Boat angle or trim of hull

Is there a way to calculate the angle/trim of a hull design of a planning style boat. In other words how it will sit in the water based on hull shape. Then add a outboard motor and see how that effect the trim, then add a fuel tank, and see how that effect the trim. etc..? Also can this be done in FreeShip? If not what software will do it?

 

Any naval design software should be able to perform these calculations.

 

Being a planing boat, the calculation would be rather different for planing speeds, to that at rest or proceeding slowly. What is the objective of the exercise ? Given also that it is a smallish boat, moveable objects like passengers can change trim significantly.

 

FreeShip cannot do this. It doesn't float your boat. Nor does your boat move through the water. You have to tell it how the boat floats, and it tells you some quantities about the stationary boat.

 

I am trying to see how the boat sits in the water in a static condition. I have seen terms like static trim, hull orientation, boat attitude and static equilibrium. This is a small 17' boat I am toying around with and am trying to see the effects of the motor weight and the fuel weight on the boats orientation at rest.

 

Freeship can give you that info, but it is a trial-and-error process.

First you need to know the target weight and CoG position (measured from the transom) of your boat. It includes the motor and the desired amount of fuel.
Then you go to the "Calculations" --> "Hydrostatics" menu and specify the trim (in meters) and the range of drafts to be examined.
Hit the "Calculate" button and Freeship will give you a table of various hull parameters for a given trim and for each draft.

Note that the trim value is positive when bow points down, negative when it points up.

In the "Displacement" column, find the cell which contains the value which is closest to the known displacement of your boat.
Then move one cell to the right and read the relative value of the LCB.

If the LCB is bigger than CoG, then decrease the trim by some small value and repeat the above calculation.
After few iterations you will find the trim&draft combination which will correctly match the calculated Displ. and LCB values to your boat's weight and CoG.
And that's how your boat will sit in the water.

Hope it helps.

 

Why not learn the basics of weight distribution on hull balance? Any basic design book covers this and then you will understand, instead of depending on software to give an answer.

 

tom28571, you are quite right in terms of basic design book, but if he does not use some kind of software will have no choice but to perform hand calculations which, in my opinion, is not desirable. One thing is to know the theory and know how things are calculated and something very different is having to hand thousands of addition, subtraction, multiplication; that's not training at all, and also can produce many mistakes that lead the designer to incorrect results.

 

Steve, if you can give use some idea of what you're looking to do, the boat (make, model year, etc.) if a new design, a set of lines and a GA, we can pin it down a little, but there's no substitute for doing the math. To determine the her static trim, you'll need to know the basic volumetric figures and the weights involved. The same is true of her running trim.

 

This calculations are done here:
http://www.bootsphysik.de/rechner/boot_e.php (i buttons provide information)
for a given hull. You can add or move weights (mass) and see the effect.

Freeship provides an export function for hull data. If you create from this a large but simple csv file for your hull
http://www.bootsphysik.de/index.php/dateien ,
I could upload it and you would be able to do trials with your own hull form.

 

can you recommend a book that covers the necessary topics?

Thanks.

 

What does the -0.100 m indicate? Does it mean that the stern is 0.100 m down and the bow 0.100 m up?

 

Trim = -0.100 m means, the draft at bow ist 0.1 m less than the draft at stern.

(Bow 0.1 m up and stern 0.1 m down means trim 0.2 m)

"Trim is defined as the difference between the draft forward and the draft aft."
http://www.otenmaritime.com/stability/reserve-buoyancy-freeboard-and-trim

 

Thanks, is that measured at the waterline (which would change) or LOA?

 

Principles of Yacht Design by Lars Larsson, Rolf Eliasson, Michal Orych

http://www.amazon.com/Principles-Yacht-Design-Lars-Larsson/dp/0071826408