Max Kg while Towing

Discussion in 'Stability' started by athvas, Apr 29, 2014.

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athvasSenior Member

How do i calculate the Max kg value for towing criteria of a tug.
Towing criteria of the tug is...
The residual area between a righting lever curve and a heeling lever curve developed from 70% of the maximum bollard pull force acting at 900 to the ship-length direction is not be less than 0.09 [m-rad];
The residual areas under the curves are to be calculated from the 1st intercept up to an angle of 400 beyond the first intercept or up to the down flooding angle, whichever is less
How to calculate the Maxkg value ?

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TANSLSenior Member

I see no clear criteria that you say, I do not understand them. To me, it makes no sense: "an angle of 400 beyond the first intercept." Check them.
What to get is that the heeling moment and righting moment equilibrate at a low angle that would produce the deck immersion or reach some flooding point. Therefore, in my opinion, you have to do is to draw the two curves, righting arm and heeling arms and see where they intersect.

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Draw the GZ curve in the condition in which you shall tow.

Then knowing the location above the baseline of the towing point, this is where the load is applied. It is the same as adding a load. In other words raising the KG. The more and more load you pull, the higher and higher the KG rises. Until the GZ curve no longer satisfies the criteria you have noted.

This is assuming the towing point is above the KG of the vessel in the towed condition of course.

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TANSLSenior Member

I have always used this formula. Is not that correct?

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NavalSArtichokeSenior Member

"The residual area between a righting lever curve and a heeling lever curve developed from 70% of the maximum bollard pull force acting at 90 deg. to the ship-length direction is not be less than 0.09 [m-rad];
The residual areas under the curves are to be calculated from the 1st intercept up to an angle of 40 deg. beyond the first intercept or up to the down flooding angle, whichever is less"

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NavalSArtichokeSenior Member

7. Joined: Oct 2008
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It also states the lever and force (from bollard pull test) for the heeling arm, just as I noted above too. Thanks for posting the link

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athvasSenior Member

Yes as #NavalSArtichoke said its a typing error it is 40 deg (last one is the deg symbol) .... I have calculated the Heeling moment while towing. I need to calculate the Max Kg while towing

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TANSLSenior Member

athvas, I think I understand you, and if I'm not mistaken, the position of KG depends on the weight distribution having boat at all times. Another different thing is how and where each force acts. The weight of the boat will be in the center of gravity, bouyancy into the center of buoyancy and towing force in winch, or on the hook.
If you actually want to calculate the maximum KG when towing, what you need to do are several towing studies with different values ​​of KG and check, every time, compliance with the stability criteria applicable to the ship. Something similar to the determination of the limiting KG curve.

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athvasSenior Member

Yes TANSL, I think its a Iteration process of changing the KG value step by step and check the towing stability criteria... I think that is the way to achieve this.

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