I just posted the exact question in the Glacier Craft section but I need answers ASAP so Iím going to repeat and ask in this general boating forumÖ..
Iím about ready to install my motors and had a few people tell me 24 inch on center spacing is where my Yamaha 200 I6ís (left and right hand) need to be. GC used a template and marked for holes at about a 34Ē on center spacing.
My question is, where did you all put yours? What is standard?
Technically motor spacing is not just distance from center. Motor height, distance from edge of hull, and degree of V at stern should be considered. The rule is that for every 12" away from the edge of your hull your motor's ventilation plate is should be 1" high. So if you have an offshore bracket that is 36" long then your ventilation plate should be 3" high. Note: I said Offshore bracket NOT CET. Where ever the last place that water comes off the hull is where the 1/12 rule applies. So if you're running a full extended bottom then you might only need to be 1" high. I have an extended transom so I'm 32" away from the edge of the hull.
If you were to take a straight edge and run from your ventilation plate to the stern mark that spot with a small horizontal line. Measure from that line down to where it intersects with the V in your hull. If that distance is 1" for every foot away from the hull, then your motor height is correct. With twin motors you can distance them as close to center or as far from center as your preference as long as you keep the above rule in mind.
Using the motor mounting vertical bolt holes you can move your motors inboard and outboard along the depth of the hull V and raise and lower your motors. Keeping the 1/12 rule in mind the closer to center you'll be using the first or second bolt holes. Farther outboard you might be using the 3rd or 4th mounting holes. Trying to keep in mind the 1/12 rule.
So, all that to say this. If Yamaha says 28" on center for your motors then start there and use the vertical mounting bolt holes to get your 1/12 ratio. My motors are twin 300's and I'm 30.5" on center. Sound Escape (GC) is 32" on center. I think Yamaha says 28" on center. I know another GC that is like 36 or 38" on center.
Then there is the issue of toe in. Yamaha recommends that your water thrust from twins should come together at about 50 feet behind the boat or about 3/8" toe in. Mine is around the 50' ft mark. Sound Escapes is closer to 75 to 100 and he gets phenominal performance/efficiency so that might be a preference thing.
Hope that helps. Sorry for the long winded explanation. I couldn't find the link to where I've seen this discussed.