What made Pilot Cutter so fast? Just rumors?

[NewAlexandria]

No conspiracy at all. Only to you because you are wrong. You all view things as if they were on land all the time, because on land apparent weight is equal to it's true weight. There is only gravity acting on all objects. No other force. You got used to this and you confuse force with mass. Every other kid in technical college knows that if apparent weight equals true weight objects sink, fall from the sky and etc.

I can use your own words against you and show you that you are wrong. You say my boat that weights on land is 464 lbs and she is 464 lbs in water. I apologize if that is not what you are saying. Let's assume you are correct 464 lbs is my weight of my boat in water. When we calculate the submerged part Fb = 7.44 * 1.94 * 32.2 we get her weight 464 lbs. So her weight is no longer in 36 cubic feet but it is in her 7.44 cubic feet up to her water line. So far good. Now, you also said there is something called reserve buoyancy above that. Well that means there is more boat above water line. That means there is more weight above water line. Which means more force. And more volume. So how come you are not calculating that additional force together with the bottom force? How come you calculate the forces for only 7.44 cubic feet if the boat is 36 feet? You can't calculate the force for 7.44 cubic feet ONLY and tell me there is extra force in reserve buoyancy. Either or. If there is extra force you need to add that.

Change the word "weight" to "force" and everything makes sense. My weight on land happens to be as my mass due to gravity only. No other force. Once in water, in space, on the Moon, on elevator, jumping up at home, my force is different and my mass is the same. I'm 180 lbs on land, am I also 180 lbs to you on the Moon?

The problem with land is that earth is dense and it's solid, you are not dropping into the inside of the Earth, and you are not floating in the earth. Gravity is the only think you have.

Go read college simple publications and they will explain you when boats sink:
Here is one: https://scienceclass.dreamhosters.co...20Buoyancy.pdf

Boats float because their apparent weight forces are negative. BUOYANT force is more than WEIGHT force. So therefore boat can't be 464 lbs in water. According to you BUOYANT force is equal boat's weight. Meaning, no BUOYANCY.

Fb = w - the w in here does not stand for weight of the boat. It stands for the weight of the water it displaces. My 7.44 cubic feet displace 464 lbs of water. If I push her down using 1782 more pounds she will displace exactly 2246 lbs. Her full weight force.

I'm leaving for 5 days into mountains to climb and ski. You guys have tons of time to recalculate this and prove me wrong. I'll be back.

[Adelie]

Originally Posted by NewAlexandria

No conspiracy at all. Only to you because you are wrong. You all view things as if they were on land all the time, because on land apparent weight is equal to it's true weight. There is only gravity acting on all objects. No other force. You got used to this and you confuse force with mass. Every other kid in technical college knows that if apparent weight equals true weight objects sink, fall from the sky and etc.

I can use your own words against you and show you that you are wrong. ...

How can it not be a conspiracy? You write that Marchaj lied. Most other naval architects agree with him on most matters and ALL others agree with him on how buoyancy works. If all naval architects are lying how can it not be a conspiracy?

How can you say that I am wrong? I have not made my beliefs known anywhere in this thread nor anywhere on CF. Since I have not written anywhere here about how buoyancy works how can you use my words against me? Are you reading my mind? Do I need to start wearing and aluminum foil hat? If I did would it keep you from reading my mind? Please stop reading my mind.

[Bowdrie]

Originally Posted by NewAlexandria

I'm leaving for 5 days into mountains to climb and ski. You guys have tons of time to recalculate this and prove me wrong. I'll be back.

Going skiing and climbing?
D**n it, you be careful.
If a tree jumps in front of you. you might not be able to type, and where would this thread go?
Watch how high you climb, the higher you go the less "apparent weight" you'll have.
If you get to high, you'll just "float" away and we'll have no more fun with this thread.

[MicHughV]

Take a rock with a known weight, say a 1 cf of concrete.....
On land this will weigh about 150 lbs...weigh it to be sure....
Once dropped into the water, buoyancy comes into play.....so subtract the amount of water the rock displaces....in this case 1 cf.....which is around 64 lbs ( 1 cf of water) to keep things simple.
Now tie a line to the rock and pick it up with a spring scale, you will note the rock now weighs 150 -64 or 106 lbs...
Now how can something that just weighed 150 lbs on land only be 106 lbs in water ??

It doesn't, it is still 150 lbs now supported by 64 lbs of buoyant force. Just as if another person is adding support.

Still don't get it. Try to pick up a man....say your neighbor....200 lbs...on land...can you do it....with a pit of huffing and puffing...maybe.
Now place that man in a swimming pool and pick him up while in the pool.....piece of cake. Why? The buoyancy of the water surrounding the man supports the man. Were that man to be completely immersed, you push him around with your little finger.
Man still weighs 200 lb, but is supported by the amount of water the man has displaced, which will be 200 lbs as he is now completely immersed.

Ok, will try one last example....we were going to use a "magic" brick as described above. ie, 1 cf of concrete weighing 150 lbs.
Throw it into a pool and what happens ? It sinks to the bottom as 1 cf of water has insufficient buoyance force to support the 1 cf of concrete.
Now insert a straw into the 1 cf of concrete and blow it up so it's size is now 3'x3'x3', ie, 3 cf of water.....throw it back into the water....what happens....the original 1 cf of rocks only displaced 64 lbs of water...but now it displaces 3 x 64 lbs =192 lbs.....just a tad more than the weight of the rock at 150 lbs.....and it will float right at the surface.

See, pretty simple....

[Christian W.]

In this part of the sailing world it is known to be a risky idea to use a concrete block for a mooring, as on immersion the block loses its dry weight. A metal 'block' like a couple of train wheels is ideal, presumably because of the metal's impermeable density, as well as its concentrated weight.

[Don C L]

Originally Posted by MicHughV

Take a rock with a known weight, say a 1 cf of concrete.....
On land this will weigh about 150 lbs...weigh it to be sure....
Once dropped into the water, buoyancy comes into play.....so subtract the amount of water the rock displaces....in this case 1 cf.....which is around 64 lbs ( 1 cf of water) to keep things simple.
Now tie a line to the rock and pick it up with a spring scale, you will note the rock now weighs 150 -64 or 106 lbs...
Now how can something that just weighed 150 lbs on land only be 106 lbs in water ??

It doesn't, it is still 150 lbs now supported by 64 lbs of buoyant force. Just as if another person is adding support.

Still don't get it. Try to pick up a man....say your neighbor....200 lbs...on land...can you do it....with a pit of huffing and puffing...maybe.
Now place that man in a swimming pool and pick him up while in the pool.....piece of cake. Why? The buoyancy of the water surrounding the man supports the man. Were that man to be completely immersed, you push him around with your little finger.
Man still weighs 200 lb, but is supported by the amount of water the man has displaced, which will be 200 lbs as he is now completely immersed.

Ok, will try one last example....we were going to use a "magic" brick as described above. ie, 1 cf of concrete weighing 150 lbs.
Throw it into a pool and what happens ? It sinks to the bottom as 1 cf of water has insufficient buoyance force to support the 1 cf of concrete.
Now insert a straw into the 1 cf of concrete and blow it up so it's size is now 3'x3'x3', ie, 3 cf of water.....throw it back into the water....what happens....the original 1 cf of rocks only displaced 64 lbs of water...but now it displaces 3 x 64 lbs =192 lbs.....just a tad more than the weight of the rock at 150 lbs.....and it will float right at the surface.

See, pretty simple....

All true, but the inertia of the mass remains when you try to propel that mass one way or another.

[Jim Cate]

Now insert a straw into the 1 cf of concrete and blow it up so it's size is now 3'x3'x3', ie, 3 cf of water..

In the interest of clarity, I think that set of dimensions would enclose 27 cubic feet, not three.

But your basic intuition is correct!

Jim

[Don C L]

Originally Posted by Jim Cate

In the interest of clarity, I think that set of dimensions would enclose 27 cubic feet, not three.

But your basic intuition is correct!

Jim

Well, 26 added right? Since it still has the concrete? But yeah, 27 total.

[MicHughV]

Yes, I muffed that.....it should be 27 cf....

Interestingly, the docks at my marina are made from concrete, long rectangular boxes, around 20' in length each x 5' wide or so. They are immersed around 3' and extend above the water by around 12-15" or so. They have some wood trim around the sides so that the concrete edges don't touch the boats.
They are quite stable when walked on by one or more person as they have so much mass.

[Rucksta]

Originally Posted by MicHughV

Yes, I muffed that.....it should be 27 cf....

Interestingly, the docks at my marina are made from concrete, long rectangular boxes, around 20' in length each x 5' wide or so. They are immersed around 3' and extend above the water by around 12-15" or so. They have some wood trim around the sides so that the concrete edges don't touch the boats.
They are quite stable when walked on by one or more person as they have so much mass.

Yes Mass is providing stability and would provide the same amount in zero gravity where there is no weight.

It is likely the hull form and righting moment of the pontoon contribute much more to stability.

An experiment comparing deflection of a static load and the same load moving at various speeds may give data to calculate the inertia stability.

[TrentePieds]

MicHugh sez: "Interestingly, the docks at my marina are made from concrete,..."

An excellent way to build a pontoon. The pontoons at my marina are also "concrete". Nor is it very difficult to build a yacht hull from "concrete" which in that application, as when used to build pontoons and basses for float houses, is called "ferrocement". What is REALLY, REALLY difficult is to build a GOOD yacht hull from that material

The first "ferro" hulls were, if memory serves, built in Italy in the 1880s.

TrentePieds

[MicHughV]

I'm a structural marine engineer by profession (retired) and have only ever come across a ferro boat one time, which was a pinky schooner design, 50' something feet as I recall, an had an opportunity to sail on it a few times, this was back in the late 70's.

I suppose the nature of concrete limits one's ability to pick and choose a boat design , ie, a light weight planing hull is likely not going to happen, but a schooner design, with it's long full length keel is apropos.

All things considered the boat sailed well, but was certainly a handful as it had a barn door type rudder, with a tiller that was around 6' long and certainly required some muscle power to handle. He never had shortage of willing male crew either, as his wife and three beautiful daughters lived aboard with him and garnered a lot of attention, and no, none of the daughters was willing to give me the time of the day, so my heroic efforts at the tiller were in vain

As an engineer, I marveled at the use of concrete for the boat material. I don't recall the scantlings, but the hull must have been 2-3" thick above the water line.

The owner/captain was an interesting guy for sure as some years later he took on building a half-scale P-51 Mustang, though he was not a pilot that knew off.

[TrentePieds]

MicHugh said: "As an engineer, I marveled at the use of concrete for the boat material. I don't recall the scantlings, but the hull must have been 2-3" thick above the water line."

For years and years abandoned ferro-hulls sat along the banks of the Mighty Muddy Fraser River because Samson Marine in Richmond near the river's mouth had done a very good job of selling the naive on the notion that "ferro" is the ideal material for home-building. Well, the chickens came home to roost when enthusiastic amatoors discovered a) how difficult is it to build a fair hull, and b) that the cost of the bare hull is/was usually less than 10% of the finished vessel's cost. One or two vessels were successfully completed. Of their fate I have no idea. I have been aboard two completed Samson designs. Their design was modestly competent, yet they were, due to the difficulty of building in "ferro" utter pigs.

The target thickness of the hull was 7/8", but that is very nearly impossible to achieve with the result that those boats that WERE completed were well over design displacement.

Weight of concrete may be taken to be 150lbs/CuFt, giving a bare hull weight (sans bulkheads and ribs) of 11lbs/SqFt IF the 7/8" is achieved uniformly. For comparison, Fir Planking weighs 34lbs/CuFt, or thereabouts, so 2" fir planking would come in at 5 3/4 lbs/SqFt or just about 50% of GOOD "ferro".

Bare hull weight might be 20% of design displacement if the planking is fir, so that is 3 tons for a 15-tonner, whereas the same "ferro hull", if exceptionally well made, would weigh 6 tons. The implications for performance and stability are intuitively clear.

TP

[MicHughV]

I built a steel boa

[MicHughV]

Whoops....
I built a steel boat back in the 70's.
At that time, steel boats tended to be built like wood yachts....ie, lotsa frames, longitudinals, etc. In addition, the plating for the hull and topsides tended to be thicker than needed.
Knowing what I know now, I could easily have removed most all the frames and have gone down in the thickness of the hull plating, saving likely 1,000's of pounds in the process.
Early fiberglass boats also tended to have rather thick hulls as fiberglass boats was still an unknown quantity.
Ferro boats was also a "thing". I guess under strict construction guidance, weight could have been saved.
I've also seen a variety of wood boats being built. Before the arrival of the WEST system epoxy or other epoxies, this was also a material that tended to be oversized.

At the end of the day, it was a learning curve for most boat builder manufacturers, who today employ such things as vacuum sealed hulls, etc.

Who knows what the future will hold regarding hull building materials ???