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TBDP©/VBDP© Porpoise Regime Analysis
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Figure 1- TBDP©/VBDP© graphic output shows the velocity at which your hull configuration experiences instability in Porpoise Regime and susceptibility to porpoising.
  Porpoising can affect any performance hull design, but when will it happen?  under what conditions?  how do we fix it?

We have developed a new analysis tool in the TBDP©/VBDP© software! XPorpoise is an engineering tool developed by AR® that helps predict your hull's inherent instabilities leading to porpoising. The technique is based on a uniquely modified Stavitsky & Day/Haag method of hydrodynamic prediction of the critical porpoise trim angle (CPA) for various hull/setup configurations, velocities and Lift characteristics.

Porpoising onset occurs when the lift is generated at a sufficiently high trim angle or sufficiently low deadrise so as to cause a dynamically unstable loading on the lifting surfaces.

By analysis of a hull's design and performance characteristics and comparison to the CPA for each velocity in performance range, TBDPV/VBDP© can predict when the hull is susceptible to porpoising and when it is performing in a stable regime.

The XPorpoise analysis is presented in standard TBDP© and VBDP© output and in graphic analysis format. It's simple to interpret when the hull is in the "Porpoise regime" or in the "Stable regime"....AND simple to change setup or design features with TBDP©/VBDP© Ver 8 to make the hull less susceptible to porpoising.  (While several design or setup or operating parameters influence the hull's susceptibility to porpoising, a hull with MORE deadrise or LESS trim angle is less likely to experience onset of porpoising.)

Figure 2 - VBDP© graphic output shows the differences in vee hull bottom designs that can contribute to instability in Porpoise Regime and susceptibility to porpoising.
©/VBDP© analyzes the porpoising stability of your hull design/setup throughout the entire operating velocity range.  TBDP©/VBDP© then presents the analysis for your design for operation in "stable planing regime" or "Porpoise instability regime".  When your hull is in the "stable planing range", the hull is less likely to experience porpoising.  When your hull is in the "Porpoise instability regime", it is susceptible to porpoising.

The ability for
TBDP©/VBDP© to present graphic view of XPorpoise analysis throughout the full operating velocity range, for TWO design alternatives simultaneously, makes comparative evaluation quite easy.  (Note view in Figure 2 that shows "shallow deadrise with pad" vee hull, compared to "steep deadrise, no pad" vee hull designs - and their relative susceptibility to porpoising in "Stable Planing" regime (less susceptible to porpoising) or "Porpoise Regime" (more susceptible to porpoising).

TBDP©/VBDP© and the XPorpoise analysis can identify the susceptibility of your hull to porpoise and show what speeds that it will occur.

So, what can I do about it?
Porpoising is a function of the lift generated by your hull, the deadrise of your running surfaces, and the trim angle that is needed to get that lift. If the hull design/setup is 'prone to porpoising', the onset of porpoising will start at a velocity that triggers a change in dynamic center of gravity (often the hump zone).

The resolution to a porpoising problem with a hull design is most always addressed by causing the boat to run with less trim.

If a boat is porpoising at a given speed and load, lowering the trim angle will reduce or eliminate the porpoising. There are several ways to get there, but the bottom line is to reduce the trim angle at the velocity of porpoising onset. Even if the hull design is operating in the "Porpoising Regime" through a full range of velocities, reducing trim in some way will improve or resolve the problem.

Resolutions to an existing porpoising problem:
-Reduce Trim Angle
-Change Static Weight Locations
-Change Dynamic Forces location
-Clean up Hull bottom condition
-Optimize Propeller Selection
-Design with Higher Deadrise (bottom surfaces)
-Trim Tabs

Research results now included in performance analysis by TBDP©/VBDP©

[more about AR's research     more about AR's publications    and    technical articles/papers]
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Material from this website may be not copied or used or redistributed, in whole or in part, without specific written consent of Jim Russell or AeroMarine Research®.