ledsliger's weight study

[shine]

Shine, In my case, a 79 jackshafted diesel that has been converted to a closed transom bracketed outboard) I have no reference to what existed before and where the cg of the boat should be.

My question is how did you design your boat and where did you find the information to arrive at your calculations?

Please understand below is an approximate way to do this....

If you moving weights around and you want to get the boat to sit close to her original lines, then you can make a simple spreadsheet of moments (length of arm x weight of object). You have to make 2 columns, one with the weights and locations of an original boat's major parts, and the second column will be the new boat with proposed weights/locations.

The "measure from" location, needs to be the same on each boat (not always easy to do since thicknesses and layouts are different, but using the outside of the transom is a good place becasue its the same). Its not so important where you measure from, but it is important that the be the same spot on each boat. So you will have distances from that spot (+ numbers forward, - numbers to the rear) and the weight of the object multiplied together. The sum of all these numbers should be close to matching on each boat. Weights are measured from their center (center of gas tank, or center of baitwell, center of motor,etc.

In my case, I found a person who had a 23CC with motor mounted on the transom and big bait well in the floor. My boat is set up very differently, but floats right where it should.

Of course this really only works if you keep the total weight of the new boat close to that of the original. If you changing the weight dramatically, then you will need to find the CG and go from there

Joel

[ledslinger]

Thanks for the reply Joel,

In my case, I might be better off guestimating the weight of the original diesel engine and drive setup since that might be closer than trying to estimate how the effect of removing one of the twin 225 mercury black max outboards on the twin bracket. the only thing i have to go by is the scum line of how it sat in the water before.

I am pretty sure that the fuel tanks and their positions are original on the port and starboard sides. The center console is original and its position doesnt look like it has changed. I have the capability to lift the boat with an overhead crane to find the balance point and can weigh it if i need to.

Were all the 23 ft boats similar in outside dimensions or were there differences dependent upon the power? In other words was the jackshafted diesel hull different than other 23 ft center consoles?

If all the static balance is good and the boat floats correctly, can i be assured that when under power, that the boat will behave properly if i keep the heaviest componets reasonably close to my new static cg?

I did have the pleasure of fishing out of a 79 Seacraft for about 5 years--I do remember my feet getting wet from time to time---I'll move my floor 2 ".

Well my pumpkin beer is in the fermenter and the smoked salmon chowder is made for tomorrow.

Hope everyone has a great Thanksgiving.

Mike

[ledslinger]

Am i doing this right?---i took moments from the transom for the estimated original configuration of a jackshafted diesel and outdrive only in the x direction

engine 136" x 475= 5383 ft#
trans 111" x 75= 693 ft#
j/s & brgs 58 x 75= 362 ft#
55 gal fuel 63" x 440= 2310 ft#---1/2 tank
outdrive 5" x 150= 62ft#
batteries 5" x 120= 50ft#

total 8860ft# cw moment divided by the weight= cg(x)=79" from the transom
-----------------------------------------------------------
New configuration 30" bracket 675# ob motor

bracket 15.5" x 140= (-180ft#)
bracket bouyancy 676ft# double bracket
motor 30"x675= (-1687ft#)
55 gal fuel= 63" x 440= 2310 ft#---1/2 tank
batteries in console= 1380 ft#

total of 2500ft# cw moment divided by the weight= cg(x)=43" from transom

So if this is correct than it looks like im looking for a lighter engine and a heavier potty---or making some new gas tanks and moving everything up some?

[ledslinger]

full fuel tanks in the original position gets me at 51"