What made Pilot Cutter so fast? Just rumors?

[sanibel sailor]

Amazing how a bunch of smart and very experienced naval architects and yacht designers haven't yet figured out these secrets that you have discovered.

[TrentePieds]

Prolly cos they've been too busy to read Smith - let alone Marx :-)!

TP

[Bowdrie]

OP, start at the basics, read the simplified version as posted by Wikipedia.
https://en.wikipedia.org/wiki/Hull_speed
Perhaps read it ten times before you get back to us.
Once again, you'll see that the #1.34 can be exceeded with some rather specific hull characteristics, (and lots of power).
Pleasure sailboats of displacement type?
Now that's a tall order.

[NewAlexandria]

"Once again, you'll see that the #1.34 can be exceeded with some rather specific hull characteristics, (and lots of power)." - Show me.

No "specific" hull characteristics can overcome the wave speed according to the wave speed theory. Object movement in water is not limited by object "characteristics". If you push two objects in the water, one long and thin, and the other same long but "fat", both have the same MAX speed in water.

I'm obviously wasting my time here, at this point. You can believe whatever you want. About 2000 thousands years ago, JESUS, Mohamand and Messiah walked the planet. No one that lives on this planet now have seen them, but they all believe in them, even though only 1 of the 3 could have been walking the planet and they all mutually exclude themselves.

Good luck.

[sanibel sailor]

Since the constant derives from the speed of wave travel, and that speed is dependent upon the material and its density, perhaps the OP has a plan to alter the density of water.

[Bowdrie]

Originally Posted by NewAlexandria

"Once again, you'll see that the #1.34 can be exceeded with some rather specific hull characteristics, (and lots of power)." - Show me.

No "specific" hull characteristics can overcome the wave speed according to the wave speed theory.

You're becoming pedantic, and obviously incapable of simply doing some internet searches.
Here's a hint, type in "Gearing class destroyer".
Check the speed, check the waterline length, do the math.
If you read the Wiki article you would have already known that the numbers can approach ~1.7, you would also know that a human powered racing kayak will exceed TWICE the "Theoretical hull speed".
Note, the racing kayak IS a displacement hull.
Give it a break New Alexandria, you're becoming "Old Alexandria".

[NewAlexandria]

@Bowdrie, not gonna reply to you anymore, you bend info to support yourself. Look at that Kayak again. It's flat. I said clearly sailboat that can't plan.

@sanibel sailor Wave Speed is not dependent on material and density. If that was the case people would build boats out of 1 material only for speed. I have no idea where you came up with this, but the original theory does not care for density. Density if fixed in the theory. And Water is not aware of material density, it is only aware of the force caused by the hull pushing it. But your post on the surface sounds smart

[wholybee]

Originally Posted by NewAlexandria

@Bowdrie, not gonna reply to you anymore, you bend info to support yourself. Look at that Kayak again. It's flat. I said clearly sailboat that can't plan.

@sanibel sailor Wave Speed is not dependent on material and density. If that was the case people would build boats out of 1 material only for speed. I have no idea where you came up with this, but the original theory does not care for density. Density if fixed in the theory. And Water is not aware of material density, it is only aware of the force caused by the hull pushing it. But your post on the surface sounds smart

An article on hull shapes and features that will exceed the 1.34 speed/length ratio-without planing. This is modern monohull cruising designs.

https://www.yachtingmonthly.com/sail...eed-myth-82832

The speed of a wave in water is absolutely dependent on density, and other factors.

https://spark.iop.org/speed-water-waves

[NewAlexandria]

Thanks for the link. Give me few days to reread it and recalculate. I already see why he wrote this, it has nothing to do with what I said, but I will give it few days, re read it, and reply.

Also, you say speed of wave in water is dependent by density of water. I agree with that obviously. I thought you meant density of the hulls material. But even though you're correct the Wave Speed 1.35 theory does not take density into consideration. And it shouldn't. In a given density the MAX speed is constant for all the sailboats of that water line length.

[Lee Jerry]

Originally Posted by NewAlexandria

One day I will create a post here on displacement boats, how they actually work, how to design one using super easy formulas, how to make them go fast easily, etc. Once I actually fully figure it all out. More, I can show you how to design software that can build the most optimal boat for you using 1 number given by you. It's all easy, but requires work. I'm on my 4th book almost and I can leave you off with some food for thought before I write my chapter.

Originally Posted by NewAlexandria

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.

Originally Posted by NewAlexandria

2. Being able to calculate speed correctly using my formulas you will be able to take all sailboats in existence and truly evaluate their hulls. This will remove marketing/hype/glory/shame from some boats. I already checked and was surprised.

Originally Posted by NewAlexandria

I already played with BEAMs of the boat, and I think I found the perfect ratios for that, but I have no way of proving it mathematically yet.

Originally Posted by NewAlexandria

But I wanted to remove the guessing and have a simple formula (btw my formulas are insanely simply, anybody here will calculate it with in few seconds) that gives us optimal designs.

I would be very interested in seeing what you've come up with. I hope you're not just a troll and actually present something.

Originally Posted by NewAlexandria

There is a method to calculate the MAX hull speed of a sailboat using hull's water line and made up speed to length ratio.

There's no such thing as "MAX hull speed." There's just "hull speed" and it's not a limit. It's just a data point.

Originally Posted by NewAlexandria

Yes, both formulas calculate the same thing, but they contradict each other. One mutually excludes the other. Either waves move with this speed and the boat speed can't be calculated separately from the wave speed, or there is no wave speed and sailboats can sail at any imaginary speed you come with.

No, they aren't calculating the same thing. No, they don't exclude each other. Hull speed is calculating the speed of a wave with a length equal to the waterline length. The other speed-length ratios are just other speeds / wavelengths. None of them are a limit. (They might be a design speed or design point, but not a limit.)

Originally Posted by NewAlexandria

We all agree there is such a thing as the most optimal hull.

No, we don't. Boat/ship/yacht design is an exercise in compromise and decisions. How you do you define "optimal?" How do you account for different requirements?

Originally Posted by NewAlexandria

I said an object in the water has to travel faster than the waves it creates in order to go faster than 1.34. Prove me it's not true. And if you do the Wave Speed theory is wrong. Read 10 times what I wrote and spend a month before you reply. Examples of some boat someone said went this and that has no meaning in physics.

The vessel is creating the wave. The wave is traveling at the same speed as the vessel. The vessel CANNOT travel faster than the wave. (Nor slower.) The wavelength corresponds to the speed.

Perhaps what you meant is that to exceed hull speed, the vessel needs to "climb" its own bow wave. That is (sort of) true. But there are ways around that and hull speed is not a limit. The SIZE of the bow wave is dependent on several (interrelated) factors, such as displacement and its distribution, L/B ratio, fineness of the entry/bow shape, etc. And the size of the bow wave determines how difficult it is/would be to "climb" it. Some ways to exceed hull speed include: brute force (i.e. more power, whether sail or dead dinosaurs), more waterline (the "effective waterline length" can change as the wave forms and as a sailboat heels), and cutting through the wave (rather than climbing over it). So light weight, fine entry equals smaller bow wave easier to "climb."

Originally Posted by NewAlexandria

Better, show me a sailboat that pushes waves and stays in water but passed the waves. Not a single picture of that because it's not physically possible. You can't have an object move in the water and not push the water. Length and power has no meaning here. It's not length or power that limits MAX speed of a sailboat.

Originally Posted by NewAlexandria

"Once again, you'll see that the #1.34 can be exceeded with some rather specific hull characteristics, (and lots of power)." - Show me.

OK. Easy peasy.

Any beach cat. Here's a Hobie 16. Hull speed would be about 5 kt. They go a lot faster. No dynamic lift from the V-shaped hulls.



Here's another - 52ft catamaran "Afterburner." Hull speed 9.7 kt.

See the round aft sections? See no straight buttock lines (if that means anything to you)? No planing going on. In the first pic (from stbd aft quarter), you can see the bow wave and the trough at or behind the stern. (The next peak is lost in the later confused seas.) She appears to be going about twice hull speed.

But if that doesn't do it for you, here's some data. She completed the 2013 Newport - Ensenada race, about 125 nm, in 7h 47m 11s elapsed time. That's an average VMG (or VMC, but not boat speed) of over 16 kt. Needless to say, she probably travelled a longer distance and surely hit even higher speeds. Well above hull speed.


Finally, not a picture of it happening, but here are the polars from my boat (Hylas 46, a moderate displacement cruising boat) and a profile view. 40 ft waterline gives an 8.5 kt hull speed.

I've highlighted the hull speed ring labels. See all the lines outside that ring? That's my displacement boat going faster than hull speed. Again, round aft sections and buttocks - no planing. Of course, these are just predictions from one of those egotistical designers you mentioned. But I've hit those speeds, greater than hull speed, without surfing (broad reaching with white sails, if that means anything to you); when we approach 10 kt it's (past) time to reduce sail. (Surfing often does accompany this, though, since the waves are there, but not always.) This is more of a brute force example.

Originally Posted by NewAlexandria

About 2000 thousands years ago, JESUS, Mohamand and Messiah walked the planet. No one that lives on this planet now have seen them, but they all believe in them, even though only 1 of the 3 could have been walking the planet and they all mutually exclude themselves.

Ummm...who's "Messiah?" No. Nevermind.

[NewAlexandria]

Originally Posted by Lee Jerry

I would be very interested in seeing what you've come up with. I hope you're not just a troll and actually present something.

There is MAX hull speed if there is Wave Speed theory. More, MAX hull speed is the same as Wave Speed. It's not a data point,because Wave Speed is not a data point. But I agree MAX hull speed is a copy of Wave Speed.

They are "trying" to calculate the same thing. It's the Wave Speed that dictates MAX hull speed. If I'm wrong, please show me how to by pass the Wave Speed without planing. Yes they excluding each other.

" The other speed-length ratios are just other speeds / wavelengths" - define what you mean "other speeds".

Wave Speed is the limit to the MAX speed of the hull. Hence constant 1.34
Either there is no limit like you are saying, or there is no 1.34. One or the other, but not both.

Good question on Optimal Hull. I did not want to go into this subject as it's the most complicated, but I would love to calculate this as my final accomplishment. By optimal I only mean Stability and Speed. I already know the optimal ratio when boat is stading still in still water. It is 2.0. Half circle. But obviously boats are moving and water is moving. I need way more research to find the sweet spot. I speculate I know what it is, but no way to prove it, so I don't mention it. Since there is compromise, it's mathematically possible to calcuate it. The first book I read says you can't calculate it, but that's wrong. There is a way. More, humans through out history were able to get very close to the optimal hull design by using: experience, eyes, feel, testing, sailing.

"The vessel is creating the wave. The wave is traveling at the same speed as the vessel. The vessel CANNOT travel faster than the wave. (Nor slower.) The wavelength corresponds to the speed." - no idea what your point is here, but we agree 100%. That's what I said or intended to say. BTW in this statement you do verify my point and contradict your initial statement.

Now, on Easy peasy. You are 100% correct. Except I was not talking about those boats you are using as an example.

Neither was I talking about boats the other guy is using in his article. "LESS than 5 DEGREES "angle exists on ZERO displacement sailboats. Bending of information to BUST myths that don't exist in the first place is not for me. I like authentic data and physics with apples to apples comparison.

[NewAlexandria]

And no, I'm not trolling, this is slowly turning into a good discussion.

[Chris 249]

Originally Posted by NewAlexandria

"Once again, you'll see that the #1.34 can be exceeded with some rather specific hull characteristics, (and lots of power)." - Show me.

No "specific" hull characteristics can overcome the wave speed according to the wave speed theory. Object movement in water is not limited by object "characteristics". If you push two objects in the water, one long and thin, and the other same long but "fat", both have the same MAX speed in water.

I'm obviously wasting my time here, at this point. You can believe whatever you want. About 2000 thousands years ago, JESUS, Mohamand and Messiah walked the planet. No one that lives on this planet now have seen them, but they all believe in them, even though only 1 of the 3 could have been walking the planet and they all mutually exclude themselves.

Good luck.

You're wasting your time because you don't understand the maths, the science or sailing. As you have already been told, both destroyers and multis prove that you are wrong.

I used to sail against Afterburner (pictured above) and my wife and I have owned a Tornado, F16 type, Hobie 20 and now have an 18 ft Formula 18 cat. It regularly goest far faster than its hull speed, as do a vast number of multihulls. It does this because the slender hull is like a destroyers and therefore the wave drag is small. Because the wave drag is small, it is not a limiting factor.

Only those who are totally ignorant of sailing or of dubious sanity would not be aware that a fast cat can go far faster than its "hull speed" and have seen that regularly.

I think you also don't understand history. The speed/length ratio was created by Froude, who worked out that was linked to wave speed. The two are not independent; they work together.

Here's a simple way to prove that you are wrong. Go to a toy or hobby store and buy a small displacement hull toy or model sailboat. Tie it to a string and run flat out through shallow water. You will find that a displacement hull CAN exceed hull speed, just as generations of children have done.

And maybe then you can stop being so arrogant and self-worshipping. It's just illogical for you to claim that all the yacht, freighter, workboat, ferry, powerboat and naval ship designers and users are morons and you are a god-like creature who is the first one in 200 years to see the light.

Also I just saw that you wrote that sailboats can't plane. That merely shows that you are incredibly ignorant of performance sailboats.

. Richard Bennett photo


Lunsmann pic



https://youtu.be/9LTRO8n_tqg?t=192

https://youtu.be/0Mu3st2RCZM
https://youtu.be/0Mu3st2RCZM

[Lee Jerry]

Originally Posted by NewAlexandria

There is MAX hull speed if there is Wave Speed theory. More, MAX hull speed is the same as Wave Speed. It's not a data point,because Wave Speed is not a data point. But I agree MAX hull speed is a copy of Wave Speed.

They are "trying" to calculate the same thing. It's the Wave Speed that dictates MAX hull speed. If I'm wrong, please show me how to by pass the Wave Speed without planing. Yes they excluding each other.

I think it might be best if you defined (again) your two opposing theories better. Particularly what you specifically mean by "Wave Speed" theory. And then, what is it that they are both trying to calculate?

Because this sentence makes no sense: "please show me how to by pass the Wave Speed without planing." Which makes it hard to answer without knowing we are on the same page.

Originally Posted by NewAlexandria

" The other speed-length ratios are just other speeds / wavelengths" - define what you mean "other speeds".

Speeds, and therefore speed-length ratios, other than hull speed (S-L of 1.34*sqrt(LWL)).

Originally Posted by NewAlexandria

Wave Speed is the limit to the MAX speed of the hull. Hence constant 1.34
Either there is no limit like you are saying, or there is no 1.34. One or the other, but not both.

Again, I'll wait for your detailed definition, because this sentence also makes no sense.

However, I will ask if you know where the 1.34 value comes from? Would it help if I explained it to you?

Originally Posted by NewAlexandria

Good question on Optimal Hull. I did not want to go into this subject as it's the most complicated, but I would love to calculate this as my final accomplishment. By optimal I only mean Stability and Speed. I already know the optimal ratio when boat is stading still in still water. It is 2.0. Half circle. But obviously boats are moving and water is moving. I need way more research to find the sweet spot. I speculate I know what it is, but no way to prove it, so I don't mention it. Since there is compromise, it's mathematically possible to calcuate it. The first book I read says you can't calculate it, but that's wrong. There is a way. More, humans through out history were able to get very close to the optimal hull design by using: experience, eyes, feel, testing, sailing.

This paragraph makes no sense to me and in no way answers the questions(s).

Is your "optimal hull" equally optimal for a couple to day sail on a lake as it is for a family of four to cruise around the world?

Originally Posted by NewAlexandria

"The vessel is creating the wave. The wave is traveling at the same speed as the vessel. The vessel CANNOT travel faster than the wave. (Nor slower.) The wavelength corresponds to the speed." - no idea what your point is here, but we agree 100%. That's what I said or intended to say. BTW in this statement you do verify my point and contradict your initial statement.

No sir, you don't understand.

If the vessel is travelling at v=1.34*sqrt(LWL), then the wave is traveling at v=1.34*sqrt(LWL).
If the vessel is travelling at v=1.0*sqrt(LWL), then the wave is traveling at v=1.0*sqrt(LWL).
If the vessel is travelling at v=1.5*sqrt(LWL), then the wave is traveling at v=1.5*sqrt(LWL).
If the vessel is travelling at v=2.0*sqrt(LWL), then the wave is traveling at v=2.0*sqrt(LWL).

That is most certainly not what you said. I have no idea what you meant. What you said was "...has to travel faster than the waves it creates...," which is not possible. That is the point.

And none of this bit says anything about whether or not a displacement boat can exceed hull speed (which it can), only that if it did the speeds are the same.

Originally Posted by NewAlexandria

Now, on Easy peasy. You are 100% correct. Except I was not talking about those boats you are using as an example.

How / why are you not talking about those three examples?

They are three examples of vessels that exactly meet your criteria* (that was: "show me a sailboat that pushes waves and stays in water but passed the waves. Not a single picture of that because it's not physically possible") and DISPROVE YOUR POINT. They are three displacement boats, that are only supported by buoyant forces (yes, that's redundant), i.e. "pushes waves," and can sail faster than hull speed.

Are you familiar with the concepts of confirmation bias and belief perseverance?


* They don't actually "pass the waves" since as previously mentioned that is not possible. But they do exceed hull speed, which I think is what you actually meant here. The bow wave just has a wavelength longer than the LWL now.

[catsketcher]

I reckon it's time for everyone to add someone to their ignore list.