will be most efficient on, (given whatever power its sails can provide and how well the boat can "stand-up" to its sails,)
In the real world of pleasure sailing/cruising the MAX speed, (as you put it,) is a nebulous number.
A good designer uses empirical knowledge gained by those who proceeded him and hopes that his work can build on that.
As a result, a good design comes from a careful analysis of the requirements of the client, an SOP, a Statement of Purpose.
He, (the designer,) then juggles all the numbers/ratios to try to satisfy the client.
I fail to see how any magic "formula" will take the place of careful work by talented people.
As L. Francis Herreshoff said, "The most important attribute that a designer can cultivate is a sense of proportion".
I might add that a streak of "art" is also involved.
I see no formula that can replicate either Proportion or Art.

[NewAlexandria]

^ very good post. I am aware of the PC. I agree it's not just about WL, DL, SA/D, SA/wetted surface, but when you add all these factors that determine that perfect balance compromise for the type of boat, the Length to Width still have to be optimal. That perfect ratio exists for a specif type of boat. That's my assumption. It has to.

"A good designer uses empirical knowledge gained by those who proceeded him and hopes that his work can build on that." - that is exactly what I'm doing.

[Don C L]

Now what would be really great is if they could invent some way to get the hull out of the equation by getting it up out of the water when you get going really fast. Ah, one can only dream.

[NewAlexandria]

Originally Posted by Don C L

Now what would be really great is if they could invent some way to get the hull out of the equation by getting it up out of the water when you get going really fast. Ah, one can only dream.

Better yet = Dynamic Hull. It gets wider or thinner depending on conditions.

[Chris 249]

Originally Posted by NewAlexandria

No one has ever attempted it. The displacement sailboat would have to be 256 feet long to even attempt it. You can calculate that yourself once you read up on planing of a sailboat.


As far as your stability post, it does not work the way you assume,but you're not 100% wrong. You say once close to hull speed the trough is big and reduces the beam, which reduces stability. You are correct that lose of beam loses some initial stability, but Total Stability is not lost. It is gained. Read:

An object when standing still in water has only Initial Stability. It does not have stability from the momentum going forward. But the second it starts moving it's Total Stability keeps "growing" because of the force forward. Now you have to overcome the force from forward momentum plus initial stability in order to tip the object. The stability from the momentum forward is greater than initial stability especially at higher speeds. Hence very often people say (even on this forum) Initial Stability does not matter. I actually disagree with that, but will write about it another time. Below is the explanation why you should not worry about "big through" taking away your stability.

The second the boat moves it creates 2 waves and a through. First, waves are small and through is small. Small momentum stability is gained. The faster the boat goes, the bigger the waves, the bigger the through. The faster the boat moves the greater the momentum force forward, and the harder it is to tip her as you need to overcome 2 forces and 1 of them is gaining. It is a progression. It is not linear. So that fast speed at close to max hull speed produces so much stability that "lost" beam has no meaning. Hence you can take a "boat" that is 1 feet wide, 2 feet tall, and 24 feet long and push her on the water, she will actually go forward, but if you only put her still and let go, she will tip over. That's why some boats are 2.4 and some race boats are 5.0. They both have stability. Race boats at speed are stable. Even though they "lost" half the beam. It's the speed that gives you everything. Push a very drunk guy forward who can't stand on his feet. Momentum force is stronger.

More, the "through", is no magic either, it is water displacement, water from the middle moved away to the Bow and Stern. So beam lost in the middle is gained at the ends. So one could even made up an argument initial stability is gained if he wanted to. And since no one can calculate it, you can walk around and preach it.

Please stop being dishonest. Sailboats DO plane. I've already posted pics and videos of sailboats planing in this thread. Look at this; clearly planing as it must be to do 18.9 knots on a waterline of less than 14'



Here's the vid with 18.9 knots. You're just straight out lying if you claim that is not a sailboat planing.

Here's an older yacht planing, despite what you say;



Your "momentum stability" argument is just ridiculous and your claim about the bow and stern wave shows an amazing inability to look at reality. The vast majority of sailboats are narrower at the ends than in the middle. When pushed to hull speed, the bow wave is normally a few feet behind the bow and the sten wave at the transom. Those areas are narrower.

Here's a classic pic of a bunch of boats at hull speed. There's a big trough in the middle of the boat, reducing the waterline beam (and therefore stability) in that area. The stern wave is right aft where the boat is narrower. The average waterline beam - which is vital to stability - is therefore significantly narrower than at lower speeds. This causes a reduction in stability.

The claim that a moving body has more stability has no basis in physics or everyday reality.

I know about planing theory. I think the seminal Savitsky paper is on the web. You should try reading it.

It's a pity you can't even troll without being dishonest.

[Lee Jerry]

Originally Posted by NewAlexandria

You say we are 80 pages in. True, and no one mathematically or logically was able to disprove anything or even tried to. I would really enjoy and respect someone that actually tied. Every counter argument was totally off in terms of physics and logic. More, it showed total lack of understanding the subject and lack of reading carefully what I even write.

No one can disprove what you say because you talk nonsense. When they do make a point to demonstrate that you're wrong you just ignore it and go on as if the post doesn't exist. Requests for clarification go unanswered.

Some examples:

- You keep saying that hull speed is the top speed a displacement hull can travel. Many have pointed out this is not true. Not for the past century anyway. One poster recommended you look at the Wikipedia entry for "hull speed." Did you? Here are a couple excerpts from it:

Hull speed or displacement speed is the speed at which the wavelength of a vessel's bow wave is equal to the waterline length of the vessel. As boat speed increases from rest, the wavelength of the bow wave increases, and usually its crest-to-trough dimension (height) increases as well. When hull speed is exceeded, a vessel in displacement mode will appear to be climbing up the back of its bow wave.
.
.
.
This very sharp rise in resistance at speed/length ratio around 1.3 to 1.5 probably seemed insurmountable in early sailing ships and so became an apparent barrier. This led to the concept of hull speed.

Do you see where it says "seemed" and "apparent?" These mean it is not an actual barrier or limit.

I asked once, and I'll ask again: do you know where the 1.34 factor in the hull speed formula came from or what it means? If so, please explain it to me. If not, just say so and I can explain it to you. (Hint - it's not that hard; it's in the definition above.)

- When I ask what you mean by "optimal" you can't answer.

- When Don C L asks you what your definition of "stability" is you say "I don't have it, I don't fully understand it yet."

How can you use these terms when you don't even know what you mean by them, let alone if anyone agrees with your definition?


If you'd like to try to present a complete, coherent argument for your position, I'm sure several here that could help show you where you are wrong, either mathematically or logically or both. But you have to do your part first...

...if you can.

[Chris 249]

Originally Posted by NewAlexandria

^ very good post. I am aware of the PC. I agree it's not just about WL, DL, SA/D, SA/wetted surface, but when you add all these factors that determine that perfect balance compromise for the type of boat, the Length to Width still have to be optimal. That perfect ratio exists for a specif type of boat. That's my assumption. It has to.

Your assumption is wrong. A boat designed for the light winds of Long Island Sound requires more stability than a boat designed for San Francisco Bay, all else being roughly equal. The two craft therefore often perform better with different beams.

[NewAlexandria]

Originally Posted by Lee Jerry

No one can disprove what you say because you talk nonsense. When they do make a point to demonstrate that you're wrong you just ignore it and go on as if the post doesn't exist. Requests for clarification go unanswered.

Show me exactly where I did that and I will reply, unless it's so off the wall and lacks any kind of understanding that I simply feel bad for the guy and out of respect I won't answer. Chris 249 is that person, so I don't answer to avoid arguments. Not only he does not have an understanding between displacement sailboat and general "sailboat" concept. He shows these planning boats and compares them to displacement boats. On top of that he does not really understand planing, what the stern has to do during planing, at what speed planning even starts, but tells me to be dishonest.

If you read the books I did, and read carefully what I wrote you would see I did not invent anything. I simply took the books (by "naval architects" - which btw has god status here), learned from them, expended concepts, questioned some, improved some formulas to make it easy for me to compare apples to apples.

We are 7 pages in and guys still can't distinguish between displacement sailboat and generic sailboat word. They keep posting these boats, stories, myth busting. All great, but nothing to do with what I'm working with.

Anyway, wait for the Stability posts and more data. I need to read few other books and spent some time on it. I devote like 1% of my time to this now because I'm restoring 2 Kawasakis from the 80's during the day, so I have no time. I just need more time to nail it all out.

[Lee Jerry]

Originally Posted by NewAlexandria

Here are the formulas for Max Hull Speed. Both are flawed, but much better than Speed to Length Ratio. Speed to length ratio has no meaning actually. Not only is the speed wrong in that formula, it does not take hull shape into consideration, so you won't even know the difference between different sailboats. Btw, the coefficient in Speed to Length Ratio is used freely in sailboat design books, rendering different results for the same calculations.

As a matter of a fact WestSail 32 and a Pilot Cutter will have the same speed according to that formula. But both boats are on the opposite ends of the extreme when it comes to displacement sailboats.

Speed formula 1:
(Square Root of the Water Line Length * Water Line Length/Beam) / 2

Sailboat: Westsail 32
(5.24 * 2.5 ) / 2 = 6.55 knots


For those that say the beam is not enough to compare boats here is another approach:

Example 2:
Square Root of the Water Line Length * [(Water Line Lenght/Displacement)*1000]

Sailboat: Westsail 32
5.24 * [27.5/19500)*1000] = 7.38 knots


The speeds are wrong, but ironically much better than using Speed to Length Ration formula. BUT what is not wrong is this: The percentage difference between boat designs. You will be able to see that one boat has 15% or 20% advantage in speed over another boat. The advantage is manifested by how easy it is to push the boat to that speed. And those % numbers are correct.

Don't post explanation about kayaks or 5 degree entry on the hull boats. I'm talking about real sailboats with real hulls where entry is like 20 degrees PLUS. Anyway, you will probably have another 20 posts how this is all wrong, and it is in terms of actual speed, but not in terms of comparison. You can now actually compare boats on paper when it comes to speed. Both formulas basically compare how much water a boat has to push, and how easy it is to push that water for 1 boat vs the other. It's simple, it's handy, and it's the closest thing that exists right now.

Btw, every line you draw now, you will be able to recalculate and see what you did for the boat in terms of her speed ability.

You previously said:

Originally Posted by NewAlexandria

1. The speed to length ratio used by designers of 1.25 to 1.5 is silly. Not only it's wrong, it's used at will based on their "assumptions". Actually knowing the number is 1.34 I came up with 2 formulas (also wrong but 10 times better) to calculate correct speeds for different sailboats depending on hull design. My formulas will finally allow you to compare boats. The difference is big enough.

Now hull speed for the W32 is 7.03 kt.

Your first formula is a speed-to-length ratio of 1.25.
Your second formula is a speed-to-length ratio of 1.41.

How exactly are your formulas "10 times better?" Or better in any way?

[Lee Jerry]

Originally Posted by NewAlexandria

Show me exactly where I did that and I will reply, unless it's so off the wall and lacks any kind of understanding that I simply feel bad for the guy and out of respect I won't answer.
We are 7 pages in and guys still can't distinguish between displacement sailboat and generic sailboat word. They keep posting these boats, stories, myth busting. All great, but nothing to do with what I'm working with.

OK, how about in the rest of this very post that you clipped / ignored?

Why don't you answer this:

Originally Posted by Lee Jerry

Do you know where the 1.34 factor in the hull speed formula came from or what it means? If so, please explain it to me. If not, just say so and I can explain it to you.

Why don't you answer this:

Originally Posted by Lee Jerry

How can you use these terms when you don't even know what you mean by them, let alone if anyone agrees with your definition?

[Lee Jerry]

Originally Posted by Don C L

What is your definition of "stability?"

Your response is way, way more diplomatic than the dozen or so that ran through my head. They were all along the lines of WTF?

Ironically, the answer to both questions wouldn't be all that different.

[Don C L]

Originally Posted by Lee Jerry

Your response is way, way more diplomatic than the dozen or so that ran through my head. They were all along the lines of WTF?

Ironically, the answer to both questions wouldn't be all that different.

Perhaps I am a bit sympathetic. When I was a teenager I used to visit the maritime museum in San Francisco looking for examples to help confirm that the design I was working on was surely one of the finest and sure to become famous. And I wondered, why had no one had tried it yet? Even a bad idea can eventually evolve into a good one with a little humility, and patience, and perhaps a few kind words of encouragement. Maybe.
We are always free to ignore the thread, but I will say we may have drifted this thread too far off it’s original intent.