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Old 22-03-2012, 02:57   #1
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Bridge Deck Clearance ? How Much 40-50ft !

Ok we're on another thread getting into the height above the water that a bridge deck should be on a catamaran. So I thought it would be very interesting to hear what others think about this subject.

We know what the designers and brokers all say based on beam, shape of bridge deck, hull width and so on. What I'd love to know is what peoples experiences are..... meaning FACTS!

I want to know what you have sailed on, conditions you had (real conditions no BS here) and what you thought and what you'd like from those experiences.

The size of Catamaran we are talking about is the popular 40-50ft range and 22ft-26ft beam which there a **** loads of out there.

Look forward to hearing what people have to say about this.
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Old 22-03-2012, 04:16   #2
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Was a big thing for me before buying.
Our Lagoon 440 has 650 mm of clearance which works really well with the big round hulls.
The nacelle at the front works well to split any waves and sends the water and force in two then going around the inside of the hull back into the sea.
We nearly bought 2 Leopard 47 and the bridge deck clearance was from memory 300-350 mm.
The narrow hull shapes need increased clearance up to 800 mm as they have more travel into the water.
We have sailed ours in big seas and choppy seas, to avoid and minimise slapping you need to be 15 deg off the direction of the waves.
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Old 22-03-2012, 05:41   #3
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Thanks Dirkdig interesting about the angle to the waves to reduce slapping on your boat. Thanks for the reply.
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Old 22-03-2012, 06:50   #4
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re: Bridge Deck Clearance ? HOW MUCH 40-50ft !

One hint - if a manufacturer doesn't include clearance in their specs, its a fair bet - its not enough.
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Old 22-03-2012, 10:25   #5
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re: Bridge Deck Clearance ? HOW MUCH 40-50ft !

I have sailed a 54' one with 4'+ clearance. It was OK.

I have also sailed some small cats 36'-42'. Those with small clearances were always noisy. They also sailed upwind very poorly.

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Old 22-03-2012, 15:17   #6
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re: Bridge Deck Clearance ? HOW MUCH 40-50ft !

My boat has fat hulls, a gusset between hull and bridgedeck and 800mm of clearance. As yet I have not been able to get it to pound but, as you are aware, finding rough water in the Andaman Sea can be a trial.
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Old 22-03-2012, 15:22   #7
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Quote:
Originally Posted by Factor
One hint - if a manufacturer doesn't include clearance in their specs, its a fair bet - its not enough.
From my experience it's rare that they actually meet the designed height and also it's very rare that they come close to polars as well.

I think there is a lot of hype surround with the marketing and sales of boats these days and this is why I'd like to hear more about the real facts from people that have been out there and done it.

Many thanks for all the replies.
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Old 22-03-2012, 15:30   #8
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re: Bridge Deck Clearance ? HOW MUCH 40-50ft !

Oram 44C, 22ft overall beam, 680mm clearance at lowest point, fully loaded for liveaboard cruising.
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Old 22-03-2012, 15:53   #9
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re: Bridge Deck Clearance ? HOW MUCH 40-50ft !

Tri Spirit,
Welcome to the forum. I don't know if you had tried this because you are new. There is a search function on the forum that pulls up old threads. You go to the search tab, hit the down arrow, and choose the second option - Google Search. If you type in "catamaran bridgedeck clearance" you will find this exact topic has been brought up about 20 times.

Not that the catamaran club isn't happy to go on and on about the subject. But if you really just want the info, it's already here.
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Old 23-03-2012, 11:39   #10
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re: Bridge Deck Clearance ? HOW MUCH 40-50ft !

Speed and sea conditions are a significant factor. If you are slamming, slow down.

My Searunner 37 had 24" under wing clearance. Very quiet . My Lock Crowther 37 has 18" and just as right.

Distance between hulls is a factor as well as speed and sea conditions. I do not believe there is a definitive answer. However - More is better.
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Old 23-03-2012, 11:47   #11
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re: Bridge Deck Clearance ? HOW MUCH 40-50ft !

On my Lagoon 42 I could barely take the 10ft RIB with 15hp Yamaha under the boat with 2 people in the dingy. It seldom pounded. Sorry dont know how much clearance that is , but more than many of the boats I see advertised.... anyone know what the TPI 42 cleanace was?
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Old 23-03-2012, 11:56   #12
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re: Bridge Deck Clearance ? HOW MUCH 40-50ft !

I am out of the OP's spec. on length and width, so I will just say welcome trimaranspirit
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Old 23-03-2012, 15:23   #13
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Quote:
Originally Posted by Cotemar
I am out of the OP's spec. on length and width, so I will just say welcome trimaranspirit
Thanks Cotemar anyone is welcome to share their experiences I didn't mean to limit it.

I've got an old formula 40 tri so it doesn't include me but my aka clearance is between 800mm at the lowest end and about 1000mm at the highest end and man when pressed in a sea do they go thru the water! Lots of spray but never really any pounding quite amazing what that little boat can do actually.

When I was a kid my father built a Tony Grainger Ocean 470 and she had nearly 1000mm of clearance. She had a 26ft beam and length of just under 48ft and was built very light. She was a fast boat and great at sea but didn't like a short sharp sea on the bow.

A close friend has bought a Schionning (26ftx49ft) Wilderness 1500 and her clearance is about 900mm. They have done a fair few miles since launch and have not really had any major slamming even in sloppy beam seas.

I think it's a pretty important factor when considering comfort and sea kindness. It's not the be all and end all, as we know many cats with much lower clearance have sailed the world but the higher the better for me.

My father also owns Fusions Catamarans (40ft x 22ft. 800mm height) Australia and I know when they did the design with Gary Lidgard it was important to have a nice chamfer and as much height as possible.

When I was a kid we also had a Seawind which we ran as a charter business on Sydney Harbor and it would slam with the wake of a ferry passing under us. It was a great boat and lots of fun but doing trips up the coast we had to watch the sea conditions closely.
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Old 22-08-2012, 03:48   #14
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re: Bridge Deck Clearance ? HOW MUCH 40-50ft !

Bridge-Deck clearance on a Catamaran.

Lets face it guys, most of the Production Cats do not have enough clearance or the have many shelves, bumps, and things that should not be there.

If it is slamming, it is causing Drag as well.

My 381 Catana does not slam with 800mm of clear space between the hulls. She points to windward at 35deg in 25/30 knots of wind and overtakes most if not all Monohulls.

For some reason unbeknown to me the Production Cats seem to ignore the 6 ingredients for good cat design, my cat had 5 out of 6 and I sorted the 6th one out, now I have 5.5 out of 6.

85% of Cats on the water are lucky if they have 2 out of 6 of the ingredients required, I know, I have 200 listed on my laptop, all with calculations saying how good or mostly BAD they are. That Is why I am launching mt Website called - What Cat NOT TO BUY AND WHY.

You can contact me on bazcatanaATyahooDOTcoDOTuk and I will send you info on my boat which is for sale and I will talk about my Web site if that is of interest.

Regards

Barry Parkinson
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Old 22-08-2012, 05:11   #15
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re: Bridge Deck Clearance ? HOW MUCH 40-50ft !

Barry, you have ETA for launch of website? Thanks.
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