Cat Bridge Deck Clearances?

[ALIAS]

Hi Guys.... anybody done some research into bridgedeck clearances from best to worst and whether they could post up a list of makes and models for us newbies?

[Seaslug Caravan]

Originally Posted by ALIAS

Hi Guys.... anybody done some research into bridgedeck clearances from best to worst and whether they could post up a list of makes and models for us newbies?

May I just say that I think it is most commendable that you are researching sailing and safety qualities of a catamaran rather than the normal "has it got a galley up option and what colour is the carpet".

I wish you well in you research.

It must be noted that manufacturers data must be taken with a grain of salt as their in the business of making money. Data such as bridge deck clearance depends on where one holds the tape measure,( Eg ever looked under a Seawind
1000) , if its measured lightship what is the published sinkage rate (good luck with that one), and displacement means different things to different marketing departments.

Have you checked out a "chincogan 40" or the smaller" Lightwave". Both designs are nice middle of the road Aus production cats.[

[mikereed100]

The information you are looking for can be found at Multihull Maven.

Guide to all trimaran, catamaran and proa models

As far as I know nobody has made a list comparing different boats, but after looking at a few you will know which have the higher and lower bridge deck clearances.

[2Hulls]

Originally Posted by mikereed100

...but after looking at a few you will know which have the higher and lower bridge deck clearances.

I think Mike is right here. As someone like ALIAS proceeds along his analytic approach, he/she will accumulate in his mind a database of boats of various attributes just by observing. When it comes to bridgedeck clearance, this is an easy discriminator. Most available pictures of cats include a stern view. Just imagine whether you can get under that boat in a dinghy? If not, it might be too low...

2 Hulls Dave

[UNCIVILIZED]

Originally Posted by Seaslug Caravan

May I just say that I think it is most commendable that you are researching sailing and safety qualities of a catamaran rather than the normal "has it got a galley up option and what colour is the carpet".

I wish you well in you research.

It must be noted that manufacturers data must be taken with a grain of salt as their in the business of making money. Data such as bridge deck clearance depends on where one holds the tape measure,( Eg ever looked under a Seawind
1000) , if its measured lightship what is the published sinkage rate (good luck with that one), and displacement means different things to different marketing departments.

Have you checked out a "chincogan 40" or the smaller" Lightwave". Both designs are nice middle of the road Aus production cats.[

+1
On this, someone once told me to use the rule of thumb of 1" (2.5cm) per foot (30cm) of beam. Though that's not exactly a standard which I'd necessarily go by. From most of what I've run across, 2' +/- on a loaded with stores & cruising gear, small to mid-sized cat is kind of the minimum starting point. With 2.5'-3' being that much better.

However, a lot of it depends upon the boat's design. Features including hull shape, the hulls being flared or not, flare built into the hull to bridgedeck connection, how far back from the bows the bridgedeck starts, how far from the end of the boat it ends, etc.

And the truly key thing, is to find out via querying owners of the various, desired candidate boats in question. IE; chatting with them on the topic to see what they think of the boat's performance, and under what conditions it slams under the bridgedeck. As to varying degrees, from everything I've gathered, most boats will slam, the key point(s) being: under what conditions, & how much?

For example, Woods Designs are small boats with a medium amount of clearance (limited due to size), but they seem to fare well in this area. http://www.cruisersforum.com/forums/...ng-132116.html
I did a decent amount of research into them (and wish that I could modify the title of that post), but they seem like good boats. Also, another place to look for designs, performance, & many other things catamaran is www.Multihull-Maven.com

I've been in touch with a bunch of good designers, so if you need some POC info, just let me know.
Good luck in your search.

PS: One important thing to state when asking this question, is the size of catamaran which you're looking at, & what it's purpose will be. There are some excellent questions to ask yourself here;
Kurt Hughes Multihull Design - Catamarans and Trimarans for Cruising and Charter
Kurt Hughes Multihull Design - Catamarans and Trimarans for Cruising and Charter

[BigBeakie]

Go have a look at Multihull Dynamics.

Multihull Dynamics, Inc. - Home


He has posted bridgedeck clearance on most multihulls and where he does not have them, it means the manufacturer or designer has asked him not to publish the data, or he has not been able to get the information.To my mind that is not a good sign, hint, hint.

I know that he talks to the boats designer directly.

You will also be able to compare boats side by side on many other parameters in order to get an idea of their safety characteristics and sailing performance.

Well worth the time to spend some time at that site.

[ALIAS]

Thanks Guys with the multitude of info.

[Palarran]

Hello Alias,
I know your new to the forum so welcome. Bridge deck clearance has been discussed many times in the past, not that it's a problem to do it again. But if you want, try searching for past threads. You can use the custom google search by clicking the search tab and selecting the second search box. I used "catamaran bridge deck clearance" and got catamaran bridge deck clearance - Google Search

[ALIAS]

Originally Posted by BigBeakie

Go have a look at Multihull Dynamics.

Multihull Dynamics, Inc. - Home


He has posted bridgedeck clearance on most multihulls and where he does not have them, it means the manufacturer or designer has asked him not to publish the data, or he has not been able to get the information.To my mind that is not a good sign, hint, hint.

I know that he talks to the boats designer directly.

You will also be able to compare boats side by side on many other parameters in order to get an idea of their safety characteristics and sailing performance.

Well worth the time to spend some time at that site.

Thanks for the GOOD link and yes not all have bridge deck clearance listed including the Leopard 42 or the Corsair 3600 just to mention two.

[RichinBoca]

Check this out:

http://www.liveantares.com/pdf/BridgedeckClearance.pdf

[Training Wheels]

More is better!


Sent from my iPad using Cruisers Sailing Forum

[smj]

Originally Posted by Training Wheels

More is better!


Sent from my iPad using Cruisers Sailing Forum

Up to a certain extent. As the bridge deck clearance rises so does the CG, so there has to be a happy cut of point.

[colemj]

The shape of the bridgedeck needs to be considered along with its clearance. I have seen bridgedeck shapes with flat panels and even vertical panels in them that accentuate slamming, noise and things bouncing off tables. Also, large bump outs can be bad - especially if they are holding the berth you need to sleep in.

Mark

[yeloya]

The worst that I've seen so far are Prouts..The best are Catana, Eric Lerouge design cats, etc. FP and Lagoons fall into the middle, Leopard probably more on the lower side. These charter oriented boats have had various models over the years and not all of them have the same bridge deck clearance.
I should add that bridge deck clearance is not the only parameter to consider if the issue is under bridge slamming; the opening between the hulls and the protrusions inside the hull or the bridge deck do equally matter. Many new models now are installing front cabins at the entry of the bridge rather than on the bows. This is not a good idea, particularly if the boat is shorter than 50-52 ft.This leads the hulls to be fatter, the tunnel underneath the bridge narrower and even if theoritical bridge deck clearance is OK, you will get a lot of slamming with the water compressing in between the hulls..
Hope this helps
Cheers
Yeloya

[valhalla360]

Beam plays a big role. Smaller 16-18' beam boats need far less clearance than a monster 25-30' beam boat.

To see why draw a sinosoidal wave:
- Now draw a boat with a beam of one wave length sitting on top of the wave. You will find that the bridge deck must be at least the wave height to avoid hitting the wave.
- Now draw a boat with a beam of 1/2 wave length sitting on top of the wave. You will find a clearance of around 1/3 of the wave height is enough to keep the bridge deck off the water.

Of course this is a simplified example and waves come in many heights and lengths but it demonstrates the principal.

In practice, you will find large cats get high bridge deck clearance. They can get away with it without becoming top heavy (both in appearance and center of gravity) and providing plenty of headroom for the bridgedeck living space.

Smaller boats must balance higher bridge deck clearance with sufficent standing headroom:
- Some boats address this by making it more of a crawl space.
- Some skip bridge deck accomodations.
- Others accept lesser clearance in return for more space.
- Then there are tricks to help such as nacels and varying the clearance with it being high at the front and lower at the back so the boat is better able to rise with the waves.

While generally a good thing, high bridge deck clearance is only one factor in designing a good cruising catamaran and other factors can take precedence.