# Seakeeping/Dynamic Stability/Manouvering Test

Discussion in 'Stability' started by Diego San, Jun 21, 2017.

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### Diego SanJunior Member

Hello you all,

I would like to ask you about what seakeeping/dynamic stability/maneuvering test you know for a planning hull boat with outboards.

Let me explain a little bit why I am asking you this.

There is a boat model made for a company (almost exclusive), and they were concern about the boat stability. Their first train of thinking was to question the intact stability, so we performed an inclining test with them and made the cross curves of stability with the COG found and finally we were able to prove them that it meets IMO regulation.

Now they want to test the seakeeping among other things (autonomy or fuel consumption, top speed, structure resistance and so on), so they asked us to perform a test which consists on placing some weights at a side (port or starboard) and then proceed to run the boat to full speed; the criteria to past the test or not is that the boat should be able to right itself just by the hydrodynamic and aerodynamic forces during the planning (without touching the outboard trim control or trim tabs).

To be honest, I have never heard about such a test, but they say there is even an ASTM standard. I have been searching thru the ASTM web page but I haven't found it yet... so I am going to you for some help on this.

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### TANSLSenior Member

I can not imagine what kind of curves you have drawn because to calculate the cross curves of stability you do not need to know the position of the center of gravity. When you want to determine the stability in a certain load condition, for which you must draw the curve of the righting arms (GZ) and the dynamic stability curve (DN curve), yes, you do need to know the position of the center of gravity in that load condition.
As for seakeeping, it is normal to check the stability of course, forward and reverse, the so-called circle of evolution, the angle of heel when performing a full speed spin, but try to make the speed of the ship compensate a heel produced by a few weights at the side, had never seen it.
You will be able to find a lot of information on ISO 12217: "Small craft - Stability and buoyancy assessment and categorization"

Last edited: Jun 21, 2017
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3. Joined: Jun 2014
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### Diego SanJunior Member

I'm sorry TANSL, I am not a native english speaker and I made a mistake writing the last comment. what I meant is that we made the inclining test with the owner (to make sure he was comfortable with the procedure) and then we draw the rigthing arm curve (GZ) and check the IMO criteria for different load conditions in order to meet the owner desires (we did it before, but the owner wasn't comfortable with the results).

I have been reading and I found a paper describing a similar test... I will post it here after lunch.

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### TANSLSenior Member

Sure, now I understand and I agree. Just one additional comment: ISO 12217 standards for small boats are increasingly used (in some countries they are mandatory) and are more comfortable to apply than some of the IMO criteria. The boats to be sold in the European Community (which is not all Europe) must comply with them.

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### Diego SanJunior Member

As I told you before, I found this article "Dynamic stability of planing boats by Donald L. Blount and Louis T. Codega" from Marine Technology Vol. 29, No 1, Jan 1992, pp 4-12.

There they describe a dynamic inclining test (page 10) really similar to the test asked by the boat owner. They said the purpose of this test is to determine if the heel angle cause by an off-center weight will change as speed increases from zero to maximum speed. They describe the test, but there is no detail on the procedure and unfortunately there is no information about any criteria.

Maybe, you know if there is an ASTM standard with this.

thank you

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### TANSLSenior Member

Sorry, I gave your questions a wrong approach.
Attached is a document that, I imagine, is the one you have. Here, page 10, tells you how to perform the dynamic incling test.
I do not think ASTM has anything to do with it. There is some paper from SNAME even though I have not found in it a procedure to perform the test.

#### Attached Files:

• ###### Dynamic Stability of Planing Boats -Marine Technology.pdf
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1.2 MB
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1,286
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