Calculate Ship's New Draft
A vessel's draft is 14-11 fwd and 14-07 aft. She loads 1,470 tons which is 40 feet aft of the tipping center with a TPI of 60 and a MTI of 1335. What is her new draft?
Solution:
We are going to solve for change of trim. After then we are going to get half trim. What to do with the half trim? Let me proced now.
Step 1. Solving for change of trim.
Trim = (w x D) / MTI
= (1470 x 40) / 1335
= 44 inches
Step 2. Parallel sinkage
Parallel sinkage = Wieght ÷ TPI
= 1470 ÷ 60
= 24.5 inches
24.5 inches ÷ 12 = 2.04166 ft
0.04166 ft x 12 = 0.5 inch
So the parallel sinkage is 2' 0.5"
Step 3. Get half trim.
Half trim = 44 /2 = 22 inches
22 inches ÷ 12 = 1.83333 ft
83333 ft x 12 = 10 inches
Half trim is 1' 10"
Step 3. Add Parallel Sinkage to the original drafts forward and aft. Also apply the half trim. Add it to to the draft aft since we are moving weight aft of the tipping center. And of course, subtract forward draft.
Forward draft = 14' 11" Aft draft = 14' 07"
Parallel sinkage = + 2' 0.5" + 2' 0.5"
16' 11.5" 16' 7.5"
Half trim - 1' 10" + 1' 10"
15' 1.5" 17' 17.5"
+ 1 - 12
18' 5.5"
So the final draft is 15' 1.5" forward, 18' 5.5" aft.
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ReplyDeletei cant understand why the answer in the preboard is different... answer is 15-01.5 fwd and 18-05.5 aft. thanks nauta!
ReplyDeleteOh my apology my friend. I forgot to apply the parallel sinkage.
DeleteI edited this post and applied the parallel sinkage to it.
Thanks for spotting my mistake.
sir nauta, in the aft draft where did you got the 1 - 12" in the last part ? THANkZ....
ReplyDeleteAngelo, what I do on the last part is that I just simplify 17 ft 17.5 inches.
Delete17.5 inches is more than one foot, isn't? That's why I subtracted 12" from it, and then I add that 1 ft to 17'. So the final answer would be 18' 5.5".