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Old 19-01-2010, 20:11   #91
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Originally Posted by Eleven View Post
Wouldn't want to do it on a mono though. Do they all broach, or is that a function of sharp bows?
You may find most of the daily traffic over some of the most notorious bars in the world is performed in Mono hull boats. If we take "Lakes entrance" alone, a catamaran crossing the bar would be a pretty rare site. Go sit and watch for a while. I have.
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Old 19-01-2010, 23:59   #92
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The "slewing around" I think may have been the effect where the water behind is moving forward faster than the boat which reverses the rudders leading edge and changes helm directional input. The correction then would have been when the boat speed picked up to make steerage and helmsman recovered the plot.

working a trawler over bars the best way was to steam in reverse when a wave knocked on your back door to keep control.

I think a monos broaching could be the force of the advancing water from aft pushing that larger (than a multihull) rudder aside and jerking the wheel right out of the skippers hands. Then with the rudder acting as a big brake and pointing wrong direction, forces the boat to beam on.
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Old 20-01-2010, 02:27   #93
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Sorry BayView, we don't have a bar in Southampton Water. Shipping terminal! Other hazards.
From all I've read cats don't tend to broach but it seems to be a fear for mono's. Is it the sharp bow and a big keel that makes them unstable as the sea lifts the stern? Are some mono's immune because of -- ?? .
I must admit I would have tried that run, now, having checked charted depth; tide height; wave height and safety factor VERY carefully. And it wouldn't have been my first choice the first time. But he's done it a few times before.
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Old 20-01-2010, 02:29   #94
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Why Me, I remember the flat stern fishing boats out of 'Frisco? used to run before a storm and many were lost until water tank trials showed bow on was the right way.
Obviously you are doing the same thing, and with more power available nowadays.
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Old 20-01-2010, 03:22   #95
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The more a mono is designed like a flat sled with a narrow keel, the less vulnerable they are to a broach. I believe a longer, fuller keel would result in less sideways "slipping" potential, and therefore less margin for directional errors at the helm. The fuller keeled mono would catch, and broach more easily.
(Disclaimer: Totally my own ideas on how things should work. No education/research to back them up! Don't take them too seriously).
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Old 20-01-2010, 04:58   #96
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Beam on breaking wave survivability

I put up some scanned design notes from the late great Loch Crowther on this thread

LOCK CROWTHER DESIGN NOTES AS PROMISED

On page 2 of the notes he talks of tanktesting hullforms in a wave tank at Southhampton.
He says that they could not capsize a catamaran in beam on seas using the largest wave generated, which equated to a 52 ft breaking wave on a cat with 40 ft beam (big boat)

Scaling this down he says that a typical 24 ft beam cat should be OK in a 31 ft breaking beam sea.

Compare that to a comparable sized monohulled powerboat that was easily capsized with a 25 ft breaking sea and a conventional 40 ft sailing mono could be capsized by a 12 ft breaking sea as was demonstrated in the fastnet disaster.
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Old 20-01-2010, 05:38   #97
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So......would it be the right math to use that ratio and say that a Gemini cat with a 14 ft. beam should be okay in 18 ft. breaking beam seas?
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Old 20-01-2010, 06:47   #98
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Cat crews get rescued too, usually because of the ride. The boats sail on. It's a fact. Go look at the 'Queens Birthday Storm'.
I'm just interested in whether mono's could be safer, ie from broaching, not by having a second hull.
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Old 20-01-2010, 11:49   #99
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A heavy displacement mono has to sit there and take it when the seas try to get onboard from astern. They do not have the ability to get up and run from the sting of the breaking seas. The construction is heavy and strong and hopefully they can take the beating. The ability to take a beating, is because of the heavy construction, and the design to take it. It's all built in. You are heavy to be able to take a beating, you are taking a beating because you are heavy
A multi is better to use its light weight and wide stability and ability to get up and run away from those moments when it is about to take a hit from a breaking sea. Or setting it up to lesson the blow by virtue of fwd. speed being closer to wave speed, so the blow is so much less. Do not lay there and take a beating in a multi, no good. You have a different boat, different tactics.
I have a question.(displacement boats) What is the least stable course you can be on?


.........................................Downwind, down swell.......took me 3 days in a stability class to actually believe what they were teaching (I am required to take this stuff for my masters license and the fact I operate in the Bearing Sea)

I can get used to the "death rolls" we have on the work boat, but it sure is nice not to have those on my little Trimaran....
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Old 01-02-2010, 12:16   #100
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Good sea story, told well, and another reason why I like multihulls. It is not that they did everything right. But a great example of a boat being able to jump away from the harmful stuff.
Lia Ditton describes sailing through an Atlantic storm in the trimaran, Moxie. Lia is presently rowing the Atlantic with Mick Birchall:

Lia Also did a transatlantic race solo a few years back in a skinny little trimaran.




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Old 02-02-2010, 13:01   #101
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I was lucky enough to meet Phil weld in Toronto, in 1976, at the first Multihull Symposium. He described how his trimaran, Gulfstreamer was capsized. A very nice man, and a great story teller.
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Old 09-02-2010, 11:43   #102
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This is necessarily subjective, but to me he came dangerously close to a broach about 50 seconds in. Had the wave been breaking, I doubt he would have managed so well.
I don't see that at all. That Captain looks to have had complete control of his boat as it went over the bar. I've done this myself on a smaller scale, and frankly it's no big deal. The captain purposely and properly surfed the break at an angle, just as a surfer would have. Had he felt the boat slip, he would have corrected his course in plenty of time. With twin engines he would have yanked the port throttle back hard and pivot on a dime. There just wasn't a need to as the guy nailed the crossing.

As to his decision to give it a try.... questionable, yet in the end, he handled it well. I'd hitch a ride with that guy anytime.
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Old 09-02-2010, 14:41   #103
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Another reason to like cats:

Coongul creek, Fraser Island. Great place for cats. Exploit your shallow draught, and drying out capabilities.



Entrance looks narrow, but is wide enough. Enter at high tide, obviously.



Following "School's Out" (Another Oram 44C)


Tide going, but she's still afloat...


....gone



Later Bob Oram joined us in his power podcat.


Good fishing, you can pump yabbies for bait right next to the boat, stroll down the beach to the mouth of the creek and pretty much keep yourself fed on whiting, bream and flathead.
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Old 09-02-2010, 14:58   #104
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Awesome...just great. And so nice to see you out using your new boat! Very, very cool. Thanks for the great shots. So you can shoot the bar, and live in thin water very contently.....ahh the mulithull fun zone is wide!

If I go aground, I can jump over the side and get my shirttails wet pushing myself off.....
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Old 09-02-2010, 15:05   #105
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I know there were a number of Cat's who were getting the google maps and were planning on a trip north on the west coast of Baja. The were going inside and using the backwater estuary's for hundreds of miles. It will be an uncharted voyage, they may have to get the skiff out and do some scouting. All sounds like fun. Avoiding the messy wind and swell in the face of the slog north. One of the boats shown here.
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