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Old 03-10-2016, 08:13   #31
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Re: Positively buoyant catamarans

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Originally Posted by lindabarzini View Post
Maybe those front parts of the forward cabins and storage under the beds could be filled with empty 2-liter bottles with the cap on tight. I read about some Gemini owners doing something like this.
The trick (problem) with this is, keeping them in place, & inside of the boat, for long enough to make it to safe harbor. As the wave action & hydrostatics definitely give them lots of incentive to move around, & try to escape.
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Old 03-10-2016, 10:39   #32
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Re: Positively buoyant catamarans

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The trick (problem) with this is, keeping them in place, & inside of the boat, for long enough to make it to safe harbor. As the wave action & hydrostatics definitely give them lots of incentive to move around, & try to escape.
Remember PlasTiki?

They placed the bottles in a netting, so that say every 100 bottles become one unit. Now they are much easier to control, tie down or immobilise in some other way.

Should work. ?

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Old 03-10-2016, 12:38   #33
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Re: Positively buoyant catamarans

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Originally Posted by MikeFergie View Post
Linda I have. Some pictures of a leopard 44(sad case) that once inverted travelled upside down from almost Australia back to Cape Town over a full year with only. With human intervention. Sadly it ripped. Apart and sank.

So for Mcel it's clear that they are positively buoyant


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Mike, I sent you a PM regarding the above statement you wrote. I would like to know how you know the Leopard 44 was ripped apart and sank? If you can point me to where you found this information, it would be greatly appreciated. Sorry for the OT question.
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Old 04-10-2016, 07:11   #34
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Re: Positively buoyant catamarans

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Originally Posted by barnakiel View Post
Remember PlasTiki?

They placed the bottles in a netting, so that say every 100 bottles become one unit. Now they are much easier to control, tie down or immobilise in some other way.

Should work. ?

b.
Actually, scenarios & setups like the above are why I posed the question. Since the efficacy of such setups, & how long they last when actually loaded up & they're supporting a vessel, is quite poor with some designs. So one needs to ensure that both a good design, & good materials are employed if you choose to go that route.

In the past, some high speed racing powerboats, have used netting to contain ping pong balls in order to meet class floatation requirements. Since ping pong balls provide the lightest form of floatation for a given amount of floatation. But there have been some shall we say, awkward goofs with keeping them in place, & inside of the boats, over the years. A few of them being quite comical.

So at times it can be cheaper & more reliable to go with more conventional methods of floatation. Especially if you have to do things such as resort to using Spectra netting for the above. So that things are both strong enough, & have enough wear resistance when subject to loading & chafing. Since if the netting gets cut at all, or develops holes, then you're sunk (pun intended).
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Old 04-10-2016, 07:23   #35
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Re: Positively buoyant catamarans

Upside down does not imply positive buoyancy. It implies air pockets.

Floating hulls with no rig does not imply positive buoyancy. It implies positive buoyancy of a bare hull.

You want positive buoyancy of the boat upright, with full rig on and all gear in.

Or do you sail boats without rig, upside down? You must be mad then.

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Old 04-10-2016, 09:31   #36
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Re: Positively buoyant catamarans

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You want positive buoyancy of the boat upright, with full rig on and all gear in.
And that boat would be the most space inefficient spartan boat with minimal tankage, tons of wasted flotation voids - but I guess you can admire the boat while all the few things aboard are sitting in a meter and half of water while waiting for rescue. Not really sure what the appeal is - seems like beyond simple bow and rudder bulkheads, everything else claimed is better for marketing than enjoyment and safety.

I've always wondered why with catamarans, builders don't just offer a simple inflating skirt/bladder under the bridge deck - if you unluckily holed in longtitutal way that collusion bulkheads won't save you from imbalanced flooding in one hull, a bladder displacing about 60 cubic feet would keep that hull out of deep water and you'll be able to stuff the breach and manually pump out.
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Old 04-10-2016, 18:47   #37
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Re: Positively buoyant catamarans

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Originally Posted by SV DestinyAscen View Post
And that boat would be the most space inefficient spartan boat with minimal tankage, tons of wasted flotation voids - but I guess you can admire the boat while all the few things aboard are sitting in a meter and half of water while waiting for rescue. Not really sure what the appeal is - seems like beyond simple bow and rudder bulkheads, everything else claimed is better for marketing than enjoyment and safety.
Actually it's not hard to build a cat with positive buoyancy, that would float quite high even with both hulls flooded and the rig still on.

Cat's generally have fine bows and sterns, which are very suitable spaces for buoyancy without major impact on living or storage space. (The ends of the hulls shouldn't really be used for storage, especially of heavy items.)
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Old 05-10-2016, 00:47   #38
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Re: Positively buoyant catamarans

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Originally Posted by SV DestinyAscen View Post
And that boat would be the most space inefficient spartan boat with minimal tankage, tons of wasted flotation voids - but I guess you can admire the boat while all the few things aboard are sitting in a meter and half of water while waiting for rescue. Not really sure what the appeal is - seems like beyond simple bow and rudder bulkheads, everything else claimed is better for marketing than enjoyment and safety.

I've always wondered why with catamarans, builders don't just offer a simple inflating skirt/bladder under the bridge deck - if you unluckily holed in longtitutal way that collusion bulkheads won't save you from imbalanced flooding in one hull, a bladder displacing about 60 cubic feet would keep that hull out of deep water and you'll be able to stuff the breach and manually pump out.
SV My PDQ 36 is positively buoyant , and does not suffer from the failings you describe. I do realize that it is not a deep sea cruiser.
Last winter in Martinique we where in the large marina where the charter bases are. One of the operations lifted the entire back end of an Outremer 55 far enough out of the water to take out both saildrives for service. It was done with a heavy-duty bag and a shop vac. Very cool
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