Wave splitter on catamarans

[Mark Peiffer]

Hi,
I have been following the forums for some time and was reviewing a posting about the catamaran Galactic Cat. To be short it included a pod that functioned as a stifening member and a wave breaker to following seas. I have seen a similar pod on the Prout 46 that extends forward. I was wondering with all the effort to lower slamming, why is a wave splitter seldom incorporated in most common sailing cat designs. And why are these pods that may stiffen the structure, so seldom seen ? Is there a real draw back to incorporating a wave splitter on a pod such as on the prout 46 ?

Thanks

[brian eiland]

As I conducted a search (search function above)I happened upon your posting that I had not seen. So I copied a portion of another posting I had made back about a year ago.

First, imagine a flat plate, on edge, mounted down the centerline on the underside of the bridge deck. This flat plate will act as a rib to strengthen the fore-to-aft rigidity of the vessel, a somewhat weaker characteristic in a catamaran structure vs. a keeled monohull. If a tow bundle (rope, etc) of carbon fiber (kevlar, PBO, etc) was laid along the bottom edge of this flat plate, the rigidity could be even greater (sort of akin to a bottom truss structure, or a flange of an 'I' beam).

Now on either side of this flat plate I propose to mount a centerboard, not a single, symmetrical one, but rather two asymmetrical ones; sort of like a single board split in half. The flat sides of these asymmetric boards would fit up against the flat plate nacelle, and rotate on oversize (possibly 1-foot) diameter bearings. The flat fit & big bearings would together supply a great big surface for the large bending moments to bear against. Only one board at a time would be lowered. In fact the two could be linked together such that the act of lifting one automatically lowers (& powers) the other down. And they both could be rigged to 'kick up' upon hitting any solid object and/or for shallow cruising. The control lines (cables) could be routed right up to the cabin top and back to the cockpit.

There are several advantages to an asymmetrical shaped centerboard. First, it requires less total board area to develop a leeway reducing force....so the board size is reduced. Secondly, since it is asymmetrical, it does not require an angle of attack (does not require the boat itself to be sailed at a skewed angle) to develop the 'board's lift' (leeway reducing force). This actually
may result in the vessel making less leeway. Plus the drag forces associated with the CB lift forces are on the centerline of the vessel, rather than off in one hull that produces turning moments about the center of the vessel.

This centerline mounting may also improve the tacking capabilities of the vessel as it allows the 'clean' hulls to slip a little while pivoting about the central board.

The front of this nacelle/plate could be configured to act as a wave splitter to actually attack, up front, the formation of those peaky waves under the tramp areas that eventually slap at our bridge deck underside. We kind of slice those waves down a bit. A lightweight fairing might also be added to this 'flat plate nacelle' so it appears outwardly much more esthetically pleasing, as well as more curvature to shed those peaky waves