So, ive got an F-150 4x4, 302, 3.55 gears, ZF5 transmission, short cab / longbed on 33" tires.

I currently tow a 3500 lb , 25' boat trailer, ~ 250 lbs of tounge weight. The tounge weight is on the light side, and while it pulls fine most of the time, I've had some issues on bridge crossing whent he wind is up with sway. I'm revamping the trailer (making it a dual axle), and wondering about the tounge. How much should I shoot for? I maybe be selling this boat and buyng a slightly heavier one, which would make the whole combo come out to about 5k.

do these trucks have any issue with 4-500 lbs of tounge weight? I'm not to worried about horesepower, If anything I will install 4.10's. Hardly ever drive anywhere far without the boat in tow anyway!

 

Yes you should have more gears, the 5.0 should have come from the factory with 3.73 gears IMO, 4.10 or even 4.56 will really improve pulling power. The bigger tires are amplifying the sway problem... more sidewall flex. Your truck is pretty light in the tail so more tounge weight may help but only if the truck already has sway bars. You didn't say if you have a reciever for this but even the stock step bumper is rated for that load, it has a class 3 rating, so the truck will handle the load either way.

 

what kind of boat is this that it sits on a 25' trailer but has only 3500lbs?

at any rate, if the boat axle is 5 bolt, its 3500lb axle - max. 6 bolt, 4200, 8 bolt 5000.

what you could do, is move the axle back a bit to increase tongue weight. (its easier than you think unless the spring mounts are welded)

As for tongue weight, Id shy away from putting any more than 250lb on these years ford frames if the hitch if bolted thru the 'ears' of the end of the frame rails. That point takes the most load, and it is completely unsupported - worse if there is any rust.

my current boat boasts a 440lb tongue weight and when I had a class 3 the year I got it, I watched the hitch actually bend when I took up the trailer. I put in a class iV the next weekend.

 

Do you mean sway bars on the truck suspension, or sway control bars for the hitch? I think I see what you mean though - more tounge weight gives me more rear traction, which helps prevent the trailer from taking over. That's a good situation to be in, because it means loading-wise, I am better off with more tounge weight. Plus, it should tow nicer (longer axle-hitch distance).

BTW, it's a sailboat. So it's essentialy a trailer, a large block of iron situated between the wheels, and then a big fiberglass shell so thin that you can pop the sides in and out. I'm actually rebuilding the trailer and adding a second axle to go along with the first, and building a suspension subframe that will bolt to the main frame, so it's a little easier to move if i get a different boat)

Yes, I've got a reciever (reese class IV ) . It is bolted and welded to the bottom of the frame, direct below a crossmember (the side plates of the hitch are at least a foot long). Should I be worried?

Right now I tow in 4th instead of 5th - it turns out that 3.55 / 4.10 is .86 and my OD is .87 , so changing to 4.10 gears make my current 4th gear, the new OD. Means I have a gear in between highway gear and 3rd gear, which would be nice for uphills (because going uphill in 3rd at 50 mph with the engine turning 3k and my foot barely on the throttle sis annoying, but with the ZF it seems like the 3-4 gap is so large that even if i wind 3rd gear up to 4500, by the time i'm in 4th I'm around 2000 and have to downshift...

 

I do agree with the 3-4 difference, maybe a few power adders could help you out though....
Just to give the truck that extra little oomph... To keep it pulling in 4th...

 

tongue weight its actually your friend. trailers with more tongue and the axle further back tow much nicer. now its only your friend until it is too much for your truck and you lose your steering. keeping the tongue of the trailer lower rather than higher seems to help sometimes depending on what your towing if it starts to sway your truck a bit. obviously you'll have to use discression, you dont want your hitch dragging or hitting the ground. its a little tougher to find the balance with tongue weight on a half ton i find but you dont want sway thats for sure.

 

How to explain tongue weight....hmmm, did you ever pull a roll-aboard luggage thingy in the airport? If you pull it standing up more it has less 'tongue weight' on your hand and it becomes more unstable, reacting to any bump in the carpet or sidealk joint and essentially swaying. this is what your trailer does, in fact its exactly what your trailer does except the trailer wont fit in the overhead.

when the tounge wieght is low, that means the moment of polar inertia is around the axle. a single axle trailer is far more susceptible to sway.

sway control for a trailer is simply a bar, sandwiched between 2 brake pads. the bar attaches to the trailer, the brake pads and housing to the truck. Its a low tech way to dampen the side to side action. (there are controls like shocks, but they have pitiful travel and cannot take abrupt sharp turns)

the trailer im thinking hits about 1000 lbs? the boat has center mass and the weighted keel over the axle? try moving the axle back about 5 inches. you literally can use a bathroom scale to get a good idea what the tongue weight is.

 

The more I think about this, the more I realize is going on.
1: I know my all-up weight is ~ 3500 lbs. I want to increase tounge weight from 250 lbs to 350 lbs

I can do 2 things: move the boat or move the axle.
Question: If I were to mount the equalizer for my tandem setup exactly over the center of the current single axle, will my tounge weight go down? Seems like I need to go back an inch just to maintain current tounge weight.

However, Not only do I want it to tow nicer, I want it to launch better. So I got new underslung axles - this means the trailer (previously level) will be 3" lower at the axle. That should shift the CG back, and remove some tounge weight. So I need to move the axle back an inch or so to correct for this, *too* just to maintain the same tounge weight

So now i'm back a little bit (~2.5") , and I still have a 250 lb tounge. 196" hitch-axle gives me 7.5% tounge weight. That means the CG is about .075*196 = 14.5" in font of the axle or 181.5" behind the couple

[(hitch-axle) - (hitch-cg)] / (hitch-axle) = TW
196-181 / 196 = 7.5
201-181 / 196 = 9.9

So I need to go back 5" to increase my TW, plus a little more to account for the TW lost by simply changing the axles. Lets say 6".


The bunks extend 1' rearward of the frame, the boat extends 3' past the frame. This is a non issue though, because the *** end of the boat weighs virtually nothing. The only weight is a group 24 battery. If I move the boat back (move winch tower) It should be easier to launch. Actually, it would be pretty cool if I the boat sat more level when the trailer is angled on the ramp. But that can wait.

Thanks guys!