Balancing the BOAT???????
 

OK..Today is a new day!! It is time to move onward and upward. I was talking to my older brother yesterday. The one that still has the fastest boat in the family. He asked me if I had my boat balanced yet. I said not really...He said that in the high performance bass boat world that they balance the boats pretty precisely before they go up around the triple digits and beyond. He said that it was a "no brain er" to move weight around add ballast where necessary to balance the boat. He says that not only does it make the boat a lot easier to drive and a lot safer but it makes it faster even if you have to add ballast (weight). In a 110 to 120 MPH bass boat they know exactly where they want this center of balance. He says that it needs to be where if you had a pointed stake sticking up and you set the boat(in their case with the driver) the boat would balance perfectly side to side and fore and aft.


My question.....Where would you want this point to be in an offshore boat like we run? Are there companies or people that ballast these boats like the bass boats? Has anyone here gone to that point of balancing to that fine of a point? If there are people here that have done that ...... what were your thoughts?

intuition says that he has to be correct. the dynamic forces in effect at even 70 mph are very large and the inertial aspects of mass location have got to be important to offset them or enhance them as the case may be. on my boat , a 10,000 lb top gun, i drove the boat before i bought it with allegedly a 1000
hp. it went 62 mph and handled "average" i thought.

i repowered to about 850 hp and worked very hard at centralizing the mass which meant getting as much heavy stuff as i could move toward the CG. i did this based purely on my own theoretical undestanding, not anything i would represent as fact based knowledge. when i got done it went 68 mph and handled much much crisper and more positive i felt.

My boat weighs about half of what yours does..Do you know if there is any kind of device to balance your boat. I know that I have talked to IMCO and Arneson and they talk about having the lateral center of gravity 4-6 feet from the transom. How do you measure where your lateral center of gravity is?

the answer to your question would be as simple as working a simple calculation based on your trailer tounge weight or with the trailer on scales... but how would you significantly change it anyway? what do you have in the boat thats really heavy that you could move around ? for me it was batteries and firesystem and a lot of spares etc. do you have 200 lbs worth of stuff to relocate ?

I think that I will have to use ballast to correct any balance issues. I don't have enough stuff to move around to make the difference.

How would this method separate out the the weight distribution of the trailer from the boat?

Jeff

I got some information today. I talked to Rick at Arneson. The Lateral Center of Gravity should be 25% of the length of your hull from the rear of the hull. He said the best way to determine where yours is would be to run a strap under your boat and pick up on it with an overhead crane or something like that.Just pick it up a little bit. If it falls forward. You LCG is forward of that point. If it falls back then it is AFT or that location. Then you can move stuff or ballast accordingly.

One problem with the weight balance with "boat on trailer" is , if you have a triple trailer, the axles carry almost all the weight. The tongue carrys very little.



Darrell.

Interesting comment on the 25%. The GC on my 30' Scarab (actually 29' 6") is at 91" or 25.7%....pretty close. There are more options to move weight than you might first think. Can you move your batteries (80-100 lbs) towards the transom? Trim pumps? Remove any misc from bow area? Varying your fuel load might help depending on the tank location. Some race boats move fuel from tank to tank during the race to maintain balance/attitude.
Extension boxes can really help as this moves the drives back 12" which will likely have a big impact on the CG.
You should be able to use a travel lift at many marinas to hang your boat in one strap. You should be at the helm and have 3-4 sand bags handy to test with. The first step is to find out which way you want to go.

you wouldn't. you don't care about the real numbers only a location. if it where a heavy boat like mine on a triple axle , i would run the center wheels up on a couple of 2 x 8's such that the took most of the load . then you look at the tongue weight.
you don't need to know it to a decimal place... just whether its a 100 or 25 or 500... you do it w/ out the boat. then you go get the boat and do the test again with the same 2x8's... if the tongue weight is the same as when it had no boat, then the cg is over the center axle. if its heavier, move the boat back until its the same... or forward if its lighter. when its the same as it was w/ no boat, then the cg is over the center axle. ill bet if you are careful, you can get it w/ in 6 inshes. if it was a 2 axle trailer, do the same thing or take two of the tires off... either way, i think you could identify a problem if one existed...

but having said all that... is your configuration so much different than others that you suspect this is a real problem or are you just trying to do whatever you can do for free to make things better ? i would think twice about ballasting a lot. weight is power. putting in the equivilent of another person will offset any balance gains you might make. especially in a low powered boat.

in my case i stripped all the junk people had hung on this boat that didn't do anything and got rid of a couple hundred pounds. i would have to believe there was a critical issue for me to consider putting it back.

Balance
 

In the end final CG is preference that is representented in a number. A well balanced boat like an airplane is a joy to operate. An improperly balanced boat or plane can kill you.


You want a boat that flies long flat and level.
Steve

thats correct. but you trim your aircraft in flight using adjustable control surfaces... just like a boat. the weight and balance are done when its built so that the cg corresponds with the center of lift of the wing. all you have to do is be careful where you put your passengers and luggage. i suspect there are similar centers of pressure both aerodynamic and hydro dynamic on the hull at speed and that it would be really helpful to have that near the cg.

the further apart you get the two, the greater the moment arm and higher the polar moment of inertia will be when you go to turn it at speed. that will translate into a sluggish reaction time and lots of scrub and drag. and , i suppose could make the boat be less user friendly in rougher water as well...

oh well... all well known and understod in the aircraft industry but theoretical as far as these boats go because the hulls are so dissimilar... it would be interesting to know what's actually true in fact.

Simple method from a friend that raced, owned a marina, etc.

He said that the most important factor was the side to side balance, put 2 peices of electrical tape on either side, measuring so if the boat was perfectly level they will match up at the waterline.

Launch the boat and move weight as needed, now you are balanced side to side and will pick up some mph.

Since evry boat chinwalks ,,,i think that doesent matter as much as the CG from front to back,,,,,,,like sayd befor if the thing fly's level at about 5-8% bow high its perfect,,,,i dont think it will rollover in mid air !!!!!

Take 20 t florjack place it with a 2x4 under the hull ,,where your back is when you sit down or lean against the bolster.
Then move weight until its perfect level on the V with running fuel and place 2 200 pound weights in the seat's.

If you did that your boat is ready to rock.
The side by side movement now also is taken care of because you lifted the boat complettly in the air with the floorjack.
By the way ,,,they also call it trimmtabs. LOL

Thank you!! That is my point!

Great idea!!

Interesting. I used 3 scales and came up with 26% Longitudinal(front to back) cg. Cool.
I'd like to post pics of my setup but this site charges extra for that, bummer.
Jeff

hey..
my bow likes to pop all over with minimal drive input. i've always thought that a few extra lbs in the bow...like 100... would "settle things down" (twin sbc's in a 26'er), thus really letting the drives and tabs do their job. a more level ride w/o dragging tabs must surely improve efficiency?
c

The 26% represents a working number to create a CG envelope. As loading and/or load locations change, the CG will move within the envelope. Therefore,variables such as a high X,heavy load,hot dry days etc. may cause the boat to have trouble getting on plane.

Therefore,is it prudent to include a forward located ballast tank in this discussion?

Cat,
We have a ballast tank in our boat but don't use it often. The thought was a ballast tank in the bow would allow us to run faster overall in the bumps while using less tab. I expect there is a balance of both ballast and tabs but we never figured it out. How do you measure the results? It seems we could exceed the speed we were comfortable with using either system.
I would like to hear move from others that use a ballast tank. Is a ballast tank mostly a band aid for a poorly balanced boat?
Steve, do you race with a ballast tank?

Yes. The tank is good because you can add to overall weight. With it being forward of the CG you have to be careful of bow steer or worse. Using the tank dampens the polar movement and gives you confidence, sometimes too much! If you do stuff the tank really aggrevates the situation.

The other nice effect I feel is you can run your CG a little aft to get the acceleration and top speed but if you need to settle things down a little water in the nose really helps.
Steve

I don't think a balast tank is a bandaid ,,,,, because water conditions change so u can change how the boat runs. AND yes i have a 35 gallon water ballast tank that i can fill or empty during the race.It helps alot.
Calm water leave it empty and as soon it gets ruf lets say 4+ footers you fill it untill it runs and fly's perfect ,,,mine fills with in 36 sec. and dry's out in 42 sec with a pump for out and electric valve and water pickup for fill.

Also it add weight even empty about 60 pounds with mounting brackets and that got my CG right on the money in calm water.

Also mine has built in baffels so where ,,if its not full all the way the water does not slap around in there.

Cool thing + i built it myself . :evilb:

Where do you get the water to fill your tank? Do you have a separate pickup? Do you come off of your water pump? It seems like a ballast tank or maybe a couple in different locations can be a good thing for a high performance boat.

Just a quick note to all you "ballancer" guys.

Remeber where your fuel tank is and how much fuel you have. A full tank boat may have a CG in a different place then when it's 1/4 full. Also the hull design is critical. A steped or double step boat may need to be balanced different then a "no step" hull. A 38' boat with a relatively "straight" bottom (keel) will need the CG in a different location (may not work with the 25% rule) then a "curved" hull. A "ballast" system will help you in different speeds, but the best thing is to experiment and see what is the boat and you are at the best CG comfort level.

Separate pickup ,,on the trimtab.

Try to get you a picture.

We use engine coolant water after the engine.
Steve

I believe where you set the CG should also take into account if you have a stepped boat. For example on my fountain I want additional weight in the back so my cg is set right at the first step from the transom. Moving it forward would have a significant effect on turning.

I agree totally...It would all center around the exact boat that you are talking about and the conditions that your would be running in. My boat has a pad but no steps so I need to get the bow up to free the hull. If you count on the prop to do all the work to get it up the boat does not take a set and get stable at speed. Look at those Cat Killer boats...they run like a bass boat back on the pad but set there just as stable as can be. I have had several people that have told me that Reggie Fountain is always talking about balance in his boats.

I'd love to hear more about how to impliment a balast tank: adding and removing water, do you need to put something in to control the water going in? What sort of pump did you use to remove the water? What do you build the talk out of? Anyone try a bladder of any sort instead of a solid tank?

Any details would be appreciated.

My boat runs bow down and I'm trying to fix the hull to get the bow out of the water when it's smooth, but I've noticed that in rough water, the ride is a LOT smoother when someone is passed out on the v-berth. It would really be nice to add a couple hundred pounds when max speed isn't an issue but a smooth ride is.

My Balasttank is an old Blastic Fueltank ,,, i had cut a hole in the top so i could stick a rule 3500 Submersable pump in it.
That is to pump the water out, the water in line is forced in by itself, have a pick up on the trimmtab with a 12V seliniod valve that holds up to 400 PSI ,60 bucks, also got a water level gauge and 2 switches (1 for pump,1 for valve) 2 more hoses are mounted in the front part of the tank to let air out while water rushes in. And thats it.(also have a 1/2 inch shut off valve in the inline ,just in case!!!)
Just make shure that the balasttank is not mounted all the way in the nose of the boat,,it should be next to a bulkhead so no stress is aplied to the bottom of the hull.
:ernaehrung004:

Here are some pics of our current set-up

That looks like someone is trying to add & dump water with nobody else seeing :)

Cat,
Nice rigging job!! After seeing this, no post of my work ballast tank work will be forecoming...Polish the (2) 90's? :drink:
Ben

Excellent topic,in the spring I also plan on finding the balance point on my boat front to rear. I am personally overweight and when I run my 4700 lb boat with no passengers in the rear seat it tends to bow steer violently at high speeds. It never seemed top do this before but I almost always have ran with rear seat passengers. lighter exhaust and cylinder heads have amplified my problem,I'm thinking Ineed to add about 100 lbs at very rear of boat. Example 1-blew a fuel pump fuse at almost 95 mph with rear seat passengers,transom settled down first and boat glided gently to a stop (had a hard time getting passengers to ride in boat again though).
Example 2-opposite-was running mid 90's with 1 passenger in front seat,started backing out of throttle and bowed dropped quickly causing boat to bow steer violently UNTIL azz end settled in.
My plan is to place weight equivilant to mine in driver seat area and same with pass seat area then sling boat to find cg fron to rear. Then I plan on mathematically calculating how much weight I need at rear of boat to be equivilant to about 400 lbs of rear seat passengers that seems to be what balances out my boat properly.
I/E-If 400 lbs 2 feet behind the fore/aft cg makes boat properly balanced,instead of adding 400 lbs there I would add 50 or 100 lbs further back to get the same effect without weighing boat down so much it hurts the ability to air out and reach top speed. I'm thinking a 80 lb water inflated ballast bag with a fill pump and a solenoid drain placed in the molded hollow swim platform my boat has. Great thread,keep the ideas coming,Smitty

Smitty,Perhaps there are other options,such as mufflers,hatch pads,etc....we are tinkering with a little different muffler design, though it is premature to go into detail.

Ben,Is it possible your boat could benefit from a bit more aft CG?

Thanks for the compliment....However,everyone would surely appreciate pictures of your ballast tank and plumbing.

Even easier way to check the balance is to lift it on a crane with strops/lifting eyes. Hang a line from the crane hook - where it lands is your centre of gravity.

Has anyone tried to hang a counter weight off the back of the transom...over the drive or something like that. It would stand to reason that the further back the weight is located the less weight that you would have to add to your boat. Like a lever. Just asking? I know that I have heard of people adding lead in the swim platform when they have those tubular add on swim platforms.

I think the most eficient way to balast is ,,,first use what u have,,,,,ancor ,batterie's,rops,cooler,trimmpumps,and all other stuff. If you can't acomplish the CG right with that, then either 2 fueltanks and pump fuel back or forth/side to side ,,,,now your not add. adintional weight to the boat ,,,at last if still not working u need a removable balast like a watertank where u can pump water in and out when and where needet.

I hate using dead weight like lead or sandbags because it will never be right when u need it since watercondition change to often .

Thats just me ,,,but a perfect CG is not just make the boat fly level its also about NOT beating the $hit out of you,,,,therefor it actually should be right behind the backrest of the seat since the force should be where u sit /stand or u beat your bones up real quick.
And like sayd earlier ,,the best way to check is with a floorjack and block of would.
Lift it up and if u can move the boat with almost no force by hand thats where your CG is when jack is placed under it.
If not there ,,,now move weights in the boat to get it there.
Remember place floorjack under backpart of seat !!!

Thats exactly what I was thinking too,removable weight at the ttranson so that 50 or 80 lbs acts like 400 lbs in the back seat. I have established from many times of running mine fast that it likes at least 1/2 tank of gas and about 300-400 lbs in the back seat area,the problem is if I bolt weight on the transom I think my boat will act like it's got 6 people in it when I do have passengers so thats why I'm looking at a ballast bladder in the hollow area behind the motor under molded swim platform.
On a side note I took my boat to Mackinaw island 2 years ago out on the big water and we took 2 people with us and all kinds of luggage,lawn chairs,full tank of gas,a small grill,3 coolers etc. the boat was really loaded down to where it felt sorta sluggish and heavy,I didn't take it over 75 mph for fear of blowing a drive 15 miles from port out on lake Huron but we ran into 3-4 footers and the boat felt the best it ever did,it crushed thru the waves like a real offshore boat instead of bouncing in every direction like it usually does,I was thinking that must be what it feels like to drive these boats that people talk about being built like tanks and heavy like a 28 foot cig or something,Smitty

I wonder if anyone has tried using a wake board boat ballast bag? Wouldn't have to worry about venting it.

Also, someone mentioned getting the water from after the engine. No worries about the heat????