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jmondl
06-03-2010, 11:37 AM
I would like to ensure my 2010 Outback sits centered (bow to stern) on my boat lift, and am trying to find the weight center (called the "moment" if my memory serves me) of the boat. Does anyone know where this information is located, or how to determine that?

rmckenney
06-03-2010, 12:13 PM
That would be hard to determine since you have dynamic variables at play. The amount of fuel in your gas tank changes as well as location of equipment which in turn constantly changes the location of "G" which is the center of gravity. Consider "G" as the point at which all downward forces (i.e. the weight of the boat) are focused. Therefore, to know exactly where it is at all times requires a calculation of all points of weight about a known point of reference for a completely empty boat (which I'm sure the manufacturer possesses, somewhere). In most simple terms the calculation would be weight x distance = moment / total displacement. But then this calculation is for a boat floating in water. Now, if your lift is floating in water, you will have to find the center of gravity of that and it's weight and add that to the calculation of the boat and weight of equipment and fuel. And that is all without calculating and knowing the free surface correction for your fuel tank and your bilge if you have any liquid in that and the estimated specific gravity of the fuel.

In a nut shell, not an easy answer and it may not even serve your purposes practically. The way I understand boat lifts is the best solution is to mimmic as closely the support of the manufacturers supplied trailer. Sorry for the long explanation. I'm a professional mariner and I love these inquiries!

deerfield
06-03-2010, 12:55 PM
jnomdi - I keep my 2007 Outback on a Shorestation lift. The lift was installed and adjusted for my Outback by the Skiers Choice dealer local to my area. You want me to post a side view picture showing the position of the boat on the bunks? - Deerfield

kaneboats
06-03-2010, 01:26 PM
Or look at the trailer designed for the boat and notice where the wheels are in relation to the engine. That should be a great hint.

kaneboats
06-03-2010, 01:30 PM
Take a look at these two pictures for example:

cab13367
06-03-2010, 02:21 PM
Or look at the trailer designed for the boat and notice where the wheels are in relation to the engine. That should be a great hint.

The center of gravity will be somewhere forward of the axle on a single axle trailer since there should be about 100 - 150 lbs of tongue weight the way they are set up from the factory.

maxpower220
06-03-2010, 04:18 PM
CG- Center of Gravity
Moment Arm- figured by the amount of weight and it's distance from the CG.

Of course these are from aircraft terms, used to determine that the weight and where it is located will allow the aircraft to fly properly.

jmondl
06-03-2010, 07:28 PM
Figuring the CG is just forward of the axle makes sense. Thanks for everyone's help. New boat should arrive next week.

kaneboats
06-03-2010, 09:42 PM
The center of gravity will be somewhere forward of the axle on a single axle trailer since there should be about 100 - 150 lbs of tongue weight the way they are set up from the factory.

Always one stickler in the bunch. :)

gus 08 mobius lsv
06-04-2010, 11:52 AM
The center of gravity will be somewhere forward of the axle on a single axle trailer since there should be about 100 - 150 lbs of tongue weight the way they are set up from the factory.

mine has a hell of a lot more tongue weight then that!
just for the heck of it i tried to lift it by myself and nothing and my dad and i barely got it off the ground

kaneboats
06-04-2010, 12:55 PM
Gotta empty that front ballast bag. :D

cab13367
06-04-2010, 01:34 PM
mine has a hell of a lot more tongue weight then that!
just for the heck of it i tried to lift it by myself and nothing and my dad and i barely got it off the ground

Is it a single axle trailer?

gus 08 mobius lsv
06-04-2010, 03:48 PM
Gotta empty that front ballast bag. :D

ah well shoot here i thought i was saving time in filling the ballast just by leaving them full! nah i'm not that dumb but hell all that stank water in my ski locker adds some weight... on a side note is it normal for the ballast bags to have a gallon or two of water left in them? i have since learned to pick up the bag so they can drain out better...not sure if anyone else goes thru that pita?

al i have a single axle

kaneboats
06-04-2010, 03:56 PM
All in good fun. My LSV has at least a couple hundred lbs. of tongue weight. I used to lift the O/B tongue all the time but this one is a no-go. I can barely budge it.

Edit: Also, it's very hard to pump every drop out. Lots of folks disconnect and drain the last bit at the end of the day.

gus 08 mobius lsv
06-05-2010, 02:07 PM
Tongue weight is the same on a single and or duel trailer in respect to the weight of your boats. If you look at the single and duel axes the wheels sit in completly different locations. This is to allow the apx the same tongue weight.

Its always designed to have 10% on your hitch. 5000 lb boat and trailer combo is 500 lbs on the hitch its self. This is why your truck sags LOL.

Single axe trailer will fool you a bit when you try to pick it up but this is due to being 1 axle and it will tilt back for you once you get it past the center line.

Duel axle you will be fighting the rear axle because you are putting pressure on it. Also the same with turning, this is why singles turn easier because on duels the front axle is dragging the tires.

yeah i understand what your saying on the single vs dual axle trailers... i was just commenting on what al said about 100-150 lbs of weight on the tongue i knew mine was alot more then that. i never knew about the 10% of total weight being on the tongue thanks for making it clear

cab13367
06-05-2010, 03:41 PM
yeah i understand what your saying on the single vs dual axle trailers... i was just commenting on what al said about 100-150 lbs of weight on the tongue i knew mine was alot more then that. i never knew about the 10% of total weight being on the tongue thanks for making it clear

Yeah, I didn't know about the 10% thing. I think the 100 - 150 lbs was a number I remembered from my previous boat (although it weighed more than 1000 - 1500 lbs). I stand corrected! Can't get away with much on this site - seems there is an expert on just about any subject matter. And that is a good thing :)

gus 08 mobius lsv
06-05-2010, 05:01 PM
Yeah, I didn't know about the 10% thing. I think the 100 - 150 lbs was a number I remembered from my previous boat (although it weighed more than 1000 - 1500 lbs). I stand corrected! Can't get away with much on this site - seems there is an expert on just about any subject matter. And that is a good thing :)

don't take that the wrong way al i wasn't callin you out i just wanted to know if my set up had an issue cause it took everything two people had to lift it up. yeah its nice to have knowledgeable people on just about every aspect of things

cab13367
06-05-2010, 10:58 PM
don't take that the wrong way al i wasn't callin you out i just wanted to know if my set up had an issue cause it took everything two people had to lift it up. yeah its nice to have knowledgeable people on just about every aspect of things

Not at all Gus. Glad you guys corrected me :)