Original COG

[boatnamesue]

I thought to calculate the COG by using the vessel's length and dry weight, however, this would assume the weight is symmetrical across its length.  But I have doubts this is correct since the hull is heavier aft of its center.

Does anyone know the COG axis point for a '76 170?  If not, any boat builders out there know how to make this calculation with only knowing the hull's dry weight, beam and length?  Thanks

[mshugg]

You'll never get it from measurements/weight alone.  There are too many variables.

Someone on another website, suggested useing the center of the fuel tank as a starting point.  This assumes that the builder would place this heavy piece of ballast at the COG.  The argument makes sense to me, and it's likely the closest approximation we can get short of rigging some sort of test to actually verify.  Unless you happen to run into an old AS engineer at the pub.

[boatnamesue]

You'll never get it from measurements/weight alone.  There are too many variables.

I agree, stumbling across this information is highly unlikely.   Center of fuel tank does sound like a feasible center point.  It would great to know the exact position, but I'd be comfortable with a round about position, +/- 1ft. 

Let's say the bow is 0ft, transom 17ft.  Measuring from bow to transom, I would guesstimate the center to be somewhere between the 10 ft and 12 ft mark.   

[mshugg]

Yeah, but think about it.  There are so many differences in boat design that would affect COG.  There's a big difference in forward hull shapes.  A boat with "Carolina" flair would have more weight forward than a classic Donzi.  Even the location of max beam would influence COG.  the classic Aquas have their max beam kind of forward with the transom being narrower.  Newer designs tend to place their widest sections further aft to provide more support for heavier four strokes.  Any estimate must take these design differences into account.

On the 170, I bet that the tank center and location of helm station ( where you would stand to operate) are close to each other.  That's a pretty big clue to COG, since the designers would want to place these weights at or just aft of COG.

[wingtime]

Just get a crane and a strap... then lift the boat with a single strap moving it around until you find the CG.  :)

It's the relation between the CG and the center of buoyancy while at rest and center of lift while on a plane that effects how the boat sits or rides.

[Woodeneye]

Just get a crane and a strap... then lift the boat with a single strap moving it around until you find the CG.  :)

It's the relation between the CG and the center of buoyancy while at rest and center of lift while on a plane that effects how the boat sits or rides.

Or a "A" frame and a chain block.......

[boatnamesue]

Unfortunately I don't have access to a crane or "A" frame.  I can't rely on the current position of the console to be located in the same position as it was 40 years ago. But mshugg makes a good point with the center of fuel tank.  If this is all I can work with as a reference point then it is what it is. 

Posting this thread was a shot in the dark, but worth a shot.  Thanks.

[wingtime]

I was kinda joking about the crane... but it would work. Usually most people just float the boat and then use sand bags to simulate weight and move them around  to get the boat floating the way it should.

[Capt. Bob]

Posting this thread was a shot in the dark, but worth a shot.  Thanks.

Not the first time this subject has been broached but you got the same basic answer.

Take a minute and read this thread. Took awhile to find it but I've never forgot it. It's one of my favs in a Forum persona featuring too much math and too little chemistry or more likely actually having neither of both.

http://classicaquasport.com/smf/index.php?topic=9161.0

Sorry we couldn't help.

[boatnamesue]

Posting this thread was a shot in the dark, but worth a shot.  Thanks.

Not the first time this subject has been broached but you got the same basic answer.

Take a minute and read this thread. Took awhile to find it but I've never forgot it. It's one of my favs in a Forum persona featuring too much math and too little chemistry or more likely actually having neither of both.

http://classicaquasport.com/smf/index.php?topic=9161.0

Sorry we couldn't help.

Appreciate it Capt, I'll take a look.