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By using multiple scales you can calculate where the center of gravity is.Quote:
Originally Posted by Dirk Pitt
If you have two boats each weighing 1350# but one has the CG 10" further back it would be a completely different handling hull.
This would be information used to help understand some of the different caricaturists on what otherwise appear similar hulls.
If 3 scales are used it helps with understanding side to side balance.
Are you interested in the CG or more focused on total weights?
Do you put setback on a boat? How do you know what that does to where the weight in in the hull. If you do not care then no issue, but if you are looking to get information then you might as well have good information.Quote:
Originally Posted by AZMIDLYF
Lets say you are considering two more inches of setback, but you can move some weight, say the battery in the hull. It might be just moving something around or removing the rear seat. What does that actually do and why did it make a change.
Myself I have a book of the weights of most everything I have built in the past 35 years, planes, boats, cars and bikes.
When I rebuilt my boat and it came out 390# lighter than when I got it, I know just what the difference is.
When I converted my Ultra 23XS from I/O to wacker on the backer power we wanted to get the weight and the C/G as they had never built one as an Outboard. We put the boat on a trailer and got a heavy long handled garage floor jack. We got a couple of those heavy rubber V bow stops from a bow and taped them to the round plate of the floor jack, then we put a piece of heavy rubber over that, just laying there. Then we measured 2/3 1/3 on the hull and started with the floor jack there. Had to move it forward and aft a few times but not many to find the balance point. Fine tuned the location a bit and found the exact Center of Gravity. Once we found that, three strokes of the floor jack and the boat would elevate off the trailer and balance perfectly on 6" round plate/makeshift V. Once we marked that, we started fiddling around adding 50lb bags of sand on top of the Paralift that I was wanting to use. That gave us a pretty good idea if the 12" setback would work properly for balance.
When done, we just put the floor jack on top of my digital scale and re-jacked the boat up to get the exact weight. Never had to use a sling or two scales. Yes, a touch red neck but gets you the data you need quickly. You can then do your fine tuning a bit later. I never did that because all my boats are slow and fugly so I did not care/need to go the extra distance.
this how I intend to weigh it, the scale goes between the lifting hook and sling, although the picture shows the boat over the water the davit swings in and I can lift it off the trailer, or cradle, the scale is digital and is good for 2000lbs
I am not sure about how much he can alter the CG of the boat. He already has the set back mounted and the motor will be added. What exactly is he going to move to adjust his CG after that? Aside from the batteries and an oil tank, where will the shift in weight come from? It sounds like some will be taken away without the rear seat but what else?
agreed:thumbsup: the cg in a boat can only be changed by adding parasite weight once the boat is rigged, yes some people put batteries, trim pumps etc in the bow, but thats guess work, and after that its trial and error once the boat is rigged, if you watch some of the 21 Tuff videos were do you think the cg is?Quote:
Originally Posted by AZMIDLYF
With respect to the C/G, I guess you have decided to keep both the 30 gallon gas tank and the 18" fixed setback bracket that came with the boat. 1,347lbs coming at 'cha.
the second tank is 15 gal, the 18" set back was Tuffs idea not McNight's, so with all due respect to Marks boat building prowess,( ive used that word before)there must be a reason for that amount of setback, my intention is to leave it in the state that John rigged it, like I said in previous texts it would be almost sacreligious to alter this boat in anyway, providing it dosent chuck me out of it:) or go 80,:nonod:( if that happens I have plan B):thumbsup:with respect to cg its not as simple as you may think, in order to find the correct CG there is formulas which require weight, arm, and moment, thats a whole other topic, and its not as simple as moving a sand bag around the boat
18 inches of setback??? U think ur gonna be able to use the boat on a regular sunday in the great south bay? Just seems like alot imo
Joe i dont know, but we will see my superboat had 16" I do know the 106 tuff has 12"Quote:
Originally Posted by progression22
This should do it, so now we can weigh boats easy come down my canal I can lift you up 1" and solve the guessing problem
Second tank? Your Tuff 21 has two gas tanks, one 30 gallon and then a second 15 gallon? Or is the 15 gallon a water ballast tank in the bow?Quote:
Originally Posted by Dirk Pitt
John Mcnight wanted more than the 30 gal fuel tank that Mark builds the boat with, he refused to accomodate his request, so John installed a second 15 gal case tank in the stern, I know 1400lbs:eek: Im going backwards :)
That's cool. now you can run up to West Point and back with 45 gallons.Quote:
Originally Posted by Dirk Pitt