Post your interesting tech. articles

[daysgoneby]

A Real Cure for Osmosis?
Mustin Marine Surveys, Miami, Florida, USA - Hot Vac-A Real Cure for Osmosis?

[daysgoneby]

Can carbon fiber car panels double as energy storage materials?
https://newatlas.com/carbon-fiber-ca...storage/56864/

[daysgoneby]

The TRUTH of Hull Speed

https://www.youtube.com/watch?v=aYlI3WK2WIw

[crankysailor]

Originally Posted by daysgoneby

The TRUTH of Hull Speed

hey very nice and interesting..Thanks for posting. This actually clarified some questions I always had.

[daysgoneby]

Dynamic Stability of a Monohull in a Beam Sea
Dynamic Stability of a Monohull in a Beam Sea | M.B. Marsh Marine Design

[daysgoneby]

Beam, Drag, Steering, and Rig Size
https://setsail.com/beam-drag-steering-and-rig-size/

[daysgoneby]

Amazing new electric boat motor based on fish fins
https://plugboats.com/amazing-new-el...-on-fish-fins/

NEW SHARROW PROPELLER
The Propeller - Sharrow Engineering

[daysgoneby]

Boats, bell spiders and rafts of fire ants.
https://www.passagemaker.com/technic...inkable-vessel

[GordMay]

The total number of ways you can scramble a Rubik’s cube is 43,252,003,274,489,856,000, and yet, every position of Rubik's Cube can be solved in twenty moves or less (God’s number).
➥ God's Number is 20

[daysgoneby]

Reasons to be paranoid about diesel
https://www.yachtingmonthly.com/gear...t-diesel-34807

[daysgoneby]

HMS Disappointment
https://www.standard.co.uk/news/crim...-a4318756.html

[tkeithlu]

I want to challenge the "The Truth of Hull Speed" video. It's not that anything incorrect was said, but some obvious conclusions were left out, and one assumption I think was misleading. I did learn why catamarans are fast, a nagging question in my mind.

First, I'm yet to hear anyone say that hull speed is the maximum speed a boat (sailing or motor) can move. The point is rather that it's the maximum speed that any boat can move without overcoming exponential resistance, starting with climbing your bow wave. If you've got the power and hull shape to climb up on top of the bow wave (plane), go for it. If you've got the wind, go for it. If you've got a very narrow hull (catamaran) you've got an advantage in less wet area resistance. Same for a spade keel. If you are long enough to be supported (think destroyer) you can do 30 knots.

The point, for powered displacement hulls, is that you cannot plane, and are going to have to climb that wave as soon as the stern wave extends until it does not support the stern. Ergo, big time fuel burn to overcome the resistance. Think that sport fishing boat that nearly ran you down. I move a 60,000 pound boat with 80HP at hull speed; they use 600HP to move a much lighter boat at 25 or 30 knots.

For sailing boats, it's the same. Most are displacement compromises, and only reach higher speeds with a following sea/wind. Around Antartica racers are surf boards and plane, but otherwise not practical cruisers. In routine cruising, you are likely to exceed the hull speed formula, but not by much, because of the increasing resistance clearly shown on the video graph.

[daysgoneby]

Originally Posted by tkeithlu

I want to challenge the "The Truth of Hull Speed" video. It's not that anything incorrect was said, but some obvious conclusions were left out, and one assumption I think was misleading. I did learn why catamarans are fast, a nagging question in my mind.

First, I'm yet to hear anyone say that hull speed is the maximum speed a boat (sailing or motor) can move. The point is rather that it's the maximum speed that any boat can move without overcoming exponential resistance, starting with climbing your bow wave. If you've got the power and hull shape to climb up on top of the bow wave (plane), go for it. If you've got the wind, go for it. If you've got a very narrow hull (catamaran) you've got an advantage in less wet area resistance. Same for a spade keel. If you are long enough to be supported (think destroyer) you can do 30 knots.

The point, for powered displacement hulls, is that you cannot plane, and are going to have to climb that wave as soon as the stern wave extends until it does not support the stern. Ergo, big time fuel burn to overcome the resistance. Think that sport fishing boat that nearly ran you down. I move a 60,000 pound boat with 80HP at hull speed; they use 600HP to move a much lighter boat at 25 or 30 knots.

For sailing boats, it's the same. Most are displacement compromises, and only reach higher speeds with a following sea/wind. Around Antartica racers are surf boards and plane, but otherwise not practical cruisers. In routine cruising, you are likely to exceed the hull speed formula, but not by much, because of the increasing resistance clearly shown on the video graph.

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.

It doesn't mean max speed of a vessel.
27 knots on a cruising sailboat!

https://www.youtube.com/watch?v=J4zg5vD_jvI

[tkeithlu]

"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."

Agreed. There are implications to that. At speeds above that you have to overcome increased resistance because the stern is no longer supported by the stern wave. I said that.

"It doesn't mean max speed of a vessel.
27 knots on a cruising sailboat!"

Agreed. It can be done. I said that. too.