# How to determine the position of boat in water?

Discussion in 'Boat Design' started by Sam M, Oct 18, 2020.

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1. Joined: Oct 2020
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### Sam MJunior Member

Hello,

I am a student and I am working with OpenFoam software to simulate a kayak in the water. First I have to determine "placement (trim and heave) of kayak hull in the domain under given (stationary) conditions such as weight, buoyancy and centre of gravity and speed".
The issue is this the first time I am working with any type of boat or ship and I would really appreciate if anyone could suggest me a link or paper or software which might help me to find it.

Thank you in advance and looking forward to your suggestions.

Kind regards
Sam.M

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### BlueBell. . . . .

Hello Sam M,

Welcome to the forum.
We don't do homework for others here, but we can help, maybe.

What are the forces involved? Lift (buoyancy), weight (gravity), ???
How much lift for one cubic meter of water displaced?
Fresh water or ocean water? Density differences?

That should get the ball rolling.

BB

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### bajansailorMarine Surveyor

Welcome to the Forum Sam.

Re 'placement (trim and heave) of kayak hull', do you really mean 'placement' (relative to what?) or do you mean 'displacement'?

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### philSweetSenior Member

Silly question, maybe, but if you have heave and trim vs speed to start with, what are you simulating in Open Foam?

Normally, the hydrodynamic forces and vessel state vector have to be iterated together until the solution converges. If you have telemetric test data from tank tests, you can validate drag prediction, local surface height, hull pressures etc. But entropic bow shock losses are proportionately higher in small craft and are notoriously difficult to account for.

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### Sam MJunior Member

Dear BB,

I would like to thank you for your quick reply. Following are what I will be given when I officially start my work
1.weight
2.buoyancy
3.centre of gravity
4.speed
and it is freshwater

since I haven't worked with ship hydrodynamics before at all. I don't exactly know where or what to look for. I have searched on internet and found some results but I wasn't sure if what I found was what I needed. So I thought experienced people suggestions for what to look for might help me to solve the issue.

I just needed some suggestions like some "Papers, Links or YouTube videos" links which would help me solve it.

Thank you

Kind regards
Sam.M

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### Sam MJunior Member

Hello bajansailor,

It is "placement" in my task sheet description.
Maybe there is some mistake in it. Please feel free to share your thoughts about it.

I have to place the kayak whose weight, buoyancy and centre of gravity and speed will be given in water. I think what I have to find might me the trim and heave of the kayak for a given velocity???

If you feel like the data which will be provided is not enough to solve the problem, please let me know what all is needed?

If possible can you suggest me any software which might be available to find the position of kayak in water

Kind regards
Sam.M

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### Sam MJunior Member

Dear philSweet,

Thank you so much for the reply
I have to calculate the longitudinal draft from the simulation. I also have to simulate the yaw motion of the boat.
From what I understood from the description of my work, I have to find the trim and heave from the given data which are:
1.weight
2.buoyancy
3.centre of gravity
4.speed
5. freshwater

Is it possible or will I need more data?
Could you please suggest and papers, link or tutorial which might help me.
I really appreciate the reply and time

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### BlueBell. . . . .

These are complicated questions they are asking for a newbie.

Centre of buoyancy versus CoG would be needed to figure static attitude in water.
But heave? Is that even calculabale?

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### TANSLSenior Member

If the horizontal distance between CoB and CoG is not very great and you want to make an approximate calculation, the data you have is sufficient. If you want to make a more exact calculation, you would need to know the variation of the longitudinal position of the CoB when trimming the boat, at constant displacement (which is not easy to determine). We are talking about the static boat position, without speed. If you want to get the planing equilibrium floatation at a certain speed, you need a lot more data.

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