Here is an excerpt taken from the master hull roster;
The Scale Unlimited Hydroplane Master Hull Roster is the governing document for the NAMBA Scale Unlimited
Hydroplane class of racing. This document contains the name and details that identify each boat so that they may be
built for R/C Scale Unlimited Hydroplane competition at NAMBA sanctioned races. Principle dimensions for each
full size craft are listed if known. Appearing underneath each principle dimension (in parenthesis) is a tolerance for
1/8 scale craft.
Each hull has been identified with a “Hull number” consisting of 4 digits. The first two digits indicate the year in
which the hull first ran, and generally, (not always) the second two digits indicate the “number” with which the hull
first ran with. Detailed National rules for the Scale Unlimited Hydroplane class can be found in the NAMBA rule
book.
Dimensions are measured in the following manner:
A. Length (+/- 1.0 inch)
B. Width (+/- 10 percent)
C. Tunnel Width (+/- 10 percent)
D. Hull Depth (+/- 10 percent)
E. After plane Length (+/- 10 percent)
LENGTH – This is the overall length of the boat as measured from the most forward point of the basic hull
to the rear most point of the basic. (Note: Tiplets and rear sponsons are not part of the basic hull)
Allowable tolerance is +/- 1 inch.
WIDTH – This is the maximum overall width of the boat. Allowable tolerance is +/- 10 percent.
TUNNEL – This is the tunnel width or sponson separation of the boat. Allowable tolerance is +/- 10
percent.
DEPTH – This is the maximum thickness of the hull. Allowable tolerance is +/- 10 percent.
AFTERPLANE LENGTH – This is the distance measured from the rear of the sponson to the rear most
point of the basic hull. Allowable tolerance is +/- 10 percent.
PICKLEFORK DEPTH – For pickle fork hulls only. Pickle fork Depth is not a principle dimension as listed
in the rule book. The dimension is listed here for reference only. This is the distance from the forward most
point of the boat o the leading edge of the boat between the sponsons. Suggested allowable tolerance is
+/- 10 percent.
An “M” listed under the hull number indicates the listed dimensions have been taken by measurement of
the actual boat.
A “P” ” listed under the hull number indicates the listed dimensions have been taken from plans of the
actual boat.
For detailed rules, see the NAMBA rule book and District rules from the area in which you plan to compete.
NOTE: Boats should be measured to the nearest 1/16 ‘ and not exceed the maximum or minimum
tolerances.
Here is the link to the master hull roster which you can download...
http://www.namba.com/content/library/scale/namba_mhr.pdf
As for the offset, I have usually seen it mirrored like the full size but with the 10% tolerance you have some options. This gives boat manufacturers and builders and designers some options in order to optimize the running characteristics of a model vs the full size hulls.
There are some really nice "scale" hulls out there and there are also some really good examples of "race" hulls as well. When you see a "scale" hull that races as fast as anything possible (Kirk Maupins 75 Atlas comes to mind), you know the builder took the time and attention to the details as well as the preparation to consider running qualities which has to be admired and appreciated.
cheers
