Balancing the BOAT???????
01-31-2009, 03:05 PM
#41
Banned
Join Date: Oct 2006
Location: Bradenton Florida
Posts: 5,927
Likes: 0
Received 0 Likes
on
0 Posts
If something would leak u cant run the engine any more.
Thats why i like to keep it seperate, if a leak apears u shut the Valve off and still run the boat safe.
01-31-2009, 03:43 PM
#42
Platinum Member
Platinum Member
Cat,
I am thinking we may have the CG too far aft today. The top speed is good, but I feel like we use too much tab in 3'+. In what Lake Erie calls 2-4' water at 80 MPH we are generally using the tabs at 3 positions from neutral with the the 380 tabs. The concept on why we installed the ballast tank was so we could run faster in the bumps with less tab but end up with more control...balance from the forward ballast.
Here's a good question. Should the GC be more forward to "fly" more level in 3'+ or should the GC be move aft and then control the attitude with ballast and tabs? Where is perfect? What is ideal in using tab vs. forward ballast? With BBC's and extension boxes on a 30' vee, perfect is allusive.
Steve, what is your experience...I need one more winter project!
I am thinking we may have the CG too far aft today. The top speed is good, but I feel like we use too much tab in 3'+. In what Lake Erie calls 2-4' water at 80 MPH we are generally using the tabs at 3 positions from neutral with the the 380 tabs. The concept on why we installed the ballast tank was so we could run faster in the bumps with less tab but end up with more control...balance from the forward ballast.
Here's a good question. Should the GC be more forward to "fly" more level in 3'+ or should the GC be move aft and then control the attitude with ballast and tabs? Where is perfect? What is ideal in using tab vs. forward ballast? With BBC's and extension boxes on a 30' vee, perfect is allusive.
Steve, what is your experience...I need one more winter project!
01-31-2009, 04:47 PM
#43
Registered
And that's on a boat that naturally runs bow down. I don't think it has anything to do with the boat being "more level" as you say, but just with the physics of having more mass up front to force the bow through the waves instead of bouncing off them. Yes, you can try to force that to happen with tabs, but it just doesn't work the same.
I'm guessing that with more mass in the front, you could still trim to the same attitude as you normally would, and still run smoother.
01-31-2009, 04:57 PM
#44
Banned
Join Date: Oct 2006
Location: Bradenton Florida
Posts: 5,927
Likes: 0
Received 0 Likes
on
0 Posts
I'm certainly no expert, but like I said previously, my boat absolutly runs better in the rough when the CG is forward. No amount of tab can smooth things out like two drunks passed out on the V-berth And that's on a boat that naturally runs bow down.
I don't think it has anything to do with the boat being "more level" as you say, but just with the physics of having more mass up front to force the bow through the waves instead of bouncing off them. Yes, you can try to force that to happen with tabs, but it just doesn't work the same.
I'm guessing that with more mass in the front, you could still trim to the same attitude as you normally would, and still run smoother.
And that's on a boat that naturally runs bow down. I don't think it has anything to do with the boat being "more level" as you say, but just with the physics of having more mass up front to force the bow through the waves instead of bouncing off them. Yes, you can try to force that to happen with tabs, but it just doesn't work the same.
I'm guessing that with more mass in the front, you could still trim to the same attitude as you normally would, and still run smoother.
Big diffrence !!
Like i said befor the best spot for CG is right where u sit / stand in the boat !!!
Then balance it for the water u run in ,,thats a fact ,,no quessing!
01-31-2009, 06:17 PM
#45
Gold Member
Gold Member
Join Date: May 2002
Location: DFW
Posts: 1,127
Likes: 0
Received 0 Likes
on
0 Posts
IMHO,after the components are located and fixed in place the point which the hull will rotate about is the empty wt.CG. Then as fuel,people and gear are loaded the CG location will probably change. Hopefully,the change will leave the CG within a safe envelope.
Hydrodynamics alone,most applicable to a V hull,one can consider the wetted surface as a friction point that scrubs speed. Therefore,as the wetted surface is running just forward of the transom there should be least friction.
Trim tabs add or subtract square inches of hull surface area. Or,tabs change the hull length,down-longer and up- shorter.
Ballast water becomes a lever arm,like the playground teeter totter. At slow speed or planing the arm starts at the transom,at high speed the arm starts at the LOADED CG.
Hydrodynamics alone,most applicable to a V hull,one can consider the wetted surface as a friction point that scrubs speed. Therefore,as the wetted surface is running just forward of the transom there should be least friction.
Trim tabs add or subtract square inches of hull surface area. Or,tabs change the hull length,down-longer and up- shorter.
Ballast water becomes a lever arm,like the playground teeter totter. At slow speed or planing the arm starts at the transom,at high speed the arm starts at the LOADED CG.
01-31-2009, 08:06 PM
#47
Registered
01-31-2009, 08:11 PM
#48
Banned
Join Date: Oct 2006
Location: Bradenton Florida
Posts: 5,927
Likes: 0
Received 0 Likes
on
0 Posts
Thats why a ballasttank is a good thing, thats what i ment with that.
But to get to that point your CG should be where stated,so u dont beat the crap out of you.
If you need more weight in the back u need to move Batt.,trimmpumps and all that good stuff to the transom.
Like i sayd CG should always be where the driver is.
Actually a hair behind that.
02-01-2009, 02:56 PM
#49
Platinum Member
Platinum Member
Carp,
The reason for the questions is because we haven't done any controlled testing to make a valid comparison of tabs to a ballast tank or to a combination of the two. On the next run in 3-4' conditions, we will back/back compare a full ballast tank (about 40 gal in the bow) to tabs only and to a tab/BT combination.
We have had numerous drunks on the boat, but it has been difficult to get them to crash in the bow together and then find anyone in good enough shape to operate the boat
The reason for the questions is because we haven't done any controlled testing to make a valid comparison of tabs to a ballast tank or to a combination of the two. On the next run in 3-4' conditions, we will back/back compare a full ballast tank (about 40 gal in the bow) to tabs only and to a tab/BT combination.
We have had numerous drunks on the boat, but it has been difficult to get them to crash in the bow together and then find anyone in good enough shape to operate the boat
02-01-2009, 03:09 PM
#50
Registered
I think you balance the boat for top speed in generally calm conditions. Than test for varying rough conditions. Once the boat has a good balance minor changes are all that is necessary.
I think 40 gallons of water is a huge adjustment. Especially if it is all the way forward.
It is harder to drive a bow heavy boat.
I think 40 gallons of water is a huge adjustment. Especially if it is all the way forward.
It is harder to drive a bow heavy boat.
