When we lay the steel rod on the water, it is submerged under water immediately. But for steel ship case, it won't happened like this one although the steel density is higher than water density.
I don't know why? ........

you don't know why? it is very simple. because volume of steel rod and volume of steel ship is different.when one thing put on the water, it is effect of two forces: weight of its own and buoyance force. steel rod has higher weight than buoyance force so it will submer. opposite, steel ship has smaller weight than buoyance so it will float. you should read again book of ship hydrostatic to find more infomation.

He knew! Because he's a Master.^^
He created this topic because he want we to practice English.
Thanks for your ideas ^^!
The steel ship is made of much more steel than a steel rod.
The steel ship replace a bigger volume of water than a steel rod.
Let's compare weight of the volume of steel ship which submerged (M1) and weight of the volume of water which replaced by the ship(M2).
Because M1 < M2. so the steel ship floats.
But let's compare weight of the volume of steel rod which submerged (M1) and weight of the volume of water which replaced by the steel rod (M2).
Because M1>M2, so the steel rod submerges.
Do you understand, Piggy?

Ahum, thank you very much, but I don't think so. According to Archimedes's law in the equilibrium state, it always have got the M1 = M2.
Please more discuss about this problem.

This is good problem and difficult, but i can't explain satisfactory
if the sewing needle make a hole then does it sink?

I agree with you, but in modern steel ship case, it won't sink if you do that. If not it will happen the Titanic disaster again.

If we lay a ship on the water,it floats ,in ship's theory major ,it's called floatability .Simply because ,when we lay a ship (or anything else) on the water , there're 2 vertical forces :
Archimedes force,created by water pressuse acted on the volume which is underwater body of ship ,Note the watertight volume .It's the upward force .This force deppends on the displacement (in m3) (abreviation V) .its regard as M1 .
Total Gravity of a ship ,created by every gravities present on a ship .It's downward force .Called M2
When M1 = M2 ,a ship floats .
M1 < M2 a ship submeged immediately .
Its so easy to understand .

Dear Corsair266, Hehe... ( just for a little bit polite)
If you say so, I can understand (just like what I was taught in high school ^_^). But there is a "BUT", What you explained above has NOT account for the question, Why does the ship float while the steel rod submerge? Actually, why does the steel rod has M1 < M2 while the ship has M1 = M2?

Re piggy
M1 and M2 ,yeah i'll tell u more clearly so that we can solve this contradiction
In fact ,when we lay something on the water ,it submerges step by step
,that make the upward force generated by water pressure(we called as
M1) increases step by step,too .The upward force increases with the
increasing of displacement ,do u agree ? Till M1 = M2 we can say that
the ship floats .
Go back to say about steel rod, when we lay a
steel rod on the water ,it submerges step by step too ,it displacement
and upward force increases step by step ."BUT" ,differ from a ship
,maximum upward force that a steel rod can attained ,it s not enough to
ensure M1 = M2 ,so its gravity > its upward force ,it submerges
u can image like this ,we have two steel rods with the same gravity and
density .U bring one of two steel rods and by some methods, shape it
like a ship (mean icreasing its tight Volume ) ,Now lay them on the
water .
I think we resolved this problem.

it's very easy. Follow archimeste law, displacement of ship when we lay a ship on the water, it is equal with water destiny. In sum, the clue is archimeste Law.
note: Volumme of sink part of ship when its laid on watar is not the steel volumme. Its steel and space volumme.