setback measurement

[280hunter]

could someone explain or show some pics on the the proper way to measure setback?
Thanks

 

[gmorgan]

280hunter, as far as I know, you just put the end of a yardstick against the back of the transom touching the jackplate on the side and read the number on the yardstick at the back of the jackplate. If your 280 is a 15 inch model, you will need to add two inches to your measurement since the clamp bracket on the 15 inch mid is set back two inches further than the stock bass mid.

 

[280hunter]

thanks gmorgan, thats what i thought, but just wanted to make sure I was measuring correctly.

 

[ally2dextreme]

280hunter, as far as I know, you just put the end of a yardstick against the back of the transom touching the jackplate on the side and read the number on the yardstick at the back of the jackplate. If your 280 is a 15 inch model, you will need to add two inches to your measurement since the clamp bracket on the 15 inch mid is set back two inches further than the stock bass mid.

 

[ally2dextreme]

Well that's not true ,if you measure the nose cone to pad on the 15 the 2 inch setback doesn't apply,from what I rember it was really an inch different

 

[Jon]

The mid may set back a little extra on a 15, but measure to some arbitrary point on the motor and let me know where that lines up. I'm interested to see the difference.

 

[90 5.0]

Need to do a search, but someone posted engineering drawings, etc a couple years back and the two inch is there , some of it is "relative" as the shorter mid travels different from the longer one.

But for all intents and purposes, if you have a 12" plate and a 15" mid, it will act like it has 14" of relative setback.

 

[ally2dextreme]

I disagree,I've measured my nosecone to the pad,it was not two inches further back when I went from 20 to 15..I believe it was an inch but the 15 needs the leverage of more set back..

 

[Jon]

Setback measurement is somewhat arbitrary and is determined by the mid, motor type (mass), and boat with load and distribution. Although the the mid may or may not have an offset, as 90 5.0 said, a longer mid travels futher during positive or negative trim. Under neutral trim, all things should be equal. The fun thing is that the weight of the engine overhead is the same, more or less, on any setup. Likely though a 15" mid will have the motor lower than a 20" mid by 5" - but the mass doesn't change concerning setback. What does change is the point at which thrust is applied.

I probably could draw this better than describe it, but we'll see... If you trim 5 degrees as an example, the radius of the arc (LU to pivot) determines the thrust point (use 1 radian as an example - google it). All that being said, you need to figure out what works best for your boat since they all are a little different and probably no 2 boats weigh the same.

 

[ally2dextreme]

I took my measurement with the pad and motor level..while running down the lake trim will not vary much from level but a 20 would have a larger arc so it seems to me the more trim from level the 20 would actually have the prop further from the pad and the 15 would stay closer to the pad as trim was added..

 

[hack02]

The angle of the transom puts the back of the gearcase at pretty close to the same point between a 15 inch and a 20 inch mid. The 15 sits 5 inches lower on this angle putting it farther forward so thats why it takes 2 additional inches to reach the same point a 20 is at because the 20 sits higher and thus farther back. So you do not add 2 inches when measuring a 15 offshore to come up with the jackplate setback number. This being measured with the propshaft level.