# How LCB, LCF, LCG affecting Trim?

Discussion in 'Stability' started by anindrafarras, Jan 4, 2016.

1. Joined: Jan 2016
Posts: 3
Likes: 0, Points: 0, Legacy Rep: 10
Location: Indonesia

### anindrafarrasNew Member

How LCB, LCF, LCG affecting Trim?
Are there any relation about LCB LCF and trim in hydrostatic curve?
thankyou

2. Joined: Jan 2011
Posts: 3
Likes: 1, Points: 0, Legacy Rep: 15
Location: USA

### jugal_dearNew Member

LCB defined as longitudinal center of buoyancy. LCG defined as Longitudinal center of gravity. LCF defined as longitudinal center of flotation.

Now, difference between LCG and LCB is your lever for trimming moment. Basically, if LCG = LCB, there is no trimming moment and so no trim.

So, trimming moment = Displacement x (LCG - LCB).

Now total trim = Trimming Moment / Moment to Change Trim 1"

Now trim is defines as difference between Aft and fwd draft.

To find change in Forward draft or forward trim = TRIM*(L/2-LCF)/L

To find change in Aft draft or Aft trim = TRIM- Forward TRim

1 person likes this.
3. Joined: Oct 2009
Posts: 4,901
Likes: 440, Points: 83, Legacy Rep: 1485
Location: Midcoast Maine

### DCockeySenior Member

anindrafarras, are you a student? Is your question from an assignment or an exam?

4. Joined: Jan 2016
Posts: 3
Likes: 0, Points: 0, Legacy Rep: 10
Location: Indonesia

### anindrafarrasNew Member

Dcockey: yes i'm a student. My lecturer ask me about that but i'm still confused to read hydrostatic curve

5. Joined: Oct 2008
Posts: 6,826
Likes: 786, Points: 113, Legacy Rep: 2488
Location: Japan

### Ad HocNaval Architect

Then may i suggest you do what all students do, read a book.
All the answers are in the books....that is the purpose of studying!

6. Joined: Jan 2016
Posts: 3
Likes: 0, Points: 0, Legacy Rep: 10
Location: Indonesia

### anindrafarrasNew Member

Thank you Ad Hoc for your suggestion. I apologize for this very basic question, I've read the book but still confused and still need an explanation. This will be my evaluation to read more books

7. Joined: Aug 2002
Posts: 15,146
Likes: 909, Points: 123, Legacy Rep: 2031
Location: Milwaukee, WI

### gonzoSenior Member

LCF and LCG will always be vertically from each other unless there is a force applied to the vessel. It is the state of natural equilibrium.

8. Joined: Oct 2010
Posts: 9,630
Likes: 832, Points: 113, Legacy Rep: 702
Location: Australia

### Mr EfficiencySenior Member

You meant LCB rather than LCF ?

9. Joined: Apr 2015
Posts: 377
Likes: 56, Points: 28, Legacy Rep: 37
Location: Berlin, Germany

### HeimfriedSenior Member

Hi anindrafarras,

maybe it helps to understand, if you virtually "play" a little bit with a boat and look at the behaviour of LCG, LCF and LCB.

This Website
http://www.bootsphysik.de/rechner/bootx.php
provides the numerically computed and graphically displayed CoB, CoG and CoF.

(Click first the button top right "English" to convert the sheet in English.)

Click "show legend" and the used graphic signs are explained (blue dot means CoB and so on).

Input a small trim angle (different to 0) in the appropriate input box, click "calculate heel / trim" and watch the moving of CoB.
The values of LCB in mm is given in the right column, called x (subscript B).
So x (subscript G) means LCG.

Use the buttons marked "i" for Information.

Let the skipper enter the boat at stern (e. g. Mass to load 80 kg, longitudinal dist. -2500 mm, then "load"). Watch LCG.
Is a momentum created?
Click "find equilibrium" and look at the reaction of the boat.

Move masses on board. Look at its behaviour.
Is the LCF a reason for a reaction of the hull, or is it a result of a reaction?
Compare CoB, CoF, CoG, which of them are representing a force and are able to create a momentum?

1 person likes this.
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.