BOAT3D Planing Boat Simulation Software
For a given boat design, BOAT3D estimates the forces on a hard-chine planing boat using an added-mass analytical approach and solves for the predicted trajectory of motion of the boat. The boat moves with 3 degrees of freedom, lunge, heave, and pitch. BOAT3D lets you
----estimate the speed you will obtain from a particular design for a given engine/propeller thrust.
----also lets you estimate the accelerations imposed on the boat occupants at a particular speed in a particular sea condition, and the amplitudes of the heaving and pitching responses to the sea.
(Since the roll and yaw degrees of freedom are not considered, BOAT3D cannot tell you anything about roll or turning stability. Also, the boat must be partially or fully planing, meaning that the length-based Froude number must be at least 0.6 ---- the boat is beyond displacement speed and at least in the "hump" regime.)
After simulating a boat test run, the user can call up the output screen and manipulate it in various ways to look at results. In the following, the user is showing numeric values of variables at 127.564 seconds into the run, the position of the boat and the water at this time, and coincidently, a plot of vertical acceleration in G's at the center of gravity of the boat vs time (many different variables can be plotted, up to 6 at one time).
The boat graphic is within what is referred to as the "video" window. The user could single-step time to explore what is happening just before or just after 127.564 sec, or he could click on "Go" and the boat and waves would move (with a choice of real-time or slow-motion).
The user can also transfer selected results to our graphics utility program EDTECH for plotting or further analysis. One of the pre-planned EDTECH printed outputs is as follows: The user may select up to 8 "snapshot" times for output of detailed force information. The program draws a snapshot of the boat's position with water surface indicated at each time, and the program gives its estimate of how water forces are distributed along the length of boat.
In the above example the solid line plot represents the total vertical lb force of the water on a boat segment (the boat is divided into 40 cross-sectional strips). The intermittent line plot represents that from the added-mass water impact force (the difference represents buoyancy). (Both lines are adjusted at the stern by the Payne "Dynamic Suction" effect.)
Various types of analyses can be performed. In one typical case (with 2 degrees of freedom) the user might specify flat calm water and a gradual increase (linear with time) of the speed over many simulated minutes. The program output estimates the boat speed, trim angle, height of CG relative to sea level, and horizontal resistance force obtained at various thrusts. If a similar analysis is performed with uniform waves, an estimate of the boat's performance in a particular wave type at various speeds is obtained.
With random waves a simulation run with 3 degrees of freedom at constant thrust or optionally, propeller rpm, is normally performed. The program then analyses the results and provides you with a statistical summary of boat behavior. This includes average speed and resistance force, and information on vertical acceleration and heaving and pitching oscillations. The vertical acceleration results provide a measure of ride comfort.
History of BOAT3D
Aeronautical engineer Peter R. Payne began designing and building fast experimental boats as early as the 1960's. He tested them in the Chesapeake Bay near his home. There were a number of unconventional catamarans in the 60's followed by a series of very unconventional monohulls called Sea Knifes in the 70's. Inspired by work of his friend and colleague J. D. Pierson of the Grumman Corp., Peter began to develop the BOAT3D program starting in the 1980's and ending with his untimely death in 1997. Peter used an augmented BOAT3D program to design his last experimental boat, the Dynafoil(tm). Digital Analytics' EDTECH program was used as the graphics tool for all BOAT3D graphical output.
The PAYNE DYNAFOIL(tm)
The last version of BOAT3D which Peter published was numbered 2.5, and there was a gap of years in development after this.
After Peter's heirs graciously allowed Digital Analytics to continue developing BOAT3D, version 3.0 was created in 2003. The language was changed from Microsoft Basic for DOS to Borland Delphi Pascal for Windows and considerable re-structuring was done. Peter was a world-class expert in the effects of vibration and shocks on the boat pilot or passenger, and certain very detailed treatments of this, and other fine details, were removed in the effort to get 3.0 running the basic calculations quickly.
This was quickly followed by 3.1, the first restructured version with the complete Payne propeller/propulsion treatment and a convenient user interface.
In 2007 I changed certain geometrical and computational details so that the shape of the boat's bottom does not always have to conform to the straight-line rule, that is, the cross-sections (frames) do not necessarily have straight lines from the keel to the chine. This version was designated 4.0 because so many internal details were changed, although the user interface was almost like that for 3.1.
Now in 2008 I have added several useful user interface changes (without changing the simulation details). This is the current version 4.1, which includes for the first time the "video" window shown above.
With each new version of BOAT3D with simulation changes (3.0, 3.1, and 4.0), I have developed a technical paper which (a) describes important technical features of and changes in the BOAT3D methodology, and (b) shows in detail how BOAT3D results compare with experimental results. There is no simple answer to the question "How accurate is a BOAT3D simulation?" and the technical paper is an attempt to provide this type of information.
Features of BOAT3D
BOAT3D and its utilities are standard Windows programs. RAM requirements are very moderate, but fast cpu speed and large disk capacity are beneficial.
As in earlier versions, the BOAT3D planing boat shape can be generated by specification of parameters for mathematical functions (developed by Payne) describing the shapes and positions of chines and keel. A trial set of parameters can be used to generate a drawing of the boat with the static waterline determined and shown in the drawing.
Also, in the new versions, users can enter their specific keel, chine, and gunwale coordinates from their existing boat design and if desired, specify curvature in the cross-sectional shape of the bottom.
The user specifies boat weight, CG position, and radius of gyration. If propeller details are being used, these are also specified.
All boat shapes are hard-chine.
New features with
version 4.0 (2007) are:
-----The line in
cross-section from keel to chine does not have to be straight. It can
be straight or a cubic polynomial curve.
-----Computations are a
little faster and more stable.
-----It is easier for me
to introduce custom changes in the boat cross-sectional shape for
special cases for which the standard cubic polynomial is not
suitable. I have to date produced two different custom versions.
New features with
version 4.1 (Jan 2008) are entirely to do with the user interface:
----- A built-in editor
for the boat shape data table.
----- A "video"
feature---while previously you could produce printed series of
graphics of the boat travelling through the waves, now you can also
produce a moving image on the screen.
Propulsion Specification
Options are:
• 2 Degrees of
Freedom: CG moved at specified horizontal velocity
• 3 Degrees of
Freedom: Specified horizontal thrust at CG
• 3 Degrees of
Freedom: Specified thrust applied in direction of propeller shaft
• 3 Degrees of
Freedom: Specified propeller rpm
• 3 Degrees of
Freedom: Specified engine torque curve
In all but the last option the specified variable (velocity, thrust, or rpm) can be constant or ramped up or down over time.
Various water surface conditions can be set such as flat calm water, uniform waves, or random waves following the Pierson-Moskowitz-Bretschneider energy density spectrum. Either head or following seas are specified.
For a given specification the program estimates the forward boat speed (3 DOF cases), trim angle, height of CG relative to sea level, and horizontal pressure and skin friction resistance forces, as well as horizontal and vertical accelerations and first and second time derivatives of trim. These and other results are written to a file for later plotting or other output.
If you have an interest in BOAT3D, I would be glad to answer any questions by e-mail or phone.
Dail Singleton, PhD