Rocker advice for Catamaran.

[conceptcat]

Hi all, I'm designing a 28-30 ft power catamaran using aluminum tubes similar to the pontoon style boats but with more an ellipse mid section shape tapering to the bows and a flatter stern section than a purely round tube, it will be powered on the low side up to 50 hp with a cruising speed goal of 9-10 knots. I was planning on reverse wave piercing bows.
My questions are, how critical is rocker in what I'm proposing as the design will become much more complicated trying to add some?
I'm guessing flat water won't be an issue but open ocean may present problems.
Thanks in advance for any thoughts.

 

[upchurchmr]

What are you going to use this for?

Where?

Why would you ever want reverse wave piercing bows?

 

[gonzo]

I think a pontoon boat with wave piercing bows will have the deck underwater a lot of the time in the ocean. If you want an ocean going cat, pontoons are not a good choice. A shape with considerable reserve flotation would be much better.

 

[conceptcat]

I think a pontoon boat with wave piercing bows will have the deck underwater a lot of the time in the ocean. If you want an ocean going cat, pontoons are not a good choice. A shape with considerable reserve flotation would be much better.

Thanks for the reply gonzo, I was trying to get away from the reserve buoyancy bows to avoid the boat pitching with each wave and being able to maintain speed , I used to subscribe to that theory but it seems like old technology to me now. The bows would be significantly longer than on a normal pontoon boat which in itself adds buoyancy. Gold Coast Yacths of St Croix built a passenger ferry very similar to what I'm trying to achieve with great success. My reference to pontoon boats was only because the construction technique is tubular and in itself can't be bent to give rocker.

 

[rwatson]

Boat of that size and style, just a bit of rocker towards the bow so you can run up onto the sand without digging in

 

[conceptcat]

Boat of that size and style, just a bit of rocker towards the bow so you can run up onto the sand without digging in

rwatson, good point.
I assume the pontoon style boats get away without rocker because they have constant consistent power when underway as opposed to sail powered where the power is more variable.
Thanks
gwatson
Ps must be chilly in tissue this time of year.

 

[Wavewacker]

I don't think there is any rocker midway to a power cat, flat would be more efficient and stable for a planing hull. The reverse bow may look cool but Gonzo is right, I wouldn't go that route with a small cat, I'd go with a modified v forward and bring the bow up higher above deck or the cabin sole.

Whatever, I'm far from being an engineer, but as mentioned, you need to state a SOR, the type of waters expected.

Do you have any drawings? Old school seems to work out the best, adding rocker seems to me like you'd be at a rodeo.