   Ship Movement
  Hey there, I have started to do some basic simualtion of ship movement, and I had to look through my old physicsbooks to fresh up my knowledge. All I want from this post, is to get some review of my calculation methods. :-) It will be nice to be told early in the process, if I far away from the right way to do those calculations.I have a ship with an 900 HP engine and a mass of 80.000 kg. Now I want to calculate acceleration and speed when I give 100% throttle.900 HP -> 671400 Watt -> 671400 Joule/sec -> 671400 Newton/meterSpeed I found by this formula:Speed = StartSpeed + ((Force / Mass) * Time) This means that without friction and 1 second of thrust, my speed will be:0 m/s + ((671400Nm / 80000kg) * 1 sec) -> 8.39 m/sThen I want to make som friction on the ship, so I can only accelerate to the point when the opposing force will be bigger than my engines force, and acceleration will be 0. Here I use this formula:Acc = (Force/Speed - DragCoefficient*speed^2 ) / MassBut I don''t think this is the right formula, because my acceleration is always positive!Is the tottaly physics nuts, or am I on the right track?If anybody know any good online ressources on ship movement, the I will appriciate it.Thanx!I know my ship in the real world, only can go 13 knots 
  What do you mean acceleration is always positive? When the speed is high enough your formula gives a negative acceleration, which is as it should be. ;  I might be wrong about this but if a force acting against a moving object is larger than the driving force, does the object not being to slow down, you mentioned:"I can only accelerate to the point when the opposing force will be bigger than my engines force, and acceleration will be 0"It''s only been a short while since I reviewed Newtonian Physics in school and I''m fairly certain (but not 100%) that when the opposing force IS bigger than the force of the engine the object will gradually slow down and then begin to move in the opposite direction.The gradient of deceleration varies depending on the opposing force compared to the driving force.Sorry I can''t be of anymore help, but your obviously looking into this deeper than I would (be able to ).Good Luck!;  Okay, at some point the acceleration will be negative...but then I have an pretty high DragCoefficient, and I heard that a typical drag coefficent is aprox. 0.1 for a big containership and 0.025 for a small ship?But I find the subject about friction and forces on a ship pretty hard to find good information about ;  The coefficient is 0.1 what?? N/(m/s)^2 ? That makes no sense whatsoever...Btw, why do you divide the force by the speed?;  I can''t answer you question, because that whats what my original post is about. I found the formula in this topic: http://www.gamedev.net/community/forums/topic.asp?topic_id=108207But I cant see the logic in it, but I can''t find anything else about the subject.But whats your suggetion to calculate water resistance on a moving ship? ;  Ok, now I see. It''s not the force, but the power, you divide by the speed. Just watch out for the case where the speed is zero...Regarding the coefficient, just set it so that you get the max speed you like. In this case it should be around 2000 (assuming SI units).;  Okay...thanx for the review! To anybody else who reads this topic. If you know any ressources on ship movement, then please let me know! I can''t find anything useful online :-( 