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Old 17-02-2011, 09:20   #31
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The hull speed is not really a law, (more like a guidline).

As stated above there are conditions in which hull speed can be exceeded. Usually not pleasant on a sailboat, but power boaters do it all the time. It is really the point in which the weight of the water you are displacing exceeds the displacement of the vessel. Or the point in which the energy required to increase speed goes up by square.
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Old 17-02-2011, 10:28   #32
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I need to understand what is so scary aboute sailing at 10-15kn...isnt this slow compared to what we are used to driving our cars on the freeway???

not being rude in anyway...clearly I dont know and have no such experience...so I am courious as to how one can get scared on a sailboat.

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Old 17-02-2011, 10:38   #33
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I need to understand what is so scary aboute sailing at 10-15kn...isnt this slow compared to what we are used to driving our cars on the freeway???

not being rude in anyway...clearly I dont know and have no such experience...so I am courious as to how one can get scared on a sailboat.

rgds
It sometimes needs a broach to instruct.... to others its just the pucker factor... some pucker quicker than others...
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Old 17-02-2011, 10:50   #34
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I need to understand what is so scary aboute sailing at 10-15kn...isnt this slow compared to what we are used to driving our cars on the freeway???

not being rude in anyway...clearly I dont know and have no such experience...so I am courious as to how one can get scared on a sailboat.

rgds
Imagine a marble on an old lumpy board. Lift the board and try to get it to roll exactly where you want it to go.
It's all about control. Displacement hulls rely on their depth to keep them straight in the water. When they lose the form then the keel has to do the work.
The shorter the keel length (fore to aft) and rudder the less control one has with the possibility of wiping out (broach) and rolling the boat.

Try rollerskating down a steep hill.

Powerboats on the other hand, as long as it is being propelled by it's motor one can maintain control.
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Old 17-02-2011, 10:58   #35
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Imagine a marble on an old lumpy board. Lift the board and try to get it to roll exactly where you want it to go.
It's all about control. Displacement hulls rely on their depth to keep them straight in the water. When they lose the form then the keel has to do the work.
The shorter the keel length (fore to aft) and rudder the less control one has with the possibility of wiping out (broach) and rolling the boat.

Try rollerskating down a steep hill.

Powerboats on the other hand, as long as it is being propelled by it's motor one can maintain control.
ok I understand now...however I was thinking that wipouts was to be expected as rutine and not a big issue with keel boats???
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Old 17-02-2011, 11:04   #36
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ok I understand now...however I was thinking that wipouts was to be expected as rutine and not a big issue with keel boats???
When one broaches it usually means the sails hit the water. And depending how bad, it could roll the boat or worse yet, turtle and/or demasting, depending on the boat. Routine? Not! One should always avoid getting in that position!
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Old 17-02-2011, 17:27   #37
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Jeesus! That does it. I'm never going sailing again.
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Old 17-02-2011, 17:33   #38
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Jeesus! That does it. I'm never going sailing again.
Bob: I want to say this publicly. I love your acerbic sense of humor. If I'm reading between the lines correctly, I think you're saying the number by itself means nothing.
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Old 17-02-2011, 17:46   #39
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Yes, the number does mean absolutely nothing, however, back in the day I did experience the "excitement" of topping the speedo (gps) on my Mirage 24 at 13.4 kts. There was a bit of breeze on, and Lake Erie does like to kick up some waves when it's breezy. Shortly after one of my crew members suggested that we should probably drop the main and just run on the jib after that. Having an accidental gybe would not have been much fun.
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Old 17-02-2011, 17:53   #40
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yes, I think most of the psots here have been right on. If you are working with "speed under power" 1.34 timke sq. rt of the DWL works pretty reliably. But under sail, on the right day with the right conditions we can apply a lot more hp to the boat and then we begin to climb out of that hull speed" trough". I had a half tonner, 30' LOA and from time to time we could hit ten knots. It was kind of fun and kind of terryfying. One bad move on the tiller or one sleepy moment on the spin sheet could send the boat rocketing up to weather in one of those "oh ****" moments. But you really need to do this a few times to call yourself an experienced sailor.

New, light boats, call them ULDB's if you like, do it far more gracefully as they are more prone to surf or plane rather than dig their bows in and fight the opportunity to rise up over the bow wave and plane.

Yep, I think that guy in the Hinterholler probably hit 10 knots. I'm sure it was white knuckle time but I'm also sure it was fun. When it was over.
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Old 17-02-2011, 17:55   #41
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Jeesus! That does it. I'm never going sailing again.
Awww, Bob, it's not all that bad! We've found that if we tow our Jordan series drogue at all times, we almost never broach, take knockdowns or get dismasted!

And for Jobi, going fast isn't really that scary or dangerous. Racers do it all the time, and many non-racers (or retired racers like Ann and I) still enjoy the speed. I can't speak for long keel boats, but all of the fin keel/skeg rudder boats that I've owned have been easily controlled while at speed, including surfing at well over hull speed. Have we ever "lost it" and broached? Well, yes, while racing with a big kite and small skills... but nothing very awful happened. Rudder stalled, boat rounded up, kite got plastered on the rig, there was shouting, and we recovered and went on sailing.

Perhaps such activities shouldn't come too early in your sailing education, but obsessive fear of going fast isn't necessary.

Cheers,

Jim and Ann s/v Insatiable II lying Towleers Bay, NSW, Oz
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Old 17-02-2011, 17:59   #42
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True... but then I remember... its either mine or someone else long term home... not a stripped down racer..
I'm happy wallowing along... if I've a choice....
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Old 17-02-2011, 18:03   #43
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Jim:
With the right crew on the right boat I'm happy to push it to the limit.
But in my car I drive like an old,,,,person.

Back in the 70's I designed a two tonner called HEATHER. It won everything in the PNW. In a blow we could bury the bow and take green water back to the mast. It was an alarming site. But at the wheel the boat was totally responsive and you just drove it under the chute to keep from wiping out. But that was a 42'er and the loads on the boat to get it from 10 to 11 knots increased violently. It was scary, I guess, but we were so young we hadn't figured out yet that life itself was scary. We looked for scary. We weren't paying the bills. "Oops, there goes the 1.5".
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Old 17-02-2011, 18:04   #44
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Jeesus! That does it. I'm never going sailing again.
Can I have your mooring ?
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Old 17-02-2011, 18:04   #45
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With all this broaching, sails hitting water and worse things that can happen, one must not forget that many sail yachts are designed to plane and they will do so without all these problematic descriptions seen in this thread.

The difference is that these yachts are designed to plane. They don't need a wave or anything to plane; hull shape and wind force alone is enough to bring them to plane and sustain planing. The thing to look for in these design is the flat parts (horizontal surface) in the aft part of the hull.

Most of these are racers and I think the Open 60 class is the most extreme example of a planing design (see video below, the last part is especially good). These do 500 nm in 24 hours and there are Youtube videos where you see them do 38 knots which is more than 3 times their hull speed.

Dashew designs like Beowulf and Sundeer are cruisers that can plane but I can't list much more planing cruisers (surely there's more though). Catamarans beat hull speed formulas too but most don't call that planing.

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