Center of Gravity - explain this?
 

When it comes to center of Gravity on a boat - what is ideal?

While making changes to my 342 I have eliminated over 200 pounds from the cabin & bow and it runs much better.

Where should the CG be on a 34 foot boat?
What should be my target?
Where should the water break at 70 MPH?
What do I need to take into consideration?

Nobody knows anything. Can somebody speculate?

BenPerfected touches on it a little bit in this older thread. If you do a search on strakes, CG and porpoising you might be able to get more of an answer.

http://www.offshoreonly.com/forums/g...-bottom-5.html

I did a lot of this eng. for race cars and in all honesty it becomes an art. You kind of just see it and feel it. No mathamatical way to really figure it out. We have great CG on the Warlock by Gas tank placement, moving weight as close to front of engine as possible. Man this is complicated to write out(: What kind of boat is it? Stepped Hull? How does it like to run stern lift,Nuetral, or nose up?
Ok Sorry its a Baja So it likes lots of trim and run bow up. I think the gas tank is big and runs long wise. We ran a t shaped tank with the T in the back for better cg. I would think good cg on your boat would be right in front of the motor. So the lighter you make it up front the better.

Yep. I have been removing everything from the bow. Even took out the cuddy cabin seats and used a hole saw to cut out areas that were not supporting anything. Also took out the bed and replaced it with a different density foam. removed old stereo wiring. Anything else that wasnt "structural" I took out and replaced with honeycomb panels. All this little stuff was almost literally 150'ish pounds. (I kept all of it and weighed it)

I work with aerospace stuff and fighter jet designers say "One pound int he bow is like 10 pounds in the stern." I am trying to stay with that mentality.

You ever work at L martin in Atl? I went to riddle and did blueprints there for a year. And yes that theory works. Weight is a killer and I assume you have a liner which adds even more); 200lbs is 20 hrspwr.

I have done extensive towing tank testing on this subject, and have published some of it in two mainstream Naval Architecture journals. That said, it isn't easy to just take a stab at optimal cg location without a lot of analysis and testing. A safe starting point is usually about 35% forward of the transom.

The faster you want to go, typically you need either more bow lift, or a cg further aft. Having the cg too far aft will cause the boat to porpoise. The most optimal setup would be one where the boat is just on the verge of trying to porpoise, because the trim angle is as high as you can go for minimum wetted surface area. If this is the case at 70 mph, then you can expect the boat to porpoise wildly without the tabs at 50. Conversely, if the cg is set right at 50, you are going to have to trim all the way out trying to go fast, and you won't be able to go as fast. My last boat was an ex-race boat, with provision to bolt in weight in the nose, and no interior. I initially ran it with 50 lb bolted in the nose, then found I could go faster with only 25 lb (77 mph), but I had to drag some tab until about 55 mph. Had I pulled out the other 25, I may have gotten a couple more mph, but I would have had to drag even more tab in the 50's, which is usually where I ran.

In summary, your best bet is to just do some of your own testing, keeping track of fuel level, passengers, and propeller selection. If the hull is not stepped, and you are not using your tabs in the midrange, then try a prop with more rake, pull more weight out of the bow, or add good weight (bigger blowers, intercoolers, etc) in the stern.

I'd be willing to bet that hull has some hook built into it to help hold the nose down when planing and at cruising speed. Removing hook will have the same effect as taking weight off the nose.

i asked about c of g once on a 42 tiger cigarette,,,they told me its somewhere between winshield and bolster seat,,,

I dont work for LMCO but call on LMCO Marietta, Orlando and Dallas. I am a sales guy and sell composite honeycomb and soft composite tooling.

Funny thing is, when you relate fighter jets to speed boats the similarities are strikingly similar. All the little tips and tricks of making the JSF and former F-22 fast and nimble all apply. Most people dont realize planes are referred to with bow, stern, port and starboard...

Well you are flying on water. I worked at the Marietta plant back in 98. C5 and c130j go to be there for the f22 first flight. To know see them in the air is amazing. Good luck with your boat. I had a 272 and loved it. It was our family boat and was a pleasure. It was stolen last year at Lanier.

The ideal mark for CG is right where u stand/sit if u want a nice and smoth ride !!!! everything else is trimm and set up !!!