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Old 27-04-2020, 11:47   #1
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Mass manufactured Cat Highest Bridge Deck Clearance

Hi. I am wondering if anyone out there has done the research or knows, the model and manufacturer of a catamaran 50 feet or under with the highest water to bridge deck clearance?

I have found this important equation is missing on the specs of a lot of boats.

Thanks in advance.
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Old 27-04-2020, 12:06   #2
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

Check out Multihull Dynamics, link below, they have a lot of data on a lot of cats.

http://www.multihulldynamics.com/default.asp

They also have brief explanantions of the data and calculated factors. Reading about the related calculations should help you come to the realization that its not just about absolute bridge deck clearance. How a given cat handles is more complex with factors like bridge deck tunnel shape, bridge deck clearance to LOA ratio, and others all palying a role.
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Old 27-04-2020, 12:22   #3
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

Thanks. Have a great day.
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Old 27-04-2020, 14:40   #4
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

The cats that traditionally have the best bridgedeck clearance are Outremer and Catana. However the older Lagoon 47 and 42TPI were pretty decent. The L55/57 and 67 were really high. FP cats had good BD back in the day, the Bahia was good.

The lowest were about all of the South African cats but that's not the whole picture because less windage can be a good thing. Many of the newer ZA cats have raised it some.
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Old 27-04-2020, 16:14   #5
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

The other thing often forgotten, is that a sailboat is designed to be sailed, in other words not directly into the wind! If you are sailing, and therefor at a sailing angle, or motoring but still with some angle, the slamming is cut way down and often eliminated. It's when you insist on motoring straight into the wind that the slamming appears worse. Hey, guess what, its the same with most monohulls of modern design. However, most "modern" sailors, and certainly charterers who are trying to stick to a schedule, insist on motoring upwind and go straight into it.....and then, of course, blame the boat.
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Old 27-04-2020, 16:36   #6
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

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Originally Posted by Oceanseven View Post
Hi. I am wondering if anyone out there has done the research or knows, the model and manufacturer of a catamaran 50 feet or under with the highest water to bridge deck clearance?

I have found this important equation is missing on the specs of a lot of boats.

Thanks in advance.
newer lagoons have pretty good clearance, actually slamming stress is just about eliminated. Nacelle is essential to lower max stresses on bridgedeck as occasionally wave comes that give big shake to boat with no nacelle and cause structural damage. I have not experience that yet on my lagoon.

You need to measure width of the tunnel vs height, and not just height.

Also note that boat can be loaded to different levels. Say lagoon 400 can have 15-20 cm difference in height from empty to full loaded. We as full time sailors sit around 10-15 cm below high mark and boat performs well even compared to loaded performance boats. I really hate to be the bearer of bad news when some racy fully loaded cat is left behind by my L 400. I mean really feel sorry for the owner paying all that money and taking cut on space and having annoying wife, just to realize he purchased boat that has quite limited carrying capacity.
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Old 27-04-2020, 22:10   #7
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

as a cat owner bridge deck clearance is something i'm always conscious of...particularly as ours is comparatively low.

however the difference between ours and a boat with 'high' bridge deck clearance seems to be no more than say 25cm

this seems pretty inconsequential when dealing with usual 1.5 - 2m seas

there is a lot more to a seaworthy / comfortable cat than just bridgedeck clearance ! 2 factors that come to mind are beam and windage

cheers,
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Old 28-04-2020, 01:42   #8
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

And don’t forget total weight of boat and payload also factor in, as well as hull flare.

A light boat with a lot of flair doesn’t “see” the same waves under the bridge deck as a heavy boat with less flair. The lighter boat is already up and over the waves by the time the bridge deck sees any possibility of slamming.

You want a catamaran that floats like a cork or styrofoam on the water, not like a half filled wine bottle. That’s probably the most important factor in slamming, though it’s seldom discussed.
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Old 28-04-2020, 03:42   #9
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

Another factor to take into consideration is the shape of the curve of the inner hull leading to the bridgedeck, ours are rounded and this seems to lessen the force of the slamming.
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Old 28-04-2020, 12:20   #10
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

Maine Cat catamarans have high bridge decks, 31" on the 38 and 32" on the 41, but then these are cats of a different colour than the typical production catamarans.
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Old 28-04-2020, 15:24   #11
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

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Maine Cat catamarans have high bridge decks, 31" on the 38 and 32" on the 41, but then these are cats of a different colour than the typical production catamarans.



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Old 28-04-2020, 17:11   #12
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

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Maine Cat catamarans have high bridge decks, 31" on the 38 and 32" on the 41, but then these are cats of a different colour than the typical production catamarans.
I doubt a loaded 41 is that high. The things certainly can't even come close to keeping up with my 34' cat or a Leopard 46 or 40 in white sails racing.
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Old 29-04-2020, 08:12   #13
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

Another consideration is length to beam ration of the hulls themselves. A narrow hull will tend to pierce the waves, bringing the bridgedeck closer to the surface where a beamier hull will tend to ride up over the waves, maintaining clearance.
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Old 29-04-2020, 09:08   #14
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

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Another consideration is length to beam ration of the hulls themselves. A narrow hull will tend to pierce the waves, bringing the bridgedeck closer to the surface where a beamier hull will tend to ride up over the waves, maintaining clearance.
It’s good to see the thinking on this topic has finally evolved.

There are many factors at work keeping a bridge deck clear (or not) of the water.

In this case, the narrow hull and wide hull boats need to be the same weight to realize the benefit of the wide hull. Typically not the case, so it’s another little layer of complexity to add to the dynamic situation of bridge deck slamming.

Also, I agree that with any cat you are using, sailing it conservatively will reduce the chances of slamming.
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Old 02-05-2020, 06:28   #15
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Re: Mass manufactured Cat Highest Bridge Deck Clearance

Pdq 44 has good clearance
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