Bridge Deck Clearance . . . How Much Have You Got ?

[Clipper4730]

Greeting Catamariners,

The admiral and I are narrowing down our search and we are looking for some specific info on a few yachts. During our research online and on the water we have realized that bridge deck clearance can be an important factor on selecting a yacht. What we are looking for is the bridge deck clearance for these yachts.

Lagoon 41
Leopard 39 (new)
Voyage 43
Fountain Pajot 40 Lavezzi

[colemj]

I don't know the exact numbers, but I can rank them from greatest clearance to lowest for you based on experience with each (except the new L39):

FP Lavezzi
Lagoon 410
Leopard 39
Voyage 43

Mark

[WillJacocks]

With the monohulls, bridge clearance is not exactly a real problem. Just have another boat pull the mast sideways and put some weight on it
and you can clear most bridges.

[Sand crab]

I think colemj has it right. Here is a link to a video from Phil Berman of The Multihull Company discussing 2 of these boats. It's about 3/4 of the way thru. And yes, I posted this before. Click on educational and it will get you to the Slapping and Pounding video.
Catamarans for Sale Bob

[smj]

Originally Posted by Sand crab

I think colemj has it right. Here is a link to a video from Phil Berman of The Multihull Company discussing 2 of these boats. It's about 3/4 of the way thru. And yes, I posted this before. Click on educational and it will get you to the Slapping and Pounding video.
Catamarans for Sale Bob

Educational slapping and pounding video? But I thought this was a cruisers forum not sex ed. I apologize I just couldn't help it.

[limejucer]

Im happy ive got a tank with a nacelle. so clearance is 0 to touch but 12 ins to block one tunnel?

[Dragon Lady]

Our Lavezzi slams every now and then, I can't imagine how bad it would be on a boat that does it all the time.
I suppose if you only sail in flat water it wouldn't be a problem.
Before anyone convinces you that it doesn't matter, experience the sensation yourself and make your own decsion.

[tuskie]

Originally Posted by Clipper4730

During our research online and on the water we have realized that bridge deck clearance can be an important factor on selecting a yacht. What we are looking for is the bridge deck clearance for these yachts.

You are right to be considering bridge deck clearance for rough water catamarans, but it is only part of the equation. Other factors that influence whether or not a hull slams due to wave impact under the bridge deck include the volume ( buoyancy) of the hulls, the distance they are apart, the load the vessel is carrying, any protuberances on the side of the hulls ("chamfer panels") and the way the vessel is operated ("seamanship"). The last factor is arguably the most important.
Try searching through old threads for many discussions and opinions on this topic. Happy cat hunting!

[cat man do]

Originally Posted by limejucer

Im happy ive got a tank with a nacelle. so clearance is 0 to touch but 12 ins to block one tunnel?

300mm (12 inch) is bugger all.
Most boats in the 30 to 50 ft range would have twice if not 3 times that.
Some in the larger size even more.

[John Webb]

Hi, We sail a Ron Given off-shore 48ft with a bridge deck clearance of 28 in (700mm) fully laden We have completed over 5000 off shore miles in the last 2 years and only had a few noticeable bangs under the hull through out this period. We weigh 10 tonnes laden.

Naturally the sea state and wave direction can change conditions but even in 40 knots to windward on the way to New Caledonia last year we found that there was no banging under the bridge deck, so just as Tuskie says the bridge deck clearance isn't everything you have to have the right weight and the correct buoyancy..

[Talbot]

Bridgedeck clearance is an important aspect to counter pounding, but the design of the hull under the bridgedeck is just as important.

The more clearance you have, the higher the superstructure is out of the water, thus affecting windage, particularly when manoeuvring in a marina, and also when going to windward. It must also impact the stability, reducing the force needed to capsize, and adding more windage and leverage to the force acting to cause a capsize.

This is one of the reasons why a Prout with it's narrow beam can work so well.

[John Webb]

Hi Talbot, you are entitled to your opinion, but I can't agree with a single statement that you have made. I have seen Cats with tremendous clearance under the bridge deck and very little super structure up top, additionally a cat that has a narrow beam is more likely to turn over compared to a well designed vessel with the correct ratio of beam to length
But I respect your opinion..
Cheers
John

[quartersplash]

I have found that it has more to do with the sea state. When we had large washing machine seas from every direction at the same time, in the Carrib, we had major pounding of the bridge deck. When we had seas of any size from any direction that had a pattern, there was no pounding.

[Talbot]

Originally Posted by John Webb

....I have seen Cats with tremendous clearance under the bridge deck and very little super structure up top, additionally a cat that has a narrow beam is more likely to turn over compared to a well designed vessel with the correct ratio of beam to length ..

Of course, a performance cat with an open bridgedeck can have great clearance and little superstructure. However, a cruising boat with decent headroom in the bridgedeck saloon has a choise of high superstructure or low bridgedeck clearance.

of course a narrow beam cat is more likely to capsize due to wave action than a wide beam

however, when you are considering ONLY the effect of wind, there is a more obvious trade-off between the different factors, and you need to consider ALL the factors rather than just "good bridge deck clearance = good"

[Don1500]

You can do it this way, too.
How to get an 80' boat under a 65' bridge.