In an effort to get some conversation in the air entrapment section...

[sirbob]

In an effort to get some conversation in the air entrapment section...

Who can tell me the pounds of air pressure that are created and at what speed for a basic tunnel hull with pod.

i.e. 40 mph = 500 pounds per square inch or foot

50 mph = 1000 pounds per square inch

Etc...

Looking for some engineering majors out there!!!

 

[Crazyhippy]

Pretty sure it is lot less pressure than you think.

Lets use a nice hypothetical boat. Say 25' long true tunnel (Outboards) and 5000 lbs.

At 100mph there is still less than 5000lbs of lift (or it would go from a boat to a plane)

For ease of math, lets assume there is 90% lift (or 4500lbs) and that the tunnel is 4' wide, 22.5' long.

We have 90square feet (4*22.5) of tunnel area supporting 4500lbs, or 50 lbs/sqft (4500 / 90). 50 lbs/sqft is .347psi of pressure. (50/144)

Super over simplified....

Sent from my SAMSUNG-SGH-I727 using Tapatalk 2

 

[sirbob]

So then...

Does a typical tunnel hull account for any "venting" out of the rear - ie losing any air out of the transom when speed or is all the air packed in with nowhere to go?

In other words does a typical tunnel (with pod) ever get completely out of the water down the center line?

 

[AzGeo]

Attack angle and Air trap 'area and rate of reduction' are the largest factors while trying to 'pack air' in the tunnels. In other words, you can have the tunnel hull with 10% reduction trimed UP to an attack angle that could 'kite to pack air'. Conversely, you can have a tunnel hull with a 60% reduction and trimmed to a low attack angle, while acheeving similar 'lifting pressures'. "Area and rate of reduction" example: Inlet opening is 2' X 2' = 4' inlet area. The size of that tunnel reduces down to 2' wide X 1' deep = 2' outlet size, and this would be a 50% air trap reduction ratio. The curved line (roof of the tunnel area) creates where and how the air pressure (lift) effects the center of gravity of the mass (boat).

 

[STV_Keith]

The Tunnel Boat Design software will give you the info you seek, if you are willing to make the measurements: http://www.aeromarineresearch.com/tbdp6_features.html

To give you an idea on total aerodynamic lift, the STV's are considered pretty good in this department, and only generate just over 400# of aerodynamic lift at 100mph. There is also hydrodynamic lift built into the hull that is more difficult to determine.

 

[Boat 405]

A few of us have done significant data logging on a 19 daytona of what is actually happening in the tunnels of a boat at 140 mph and it is mind boggling to understand. To say the least it is very complex. Its not a simple packing air and release out the back.