# Sever Wind and Rolling criteria

Discussion in 'Stability' started by kiddo14, Dec 16, 2015.

1. Joined: Apr 2015
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### kiddo14Junior Member

I was doing a Sever Wind and Rolling criteria calculation for a fissing vessel. But my vessel always fails. What is the remedy when a vessel fails in sever wind and rolling criteria. I mean when a vessel fails due to high VCG we usually use solid ballast in thw lower most point to reduce the value of VCG. So what to do if a vessel fails in sever wind and roll? I have tried to reduce the lateral projected area by rearranging the superstructure. But no significant improvement. Please suggest what to do in such circumstance ?

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### TANSLSenior Member

What load condition this problem occurs ?. A fishing boat is not required to pass this criterion more than in any situation very determined.
Before placing ballast, which increases the displacement and therefore can not be the right solution, I would try lowering existing weights, such as freight, to reduce the height of the center of gravity. The effect of a bilge keels may also be beneficial.

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### kiddo14Junior Member

Vessel particular:
LOA=41m
LBP=36m
B=09m
D=4.8
Draught=3.8

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4. Joined: Sep 2011
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### TANSLSenior Member

With these data we can not do anything.
I assume you're using MaxSurf. You calculate if the ship meets the stability criteria for fishing vessels at that load condition.
I do not know what they say other administrations but the Spanish administration says, for fishing vessels, if any loading condition the value of the DN at 30ยบ is less than 65 mm x rad, should be studied wind, waves strong balance and water on deck at that load condition.

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### NavalSArtichokeSenior Member

You've got a lot of slack tanks in the loading condition. Having all these partially filled tanks creates a lot of free surface. From an operational standpoint, you should burn out one pair of fuel tanks completely before switching to another pair. By the time you have reached 10% fuel capacity, only the fuel oil day tanks should have any fuel in them.

Also, the Severe Wind & Rolling Criteria depends on the wind profile of your vessel, which has not been included. A loading condition alone is insufficient to evaluate your problem.

If you have a copy of IMO A.749, you should study section 4.2 very carefully.
For fishing vessels with L > 24 m but L < 45 m, different wind pressure values are specified, which are lower than those specified in chapter 3.

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If it is still at the design stage, you can of course increase the beam too.

7. Joined: Sep 2011
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### TANSLSenior Member

The L/B ratio having this boat, for a 40 m fishing boat, is entirely correct. Increase the breadth is too drastic measure and should carry out further studies to see if it is effective or how far it is. A good designer, knowing the rules applicable to the ship, should try less traumatic solutions. Improvements can be made, and should achieve, without changing the shapes of the ship, which must be defined by other criteria.
NavalSArtichoke solution is more practical and is totally logical. One of the instructions to the Master to be included in the stability booklet is the sequence of consumption of fuel in the tanks.
You should try to lower the center of gravity and/or reduce the windage area. Bilge keels and box keels have a very positive effect as they can reduce up to 30% the angle of heel due to waves.

Last edited: Dec 20, 2015

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### RabahSenior Member

Hi kiddo14,
In your table of the loads for 10 % store and fuel there is an error.
It is the extremity of the trip - all reserves should be taken with weight 10 % from full, switching on and the fresh water which you have accepted=0, and it is abnormally.
There are some methods for solution your problem:
1. Acceptance of dry ballast it is not solution. It is practice only for sailing yachts with a ballast keel, but not and for fishing ships.
It is necessary to try to take fluid ballast without free surface. At the end of trip it is quite allowable for Stability.
2. Try to change the design location for the downflooding point - to move maximum up /about a cut-out for ventilation Engine Room/.
3. If the higher said has not helped, then it is necessary to offer the client change the navigation area-for example from unlimited on R1/RestrictedI/. Then wind pressure will be changed and the beneficial effect is possible.
4. If the client disagrees with p.3 then it is possible to change the material of the superstructure and wheelhouse from steel to alloy of aluminum. So Center of Gravity will be sunk a little in the bottom.
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