Calculating Toungue weight
 

I have been making a lot of changes to my boat. Well yesterday while I was working on the trailer I realized that I have taken out so much weight that I now only have about 50 pounds of toungue weight. Is there any mathematical way to figure out how much I will need to move the boat forward? Or am I just better off moving forward and weighing?

Wow....seems to be so many variables in there that would almost have to play around at a scale.

Spare tires and a tool box will help, but will probably only net you 200 or so pounds. You are better off moving the boat forward and inch or so at a time.

the ideal amount is 10% of the total for boat and trailer

Ya the problem that I have is that I have no idea how much I am taking out of the boat for weight. I guess a lot more then I thought and I still have a lot more weight that I am going to be taking out. I am building new bunks so I was hoping to get it all figured out but I guess that I am just going to have to build what I know now and figure out the rest as the project progresses. I know that I am going to be adding a little bit more weight then I have in the engine room because I am going to BW trannies from the Merc Trans. and also going to blower motors.

I know that when I started all this I needed two 2 ton jacks to lift one side of the trailer. Now just one does it easily!!! :ernaehrung004::ernaehrung004::cool::cool:

tow the boat and see how it feels, then you can move the boat back and forth until it feels right

Place a block under your trailer tongue so the trailer is level. Place said block on a scale big enough to handle the weight. Move boat back and forth until 10% of the total weight is showing up on the scale. Baddabing...perfect tongue weight for that set up.

Read the hitch! most say 1000lbs max!!!!!

That is easier than it sounds... I can only move the boat when it floats in the water and it can be one long a$$ process to go back and fourth to the scales and then drop the trailer tung on the scale for weight.
There is got to be an easier way to adjust and configure. I never really know what the tung weight is I go by how it looks based on the load level at the rear of my vehicle and how it pulls.

I know....not really an easy way to do it. But that seems like the only way, IMO, to get the tongue weight dead accurate. I guess a mathematician or an engineer could figure out exactly how w/o all the trial and error....but good luck.

Why guess, give this a try, they are a little over $120 and worth it.

http://www.sherline.com/lm.htm

I have one of them and it's great. Most trailer shops should have one. Start calling around or just buy one. I'm sure they are on ebay for a smaller fee....................

YOu can move the boat on the trailer, just figure out the direction that you need to move it and go about 15mph and slam on the brakes. it won;t move that much and do it enough times to move it where you want. I do it ll the time if the boat is not on the trailr correct. works like a charm

You can use a bathroom scale.

http://www.curtmfg.com/index.cfm?eve...ntpieceid=1347

Now you can do it at the ramp on a slow day. You'll have to adjust the length on the tongue end to get to 1K#.

You're supposed to put one of these... ;) when you're making a joke.

Chris , what joke, some dealers load the boat on the trailer 1 foot to the rear. the only way for me to move it foward is to slam the brakes a couple of times to bring the boat foward where it needs to be. On the reverse if the boat needs to go back, I loosen the cable by two inches and back up and do the same thing. crude but it works when you can;t dunk the trailer

I watched a guy shear off the winch stand and shove his Fountain's beak about 4' into the back of his Suburban at the Catawba ramp on Lake Erie. Wet bunks didn't help things.

I set it up with the scale like Chris's link. Do you calculate with the weight of the trailer or just the boat? I am going to set up the tounge weight for basically an empty boat with no fuel. Then since the tank is centered just in front of the front axel it will just add weight. So far I slid the boat about 1 1/2 feet forward and have about 800 pounds of weight now. When my brother gets on the back of the boat to represent the added weight of the Konrads and new transmisions it goes down about 120 pounds. Then I will be taking weight out of the bow..... My guess is I will be moving the boat even farther forward but at leaste for now the tounge is solid on the floor and I am close to what it should be. I put boat jacks under the back of the boat and by lifting them up was easily able to slide the boat forward using the winch. Boat looks much better on the trailer now and it has gained me some much needed room in the shop!!! Now I just need to find some metal stock to make the side bunks and I should be good to go and get back to work on the boat!!!! :D

And if the boat has a good coat of wax on it it moves real easy. When I had my 42 Sonic I acid washed the bottom and waxed it, then put it back on the trailer. On the way home I had to slam on the brakes, the boat was only hooked to the fornt. The boat slid about 6-8 feet foward totaly pushed the winch tower over. I could stand in the 8 foot bed and touch the boat and the cab at the same time. About 5 full boost powerbrake hole shots and the boat was back where it belongs. I welded the winch tower back together added a 5 foot long galvanized fence post to the tower and it's still like that today. So if you ever see a 42 Sonic on a Rocket trailer with this funny pipe going up the front of the trailer thats my old boat.

But this is the way I would do this too, but as long as it tows fine I wouldn't worry to much, My 50 Nortech has maybe 250# up there and it tows fine with the right truck.

A buddy used silicone spray on the Bunks ..He usually would unhook everything on the boat and back the trailer down into the water and the boat would float loose and he could take a line and pull the boat free .... first Time with the silicone he backed down the ramp and the boat flew off the trailer out into the river!!!

Don't forget you need to have the tongue the same height on the scale as it will be when hitched to the truck.

Any pics of when this didn't work so well? Like when a 35 Fountain is sitting in the back of the pickup or laying in the street!

weigh the trailer empty, then weigh it with the boat.

do the math to determine where the cg of the boat is, and where the cg of the boat needs to be to get 10% on the tongue.

the boat pivots around the axles, so when you go to the scale, pull up so the rear bumper of the truck is hanging onto the scale, and weigh it with it hooked to the truck, then weigh it with it resting on the trailer jack. the difference is your tongue weight (doesn't matter that the trailer jack is further back than the actual hitch)

you need to know tongue weight empty, tongue weight loaded, axle weight empty, and axle weight loaded. consider all the axles together, it doesn't matter if there's one, two, or three. call these numbers twe, twl, awe, and awl. you will also need the length of the distance from the axles to the tongue (average of the 2 or 3 if a multi-axle trailer)... call this d, and call the location of the cg in front of the axles cgd (cgdl for loaded trailer, cgde for empty trailer, cgdb for boat without trailer, but still referencing trailer)

twl/(twl+awl) = cgdl/d -> twl+awl is not going to change as you move your boat, twl will though. d doesn't change. cgdl/d has to equal .1, but it doesn't now, so do this calculation twice, once with cdgl/d = .1, solve for twl, call this twl1, and once with your actual measured twl solve for cgdl (cgdl = twl*d / (twl+awl).

twe/(twe+awe)=cgde/d -> twe, awe, and d are measured, calculate cgde -> cgde = twe*d / (twe+awe)

(twl-twe)/((twl+awl)-(twe+awe)) = cgdb/d = (cgdl-cgde)/d -> it follows that cgdb = cgdl-cgde.

measure everything (twe, twl, awe, and awl, and d), calculate cgdl, cgde, and cgdb as is. be consistent in units, the way i wrote everything, it's all unitless, but when you actually start calculating you need to stick with lbs or stick with kgs, and stick with inches, feet, or meters.

set cgdl/d to .1 and solve for cgdb. subtract the calculated cgdb of your boat the way it is sitting from the cgdb you calculate when you set cgdl/d to .1, and that's how far you need to move your boat forward.

or something like that. I think i got it right but i'm not garaunteeing i didn't miss something. Also, if you have a multi axle trailer, as you move the weight forward more weight will go on the front axle of the trailer, slightly throwing off the calculation by effectively reducing d. Shouldn't be enough to invalidate you calculations, as you're only looking to be in the ballpark of 10% anyway, a little less even.

Must be getting real close to launching the Formula if you're down to the tongue weight dialed in. :D:D