Inclining experiment

Is the catamaran too large for an air inclining test as described in ISO 12217? I do not have a copy of the standard. An air incline test is independent of the hydrostatics of the vessel.

 

The more I think about it; the more I doubt they used a ram. The ram was probably really a crane ram lifting weights and I assumed they were loading and using some magical means.

I do my best to stay out of threads I don't belong; not this time.

 

Would an air mattress inflated under one hull provide suitable results?

 

As inclining experiment has gotten necessary for existing ships in my country by the administrator, we have tested many methods depends on their cost. But in this case we don't have enough space for weights outside and even inside. We have strong cranes in the port which can lift the ship. This ship is made bu AL.
Can we install pade eyes on both sides and apply force by crane to incline the ship?

 

@naserrishehri could you perhaps post some photos of the catamaran, and / or a copy of the General Arrangement drawing please?

I am wondering if it would be feasible / possible to cut apertures in the superstructure deck to allow weights to be lowered vertically in to the vessel amidships, so that they can sit on the weather deck there?
The same principle is often used for changing engines, so it might work here without too much cutting (and subsequent re-welding) involved (?)

 

Not to incline it but to lift it up in the air
There is a procedure to calculate the weight and CoG of the ship by lifting it with cranes. What I don't know is for what size of boats and weight this procedure is suitable.

 

I'm sure you remember seeing that the weights have to be placed on one side and the other, performing these movements on several occasions. Only at the beginning of the test are the weights placed in the center line to obtain the draft of the ship at that moment.

 

From a vector mechanics point of view, there's nothing to say a heeling couple can't be applied by lifting on one side (changing displacement by reducing weight by that force,) instead of applying the heeling couple by adding weight (changing the weight by adding that force). In either case a force couple is created between CofG, and the new centre of buoyancy. As a percentage of net mass of the boat, the force needed to impose a 3° heel is relatively small, so lifting vs loading should give very similar values.

 

If the inclining test is done in the water, the boat must be completely free to move, it cannot be subject to anything and even less to a crane. The weight of the boat cannot vary in experience.
The determination of the light ship weight and its CoG is something very serious that we should not be kidding.

 

The first inclining ex we did, we just used people, 6 or 8 i remember. We just have to hunch to keep the CG low.

The inclining experiment we used for another small boat was just sandbags. We filled it up with sands, weighted it and carried it inside the boat.

For slightly bigger boat and a catamaran at that, we used bricks. Lots of it. I think about 2 tons and a lot of guys.

For the ship, we had 2 forklifts weighted, lifted it into the lower deck and under its power, shifted it around.

Empty gallon drums seems a good idea. Just fill it up with water when aboard.

 

Please don't be offended if I don't answer you. Read some writing where it is described how the inclination test should be performed, you don´t need to be a NA, just read it.

 

Apologies Tansl, when I said 'amidships' I meant amidships longitudinally, not transversely.
I am thinking of apertures cut in the roof on the port and starboard sides, amidships.
Ideally one should have all the weights on the centreline amidships as well at one stage during the inclining experiment, but this would then need another aperture cut in the roof on the centreline.
Instead of the situation during the inclining experiment where all the weight is concentrated on the centreline amidships, would it be possible to have half the amount on each side instead?
If you had a mobile crane, with known dense weights, then it should be possible to hoist weights in and out fairly quickly (?)

 

Yes, you are right, but the problem is, apparently, the difficulty of placing them on board and, in addition, of moving them from side to side.

 

@bajansailor, you must place all the weights in the center of the boat, longitudinally, measure the drafts of the boat to obtain the total weight of the boat at the time of the test (this total weight cannot vary during the entire test, with angels or without them). Then you need to put ALL the weights on one side and measure the heel angle of the boat. Pass ALL the weights to the other side and measure the inclination of the boat. Ideally, also, is that the trim of the boat does not change in all these maneuvers. These movements must be repeated 4 or 5 times to calculate the mean deviation of the pendulum that measures the heel achieved in each case (if the boat is very long, two pendulums must be placed, fore and aft). Imagine the work involved in moving ALL those weights so many times. You will now better understand the difficulties facing the OP. It is not like to trivialize the subject.

 

Good answer.