Catamaran Bridgedeck Clearance

[brian eiland]

Reading thru a number of older subject threads, and ran into a few videos of catamarans sailing into pretty good seas. It's interesting to see how their bows create some of the disturbances that end up slapping at the undersides of our bridgedecks,..

 

[brian eiland]

I wonder how this bow design might improve the 'attack into the sea'

 

[TANSL]

That's why we need to study the overpressures that occur in the bow of multihulls. We need to study the interior of the hulls, in the "tunnel" area, and the wet deck. I'd never heard of these disturbances reaching the bridge deck.

 

[brian eiland]

How about adding some slight bulb shape to those bows above. #2

I also began to think back about the numerous bulbous bow discussions, photos, and videos I had seen. That video that UponStands posted shows how dramatic the bow wave of a ship can be subdued by a certain 'sickle shape'

(Look at minute 3:49 of that video

)

It certainly cuts down on that bow wave climbing up the bow(s)

Some more IMAGES of bulb bows

Even the newest Zumwalt destroyer has a shallow bulb down below the waterline

If I remember properly Lock Crowther experimented with them as well.

 

[TANSL]

On warships, that bulbous bow does not serve any hydrodynamic advantages; it simply serves to house sonar or similar equipment.

 

[fallguy]

I wonder how this bow design might improve the 'attack into the sea'

The main thing these extensions do is offer forward displacement and waterline length without fuller bows. I have them on my boat, but made the tips match the hull angle for aesthetics.

I think the clearance issue is 6% or bang.

My boat had one problem to address. I have a 2” clearance between my bdeck and hulls; when I get into even modest seas, the area gets a blast of sea that blows through the cockpit and I need to stop it with more than a cover. May I hijack?

 

[brian eiland]

I have a 2” clearance between my bdeck and hulls; when I get into even modest seas, the area gets a blast of sea that blows through the cockpit and I need to stop it with more than a cover. May I hijack?

I imagine you meant to say 2 ft,..not 2 inches
No problem with hijack, .....lets here problems and solutions.

 

[Ad Hoc]

....I think the clearance issue is 6% or bang....

Yes, 5-6% at midships, and 10% at the bow.
This is for powered cats, sailing cats are different.

 

[brian eiland]

On many ships the bulbous bow helps to keep the bow wave from being so large, and helps keep it from climbing up as high on the bow.

I would be looking for them to help keep the wave peaks the bows are creating,....down in size. I've seen a number of cases where the two peaks from each side join together in the center of the tunnel to contribute to slapping the bridgedeck.