Proa questions...

[Guest625101138]

Originally Posted by rob denney

.... Why would you put rocker and a V in the ww hull?

....

rob

Rob
I have attached a linesplan of what I am thinking about for a windward hull. The aim is to increase the waterline length substantially as it carries more load. Likewise reduce length and wetted surface is it unloads.

The dimensions are for a heavier boat than you are building but the idea is the same for lower displacement.

I have shown waterlines at 100mm spacing so you can see how the waterplane changes with draft.

The hull would be suitable for flat panel but a bit more complex than the simpler trapezoidal section of the lee hull.

[Guest625101138]

Originally Posted by rob denney

...
Flotilla results will be very interesting, particularly what happens to the rounded chines/flat bottom when they are at an angle to the water flow.

....
rob

Rob
I have attached the Flotilla comparisons from the two hulls at 1 tonne displacement.

The drag is almost identical.

The pitching moment from the flat bottom is quite a lot higher.

Likewise the allowable height of the sail CoP to keep level trim is significantly more for the flat bottom than the round section. This is based solely on hull drag so there is no allowance for the rudder drag. On the other hand I have not included any offsetting moment for crew weight distribution.

If you had some idea of the rig CoP it would be possible to design a flat bottom hull to stay bow up to level trim through the speed of interest. This seems to be what they have achieved with the amas on BMW Oracle - likely the curved board helps too.

The Flotilla analysis does not include any lift from planing forces. Having a sail moment that maintains level trim would reduce the tendency to lift but the flat bottom would have greater lift than the round bottom because of the slight rocker.

I think it noteworthy that the flat bottom hull is 2m shorter than the round bottom but can produce a considerably higher pitching moment to counter sail moment.

[rob denney]

Rob
I have attached the Flotilla comparisons from the two hulls at 1 tonne displacement.

The drag is almost identical.

The pitching moment from the flat bottom is quite a lot higher.

Likewise the allowable height of the sail CoP to keep level trim is significantly more for the flat bottom than the round section. This is based solely on hull drag so there is no allowance for the rudder drag. On the other hand I have not included any offsetting moment for crew weight distribution.

If you had some idea of the rig CoP it would be possible to design a flat bottom hull to stay bow up to level trim through the speed of interest. This seems to be what they have achieved with the amas on BMW Oracle - likely the curved board helps too.

The Flotilla analysis does not include any lift from planing forces. Having a sail moment that maintains level trim would reduce the tendency to lift but the flat bottom would have greater lift than the round bottom because of the slight rocker.

I think it noteworthy that the flat bottom hull is 2m shorter than the round bottom but can produce a considerably higher pitching moment to counter sail moment.

Noteworthy indeed! Once I have changed the beams and sorted out the rig, looks like I may have to build a new lee hull. Thanks for your efforts.

Not sure yet how high the cop will be. The telescoping mast sections are designed at 7 and 8m, (cop 8m) but the more I think about it, the more sense (not the right word!) it makes to have them 12 and 11m (cop 11m) to really find out what is possible with a telescoping rig.

The veed ww hull is less obvious to me. The time you want min resistance is when the boat is just starting to move, post shunt. What happens between then and hull flying is not really relevant as if you are cruising, you will never come close to flying the hull and if you are racing, you will be flying it as often as possible. I could be wrong. As with all possibilities on a proa, it would be great for someone to try them and report back.

rob

rob

[Alex.A]

With all this "fastest boat" nonsense - what about a foiling proa?

[Guest625101138]

Originally Posted by Alex.A

With all this "fastest boat" nonsense - what about a foiling proa?

It is a challenge to protect rudders. Foil add a whole new dimension to what can get broken off and can you imagine the fun in making them reversible.

[Alex.A]

Yeah but imagine a BMW oracle (minus a float) with all its hulls/floats in the air.....