# Drag on a turning boat

Discussion in 'Hydrodynamics and Aerodynamics' started by jubarte123, Feb 23, 2017.

1. Joined: Feb 2017
Posts: 2
Likes: 0, Points: 0, Legacy Rep: 10
Location: Brazil

### jubarte123New Member

Hi everybody,

I have been trying to understand the forces on a boat while motoring on the water for some time, and I am kind of stuck now when I get to equations of forces on a turning boat. I was searching a lot to find adequate information on this, and still having problems, so some professional help would be really appreciated. (I hope my english is understandable enough.)

First of all I understand the forces on a boat's hull and rudder while moving straight, the equations of the total fluid resistance etc.
see here: https://en.wikipedia.org/wiki/Drag_(physics)

I also understand the forces acting on the rudder, when the boat is turning, and the momentum it creates, see here:
http://www.marineinsight.com/naval-architecture/rudder-ship-turning/

But what is missing for my understanding is: what about the fluid resistance when a boat is turning?
For some reason I feel that the previous equations might not be used, -or with modifications- as the boat is turning(yawing) and drifting(sway and surge), and there is an even stronger overall drag on the yawing hull while its relative surface area also constantly changes with the rotation motion to the resisting fluid..
Probably the flow around the boat also becomes more and more turbulent, and not laminar any more..

So, how would you describe the total fluid resistance in this situation with the equations, drag coefficients, and connected with the forces?
Or, where could I find more material on this?
Please feel free to send them in private mail, as well, if.

2. Joined: Apr 2006
Posts: 2,622
Likes: 430, Points: 83, Legacy Rep: 1669
Location: Washington

### IkeSenior Member

Your question is too general. You need to clarify it. What kind of boat? How big? sail or power. We need specifics to answer your question. From the link you provided are you talking about a ship?

3. Joined: Feb 2017
Posts: 2
Likes: 0, Points: 0, Legacy Rep: 10
Location: Brazil

### jubarte123New Member

Hey Ike,

Well, I do not have anything in particular beside my general curiosity, so lets say I will pick now two different kinds of boats for you, so their different cases may help me better understand the relevant physics.
So lets say we have:

Boat A.) a 10 feet long powerboat, with a rigid-inflatable-body and an outboard engine. A small dinghy.
This is really not deep inside the water comparing to the other, which is lets say:

Boat B.) a 30 feet long sailboat, a sloop with full keel - thus making the fluid resistance much bigger -, and it is only motoring now, all sails furled. The rudder is attached at the end of the keel right aft the propeller.