Does anyone have any article or information about prediction of backing (astern drive) speed ?

[ckutlu]

Ive been searching for a prediction method for backing speed,but I have not found yet.If can anyone help ab this issue ,Ill be grateful.

 

[gonzo]

It would not be much different from going ahead. You calculate wave making resistance, etc, vs thrust from the propeller in reverse.

 

[TANSL]

What items are included in "etc" ?.
When the drag is calculated under normal conditions, nothing is calculated vs. thrust from the propeller. Why do you have to do it, in reverse?

 

[Kailani]

When the drag is calculated under normal conditions, nothing is calculated vs. thrust from the propeller. Why do you have to do it, in reverse?

To calculate the speed of the boat, you have to figure the force moving it. Don't you?

 

[TANSL]

I totally agree with you. It is clear that you know the subject. Although what I usually calculate, according to the various procedures that exist, is the relationship between power and speed. From there to deduce the thrust of the propeller is another process that, I have to be honest, I do not know well.

 

[gonzo]

The power absorbed by the propeller is what should be used to calculate speed of the boat. The thrust=resistance of the boat at a steady state. If the thrust is larger than the resistance, the boat will continue accelerating until it reaches steady state. This link explains the basics:
https://ocw.mit.edu/courses/mechani...icles-13-49-fall-2004/lecture-notes/lec12.pdf

 

[BlueBell]

OP,
Unless it's a proa, your boat is not designed to go backwards.
Props are about 40% efficient at reversing vs about 75% going forward.
Boat efficiency would be about the same forward and reverse at low, low speeds.
So, do the math.

 

[gonzo]

The wave making resistance will be much higher.

 

[BlueBell]

Not at "low, low" speed which is all one expects in reverse, no?

 

[gonzo]

Depends on the application. Some vessels back at full power.