From: TBPNews [webnews@aeromarineresearch.com]
Sent: Saturday, November 10, 2001 12:22 PM
To: jimrussel@sympatico.ca
Subject: TBPNews - Nov. 10/01

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>> Tunnel Boat Performance News >>>>>>>>>>>>>>
==================================================================

TBPNews/#7 - Aerodynamic Lift  where does it come from?  

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>> Tunnel Boat Performance News >>>>>>>>>>>>>>
==================================================================

Aerodynamic Lift  where does it come from?  

We have had many questions about how the tunnel boat generates lift.  The following summarizes some of the background.

A tunnel boat must count on the sponsons for some of the lift for the hull, just as a vee boat must depend on its narrow running surface (pad) to support its weight.  The tunnel hull however has the additional advantage of being able to further reduce the water drag drastically by supplying lift from it's aerodynamic surfaces.  

A properly designed tunnel hull is considered, at high speeds, as a wing in what is known as 'ground effect', (even though it's water that it is 'flying' over).  The important point to note here is that every pound of lift that can be generated by this wing is one less pound of lift that doesn't have to be supplied by the sponsons.  So, the trick becomes to squeeze as much lift out of the tunnel and deck surfaces as we can so that we can take some of the load off the sponsons. 

The 'air lift' of the Tunnel Hull is what sets this type of hull off from all the rest.  Although the many factors affecting the aerodynamic forces generated make this a complicated matter at times, the effort is clearly worth it.  So, let us look at what factors are involved in creating the lift generated by the tunnel and the deck surfaces, or this 'wing' we have talked about.  The main ones can be summarized as follows: 
(a) Airspeed 
(b) Angle of attack 
(c) Surface Area of Tunnel 
(d) Aspect Ratio of Tunnel 
(e) Height of mean camber line above the water surface 
(f) Aerofoil shape of tunnel cross section 
(g) Surface condition of exposed areas 

The design and performance effects of each of these contributors (ant others) are outlined in detail in the STBD book.  For now, as an example of what this aerodynamic lift can do for us, let us compare a tunnel hull and a vee hull design of equal weights.  Each of these boats must generate, in their own way, the same total lift to support their weight.  The vee hull will produce virtually all the required lift as hydrodynamic lift.  The tunnel hull however, can contribute an amount of aerodynamic lift, leaving a smaller part of the total to be made up as hydrodynamic lift by the sponsons (running surfaces).  

By reducing the wetted area of the water planing surfaces, a significant reduction in drag is realized   and maximum velocity is a function of only the drag and available power.  

Water drag in any type of hull is what most heavily affects the ultimate speed, and so we can see that the tunnel hull with its aerodynamic lift and reduced water wetted surface will have an advantage, when properly designed.

/Jimboat
www.aeromarineresearch.com

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Note: The articles presented over the past few weeks in TBPNews are edited excerpts from the Secrets of Tunnel Boat Design book, by Jim Russell, published by AeroMarine Research.  The STBD book explains the theory in full, and outlines example design calculations, step by step.  The Tunnel Boat Design Program for Windows 98, software, does all the force calculations, dynamic force balances at all speeds, and reports the analysis automatically, including complete graphical performance results for any tunnel or modified vee hull design.

Let us know any ideas you have, requests for articles, questions or comments on our TBPNews.

/Jimboat
AeroMarine Research
TBPNews@aeromarineresearch.com
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>> Tunnel Boat Performance News >>>>>>>>>>>>>>

Let us know any ideas you have, requests for articles, questions or comments on our TBDPNews.  Send your comments to TBPNews@aeromarineresearch.com
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Get your full, illustrated, 10th edition copy of the world known "Secrets of Tunnel Boat Design" book.  GO TO: www.aeromarineresearch.com

Also, the publications "History of Tunnel Boat Design" book, "History of Propellers" e-book, the "Tunnel Boat Design Program for Win98" software, and the "PropWorks2" software for speed prediction and propeller selection at the Aeromarine Research web site.  
GO TO: www.aeromarineresearch.com

"Secrets of Tunnel Boat Design" book
"History of Tunnel Boat Design" book
"History of Propellers" e-book
"Tunnel Boat Design Program" for Win98 software
"PropWorks2" software for propeller selection and powerboat speed prediction

GO TO: www.aeromarineresearch.com

>>>>>> Tunnel Boat Performance News >>>>>>>>>>>>>>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
AEROMARINE RESEARCH - Tunnel and High Performance boat specialists
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~




Click on the link below to be removed from the TBPNews mailing list.
http://www.aeromarineresearch.com/cgi-local/subscribe.pl?jimrussel@sympatico.ca


