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Old 18-08-2014, 00:15   #1
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Hunkering down: Adding 30 tonnes

I am looking for some feedback on this situation.

Picture a big trimaran on moorings facing into 100+ knot winds. A storm surge is about to hit.

When the storm surge lifts the bows high, large areas will be exposed to the wind. Things may get interesting.

I can easily load the bows with tons of water to help prevent both the rise and counter the wind.

1. Ever here of someone doing this?
2. Opinion?

At sea, is the same concept valid but only load two ama evenly?

Have any big trimarans NOT under sail been turtled?

Thanks


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Old 18-08-2014, 04:41   #2
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Re: Hunkering down: Adding 30 tonnes

PS Momentum is a concern since breaking load on the lines is approximately 150,000 lbs. I spread loads between 5 attachment points. Two are expected to break at impact. Not a biggie.

I am not concerned about the stern mooring and lines since the surge will spread out into the mangroves.

Unlike Yolanda (Haiyan) where I ran 14 lines to shore in all directions, shore here is too far.
Like Yolanda, everything must be planned in advance since no one is permitted aboard upon strike.

The one alternative suggested to me is to beach her. Someone did that with a big cat previously. Not easy for me since I have a deep fixed racing rudder.


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Old 18-08-2014, 04:59   #3
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Re: Hunkering down: Adding 30 tonnes

PPS The other alternative is to head to sea. I freely admit being out at sea in 100+ knot winds is daunting. The mast rigging will hold till at least 144 knots. I sized based on Paka in Guam. It already has seen 100 knots when Yolanda's eye hit 40 km to my North.

Which alternative seems better for a light trimaran? Hunker, or go to sea into possible more harms way?

Yes, eventually I must elect. I do appreciate opinions to consider.




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Old 18-08-2014, 05:00   #4
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Re: Hunkering down: Adding 30 tonnes

I think this is a very real worry for you.

The safest way is to open your sea cocks and sink your boat and then recover it after the storm and surge.

BTW the storm surge must come in quickly on your parts of the world.
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Old 18-08-2014, 19:36   #5
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Re: Hunkering down: Adding 30 tonnes

Mark thanks. I have considered sinking in advance. I have heard others mention this radical solution. However, openning the sea cock would not sink this boat. Maybe about three inches lower but thats it. At best if I pump everything full, her cock pit would still be high and dry.

Besides the piano....

Last night I was discussing this issue with a Lagoon 380 owner. Last year he felt the wind get under his vessel while anchored. "It scared the h out of me because I knew what the wind was doing and physically felt the whole vessel rise."

In 2008 a Lagoon 410 at anchor turned turtle with the owner inside. He safely got out.

Based on these two reports, my planning before a storm strikes seems prudent.

One new conclusion I came to is all 4 tramps off and not just the front two.

Also I did another check and now conclude I can easily add 60 tonnes.

I will move this question to boatdesign but feel free to post any experience with this topic.

Philip


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Old 18-08-2014, 19:40   #6
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Re: Hunkering down: Adding 30 tonnes

A piano on a boat? Ok that's it I give
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Old 18-08-2014, 20:48   #7
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Re: Hunkering down: Adding 30 tonnes

Quote:
Originally Posted by Scot McPherson View Post
A piano on a boat? Ok that's it I give
I felt the same way when I found out the Russians had a pool and a gym on their Akula (Typhoon) class sub. LOL
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Old 19-08-2014, 06:52   #8
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Re: Hunkering down: Adding 30 tonnes

A sub is a ship, we are talking yachts here...not exactly the same thing eh?
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Old 19-08-2014, 09:17   #9
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Hunkering down: Adding 30 tonnes

It shouldn't be too difficult to calculate how much "wing" area you have and from that determine amount of possible lift. I'd be surprised if it were in the dozens of tons category unless your boat is truly huge.


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Old 19-08-2014, 11:46   #10
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Re: Hunkering down: Adding 30 tonnes

Quote:
Originally Posted by pbmaise View Post
Have any big trimarans NOT under sail been turtled?
I have heard of few of cruising cats flipped (or maybe turtled) at anchor, but never a tri.

What about a few triangle stabiliser fish from the extremities? You add stability without adding mass.
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Old 19-08-2014, 12:21   #11
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Re: Hunkering down: Adding 30 tonnes

What if you drop very heavily loaded thick canvas 'curtains' in each of you hull-to-ama spaces?

If the wind cannot get under the deck joining the hull and the ama, it cannot lift the boat.

Right? Wrong?

b.
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Old 19-08-2014, 12:58   #12
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Re: Hunkering down: Adding 30 tonnes

I was thinking possibly spoilers? pretty common when you tie down airplanes with really bad storms coming to put even 2x4's on tops of the wings in the right place, it spoils the lift and your airplane doesn't get blown away
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Old 19-08-2014, 13:06   #13
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Re: Hunkering down: Adding 30 tonnes

I wonder if the hulls structure can handle the added water weight + sea and wind state stresses.
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Old 19-08-2014, 14:20   #14
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Re: Hunkering down: Adding 30 tonnes

How about anchors to both amas as well as the main hull? The pull of the anchor lines will be against the wind and will be downwards. They should help counter wind lift.

I think your idea of adding weight in the bows is good, so long as it is done well. Adding water, if you are just going to flood bilges, is going to give a huge amount of free surface effect. The sloshing could be pretty destructive. If you are containing the water is some type of containers then that has to be to the good. Bladders could be stored and filled when needed.

Good luck with it.
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Old 19-08-2014, 14:42   #15
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Re: Hunkering down: Adding 30 tonnes

I have discussed essentially the same idea, and am saving up all my 1 gallon containers so I can fill them with ballast to 'hunker down' the hulls in the boat when it is left unattended and keep it from blowing away in a storm.
(And when underway they are empty so its bouyancy).
Seems like a good plan. The downside is once it starts moving, the damage it will cause when run into something will be much worse.
My boat may be as big as yours, so hauling it in a boatyard isn't attractive.
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