Vessel Accelerations on Offshore Structures

[SubseaDeep]

Hi,

I have a question please. Consider two scenarios:

In the first scenario, a component or equipment is subjected a load of 5 kgs. We then put a factor of 2 for dynamic/shock loads. So the total load which the equipment will undergo/will have to withstand is 10 kgf. This equipment is sitting on land.

In the second scenario, the same equipment is there which has to withstand the same load of 5 kgs. We again put a factor of 2 for dynamic/shock loads. But this time it is on a boat, so as per DNV or ABS criteria, we put accelerations of 1.75 g in all three directions on the equipment.

My questions are:

1. For the boat scenario, is the load on the equipment equal to 5 X 2 X 1.75 = 17.5 kgf?

2. Are accelerations of 1.75 g or 2 g the same as factors of 1.75 or 2? That means if someone says that use a acceleration of 1.75 g, we just multiply the original load with 1.75? Or do we have to look more closely when accelerations are taken into account?

Answers from all would be appreciated.

Regards,

SubseaDeep

 

[EricFrance]

Bonjour,
Firstly, you must define your "Safe working Load (SWL)"; For example, if maximum load lifted is equal to 50 kg, Swl = 50kg.
Secondly, you must calculated Dynamic Amplification Factor (DAF). Effectively, ABS give, for Launched and recovery system, a DAF = 1.75g. Other rules allow to define one DAF and to take account of effect to seastate (Dnv, Nfen, lloyd...)
Therefore, the Design Load is equal to : 50x9.81x1.75 = 859N (or 87.5 kgf).
This is true for vertical and horizontal loads.

EricFrance