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**Bunkerbarge** · 03-10-2005

Chris,

Just think of the ship as your fibre-glass shell sat in the bath. When it is loaded the downwards forces acting on the hull are the main machinery which is all located aft so the centre of gravity of the mass would be somewhere below the funnel area, plus the cargo, located below the main hatch so the centre of gravity would be somewhere in the area of the centre of the hatch. The resultant centre of gravity would be somewhere in the centre of the vessel.

As you unload the cargo the resultant centre of gravity moves aft until, when unloaded, the only downwards force is from the main machinery. The resultant centre of gravity is now somewhere below the funnel.

The hull is designed to be at its most efficient at it's loaded condition as the ship is expected to be in this situation for the majority of its life. An empty ship isn't making any money so that was avoided at all costs. Larger and more modern ships are fitted with a ballast system to compensate for this effect but 1920's coasters were pretty basic in thier design.

Consequently, as you say, when the ship is unloaded the bow is a lot higher out of the water than the stern. In this condition the propeller and rudder are usually not fully submerged and so neither are working at thier most efficient. I have deliberately ballasted my Ben Ain to put her right down to her marks at which level she is suprisingly manoeuverable. The only trouble there is that she weighs in at about 2 stone 2 pounds, which takes a bit of lugging around.

I am just about to go back to work for three months so all building will be halted for a while. I expect when I get back that you will be further ahead than I am!! Post some pictures at some point or even start your own thread so we can see how it is going.

All the best

Richard

03-10-2005	#26 (permalink)
Bunkerbarge Moderator Join Date: Jul 2005 Location: Halifax, Yorks: Nassau, Bahama's:Port Canaveral, USA: and all points in between. Real Name: Richard My Models: Robbe U-47, Deans Marine Cossack, Steam Coaster, Revell U-Boat, Motorcycles. Visit Bunkerbarge's Gallery Posts: 3,671 Images: 230	Chris, Just think of the ship as your fibre-glass shell sat in the bath. When it is loaded the downwards forces acting on the hull are the main machinery which is all located aft so the centre of gravity of the mass would be somewhere below the funnel area, plus the cargo, located below the main hatch so the centre of gravity would be somewhere in the area of the centre of the hatch. The resultant centre of gravity would be somewhere in the centre of the vessel. As you unload the cargo the resultant centre of gravity moves aft until, when unloaded, the only downwards force is from the main machinery. The resultant centre of gravity is now somewhere below the funnel. The hull is designed to be at its most efficient at it's loaded condition as the ship is expected to be in this situation for the majority of its life. An empty ship isn't making any money so that was avoided at all costs. Larger and more modern ships are fitted with a ballast system to compensate for this effect but 1920's coasters were pretty basic in thier design. Consequently, as you say, when the ship is unloaded the bow is a lot higher out of the water than the stern. In this condition the propeller and rudder are usually not fully submerged and so neither are working at thier most efficient. I have deliberately ballasted my Ben Ain to put her right down to her marks at which level she is suprisingly manoeuverable. The only trouble there is that she weighs in at about 2 stone 2 pounds, which takes a bit of lugging around. I am just about to go back to work for three months so all building will be halted for a while. I expect when I get back that you will be further ahead than I am!! Post some pictures at some point or even start your own thread so we can see how it is going. All the best Richard Last edited by Bunkerbarge; 03-10-2005 at 10:26.