Needed: Equation for line drag in water

[Tully]

First off, a thousand apologies if this is in the wrong forum!

I have seen the other posts regarding calculating line drag in water for things being towed in water, however, I have the somewhat opposite requirement.. Here is what I know:

• hydrodynamic object being towed along surface by underwater vehicle
• depth of underwater vehicle: 30'
• water type: salt water
• line diameter: <0.25"
• line length: 45'
• speed of underwater vehicle: 5kts or 2.6m/s

What I am hoping is that someone could provide an equation that would give me the maximum drag. My thinking is that if I have the maximum drag then I will know the minimum line strength required as well as minimum buoyancy required for the towed object on the surface, right? I'm also hoping that I can change the line diameter and line length variables to change the final drag value.

As you can tell, these types of calculations are not my area of expertise, and any additional input/guidance is greatly appreciated!

 

[anorlunda]

Here is how to calculate it for pulling a barge. It should make little difference if the towboat is on the surface or submerged.

https://thenavalarch.com/bollard-pull-calculations-introduction/
I'm curious. What is it you are trying to do? Towing a boat from a submarine is pretty odd.