Originally Posted by Honey Ryder
i was having lunch in a restaurant in london last week and was lucky enough to share a table with one of the three men
who took a 46' 1986 nordhavn around the world, the wrong way.
he said it took them two and a half years, and said it was easy, but rough in places (the pacific).
i bumped into another norhavn owner in sardinia two years ago. he had crossed the atlantic with his wife and was cruising the med. this gentleman was in his late 60s. last thing i heard they were in central america
I'd guess that trawler
style boats with the right ratios (see beebe's "voyaging under power"), sailed well, are very safe. of course, if water gets into the boat and the pumps can't keep up, then it will sink, in "the perfect storm", a paravane broke a window and the storm boards were not fitted so when it went over if filled up.
keep the water out or have plenty of pumps and you should be ok is my guess.
Let me see if I can illuminate from my experience.
Beebe's ratios are interesting, but clearly they are simplistic. His lack of experience with 3D animated color dynamic modeling on PCs (because it basically was not done for another two decades ;-) means his insights are limited. Not worthless: he describes things as they appeared to him and others. But like the observation that feathers fall slower than bricks obscures the fact that acceleration near Earth is independent of the weight of the falling body (for those of you who really understand gravity, please ignore my simplification), Beebe's ratios obscure the truth and should not be used to judge boats far from Beebe's experience.
All simplifications, like hull speed
or Beebe's ratios, apply best to vessels that are similar to those being observed when the simple "rules" were coined. Hull speed
applies less and less as displacement
length ratios get lighter, and length-beam ratios get longer and thinner. For example, a 27 foot Express 27, 25 feet on the waterline but 2400 lbs (empty, probably 3200 lbs with the crew and gear) Their best day's run on the 11-day crossing was 320 miles, which meant they averaged 13 knots for 24 hours in the 1984 Pacific Cup.
Really, Beebe describes boats he saw as being successful and appropriate. The ratios describe those boats.
But using 1.34 x sqrt(LWL) to predict boat speed for an Express 27 sailing downwind is as inappropriate as suggesting that only boats that conform to Beebe's ratios are the only boats good for passagemaking.
Specifically, some power cats can be very good passagemakers. Some are horrible. The bridge deck
height .vs. bridge deck
span is a critical factor, yet of course does not appear in the Beebe ratios. Beebe did not experience successful power catamaran
passagemakers, so he did not describe them.
Beebe was trying to describe valid characteristics of dynamic motion, but the functions that lead to such actual dynamic motion is very, very far from Beebe's ratios. They happen to correlate to his observed data set, but they are not useful to predict if a given boat is appropriate or not for passagemaking.
For example, one time I crossed the Atlantic on a Swan 65. Another Swan 65 was crossing just a few days before us. They had severe problems. We had zero problems. Its not just the logo on the boat, its also the total history
of the boat, including the person who oversaw the original build, the systems, the maintenance
, the crew, and luck (weather is formally chaotic, so weather
forecasts are of limited value more than a day or three in the future, depending on where you are).
Today, naval architects can and should do animated dynamic simulations of passsagemaking vessels. Steve Dashew sometimes posts such animations of his boats.