BALLAST, where and how much

[Oryen]

Hi

I am refitting a boat. The new equipment is heavier than than the old equipment. I am wondering whether I should add ballast to the bow.

Specs:
Mono Hull Motor yacht with flybridge
LOA: 43?
Max Beam: 11?
Previous displacement: 8.5 ton
Centre of Buoyancy: 3.5m from transom

I am adding an additional 700 kg (+-) of weight to the engine room (additional to the previous equipment?s weight). How do I calculate the position and amount (weight) of ballast to add? Is there a formula to calculate this?

The weight is added as the engine size has increased along with some additional equipment.

See attached for drawing of vessel.



I would appreciate any assistance regarding ballasts.

Regards
Oryen

 

[Woodonglass]

Re: BALLAST, where and how much

This might be of interest.

4 Steps for Calculating Boat Ballast Requirements

1Calculate the number of cubic feet of water your vessel is currently displacing. Subtract the amount of current freeboard (how far your boat sticks out of the water, from the deck to the level of the water on the hull) from the molded depth (available in your boat owner's manual or your boat's documentation) of the vessel. Multiply the result by the length of the vessel at the waterline (LWL) and the beam (width) of your vessel. This is the number of cubic feet of water your vessel is currently displacing.
The formula for this calculation is (D-f)LWL x B,
where
D = molded depth,
f = freeboard,
LWL = vessel length at waterline and
B = beam of the vessel.



2Divide the amount of ballast to be added or removed by 64.1. Seawater weighs 64.1 pounds per cubic foot. The weight of the ballast equals the weight of the water it causes the vessel to displace.
If you remove 64.1 pounds of ballast, then the vessel will displace 1 cubic foot of water less than it did before the 64.1 pounds of ballast was removed. If you add 64.1 pounds of ballast, your boat will displace 1 cubic foot more than it did before the ballast was added.



3Insert your vessel's dimensions in the formula to make the desired calculation. If your vessel's LWL is 20 feet long, with a molded depth of 5 feet and 3 feetof freeboard and a beam of 8 feet, the formula becomes (5-3) x 20 x 8, or 2 x 20 x 8 = 320, and you learn that your vessel is displacing 320 cubic feet, or 20,512 pounds of seawater.



4Calculate how much effect adding or removing 64.1 pounds of ballast has on your boat by dividing the weight of water your vessel is displacing by your draft--which equals the difference between your molded depth and your freeboard.
If your molded depth is 5 feet and your freeboard 3 feet, your draft is 2 feet. If the weight of the water displaced (called deadweight tonnage of the vessel) is 20,512 pounds, then each foot of draft is displacing 10,256 pounds of seawater and each inch of draft (10,256 / 12) represents 855 pounds of your boat's deadweight tonnage, including the ballast.