Innies and Outies - architecture: naval not navel

[benjenbav]

We argue amicably and often about deepness of vee and its various benefits. However, given the centripetal force at work in any turn, I started wondering just how shallow a vee would be necessary for a boat to tend to lean outwards in a turn. Indeed, to what extent would even a flat-bottomed lake boat grip the water and lean outwards rather than sliding across the surface away from the centre of the turning circle.

My trusty hydrodynamic testing facility being temporarily out of commission, somehow, I knew the answer would be on here...

 

[benjenbav]

Here's an outie:

 

[davidej]

deleted

 

[Portofino]

Here's an outie:

And here’s why

If I have understood the post correctly?

Steering planing boats .

Why they are “ inners “

Rudder forces
When a blade is laid to port ,it sets up,a force in the water which reacts on the hull and throws the stern to starboard .
This reaction is translated into a angular motion which in term causes the stb chine to become the leading edge of the plane.
Meanwhile the hydraulic forces on the rudder act as a centre of rudder pressure .

The distance between the centre of lateral resistance of the hull and this centre of rudder pressure is a lever arm tending to bank the hull inboard this in a turn .

Opposing this this inboard tendency is the lever arm of upward to the boats centre of gravity.
The moment of centrifugal force , acting at the centre of gravity, tends to give a hull a outboard list in proportion to the square of the speed and tightness of the turn .
If the rudder force is exceeded the turns outboard can become alarming.
As seen in the pic posted ^^^ .

The opposite is true of planing boats hulls since turns are made up against the safe inboard side .
This is because as mentioned, there’s a self created wave due there the greater lift of the now leading chine pushes the outboard side up .
This lift due to hard chines s often 10 x that of rudder pressure alone and is always normally enough overbalance the centrifugal force that tips “ outers “ on a properly loaded planing hull .

Summary in planing hulls rudder force and chine lift operate together and in conjunction with each other and normally provide the banking “ inner “ forces to allow safe turns in any sea conditions.

Displacement boats with round bottoms and soft chines will be “ outers “
Like the military vessel pic above

Hope you all understand
Porto

If I have understood the post correctly?

Steering planing boats .

Why they are “ inners “

Rudder forces
When a blade is laid to port ,it sets up,a force in the water which reacts on the hull and throws the stern to starboard .
This reaction is translated into a angular motion which in term causes the stb chine to become the leading edge of the plane.
Meanwhile the hydraulic forces on the rudder act as a centre of rudder pressure .

The distance between the centre of lateral resistance of the hull and this centre of rudder pressure is a lever arm tending to bank the hull inboard this in a turn .

Opposing this this inboard tendency is the lever arm of upward to the boats centre of gravity.
The moment of centrifugal force , acting at the centre of gravity, tends to give a hull a outboard list in proportion to the square of the speed and tightness of the turn .
If the rudder force is exceeded the turns outboard can become alarming.
As seen in the pic posted ^^^ .

The opposite is true of planing boats hulls since turns are made up against the safe inboard side .
This is because as mentioned, there’s a self created wave due there the greater lift of the now leading chine pushes the outboard side up .
This lift due to hard chines s often 10 x that of rudder pressure alone and is always normally enough overbalance the centrifugal force that tips “ outers “ on a properly loaded planing hull .

Summary in planing hulls rudder force and chine lift operate together and in conjunction with each other and normally provide the banking “ inner “ forces to allow safe turns in any sea conditions.

Displacement boats with round bottoms and soft chines will be “ outers “
Like the military vessel pic above

Hope you all understand .

Porto

 

[Portofino]

Having established why planing boat are “ inners “ now let’s look specifically the difference a deep V and shallow V planing boat turn .
Which I think is part of the OP ,s question if I understood it correctly?

Ok let’s refresh my first post ^^^
Keeping it simple so,s not to loose anyone sat at the back —-
When a planing hull banks on its turn the stern ride up on its own self created wave along the outboard chine .
The pattern of pressures and importantly suction which are created varies according to the hull type .

Excessively flat ,or low deadrise hulls tend to have the highest pressure upwards on the outer side thus it lifts higher also a bit more suction inboard on the downward side so the result is they heel inboard more .

Where as a deeper V planing hull due to the less favourable angle on the outer side does not generate as much outer lift ( and less inboard suction too ) so it turns flatter , banks over in less .

 

[BruceK]

you lost me, now my head is spinning. All I know is mine says not to hard lock at speeds above 40knts. It doesn't say why, it just says dont. Right on the tin plate by the helm. It's completely arbitrary though. My boat has never seen 40 knts in its life.

 

[benjenbav]

you lost me, now my head is spinning. All I know is mine says not to hard lock at speeds above 40knts. It doesn't say why, it just says dont. Right on the tin plate by the helm. It's completely arbitrary though. My boat has never seen 40 knts in its life.

That warning sounds a bit like the sort of thing in the press pack for journos touring with Led Zep, back in the day. That one read:

"Under no circumstances should you make any form of eye contact with John Bonham. This is for your own safety."

 

[Mr Googler]

I got lost reading Porto....nothing new there

Is it not just upper deck height/weight?

If there is enough weight above the waterline pushing outwards during a turn to over come the resistance the hull gives, it will roll outwards?

Take the same warship, turn it into a centre console boat (how good would that be!) and it probably wouldn’t roll outwards.

No doubt I’m being too simple

 

[rubberduck]

On our PB2 my son asked the instructor how far over you have to go to turn the boat over. Several 35knt sharp turns proved it to be pretty difficult.