bow entry angle

is there anyone who can help me to explain how to determine the good angle of bow entry for optimazimation seakeeping analysis?
thanks...

 

The first step is to determine the operating conditions, size of the vessel and intended use. Everything else will be determined by those basic restrictions.

 

Inconsistent advice. I imagine that if the OP is in the design phase to make a "seakeeping analysis" it is because he already knows many other things about his boat.
In any case, cristianon, if you give more details, it is possible for someone to help.

 

Need length of boat
need width (beam) of boat
need usage of boat such as fishing or inter island delivery's

 

here's the details:
Lwl: 50m
Lpp:48.5m
Boa: 21.25m
B1: 6.25m
T:2.5m
Cb: 0.386
separation ration Ratio: 0.3
Type: ferry catamaran
operation: rough water with wave height up to 4m
thank you...

 

sorry i've forgot about the speed
max speed: 25knot
separation ratio: 0.3

 

Take a look at comparable existing vessels of much the same proportions, see what the range of entry angles is for them. It is unlikely they have all chosen an angle that gives unfavourable sea-keeping characteristics.

 

I'm out of my league here and maybe should not post but looking at pics of 90' cats the angle of the bow appears to be 70* off vertical. However maybe you should consider in 12' to 14' seas a Bulbous Forefoot. I hope that is the correct term for a extension of the 2 bows under water. Just an idea with no knowledge backing it up. However. I see it done on larger boats that travel in HARD water.

 

Stan, I think this poster is looking for an optimum "entry half angle", which is dependant on several factors. The simple answer is there's no generic angle that is ideal, because of the multiple concerns that might affect it. This said, there are averages that can be used comparatively, to see if what you have is in the range with others of similar configuration.

 

With such a prescriptive set of principal data, it matters not what the angle of entrance is or shall be. The above principal dimensions shall dictate the motion response in a given seaway already. It is cart before the horse!!

 

I think I mentioned somewhere a fast commercial cat that I went for a day trip on, that seemed unusually full at the waterline forward, and the designer came on here and said it was to provide more room for people in an underwater viewing area(s) up forward. It seemed to have little effect on performance, so obviously a degree or two would be inconsequential.

 

thank's for all of your answer, maybe i'll change the question.
if i've to change the angle of entrance which parametric i could keep or change.
or is there any limit to change the angle?

 

The angle in which plane? For example, you can have a fuller entry on the horizontal plane with a shallower vertical plane, or vice-versa. The flare will also influence seakeeping characteristics. Basically, each time you change one parameter, all others have to be checked out again.

 

I imagined he was talking about waterline half angle at the bow.

 

thank you for your answer i'll try lackenby method to change the angle