4 ms·

Hull speed (maximum speed for a non-planing aka "displacement" hull) is proportional to the square root of the length of the hull. The article says he has a "hu

by crdb 9y ago

Hull speed (maximum speed for a non-planing aka "displacement" hull) is proportional to the square root of the length of the hull. The article says he has a "hull speed of just 2.5 knots". Most (well, all) crossings are done on much longer boats.

tgb 9y ago
Wikipedia on Hull Speed [1] is very interesting: > Though the term "hull speed" seems to suggest that it is some sort of "speed limit" for a boat, in fact drag for a displacement hull increases smoothly and at an increasing rate with speed as hull speed is approached and exceeded, often with no noticeable inflection at hull speed. Which makes it sound like Hull Speed is not very relevant to look at, but later it also says: > This very sharp rise in resistance at around a speed-length ratio of 1.3 to 1.5 [where hull speed is reach] probably seemed insurmountable in early sailing ships and so became an apparent barrier. This leads to the concept of 'hull speed'. The page on Wave-Makign Resistance is related [2]. So it sounds like hull speed is not a hard limit (and is surpassed easily in powered boats or in specific boat designs like racing kayaks) but would be a reasonable upper bound for how fast this particular yatch could go even though nothing truly specific changes right at hull speed. Can anyone elaborate? [1] https://en.wikipedia.org/wiki/Hull_speed https://en.wikipedia.org/wiki/Hull_speed [2] https://en.wikipedia.org/wiki/Wave-making_resistance https://en.wikipedia.org/wiki/Wave-making_resistance
- crdb 9y ago
  It's a useful rule of thumb in terms of "where you'll stop accelerating with the wind on a normal boat", not absolute hard limit. You can play with length to start planing earlier which is the source of many a fun design (e.g. [1]). Some boats don't have a hull [2]. There's many other variables (weight, beam, etc.), here's a fun one: we once rented a 25 footer mostly because it was incredibly cheap (something like 150 EUR for a week). It was surprisingly slow for its size, even in fairly involved wind where we needed engine help to tack it had trouble breaking past 5-6 knots, to the amusement of not-much-larger yachts that overtook us like a German traveling salesman on the Autobahn. I took a dive under to see what was up with the hull and was faced with a scene not too different from the rocky bottom of the sea: barnacles, algae, some of them trailing foot long appendices... The OP "yacht" is very strange to me as it looks like the guy put a keel and a sail on a buoy. The sailing dynamics appear to involve pitching forward instead of heeling (leaning sideways). I'm amazed he can do as much as 2.4 knots. [1] https://www.youtube.com/watch?v=8CbJS_ZHs6g https://www.youtube.com/watch?v=8CbJS_ZHs6g (Formula windsurfing) [2] https://www.youtube.com/watch?v=Y7ie5C1-b3w https://www.youtube.com/watch?v=Y7ie5C1-b3w (Mirabaud LX: foiler, without hull)
  - wycx 9y ago
    > The OP "yacht" is very strange to me as it looks like the guy put a keel and a sail on a buoy. The photos on this [1] page make me think of a keel welded to a sandblasting cabinet... [1] https://carrie-soltis.squarespace.com/specs https://carrie-soltis.squarespace.com/specs
dzhiurgis 9y ago
Yep, you are expected to sail at around 5 knots on a quite common size of 32 ft. In reality you can push it to 6 or 7 knots, but you don't wanna push it in the middle of the ocean. The shortest path is from Cape Verde to Brazil, around 1350 nm, but doldrums (area with not wind) is there, so not the smartest place to sail.

by crdb 9y ago

tgb 9y ago

Wikipedia on Hull Speed [1] is very interesting: > Though the term "hull speed" seems to suggest that it is some sort of "speed limit" for a boat, in fact drag for a displacement hull increases smoothly and at an increasing rate with speed as hull speed is approached and exceeded, often with no noticeable inflection at hull speed. Which makes it sound like Hull Speed is not very relevant to look at, but later it also says: > This very sharp rise in resistance at around a speed-length ratio of 1.3 to 1.5 [where hull speed is reach] probably seemed insurmountable in early sailing ships and so became an apparent barrier. This leads to the concept of 'hull speed'. The page on Wave-Makign Resistance is related [2]. So it sounds like hull speed is not a hard limit (and is surpassed easily in powered boats or in specific boat designs like racing kayaks) but would be a reasonable upper bound for how fast this particular yatch could go even though nothing truly specific changes right at hull speed. Can anyone elaborate? [1] https://en.wikipedia.org/wiki/Hull_speed https://en.wikipedia.org/wiki/Hull_speed [2] https://en.wikipedia.org/wiki/Wave-making_resistance https://en.wikipedia.org/wiki/Wave-making_resistance

crdb 9y ago
It's a useful rule of thumb in terms of "where you'll stop accelerating with the wind on a normal boat", not absolute hard limit. You can play with length to start planing earlier which is the source of many a fun design (e.g. [1]). Some boats don't have a hull [2]. There's many other variables (weight, beam, etc.), here's a fun one: we once rented a 25 footer mostly because it was incredibly cheap (something like 150 EUR for a week). It was surprisingly slow for its size, even in fairly involved wind where we needed engine help to tack it had trouble breaking past 5-6 knots, to the amusement of not-much-larger yachts that overtook us like a German traveling salesman on the Autobahn. I took a dive under to see what was up with the hull and was faced with a scene not too different from the rocky bottom of the sea: barnacles, algae, some of them trailing foot long appendices... The OP "yacht" is very strange to me as it looks like the guy put a keel and a sail on a buoy. The sailing dynamics appear to involve pitching forward instead of heeling (leaning sideways). I'm amazed he can do as much as 2.4 knots. [1] https://www.youtube.com/watch?v=8CbJS_ZHs6g https://www.youtube.com/watch?v=8CbJS_ZHs6g (Formula windsurfing) [2] https://www.youtube.com/watch?v=Y7ie5C1-b3w https://www.youtube.com/watch?v=Y7ie5C1-b3w (Mirabaud LX: foiler, without hull)
- wycx 9y ago
  > The OP "yacht" is very strange to me as it looks like the guy put a keel and a sail on a buoy. The photos on this [1] page make me think of a keel welded to a sandblasting cabinet... [1] https://carrie-soltis.squarespace.com/specs https://carrie-soltis.squarespace.com/specs

dzhiurgis 9y ago

Yep, you are expected to sail at around 5 knots on a quite common size of 32 ft. In reality you can push it to 6 or 7 knots, but you don't wanna push it in the middle of the ocean. The shortest path is from Cape Verde to Brazil, around 1350 nm, but doldrums (area with not wind) is there, so not the smartest place to sail.