Relation between Deadweight and Draft ?

zaidmarkabi
(not verified)
Posted in: , on 3. Aug. 2013 - 02:45

What is the relation between DeadWeight and Draft ?

I mean, if we have a vessel with DeadWeight = 4000 tonnes.

We want to increase DeadWeight to 5000 tonnes.

How Draft will be changed ?

* we have all data.

Thanks for your time.

zaidmarkabi
(not verified)

Tpc Is Unknown

Posted on 3. Aug. 2013 - 01:14

of course TPC is unknown, or problem will be solved simply.

DWT is known.

Draught (D [m]) is known.

we want to add new weight (W).

If TPC is known, we may say:

New draught is Dnew=D+W/TPC

My problem is TPC is Unknown.

Thanks in advance.

Re: Relation Between Deadweight And Draft ?

Posted on 3. Aug. 2013 - 08:37

Dear zaidmarkabi,

The deadweight and the draft of a ship is a choice of the designer.

He can design a ship with an equal deadweight for shallow waters or deep waters or for

narrow locks or wide locks.

For seagoing ships, a general regression formula is:

Draft = 0.4991 * DWT^0.2991

If you want to increase the deadweight of an existing ship from 4000 tons to 5000 tons, lengthening is probably the only option.

Just overloading the ship by 1000 tons (25%) would sing the ship, or at least destroy the freeboard and/or the stability of the ship and thereby the safety.

Take care

Teus

Teus

Re: Relation Between Deadweight And Draft ?

Posted on 4. Aug. 2013 - 09:23

Dear zaidmarkabi,

TPC can be calculated from the Draft table.

TPC is the tangent of the draft table at a certain draft

Formula : TPC = d(DWT)/d(Draft)

Example for the TPC at maximum draft:

TPC = (DWT(max) – DWT(max-1cm)) / (D (max) – D (max-1cm))

TPC is increasing with the draft.

For a 4000 dwt ship:

TPC at maximum draft = (4000 –3989) / (5.96 –5.95)= 11 tons/cm immersion

If you do not have the draft table, you can load the ship by known cargo masses and measure the drafts.

This will give you the approx. draft table, which is not official and cannot be used for commercial purposes.

Best regards

Teus