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SpeedboatPerformance.com's all-new online performance prediction program,
SpeedboatDynamics is the first of it's kind. There are several simple prop calculators
and other applications that can be found on line, but never before has a full-featured
numerical routine been released for public use. The coding behind
SpeedboatDynamics actually computes the conditions present under your boat in
great detail, using specialized methods to account for the details and features found on
today's powerboats. By marrying a code which can accurately predict the resistance
with one that can accurately predict propeller performance, we have developed a truly
useful and instructive tool.
Version 1.0 of SpeedboatDynamics works as follows: You input parameters
describing your boat, register an account with us, and our servers will do the rest. You'll
be provided a full report, predicting your boat's expected performance, right down to
engine RPM vs. speed in a matter of seconds.
SpeedboatDynamics is very sensitive to your inputs. That means that you will see
some measurable change in performance based on configuration changes, or even
environmental changes that you may submit.
2.0 Data Handling
To submit your job for processing, go to the Data Input page of the website. There,
you will be presented a form which has many fields starting with your username and
e-mail address. Many people who use this service are setting up for Poker Runs or other
races, and do not wish to divulge their true identity. That is fine. Our staff maintains
your data in strict confidentiality, and will not release or publish it to anyone but the
authorized user. Due to the availability of AutoComplete on most web browsers, we rely
on your computer to recreate your input data.
Once an account has established, you can change the inputs to simulate a different
setup. The only things that must stay the same are the E-mail address, and Password.
The data blocks are as follow:
E-mail: Enter the SAME E-mail address to which your PayPal account is registered. If you
do not have a PayPal account, not to worry. You can still check out using PayPal, but you
must give PayPal the same e-mail address as you have on file with us.
Password: Enter your password. Registering a new account is the only time passwords
will be issued or changed. The only exception is if you happen to sign on through PayPal
prior to registering with us. In this case, the first time you simulate a run, your
password will be changed to what you entered. After that, the password will remain the
same.
Name: Enter your name. You can put anything you want, but whatver you enter is what
we are going to refer to you as.
Manufacturer: Enter the make of your boat.
Model: Enter the model name and year of the boat.
Length: Enter the length overall of your boat, measured in feet.
Beam: Enter the boat's beam measured in feet and inches in the two blocks provided.
Manufacturer data is acceptable for this. Due to the nature of the code, beam data is
used mostly for calculation of wind resistance.
Weight: Enter the boat's weight in pounds, in the condition you want the predictions run
for. Typically manufacturer's estimated weights are without fuel and people. If you don't
have an actual weight from a truck-stop or sling scale, you can estimate by adding
500-1000 lb to the manufacturer's published weight depending on the size of the boat.
Deadrise: Enter the boat's deadrise angle in degrees as measured at the transom. This
is the angle that the "V" makes with a horizontal plane at the keel. This is usually
published by the manufacturer. If not, you can measure it by measuring according to the
following drawing.
Hull Depth: Enter the overall height of your boat in feet as measured from the keel all
the way up to the top of the windscreen or superstructure.
# of Running Strakes: Choose the number of running strakes EXCLUDING any keel pad.
This should be an even number for a symmetrical hull. Do not count the reverse chines.
For example the boat in the figure above would have 2 running strakes.
# of Transverse Steps: Chose the number of transverse steps, if any, built into the hull
bottom. Only count the steps that are fully ventilated, meaning that there is either
ductwork or a sizable cut at the chine to allow air to be drawn in behind.
Keelpad: Select "Yes" or "No" based on whether the boat has a keelpad installed. This
will look like an extra piece of hull bottom sometimes as much as two feet wide near the
keel.
Type of Cockpit: Choose the type of cockpit which best reflects the construction of the
superstructure of your boat. Most boats will be considered "open" cockpit designs,
meaning that very little, if any consideration has been given to streamlining the area.
Many poker run boats are built with one or two quarter-canopies, which are more
streamlined, but still open at the top. Fully enclosed boats look like what you see in the
APBA or SBI racing circuits, with very streamlined superstructures.
# of Engines: Select the number of engines installed in the boat. This actually fixes
many parameters in the program, including the number of outdrive units. If you are
running something way out of the ordinary, such as a single turbine powering two
drives, or multiple engines per drive, contact us, and we'll adjust to accommodate.
Engine Displacement: Enter the engine displacment of EACH engine in cubic inches.
This, along with other engine parameters helps us fine-tune the available power curve.
Again, if you are running a turbine, contact us, and we'll be more than happy to adapt
the code for you.
Engine Aspiration: Choose the means of induction for your motor(s). Pay careful
attention to whether you select Intercooling or not. This affects how we adjust your
motors' output based on air and water temperature.
Engine Redline: Enter the maximum engine speed you will allow, either based on
design, or the Rev Limiter. This input, along with the engine power data section helps
determine your engines' characteristics, but mainly comes into play when you selected a
propeller with too low of a pitch angle for your application.
information you have available. The program will use only one or the other methods
described below.
If you DO NOT have an actual dynosheet from a test of your motor(s), then use Option 1.
This will assign your motor a "typical Big Block Chevy" power curve based on your inputs
of power rating and RPM. Option 1 is fine for engines with stock tuning, and will be a
reasonable approximation for most motors.
If you DO have dynosheet data, then select Option 2. For each pair of blocks, input an
RPM rating and the corresponding BHP value. The RPM values used in Option 2 must
correspond to the measured BHP (Brake Horsepower) for that RPM from your dyno test.
Using Option 2 is recommended for high horsepower applications. These tend to be
either peaky if normally aspirated, or non-standard power curves with superchargers or
turbochargers. High-powered applications that use high-pitched props benefit from
actual dyno curves.
When inputting dyno data, select your points according to the following guidance:
First point: Between 2000-2500 RPM
Second point: Between 3000-4000 RPM
Third point: At the torque peak
Fourth point: At the power peak
Fifth point: At redline or a point past the power peak which clearly defines the motor's
ability to breathe. Note that the engine redline input you made above is still active, and
the program will not allow the motors to run above that speed. As with the real boat, if
you are propped correctly, you won't quite hit the redline.
Select Driveunit: The program contains a library of many popular stern drive and
outboard configurations. Each has its own hydrodynamic properties, and interaction with
the propeller. If you have a variant or entirely new drive system which is not included,
please contact us, and we will do the necessary research to add new drives to the library.
Select Transmission: If you are using a Bravo-Style drive which does not have a separate
bell-housing mounted transmission as found on the SSM drives, select "None-Bravo".
Otherwise, select the transmission from the list which best represents yours. Follow-on
versions of the program may include provision for inputting transmission dyno results.
Enter Drive Gear Ratio: This block is for input of the outdrive's gear ratio. Enter the
overall gear ratio, being aware that many drives accomplish their reduction in two steps.
In almost all cases the number entered is >1.0. A link to a Gear Ratio Summary page is
provided, which shows ratios available for most popular drive units. This page will open
automatically in a new web browser window so as not to interfere with the data entry
process.
Select Propeller Type: There are several types of propellers to select from in the list box.
Pick the one that most accurately reflects your prop. This input, in conjunction with the
drive unit selection, allows the program to model propeller performance.
Number of Blades: Enter the number of blades on each prop. This is crucial in
determining the actual pressure loading on the prop blades.
Enter Prop Diameter: Enter the diameter measurement for your propeller(s) in inches..
This can be found stamped on the hub as the first number (i.e. 15.25x29RH means
15.25" diameter). If you cannot see or find the stampings, measure the radius from the
propeller shaft center to the blade tip and double it.
Enter Prop Pitch: Enter the pitch measurement for your propeller(s) in inches. In the
example above, the pitch would be 29". If you cannot see or find the stampings, consult
the prop manufacturer, or take the prop to any competent propeller shop to have it
measured.
Enter Prop Setback: First, trim the drive unit down to where the propshaft is parallel to
the running surface of the boat (i.e. zero trim). Measure the distance from the end of the
running surface (this will be ahead of the transom on a boat with a transom notch) to the
front end of the propeller hub (not the gearcase bullet). This measurement is used to
predict the wave rise behind the boat and immersion depth of the propeller(s) at
operating speeds.
Enter Prop Height: With Prop Setback, this measurement is used to determine the
operating immersion depth of the propeller(s). Measure, with the drive in the same
position as above, the vertical distance in inches between the propeller shaft axis and
the bottom of the boat, directly in front of the propeller(s). For cases where the
propshaft is located below the bottom of the boat, the value will be positive, and
negative for setups which have the propshaft above the running surface. A quick note
on this: Yes, you can trim your drive way out, and make it ventilate to the point where it
loses efficiency. While we could put another routine in the program to handle that, it
wouldn't do you any good, and we have found that as long as you only trim the drive up
as necessary to carry the nose and achieve your top speed, the arc the drive moves in
coincides well with the direction of waterflow. This is not to say that everything will work
properly if your boat's LCG (longitudinal center of gravity) is off, and the drive must
trimmed up too high to achieve optimum performance.
Select Water Type: Use this list box to pick the type of water to simulate your boat in.
This does make a difference, independent of altitude. The density and viscosity values
are somewhat different, meaning that your boat will have more hydrodynamic lift and
more propeller thrust in salt water than in fresh. The boat's hull can support itself with
less trim angle, which causes it to require less power. This is somewhat offset, however,
by the increased drag on the drive units and propellers.
Enter Altitude: Enter the altitude above sea level in feet where you intend to simulate
operation of the boat. For operation at sea level, simply enter '0'. This is used not only
to calculate the wind resistance on the hull of your boat, but also the aerodynamic lift,
and the loss of engine power that comes with higher altitudes. The code does assume
that you have either an EFI system or that you have properly rejetted your
carbuerator(s) for high altitude operation.
Enter Temperature: Similar to altitude, air temperature affects the air density. This value
is entered in Degrees F. You'll find, especially with supercharged applications, that
power will drop dramatically at higher temperatures.
Interpreting your results. To keep things reasonably simple to understand, the user is
spared the millions of iterative calculations required to arrive at the final results, and
presented a report of speed in MPH versus required BHP, available BHP, engine RPM,
optimum keel wetted length, and propeller advance. To find your speed in knots, simply
divide the speed values in MPH b 1.15. The code publishes results above 25 MPH, since
the code is not equipped to properly handle speeds in the "hump" region. For this
reason the code cannot guarantee that a given propeller selection or setup will actually
get the boat on plane. You've probably seen all the tricks like forced ventilation and other
methods on ultra high-performance rigs to get them going.
The program is configured for the user to input a current setup, then make changes to it
to predict the changes. The tool can be used to configure a completely new setup, using
your best guess to start with, then iterating to find the optimum.
