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

Discussion in 'Boat Design' started by ckutlu, Sep 14, 2017.

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1. Joined: Sep 2017
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### ckutluNew Member

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.

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### gonzoSenior Member

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

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### TANSLSenior Member

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?

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### KailaniSenior Member

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

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### TANSLSenior Member

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.

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### gonzoSenior Member

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### BlueBellAhhhhh...

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.

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### gonzoSenior Member

The wave making resistance will be much higher.

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### BlueBellAhhhhh...

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

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### gonzoSenior Member

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

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