April 22, 1959
SERVICE BULLETIN NO. SB713
BOAT TRANSOM HEIGHT
Investigations have revealed that excessive propeller cavitation is
occurring as a result of certain boat builders constructing boats with
transoms higher than that prescribed by O.B.C.
As a reminder, there are only two transom heights; one is 15" for the
standard shaft engines and the other is 20" for the long shaft models.
We have found quite a number of boats with transoms varying from 3/4" to
1 3/4" too high and it is these boats that have caused propeller cavitation.
It is strongly recommended that you study page 5 of the 1959 O.B.C.
Standards Manual which you have just recently received and make certain
that all of your boats are in accordance with these recommended practices.
Such items as engine well dimensions, cutout dimensions, transom angle,
etc., should be studied thoroughly so that the maximum of safe and efficient
performance may be obtained with every rig that you sell.
Also, you should measure your boats yourselves to make certain that all
recommendations are followed. We have found some boats with dimensions
that do not correspond to their factory specification sheets.
In addition, it is suggested that every dealer exert as much pressure as
possible on his boat suppliers so that all boats will be built to O.B.C.
recommended specifications. Only in this manner may we obtain the safety
and efficiency which we in the marine industry owe our customers.
JOHNSON MOTORS
Jack Penland
Service Department
JP:eb