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Old 03-15-2015, 11:16 AM   #41
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James recently moved his blog to a new host, and now his in-depth posts/articles are easy to find. I think the write up in the link below of the knock-down is a lot more informative than the initial link I posted, or for that matter the mag. article. 69.1 degrees | MV Dirona
Good bump. And good on James and Jennifer for sharing this humble moment in detail. It makes us all a little more aware, and therefore safer.
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Old 11-14-2018, 07:45 PM   #42
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Wow, I have read some of their blog accounts, but not this bar crossing. I would think a 69 degree roll put that boat at its limit. Their hydraulic bilge pump is a beast. Amazing couple living life to the fullest.

Reading through the Nordhavn list. Just realized I resurrected an old thread.
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Old 11-15-2018, 11:52 AM   #43
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Wow, I have read some of their blog accounts, but not this bar crossing. I would think a 69 degree roll put that boat at its limit. Their hydraulic bilge pump is a beast. Amazing couple living life to the fullest.

Reading through the Nordhavn list. Just realized I resurrected an old thread.

Thanks for the bump. That had to be an intense few minutes.
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Old 11-15-2018, 12:13 PM   #44
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69deg roll data came from a gps direction finder (??? something GPS). I don't doubt it was a harrowing ride, but wonder how accurate that instrument is in a highly transient situation.
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Old 11-15-2018, 01:20 PM   #45
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69deg roll data came from a gps direction finder (??? something GPS). I don't doubt it was a harrowing ride, but wonder how accurate that instrument is in a highly transient situation.
Prolly as good as the one in a Wii or iPhone. Which is plenty good for this! No need for any GPS data, actually.
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Old 11-15-2018, 02:55 PM   #46
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That bar should command plenty of respect, plenty of boats lost there.
I have been through there 50+ times and was surprised to read someone of their experience leaving moreton bay in building southerlies with that crossing in mind.
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Old 11-15-2018, 05:28 PM   #47
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The permanent clench marks I would have left in the seat vinyl would have confirmed the telemetry.
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Old 11-15-2018, 07:10 PM   #48
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A 69 degree roll is not surprising when knocked down by a wave like that in a bar. They were lucky to have the bilge pump capacity to handle it. And lucky nobody was injured by the "waterfall" of loose teak furniture. I would have thought they would have secured everything prior to attempting a bar crossing under sketchy conditions.

I agree with Insequent regarding the air intake design. It shouldnt be the limiting factor for a boat sinking in a knockdown.

Any knock down is certainly a butt clencher. I experienced one when hit on the beam with a sudden microburst of wind under full sail. No idea of the angle of roll but it was enough to make the rudder useless. They don't do much when close to horizontal. I was pinned down for about 30 seconds before I managed to point into the wind. External air intakes would have caused me a lot of grief. My air intakes are inside the cockpit, protected by wide combing and therefore I took on minimal water.

I would have expected a Nordhavn to have a system at least as good as this.
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Old 11-16-2018, 09:32 PM   #49
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the permanent clench marks i would have left in the seat vinyl would have confirmed the telemetry.
hahhahahha!
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Old 02-26-2019, 07:00 AM   #50
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Just to give an indication of how rough it can get there, Cyclone "Oma" just went by, but still 100's of miles away, and record 13m (40+ ft) waves were measured just off the coast where Dirona experienced her 69 roll .
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Old 02-26-2019, 03:39 PM   #51
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Just to give an indication of how rough it can get there, Cyclone "Oma" just went by, but still 100's of miles away, and record 13m (40+ ft) waves were measured just off the coast where Dirona experienced her 69 roll .
Those kind of waves no doubt moved a lot of sand around. So I imagine the area will need to be checked out, by the Tin Can Bay Coastguard at least, and possibly new marks established for the initial bar crossing area. I won't be up there until later in the year, and there should be a stable entrance area well before then.
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Old 02-26-2019, 03:56 PM   #52
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Looking at the designs proposed to me by numerous shipyards, the worst (smallest) AVS I've seen was 72 degrees. I understand that Nordies are generally about 90 degrees.

Who here actually knows the AVS for their vessels, and do you make open ocean passages?
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Old 02-26-2019, 05:00 PM   #53
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My AT34 isn't ocean going, AVS is supposed to be around 65-70 deg. On my sailboat, about 132 deg. Ocean passages on the sailboat not a problem, I'd be hesitant on the AT.

Another very important figure is the down flooding angle. Once you've rolled 50 or 60 deg on many trawlers, the engine room vents and other openings are underwater and you're beginning to flood.

Dashews boats are supposed to be self righting, as are the Ellings. Self righting doesn't mean an AVS of 180, but rather a high number, and the area under the negative stability part of the curve is something like 20% or less than the area under the positive part. Also deck/house structure are designed to be sufficiently watertight in a knockdown or roll over. The area thing ensures that in any sea condition that causes a capsize, you will very quickly encounter another wave that will right it. Of course much of the world's fishing fleet goes to sea in boats not meeting any of that criteria - but they also die at an alarming rate.
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Old 02-26-2019, 05:25 PM   #54
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Another very important figure is the down flooding angle. Once you've rolled 50 or 60 deg on many trawlers, the engine room vents and other openings are underwater and you're beginning to flood.
I've read many suggestions about running your fresh air intake duct down to the level of the sole, or even below the floorboards, in the engine room. That way in case of a roll over water will naturally not gush through this large intake.

For those who do plan Bluewater passages this may be something to consider. Also I suppose other advantages would be that condensation and drips run into the bilge instead of dripping all over, and it would help to keep the engine room bilge sweet with lots of ventilation.
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Old 02-26-2019, 06:14 PM   #55
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https://mvdirona.com/2014/09/69-1-degrees/
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Old 02-26-2019, 09:18 PM   #56
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You need only run the engine room air ducting in towards the middle of the boat. That will keep the inside end above the heeled waterline. If the inside end is lower than the outside end at any conceivable heel angle, there is the possibility of starting a siphon. Of course you could add a siphon break at a high point.
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Old 02-26-2019, 09:46 PM   #57
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You need only run the engine room air ducting in towards the middle of the boat. That will keep the inside end above the heeled waterline. If the inside end is lower than the outside end at any conceivable heel angle, there is the possibility of starting a siphon. Of course you could add a siphon break at a high point.
That's where ours are

Multiple large PVC tubes in a fordeck box coming down either side of the central doorway into the ER so about 5 ft in from the side.

Hot air out is via 2 large Davies Craig fans ducted to the rear 1/2 of the rooftop funnel.
Clean cool salt free air for the engine is ducted in through the fwd 1/2 of the rooftop funnel down to a sealed air box with filter then into the engine.
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Old 02-27-2019, 05:33 AM   #58
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For these duct arrangements, is there no heal angle where they can down flood, for example when the duct is horizontal? I'm having a hard time envisioning an arrangement where no flooding can happen.
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Old 02-27-2019, 06:53 AM   #59
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Brian,

Can you post a location (map) of Wild Bar Bay for us curious folks?
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Old 02-27-2019, 02:41 PM   #60
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Brian,

Can you post a location (map) of Wild Bar Bay for us curious folks?
Wide Bay Bar

https://goo.gl/maps/9JB5LRwqohn

https://noticestomariners.com/2018/0...ay-bar-status/
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