Estimating CG Shift with Heavy Engines

[Capt Terry]

It seems there are questions and discussions about heavy outboard engines, outboard brackets, boat handling, and center of gravity at least a few times a week on CSC. Our performance moderator, Bushwacker, reminds us the engines when Moesly designed the SeaCraft outboard engines were considerably lighter than today’s engines and particularly four strokes. (The weight of my 1976 Merc 150 inline 6 was about 300#; my 1985 Merc 150 V6 about 375#; and my 2012 ETEC 150 at 418#.) Bushwacker has also been very candid sharing what he has learned in using his 20’ Seafari conversion to a full height transom with a Hermco bracket for his ETEC 150 HP, including his pros, cons, and cautions.
As a retired mechanical engineer from the jet engine and then gas turbine world, I decided to try putting a bit of science to assist SeaCraft owners in estimating center of gravity shifts for their engine and bracket decisions. Please realize the attachment is a tool primarily for estimating the change in center of gravity of adding or relocating heavy equipment, not a precise center of gravity calculator.

Estimating CG Shift rev7 pdf.pdf