Recent content by Jimboat

A shallow deadrise (less than 8 degrees) will provide the most efficient lift. Deeper deadrise angles (like 12 to 20 degrees) will make a much cleaner presentation to the water surface in rougher water conditions, exhibiting a much more comfortable ride, but less efficient lift. Again, a design...

moparbarn - the notes in moron's post is referencing some of my notes in preparing an article that I wrote for Hot Boat magazine (April 2007 issue) on "Hump Zone/Porpoising". You can get my full article on my website. You might also find my article on "Chine Walk" (Hot Boat magazine Jan 2008...

The location of the motor mount (setback) affects the amount of "bow lift" generated by the drive system (propeller). The "moment arm" distance from propeller to sponson aft location has a determining influence on vertical force generated. Trim (if available) also contributes to solution, of...

PropJockey - well, going fast, faster...and especially FASTEST...isn't always easy!

Hi guys.... Sorry I haven't dropped in for a while. Let me know what you're looking for, and I'll help if I can. FYI...David Homer is right! The principles of tunnel hull design work for any size of boat, because the performance and analysis formulae are based on "first-principles"...

Geraghty & Tom - There are indeed quite meaningful relationships to tunnel height, width to performance and dynamic stability. As for your "diffuser effect" - if you mean the "angle of attack" of the aerodynamic "wing" formed in part, by the tunnel roof (often called 'air compression'), then...

What an interesting thread! Allot of you guys have made a real study of your hull designs. Very Cool! It is certainly correct, that a tunnel boat design should match its intended purpose. The tricky balance of aerodynamic forces and hydrodynamic forces is unique to tunnel hull design. That...

GT - The location of the hinge pin will determine where the drive (motor lower unit) will generate it's force (thrust) from (fore/aft of sponsons). Since you will have the bullet of the drive located at some dimension above/below the planing surface of sponsons, this makes the location of the...

Sponson Deadrise Shallow sponson deadrise angle will give much better acceleration and often better top speed. But steeper deadrise will be much more forgiving in choppy water, and can prevent wetting down of otherwise flat, dry surfaces on a tunnel boat. The sponson deadrise angle is usually...

Izi - actually, the lift/drag ratio effects of a lower height above surface is not really exponential, but it is heavily influenced by the height. The changes to L/D due to h/c (height vs. chord length) are different for wings of varying aspect ratio and thickness and shape.

Gene – the ‘volume’ in the tunnel does not directly influence the lift generated. The lift is a function of total plan area of the wing (width X chord length), aspect ratio of the wing, thickness of the wing, and height of the wing above the surface. Of course, the performance characteristics...

GT – reducing the tunnel height (making it shallower) will INCREASE the lift generated. There isn’t a “rule of thumb”, though…that’s what I’ve spent all the years of research developing. TBDP software incorporates all the design relationships and algorithms for calculations. STBD book...

Kez - yes, you have it right. A shallower tunnel will definitely generate more lift than a deeper tunnel. The tendancy to ‘blow over’ can be caused by several design issues, though. For example, if your hull is simply dynamically unstable due to the location of forces, then reducing lift will...

Chris - Yup! You've got it! Adding thickness is pretty easy...so is making the h/c ratio (height above the water surface) smaller - which also increases lift alot.

Chris - the "curved" tunnel roof shape you are refering to is really just a different design of aerofoil used in the design for "enhanced" aerodynamic lift. For example, a high-camber aerofoil shape...We've done alot of research with NACA aerofoil types in application for tunnel hulls (low...