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26-07-2014, 19:36
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#331
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cruiser
Join Date: Apr 2014
Location: West Coast, Canistan
Boat: Westsail 42
Posts: 185
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by StuM
Wave height is dependent on three factors:
1. Wind strength
2. Wind duration (how long it blows in the same direction)
3. Fetch (the uninterrupted distance over which the wind blows in the same direction)
The third factor is the critical one when talking about ocean waves. A steady 20 knots will build much bigger waves over 1000 miles of ocean than they will over a couple of miles in a lake.
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Yes, I never gave thought to the amount of surface area. That stands to reason. Thanks for that StuM. Can you tell me if the wind and seas are a greater problem at times for a mono or a multi? I'm going to guess a multi will handle it a little better just because of the multihulls alone covering the surface area greater to give more stability.
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26-07-2014, 22:20
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#332
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Registered User
Join Date: Sep 2009
Location: on board, Australia
Boat: 11meter Power catamaran
Posts: 3,648
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by robert sailor
I get a kick out of some of you guys and your discussion of rough seas. Now we have a 19 ft. runnabout that is going to take on some weather....when I read that I know you haven't really been out in anything really big because some of the stuff I've been in a 19 ft runabout would be swamped within a few minutes.
I don't have any experience in big seas and Cats but I expect a Cat would do OK although I wouldn't want to be sitting up on one of those fly bridges.
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Valid point made however the discussion point I responded to was scary seas in the Whitsunday Islands and I have been on plenty of vessels there. This area is where I live and I have spent lots of seatime on various charter boats, trawlers as well a small powerboats and two sailing cats. It is a safe area for the many charter vessels of all types just need to watch the tidal rip areas.
Lots of places I don't want to be in a 19ft powerboat but it was fine in the Whitsundays.
Point is it is a safe area by comparison with breaking open seas except for when a cyclone is in the area.
cheers
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26-07-2014, 23:28
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#333
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Registered User
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,891
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by Razoo
Can you tell me if the wind and seas are a greater problem at times for a mono or a multi? I'm going to guess a multi will handle it a little better just because of the multihulls alone covering the surface area greater to give more stability.
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It may be apocryphal, but you can come across this story in various places:
"at the time of the famous Fastnet disaster, of which volumes have been written, there were two Prout catamarans in the vicinity. They were shadowing the fleet as unofficial entries. The racing fleet sailed into a serious storm. The carnage caused by the storm was so great that a Committee On Safety From Capsizing was formed. It consisted of the Society of Naval Architects and Marine Engineers (SNAME), the United States Yacht Racing Union (USYRU), and the United States Naval Academy (USNA), and others. The purpose of this committee was to design a minimum stability formula for ocean racing monohull yachts. The weather that was disaster to the Fastnet fleet was considered merely "beastly weather for sailing" by the two adjacent catamarans"
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27-07-2014, 00:40
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#334
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Registered User
Join Date: Sep 2012
Posts: 5,986
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Re: At The Risk of Starting WWlll
I can't say either way but "in the vicinity" often isn't the same as being there. I remember many boats "in the vicinity" of the queens birthday storm that had very few problems while some boats that were in the teeth of it were rolled and pitch-poled.
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27-07-2014, 07:03
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#335
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Registered User
Join Date: Apr 2007
Location: Marina del Rey, California
Boat: President 43 Sportfish
Posts: 4,105
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by robert sailor
..."in the vicinity" often isn't the same as being there...
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Couldn't have said it better.
__________________
1st rule of yachting: When a collision is unavoidable, aim for something cheap.
"whatever spare parts you bring, you'll never need"--goboatingnow
"Id rather drown than have computers take over my life."--d design
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27-07-2014, 08:12
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#336
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CF Adviser
Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 10,280
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by Razoo
Yes, I never gave thought to the amount of surface area. That stands to reason. Thanks for that StuM. Can you tell me if the wind and seas are a greater problem at times for a mono or a multi? I'm going to guess a multi will handle it a little better just because of the multihulls alone covering the surface area greater to give more stability.
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It is not as simple as that.
The dynamics of a huge breaking sea interacting at just the wrong moment with a cross sea... will cause a Cat to sit on edge exposing the underside of the bridge deck to incredible wind forces and the powerful rolling forces of wave shape.
This primer explains the hidden forces of a wave.
http://hyperphysics.phy-astr.gsu.edu...s/watwav2.html
Now imagine a 50-90ft breaking wave catching the Cat sideways and burying one hull.
Still.prefer a mono with heavy ballast and a righting moment at all angles in those survival conditions.
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27-07-2014, 08:17
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#337
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Registered User
Join Date: Apr 2010
Location: Shoreline, CT and Portmouth Harbor
Boat: Standfast 33, building a 65 ft Wooden Schooner
Posts: 636
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by Pelagic
In analysing the Seas you will face in heavy weather...these are some of the factors to consider.
Wave Period/Height /Fetch/History/secondary swells/topography/ocean current direction
Noting that a wave period the same length as your boat is the most critical and dangerous situation (anywhere).
Worth reading
http://www.stormsurf.com/page2/tutor...vebasics.shtml
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Wave period? That doesn't make any sense. A 30 ft boat in a 30 ft wave period is going to experience what 3ft waves? 3 ft waves might be annoying and toss stuff around because the boat is locked in a too and fro rock, but dangerous?
It's the tall breaking waves that are dangerous.
Unless you mean in a following sea, that I could understand somewhat that the "apparent" period while underway with following seas is much longer, therefore would lead to taller and faster waves following in sync with the length if your boat. That could be really annoying and leading to broaching because the boat is pre-loaded to surf down each wave.
Scot McPherson
Sent from my iPhone using Tapatalk - now Free
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27-07-2014, 09:01
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#338
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Registered User
Join Date: Nov 2007
Boat: TRT 1200
Posts: 7,275
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by Pelagic
It is not as simple as that.
The dynamics of a huge breaking sea interacting at just the wrong moment with a cross sea... will cause a Cat to sit on edge exposing the underside of the bridge deck to incredible wind forces and the powerful rolling forces of wave shape.
This primer explains the hidden forces of a wave.
http://hyperphysics.phy-astr.gsu.edu...s/watwav2.html
Now imagine a 50-90ft breaking wave catching the Cat sideways and burying one hull.
Still.prefer a mono with heavy ballast and a righting moment at all angles in those survival conditions.
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But then again, the monohull will trip on its keel in much smaller waves while a well designed multi will slide down the face of the wave. This could be argued over and over.
Sent from my iPad using Tapatalk
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27-07-2014, 09:16
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#339
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Registered User
Join Date: Apr 2011
Location: Sacramento, California
Boat: Solar 40ft Cat :)
Posts: 1,522
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Re: At The Risk of Starting WWlll
You can also have a multhull with ballast, for example..
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27-07-2014, 15:34
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#340
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CF Adviser
Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 10,280
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by Scot McPherson
Wave period? That doesn't make any sense. A 30 ft boat in a 30 ft wave period is going to experience what 3ft waves? 3 ft waves might be annoying and toss stuff around because the boat is locked in a too and fro rock, but dangerous?
It's the tall breaking waves that are dangerous.
Unless you mean in a following sea, that I could understand somewhat that the "apparent" period while underway with following seas is much longer, therefore would lead to taller and faster waves following in sync with the length if your boat. That could be really annoying and leading to broaching because the boat is pre-loaded to surf down each wave.
Scot McPherson
Sent from my iPhone using Tapatalk - now Free
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Scot... The explanation about critical wave period was general
However the interation of 2 or 3 high wave sets from different angled and origind can create that critical wave period in a small vessel
http://www.coastalwatch.com/surfing/...riod-explained
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27-07-2014, 15:59
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#341
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CF Adviser
Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 10,280
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by smj
But then again, the monohull will trip on its keel in much smaller waves while a well designed multi will slide down the face of the wave. This could be argued over and over.
Sent from my iPad using Tapatalk
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I agree, but rather than argue over and over... maybe if everyone would download these 2 Wolfson reports... We could discuss this more intelligently.
Not to prove one better than the other...but to clearly understand the different critical survival scenarios for each design solution in that 'Perfect Storm'
I am more focused in identifying the non linear events in dynamic stability
http://www.wumtia.soton.ac.uk/servic...ltihull-safety
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27-07-2014, 20:32
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#342
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Registered User
Join Date: Nov 2007
Boat: TRT 1200
Posts: 7,275
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by Pelagic
I agree, but rather than argue over and over... maybe if everyone would download these 2 Wolfson reports... We could discuss this more intelligently.
Not to prove one better than the other...but to clearly understand the different critical survival scenarios for each design solution in that 'Perfect Storm'
I am more focused in identifying the non linear events in dynamic stability
http://www.wumtia.soton.ac.uk/servic...ltihull-safety
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The link wouldn't download the pdf's.
Sent from my iPad using Tapatalk
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27-07-2014, 22:11
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#343
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CF Adviser
Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 10,280
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Re: At The Risk of Starting WWlll
Strange... I tested twice with my posted link and then downloaded Phase I and II of the report
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28-07-2014, 01:55
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#344
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Moderator
Join Date: Jul 2007
Boat: Bestevaer.
Posts: 14,678
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by Pelagic
Strange... I tested twice with my posted link and then downloaded Phase I and II of the report
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The links worked for me.
It is great to read a scientific study on the subject.
Essential reading
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28-07-2014, 02:15
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#345
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Marine Service Provider
Join Date: Dec 2006
Location: Brisbane Australia
Boat: Multihulls - cats and Tris
Posts: 4,859
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Re: At The Risk of Starting WWlll
Quote:
Originally Posted by Pelagic
Still.prefer a mono with heavy ballast and a righting moment at all angles in those survival conditions.
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Thats Excellent - I don't - still prefer a boat that can't sink (please note i didn't say or suggest that all multis are unsinkable or that all monos are sinkable). But each to his own.
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