The Physics of Boats

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Күн бұрын

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Join marine physicist Dr. Patrick Rynne as he explores the science behind boat hull resistance, the Froude number, and how to estimate how fast a boat can go simply by looking at it.

Пікірлер: 23

@joehopfield Жыл бұрын

Nicely done. Also the paddling demo was really helpful and the best low key product placement I've seen.

@ron9543 Жыл бұрын

Well produced, very informative. Thank you.

@Bryn0x Жыл бұрын

Very good explanation, but it misses the part "wavemaking resistance" or "pressure resistance". It's not so much the frictional resistance which causes the resistance to rise sharply around "hull speed", it's the wavemaking resistance. The frictional resistance increases more or less linearly with speed. Many ships (e.g. naval ships, patrol vessels, motoryachts) are too heavy to plane, but they "beat hull speed" with a slender hull form and a lof of power, often using features to reduce wavemaking, such as a bulbous bow on the front and a Hull Vane on the back. We call this "fast displacement" when the ship is not lifted out of the water, or "semi-displacement" if they are reasonably light and are lifted somewhat out of the water due to hydrodynamic forces on the hull.

@gefginn3699 2 жыл бұрын

Great post my friend. I have plans to build my own Trimaran and information like this will be crucial to my dimensions. 🤩⛵

@danielhaynes9262 2 жыл бұрын

In the example calculation of the 20 meter boat, the left side of the equation should be multiplied by a factor of 1.94384 knots/meter/second. Otherwise the result will be in meters/second not knots.

@rachidtayeb1465 4 ай бұрын

Thank you for better video, can you but a video for a planing boat

@josephlai9759 Жыл бұрын

There is another formula which I find more handy. The hull speed is calculated directly in knots. It is 1.34 multiply by the square root of LWL (in feet).

@Waterlust Жыл бұрын

That formula comes from Froude number experiments, just a more simplified way to express it (and easier to remember).

@sailorgeer 9 ай бұрын

@@Waterlust also worth noting that the way you expressed the Froude number formula is dimensionless and it works for any (self consistent) set of units whether inches, feet, meters, nautical miles, or astronomical units !

@EngRMP 9 ай бұрын

Very cool! I often heard hydrodynamicists talking about "transverse waves".... I always thought they were the V-shape waves... now I finally have the true picture. And, I've felt that extra push that is needed to get "over hump"... now I understand the physics better.

@Waterlust 9 ай бұрын

Glad it was helpful! More ocean science videos like this coming, stay tuned!

@crackedemerald4930 2 ай бұрын

didn't Froude also make a number where you can slow the footage of model ships by to get accurate boat simulations?

@user-mp6fg8fh6x Жыл бұрын

05:30 estimating their length Should length refer to the observation wavelength and be able to calculate the ship's speed?

@crackedemerald4930 2 ай бұрын

4:07 if the froude number is the highest efficiency, wouldn't it be the valley before the big ramp up? in this graf, it looks like the least efficient speed, because at least, you get faster for the other ones.

@francoistelemaque6429 2 жыл бұрын

Good information however modern racing sailboats from small to large do plane and without to much difficulty

@jimbo_davis Жыл бұрын

how can you estimate the hull speed?

@Waterlust Жыл бұрын

Use the equation in the video. By estimating the boat length, you can calculate the hull speed using the Froude number 👍

@user-mp6fg8fh6x Жыл бұрын

@@Waterlust Should length refer to the observation wavelength and be able to calculate the ship's speed?

@ratandmonkey2982 9 ай бұрын

your resistance vs Froude # graph did not make sense with your explanation. Why the dip (less resistance) with a higher Froude #?

@Waterlust 9 ай бұрын

The “hump” in the plot at 04:07 is caused by the dramatic increase in resistance when a boat tries to overcome its primary transverse wave. If it’s able to, some boats will experience a brief region of reduced resistance. Note, every boat has a different resistance curve, so the size and shape of the hump varies a lot. One way to prove this phenomenon to yourself is by going in a small planning boat and setting the throttle so you’re stuck at that awkward hull speed with the bow up. Then have somebody carefully move to the bow to help the boat initiate planning, but don’t change the throttle. Works really well in small inflatables. What can happen is the boat starts planning and going dramatically faster despite the engine producing the same thrust. The only way this acceleration can happen is if the overall resistance on the hull were to drop, which supports the idea of the resistance dip at speeds slightly above the critical Froude number. Great question!

@user-mp6fg8fh6x Жыл бұрын

05:07 At 950 feet long, the cruising speed of a Panama container ship is around 25 knots. In the film, a Panamanian container is described with a captain of 950 feet and a cruising speed of approximately 25 knots. But when the hull speed is calculated to be 40 knots, why do most container ships only have 25 knots? Does not match the hull speed.

@williamstrachan Жыл бұрын

Fuel efficiency most likely. MAN Energy Solutions has a paper out titled "Propulsion of 14,000 teu container vessels" and shows (amongst other things) that identical ships are vastly more efficient at 21.5kts instead of 23.5kts. Eg. At 23.5kts their example ship consumes 197.9 tonnes of fuel/24 hours, but at 21.5kts it consumes 145.4 tonnes of fuel/24 hours. I can't imagine the fuel burn at 40 😬😬

@cowchin8 8 ай бұрын

@@williamstrachanslow speed is definitely burning less fuel as it travels less distance. There is a relationship between fuel oil consumption & ship speed & power. It is not a linear relationship. Therefore, all the vessels go slow-steaming in the poor economy period.