Center of Gravity

[Dustin Barbaglia]

I am sure there has been plenty of talk in the past about this, but i wanted to get some opinions.

to figure center of gravity on a large mono i have heard its based on power and hull attitude. read somewhere that on a smaller hp boat CG should be between 20 to 25 % of the hull. boats with more hp, CG should be around 30% of hull lenght.

i have even heard of guys in the past useing heavy weighs in the front of thier boats to help "control" the ride..... seems like a good way to just weight down the boat.

Although if your trying to balance the CG, and few ounces of weigh in the nose might be a good way to go. I realize there is more to the CG of a boat than just forward and aft. but this is the area that i have heard alot of different things. Thanks for any insight

 

[Neil LaGarry]

I took this out of a old RC boating mag, written by ,John Finch It's still relevant today.

 

[Michael Costanzo]

once you find a good starting point,then you can add some weight to the nose if water conditions get a little rough.just don;t put the weight right at the very nose(bow) move it back just a little bit.put it on with duck tape or any other water resistent tape.you can always remove later when the water calms down.

there is no set % only a starting point and all hulls and motor combonation vary.keep testing and keep notes.good luck,mike.

 

[Dustin Barbaglia]

anyone ever used a ballast tank, install a tank in the nose area, and then depending on conditions be able to pump water in, or take it out on the fly... wondering if this would be problematic, or be functional. seems to me it would be a quick and simple way to increase or decrease weight and change the CG.

 

[Neil LaGarry]

Dustin , their are 2 CoG .you have port and starboard or don't keep your tuning pipe fuel tank and batteries on the same side. Try to get even weight disbursement.

 

[Dustin Barbaglia]

your most certianly right, as i meantioned above i was just curious as far as from bow to aft.

 

[John Finch]

The 29 to 30 percent CG is good for aerodynamic flight when the boat leaves the water. Problem with adding weight to the very tip of the boat is that you build in a pendulum effect. The best place for all the weight in the boat is low and close to the CG. When the water gets rough simply add weight under the motor mount rather than shifting it way up front and keep the same CG. You can tell if you boat is tail heavy by when it leaves the water and the tail falls first. Same with weight too far forward.....the nose falls first. There is more to it than what I just said and not all boats work with the same CG. A dipped bow deck will force the front of the boat down too. It may be what keeps the boat from blowing off the water at high speed. The rudder width, depth, and distance from the transom will also effect the ride of the boat as will trim tabs, prop depth and design, etc. So to make it simple. A good starting point is 29 to 30 percent and make it work aerodynamically when the boat leaves the water.

John

 

[Dustin Barbaglia]

Very well written john, thankyou for the input.

 

[John Finch]

Very well written john, thankyou for the input.

Your welcome Dustin. I hope you have fun with the boats!

 

[Neil LaGarry]

John

Here is the second pic on your CoG post, from a few years ago. this is what you want to see when setup right.

 

[John Finch]

John

Here is the second pic on your CoG post, from a few years ago. this is what you want to see when setup right.

looks like a solid ride. The less boat in the water the faster she goes, but we can all fall to the mistake of setting the trim on a calm lake only to lose control at the races. The biggest problem with setting up a mono is that you have to trim it with other boats on the pond to get it ready for heat racing. A well set up mono for heat racing looks like a dog in calm water. After the first lap of a race it is rough water no matter how calm the pond was before the race started. If you set up the boat at the local pond in calm water it will most likely blow off the water or do something stupid racing with 5 other boats. Keep that in mind when you set up the boat

 

[HOTWATER]

Very true...I have found that out myself...racewater is definately the way to find out what is going on.

Thank goodness for the veterans like Don Ferrette, Steve Sutton and Steve Speas for showing me the way while you weren't able to make some of the D.12 races...

Rock on John!

-Kent

 

[Neil LaGarry]

John

Here is the second pic on your CoG post, from a few years ago. this is what you want to see when setup right.

looks like a solid ride. The less boat in the water the faster she goes, but we can all fall to the mistake of setting the trim on a calm lake only to lose control at the races. The biggest problem with setting up a mono is that you have to trim it with other boats on the pond to get it ready for heat racing. A well set up mono for heat racing looks like a dog in calm water. After the first lap of a race it is rough water no matter how calm the pond was before the race started. If you set up the boat at the local pond in calm water it will most likely blow off the water or do something stupid racing with 5 other boats. Keep that in mind when you set up the boat

Will do John

 

[carlnoki]

IF you look at the picture of my Twin FE mono, I have the CG set so that the ride attitudeboth on and off the water are

pretty much the same. I have read John's books and have learned alot from the folks over the years. My boats aren't the fastet

things out there, BUT, they finish almost every heat they run in.

hope I made sence...............

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[Dustin Barbaglia]

you made sense, no worries. what precentage of the hull lenght did you find your sweet spot ?

 

[carlnoki]

IF memory serves (sometimes it doesn't. age thing) it is 11" measured FROM the transom on my boat.

I will have to actually measure it tomorrow for you to be sure.

then again, that is just for my hull.

each one is a bit diferent.

 

[moparbarn]

carl, that boat has been fast & reliable as both a nitro & a fe mono B) . oh yeah, & an alky one too .

 

[carlnoki]

LOL thanks Robin.

 

[Leo Ho]

CG at 28% hull length, measured from the transom:

http://www.amazon.com/Advanced-R-C-Boat-Modeling/dp/0911295216

 

[HOTWATER]

I run my P- Mono around 32%...started at 27% and kept moving it up slowly until it ran smooth, catching air and staying pretty much level.

Like Carl said, every boat will be a bit different.....ecspecially in race water.

-Kent