center of gravity, center of buoyancy

[dburr]

But trying to work it a little in reverse.  I will end up with the LCG at the intended location.

I have everything out the boat now, just down to the bare hull, so doing the balancing act will not work to find the original CG now.

The LCG should be somewhere in the area of 40% of the planing surface --measured from the stern. SO that is probably under the console or near there. I was planning on moving the fuel tank a little forward from original location to compensate for the additional 12 or so inches the outboard will be hanging off the transom.  I just don't want the boat to run stern heavy. I have seen to many boats, originally designed for transom mounted outboards, with brackets and the stern dragging low in the water.

I am putting a larger fuel tank under the deck and adding a paralift. These additions will alter the location of the weight the boat is carrying.  I think proper placement of this weight is key to the boat operating as it was designed.

I think I can figure it out, by playing with it, finding the LCG by determining where the LCG was with the original tank and engine placement, but it never hurts to ask for more info.

I think the question was how to prevent squatting with a bracket and paralift added. The answer, you have got to get more (bunch of) weight forward.  How much?  Where are you going to keep you fuel level and what engine you going with?  How much does the paralift weigh and what other stuff are you going to put in the boat and where are you going to put it?

Some quick math based on an average of half tank of gas (40 gal) at 6.073 Lb/gal and a 500 lb engine shows an arm (CG) shift aft of about 6 inches.

Moving the tank forward “a little” directly over the CG will do nothing to offset a 500+ pound motor being shifted aft away from the CG 12 inches at the end of an existing arm of like 6-7 feet with no reserve buoyancy added (unless the tank is kept slam full 80 gal + and even then it is a slight aft shift).

As part of the exercise, in order to advise, if that is what you would like, we need to know the weights of the engine and paralift and what size tank.

There is an infinite amount of info available on excepted weight of different types of glass etc. Go here as an example and select the weave and read the blurb..
 http://www.cfsnet.co.uk/acatalog/CFS_Ca ... S_291.html

 If you know what your building schedule is going to be then take the time to put together a spreadsheet and you will get an idea of what is going to happen..

If I am preaching to the choir I apologize.. Weight*Arm=Moment.. You add all the weights and their respective moments, then divide the total weight by the total moment and that gives you the gross weight, arm (cg) and moment… You add this to the number you got from your empty weighing and you will know what to expect.

And remember that 40% planing surface is just that, not the waterline length where she sits pretty. The gofasters with 1.2E57 hp all squat at rest..

Good Luck...

[GoneFission]

 The gofasters with 1.2E57 hp all squat at rest..
Good Luck...

That would be 1,200,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 horsepower!     Yep, that would go!  Like to see those motors.   :twisted:

[gran398]

Is there a name for that number? Like 12 trillion gazillion

[GoneFission]

Is there a name for that number? Like 12 trillion gazillion

I think I would just call it "more than adequate."  

[seabob4]

I didn't count the zeros...

[seabob4]

 The gofasters with 1.2E57 hp all squat at rest..
Good Luck...

That would be 1,200,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 horsepower!     Yep, that would go!  Like to see those motors.   :twisted:

Throw about 13 or 14 of these babies in the ass end, might come close...



They spool up kind of slow, though...

[dburr]

Gentlemen, I do beleave that number is called "a Brazilian"... (Fletch that one is for you)  

[GoneFission]

Gentlemen, I do beleave that number is called "a Brazilian"... (Fletch that one is for you)  

I thought a Brazilian was more like this:

 

Don't know how many horsepower that's got!

[gran398]

That has my vote

Received a PM tonight regarding this topic, and if perhaps the vessel could be placed vertically and be readied for outer space. I'm not sure, never was much at math, but okay at marketing, so here ya go

http://www.youtube.com/watch?v=xaLtMaSF ... re=related

[louiefl]

Way back when I was a freshman in ocean engineering college they taught us a phrase called metacentric height. It is basically the difference between the center of gravity and the center of buoyancy. If you COB is higher than your COG, your boat likes to flip over. Google the term, Wikipedia does a great job explaining ship stability and how metacentric height helps determine stability and passenger comfort. Hadn't thought about it for 30+ years...