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Old 12-09-2020, 20:30   #46
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Re: Positively buoyant catamarans

Very glad to hear from you Mike. I have gotten interested in the Snowgoose since my sailing friend sent me a listing for one. I searched and saw there are quite a few for sale. They certainly tend to be less expensive than the bigger, newer cats. I'm not after the space, I'm interested in the stability, compared to the bobbing and heeling in a monohull. That motion seems like a real problem to daily living to me so I'm motivated to find a cat. The other thing I wanted is the "unsinkableness," so I'm sorry to hear you think they don't have positive buoyancy (meaning you think they'd sink, right?). Still, for the price, getting the stability still seems like a great deal.

How long have you had yours? What do you like (and not like) about it?

It's the boat I'm looking most at. I understand they also do not have later cats' speed, doing about the same 6 knots as a monohull, from my reading, which is fine, considering the prices. I haven't seen any other cats that come close in price, which seems to start around $50K and go up for newer ones.

Thanks...hope to hear from you.

As for the info on the Med, it comes from this video:


I have little to go on except web pages and youtube. What they say is pretty opposite to what you say. But, they are a young couple (compared to me) and are speaking about "what they've heard." I like your report much better. They didn't specify but it seemed they were comparing the Med to the Caribbean.

I tried to google COE, without luck. Thanks.



Quote:
Originally Posted by mikedefieslife View Post
Earlier Snowgooses like mine are solid fibreglass throughout. That is hulls, bridgedeck, coachroof, everything. From then on they went solid glass down below, and cored decks and coach. No foam is used. I severely doubt the construction materials alone give them any buoyancy.

They all have sealed compartments in the four corners. There's are around 1.5m3 on my boat. Probably more on the larger boats.

Considering the huge numbers produced, very few have been lost or flipped. One that was lost a year or so ago had the buoyancy chambers cut open to be used as storage (unbeknown to the new buyers).

As to Med marinas, the beam doesn't mean anything. A 7m wide lagoon will be charged the same rate multiplier as a 4.67m wide Prout. There are a few marinas where they use total area, but not many.

The static and dynamic stability (the latter just being a division of the former), it pretty high despite the narrow beam, due to the low COE.

Where is it that you think the Med has less options to anchor than? In my experience so far, the Med has far more anchorages than the Caribbean by a large margin, but those anchorages are much smaller, and you need to watch the weather as one day you might have a mistral, and a few days later a sirocco (wind, not the boat). You'll have no need to visit a marina at all during the spring and summer. Most people winter in a marina, and those with cats choose ones that don't charge any extra.
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Old 12-09-2020, 20:34   #47
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Re: Positively buoyant catamarans

Quote:
Originally Posted by Cheechako View Post
That's right. a cubic foot of air gives you about 64# of bouyancy. So for a 15000# boat you need 4 ft x 4 ft x 16 ft of enclosed air.

So for example, a Lagoon 42 the dry weight is about 25000 lbs. Figure 30000 lbs loaded?
You need 470 cubic feet of air. 4 ft x 4 ft x 29 ft long!
A cubic yard or a cubic metre, will displace one Ton of seawater,
3 feet by 3 feet by 3 feet, = One Ton of displacement,

It can be in sealed plastic one gallon jars, Hidden under beds or bunks,
It doesnt need to be in one big container,

30000 lbs is approx 5 Tons, so you need 5 cubic metres of sealed air to keep 5 Tons afloat,
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Old 12-09-2020, 21:33   #48
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Re: Positively buoyant catamarans

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Originally Posted by thinwater View Post
I would not foam a crash tank in a cat. A real mess if it gradually gets wet. It is simply unnecessary, since even holed it controls flooding. The important thing is to divide the tanks and to make them long enough (restrict the floor length).
Fill them with ping pong balls or foam pieces from a swimming noodle glued together.
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Old 13-09-2020, 06:36   #49
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Re: Positively buoyant catamarans

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Originally Posted by river251 View Post
The other thing I wanted is the "unsinkableness," so I'm sorry to hear you think they don't have positive buoyancy (meaning you think they'd sink, right?). Still, for the price, getting the stability still seems like a great deal.

How long have you had yours? What do you like (and not like) about it?
I don't think they'd sink. As I said they have large sealed compartments that should be enough to keep the boat afloat. In fact it's proven in the ones that have got into trouble in the past.

Previously you and others were talking specifically about cored hulls being unsinkable. I was merely saying the material the Prout is made of, has no buoyancy itself. So is reliant on the 4 sealed chambers.

That was why one sunk off Puerto Rico because an idiot previous owner had cut open the buoyancy chambers which put the new owner was unaware.

I have bottles in chambers on mine. I think reinforced inflatable bladder would be better.

I have had mine for over 3 years. Sailed the Med over a couple of years and crossed the Atlantic solo. Bear in mind mine is the 35, so a little smaller than the 37 and Elite, but with a better SA/D.

Full with my cruising gear it weighs 4,500kg. Downwind even surfing at 15knts is a perfectly comfortable. I tend to reef at about 7.5 knts.

Anything on the beam or upwind with short seas is ridiculously uncomfortable. I remember 2m waves at 6 seconds in Tenerife. Being bad enough that you couldn't stand up without holding on. And going into short steep waves being violent enough to break a few things. It's not all bad, and many Prouts have sails all over the world, so perhaps it's just me, but I've had some nice sails in it too.

Speed can vary. I had a nice downwind sail from Menorca to Mallorca, averaging around 8-9 knts. 7.5-8 knts in about 16knts on the beam. I plan mostly at 5 knots.
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Old 13-09-2020, 15:31   #50
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Re: Positively buoyant catamarans

Quote:
Originally Posted by Mr B View Post
A cubic yard or a cubic metre, will displace one Ton of seawater,
3 feet by 3 feet by 3 feet, = One Ton of displacement,

It can be in sealed plastic one gallon jars, Hidden under beds or bunks,
It doesnt need to be in one big container,

30000 lbs is approx 5 Tons, so you need 5 cubic metres of sealed air to keep 5 Tons afloat,

Keeping a 5 ton Gemini afloat would take a lot less than that. 5 tons of floatation could keep the entire boat high and dry and out of the water if the floatation was under the hull. The issue is that the materials that the boat is made of displace water, so keeping the whole boat at or above neutral bouyancy (ie just afloat) would take dramatically less floatation. The metals have a high specific gravity and thuswould contribute little to bouyancy, but as a wild guess there is probably slightly over 1000 lbs of metal (400 lb diesel, a few hundred lbs for mast and wire, and miscellaneous, say 1200 lb, requiring 1000 lbs floation ??? plywood and wood is positive bouyancy. Lots of fiberglass at 1.3 SG so only needing ~30% extra flotation. you'd have to do this in a more detailed way, but 4000 lbs (2 cu meters) would probably keep you up and bobbing. I'm sure the flotation tanks would displace well over 2 cu m total. Now that's to keep you up, the idea of extra flotation (mattresses inflated) would make help keep you up further which would be practical and comforting.

DougM
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Old 13-09-2020, 18:29   #51
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Re: Positively buoyant catamarans

Quote:
Originally Posted by DougM View Post
Keeping a 5 ton Gemini afloat would take a lot less than that. 5 tons of floatation could keep the entire boat high and dry and out of the water if the floatation was under the hull. The issue is that the materials that the boat is made of displace water, so keeping the whole boat at or above neutral bouyancy (ie just afloat) would take dramatically less floatation. The metals have a high specific gravity and thuswould contribute little to bouyancy, but as a wild guess there is probably slightly over 1000 lbs of metal (400 lb diesel, a few hundred lbs for mast and wire, and miscellaneous, say 1200 lb, requiring 1000 lbs floation ??? plywood and wood is positive bouyancy. Lots of fiberglass at 1.3 SG so only needing ~30% extra flotation. you'd have to do this in a more detailed way, but 4000 lbs (2 cu meters) would probably keep you up and bobbing. I'm sure the flotation tanks would displace well over 2 cu m total. Now that's to keep you up, the idea of extra flotation (mattresses inflated) would make help keep you up further which would be practical and comforting.

DougM
I never went into the materials themselves floating,
I never even gave that a thought,
I just thought, I weigh approx 5 Tons loaded,
Whats the easiest way to keep my boat on the surface,
And cheaply,
I had thought of big tractor tyres tied under the hulls,
One under each corner, Easily stored in the back bedrooms,
But in rough weather, That would be impractical and dangerous,
A lot of fart arseing around to get them in place and blown up,
Plus a lot of time to get them blown up as well,
Where Im going there are very big crocodiles,
I dont want to be in or near the waters edge,

Then I went into blow up bags, The cost of those is over the top, Exy,

The Queen size double height mattress was on sale and cheap, $50-00
That would be very nice to sleep on,
But its too high on my bed, there is no room above the bed, so its Impractical,
It takes 3 minutes to blow up with its own built in pump,
I just have to plug it in,
Then I calculated out the area they have, Inflated, 2 tons displacement,
My problems solved,
The blow up mattress I left under my Queen sized bed mattress deflated,
It takes up no room under there and its out of the way,

Then I worked out the displacement of the double height, double bed, blow up mattresses, They give me another 2 Tons displacement,
They can go under the double bed mattresses in the rear bedrooms,
Deflated as they are too high in there too,

To blow up the 3 mattresses take 10 minutes, with out stress or getting any thing into position,
Dragging them out and tying them to some thing, Etc Etc,
I just plug the electrical lead into them where they are and blow them up,
I have instant bouyancy,

Problem being, They dont work till they are up against the roof,
But it would keep my batterys and motor dry, They would still be above the water line,
Even half submerged, I can still sail it to some where where I can get the holes fixed,
Run it up the beach at high tide, Fix the holes at low tide,

Waking up in the middle of the night, on the rocks and 2 feet of water inside my boat was incredible, Unbelievable,
My mind was racing at 10 million miles a second,
Get the pumps working first, Their all submerged,
How safe am I , Have a look around outside,
Im in 3 metre waves coming up the inlet,
Im half on the beach, The Transom is nearly under,
The front is sitting on the beach, The boat cant sink,
We are Safe,
The boat is rocking on the rocks under it,

The batterys being low, They shorted out leaving me with no power, Hence no pumps, No lights, your down to a torch, to see any thing,

The water is full of every thing that used to be in the cupboards tucked away neatly and cleanly,
Your walking with bare feet thu this garbage, sharp pointy things are sticking into your feet,
You cant find any thing as its all submerged, Including your clothes,

In this situation, My Blow up mattresses would not have been effective as I had not sunk low enough for the bouyancy to take effect,

I have no idea on how well the inbuilt bouyancy tanks work or how effective they are in a real sinking at sea,
And Im not about to find out or rely on them to keep me afloat,

So I am working on the presumption of total bouyancy to keep me on the surface in all conditions at sea, when and if it may be required,

I am about to do a 12,000 mile voyage, and sinking wont be a problem to me as humanly possible, Or as much as I can prepare for it,

The Tasman Sea, Indian Ocean and Southern Ocean are a part of my voyage, I have a very capable boat with beefed up hulls,
So its should be a good trip,

Cheers, Brian,



,











,
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Old 13-09-2020, 19:52   #52
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Re: Positively buoyant catamarans

That is going to be some trip on Gemini 105. Will be interesting to read about about it in the future.

I'm sure like me you have storage space that isn't much use for heavy items. I put my empty 20l water and fuel jugs in them, which will aid buoyancy.

I mentioned before that I have plastic bottles in my buoyancy chambers. I don't like the bottle idea though. They degrade over time, and become flat. I would prefer something like pool noodles, but they aren't UV stable, or tractor inner tubes. The type used for running on rivers or snowy peaks. they are tough and supposedly UV stable. They would loose air, so you'd need to inflate fully before a voyage. I imagine they would also work for lifting a cat up if it was partially beached.
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Old 13-09-2020, 22:56   #53
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Re: Positively buoyant catamarans

Thanks again Mike. Is this characteristic of catamarans in general?

Quote:
Originally Posted by mikedefieslife View Post
Anything on the beam or upwind with short seas is ridiculously uncomfortable. I remember 2m waves at 6 seconds in Tenerife. Being bad enough that you couldn't stand up without holding on. And going into short steep waves being violent enough to break a few things. It's not all bad, and many Prouts have sails all over the world, so perhaps it's just me, but I've had some nice sails in it too.
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Old 14-09-2020, 05:02   #54
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Re: Positively buoyant catamarans

I don't know. Possibly not. Or possibly my tolerance for bumpy ride is less than others'.

Seakeeping and comfort is perhaps something you would have to canvass owners on. I previously had someone crewing on board, and she was happy to sail into 30 knts of wind and did so with a big grin on her face, whilst I would rather have been chilling out back in the calm anchorage.
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Old 14-09-2020, 13:50   #55
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Re: Positively buoyant catamarans

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Originally Posted by river251 View Post
Thanks again Mike. Is this characteristic of catamarans in general?

No, it’s a characteristic of a relatively short and heavy catamaran with relatively fat hulls (for the length).

As you add length to the hulls the ride upwind smooths out. Not unlike a short and relatively fat monohull (my family used to own a Rawson 30) vs a longer and relatively lighter and narrower monohull.
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Old 14-09-2020, 15:25   #56
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Re: Positively buoyant catamarans

Quote:
Originally Posted by mikedefieslife View Post
That is going to be some trip on Gemini 105. Will be interesting to read about about it in the future.

I'm sure like me you have storage space that isn't much use for heavy items. I put my empty 20l water and fuel jugs in them, which will aid buoyancy.

I mentioned before that I have plastic bottles in my buoyancy chambers. I don't like the bottle idea though. They degrade over time, and become flat. I would prefer something like pool noodles, but they aren't UV stable, or tractor inner tubes. The type used for running on rivers or snowy peaks. they are tough and supposedly UV stable. They would loose air, so you'd need to inflate fully before a voyage. I imagine they would also work for lifting a cat up if it was partially beached.
I have had my boat sitting on 4 rubber truck tyres on the concrete slipway for a week,
Repairing my drives Universal joint,
Tied to the boat so they didnt move out with the changing tides,

The bottles are in a sealed container, So no UV effect, But as you use bottles, You can replace the bottles from time to time,
You should get at least two years before replacing the bottles entirely,

Not sure if the mattresses would lift my boat if its on the beach, But its a good thought, Easy to get under it, Deflated, and then pump air in once the boat has settled and the tides out,

My hulls are now 13 mm thick, Beefed up from OEM, 5 mm, So its highly unlikely I will get a hole punched in them,

Across the transom is one large hole with the motor in the middle, Lockers both sides on the top of the rear steps, Its all sealed from the inside, and outside,

Its a part of the upper hull, so the bottom is sealed off from the hulls under it, So it cant be holed from under the hulls,
So that should keep the rear afloat, Minimum size 2 feet square by 14 foot long,
Air in my water and fuel tanks is extra bouyancy,

Interesting thought, Would a spare diesel container float, full of diesel,
I might try that, The empty ones will,
I carry seven of them, 25 litre ones, Just in case, nearest diesel can be 500 miles away,
I ran the diesel for four days solid coming home when I had no wind at all,


Only twice Ive ever had water over the transom, from following seas, Waves following and waves from the side at the same time,
It filled the cockpit to my knees, But drained very rapidly,
That was a pretty wild storm, Big waves and high winds, middle of the Coral Sea,
But Ive been in big seas with over 40 knot winds and never came close to water over the transom, In Bass Strait,

The wind is very finicky, I did a 7 day shake down trip in Bass Strait, I had wind for one day only, Motored for 6 days, Duhhh I am a sail boat,
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