Actual weight by angle, how to calculate?

[frantically relaxing]

I'm no math whiz, for sure... So what I'm asking is essentially this:

When pulling a boat up an 8° angled launch ramp, how do you calculate the actual weight the tow vehicle is pulling?

I ask because I'm going to attempt to pull our SkipperLiner out this weekend, with our motorhome...

The boat is 53' x 14', steel hulled, and doing a water displacement measurement I get 36,100 pounds. The trailer I've estimated at 7200 pounds. Connected to the trailer is a dual axle connector dolly (congear), no clue what it weighs but I'm guessing close to 2000 pounds. So I'm somewhere around 46,000 pounds total.

Our motorhome is a 40' diesel pusher, 8.1 Cummins, 6-speed Allison Automatic. The hitch receiver is part of the subframe that's holding up the front of the engine and the radiator, I doubt it'll be an issue. It'll connect to the congear via a 20,000 pound rated pintle hitch.

I'm not too worried about anything, last time we pulled it out with a Sterling work truck...

-- but I'd still like to know approximately how much actual weight I'll be moving up the ramp!

 

[bruceb58]

Sine of 8 degrees = 0.139 so the weight you are pulling in a vertical direction is 0.139 * 46,000 = 6,400 or so. Of course that just adds to the normal force of what it takes to move the rig at 0 degrees.

 

[SolingSailor]

How about adding the weight of the towing vehicle if it's also going up the ramp?

 

[frantically relaxing]

The motorhome weighs just shy of 27k if memory serves. I'm mostly concerned with 'dead' weight that the hitch and all will be subjected to, and braking effort I may need since the trailers won't have brakes.

Also, I bought a 12k# electric winch to help pull the boat onto the trailer. Won't be installed in time for this pull, but it sounds like it'll be enough winch, especially if I double back the cable.

 

[glenn property of pam]

rolling resistance has formulas to work out the force needs to move a load. The problem is that you would have to know the resistance due to the deflection of the tires under load. With the amount of weight and tires it would take a rather large sum just to come up with a number that may not even be close to reality. Then for fun you would have to calculate the speed at which you plan to accelerate up the incline as more force is used not only to move the load but to bring the load up to speed (even if its only 2 mph). The next problem would be calculating it to a number that would make sense in the real world. Then add on bruces calculation for the addition force required for the 8 degree incline.
I wouldn't worry about stressing the frame as the axle which is driving the load plus the rv will fail before that becomes a problem. The weak link will be the half shaft in the axle. Where I work they snap yard dog axles all the time (single axle articulated trucks used around the yard towing full trailers). To avoid that try to be smooth with the power and if the tires start to skip back off the power as the jerking multiplies the stress on the axle. The advantage of a 4 wheel drive heavy duty truck is that the power is shared to another axle and the truck is lighter that the rv thus requires less force to get it rolling. (unless the rv has dual rear axles)

 

[UncleWillie]

Sine of 8 degrees = 0.139 so the weight you are pulling in a vertical direction is 0.139 * 46,000 = 6,400 or so. Of course that just adds to the normal force of what it takes to move the rig at 0 degrees.

Rolling friction of 10% is commonly used as a ballpark number in lieu of real numbers. So 6400 + 4600 = ~11,000
Lets be optimistic and call it 10,000.

If the winch is rated for a 12,000 lb boat instead of 12,000 lb dead pull... it will be closer to 4000 lb pull or 8000 lb doubled.
It will be straining to pull the 8,600 lb of a Roller(10%) trailer. Closer to 14,000 lb if pulling it onto bunks(25%) and up the 8 deg ramp.

 

[NYBo]

23 tons of boat and trailer without brakes being towed by a 13.5 ton tow vehicle?? Am I missing something here?

 

[UncleWillie]

23 tons of boat and trailer without brakes being towed by a 13.5 ton tow vehicle?? Am I missing something here?

The boat weighing more than the Tow is not unusual.
It is in Utah and the season is at a close.
I assume he is just pulling it on shore and will not be going down any highway with a 14 foot wide boat behind a motor home.

That would be something to see however!

 

[NYBo]

It was the "going down any highway" part that had me scratching my head!

 

[frantically relaxing]

It won't be going down no highway, just a simple (ahem) pull up the ramp, then another 200' or so, park it and block it.

The winch isn't a "boat" winch, it's a receiver mount ORV winch. I just need it to pull the boat onto the trailer a few inches, and to help keep the boat ON the trailer. Right now a big tow chain does the 'keeping' part.

 

[NYBo]

It won't be going down no highway, just a simple (ahem) pull up the ramp, then another 200' or so, park it and block it.

:redface:

 

[smokeonthewater]

personally I would be VERY hesitant to use such an expensive vehicle to do the heavy pulling it wasn't designed for... I would strongly consider hiring a truck before risking damage to the trans axle in the MH

 

[H20Rat]

personally I would be VERY hesitant to use such an expensive vehicle to do the heavy pulling it wasn't designed for... I would strongly consider hiring a truck before risking damage to the trans axle in the MH

That is my thought also... Low speed stump pulling like this can easily destroy axles, half shafts, and transmissions. It is far more abusive than going down the highway with a load behind with that big diesel putting out 100% power.

 

[frantically relaxing]

I figure if Dodge can build a pickup truck that will drag a 30,000# boat up a ramp, my Freightliner built motorhome should be able to manage pulling half again that much. Maybe I'm wrong. I have access to a semi, but the problem has always been getting the trailer in far enough without flooding the truck's axle(s).

But none of that matters much anyway, doing a test dunk with my pickup today I couldn't get the trailer in the water far enough. The harbor's only about 5' deep right now, and the end of the trailer is hitting the bottom of the lake and stopping the trailer about 20' short. I spent last weekend hanging an axle in front of the trailer's bumper in hopes it might roll along the bottom, but the gray mud just swallowed the tires & axle and stopped it cold.

Next option: float the rear of the trailer... Anyone know where I can get some really big air bags?

 

[UncleWillie]

...Next option: float the rear of the trailer... Anyone know where I can get some really big air bags?

An old trick for when you drop the wheels and axel of a trailer into the hole off the end of the underwater ramp,
is to run the winch cable UNDER the last cross-member of the trailer and attach it to the Bow eye of the floating boat.
As you winch in the cable, the trailer in lifted up to the floating boat.

Perhaps a variation on this theme would allow you to use the boat to support the far end of the trailer while backing it in.
I am not sure if you will be able to pull the trailer and boat out of the mud and up the ramp with the boat on it.

 

[smokeonthewater]

plastic barrels float really well

 

[gtochris]

Most motorhomes are near their limit simply towing a car, I wouldn't even consider this, heck- with that much weight I wouldn't even do with the most HD dullie on the market, too many parts to break/ stress. Borrow something industrial or pay the marina.

 

[smokeonthewater]

If you can't use the semi without putting the axles under water you probably need to use a large 4x4 farm tractor

Another option might be to set your trailer up with bunk sliders.... Buy a piece of HDPE and cut your own sliders.... Then use your winch to pull the boat up the trailer

 

[frantically relaxing]

I like the float-the-trailer-with-another-boat idea, but we're talking a 7000# trailer, and, the boat extends past the back of the trailer by at least 3', which leaves no way to lift the trailer..

Our lake is only 9' deep at full pool, right now it's about 55% full. Not conducive to getting 50' trailers under water! My marina consists of 2 ramps, couple of rental slip docks and 1/2 acre of fenced storage. It's simply a place to go boating. Everyone is on their own as to getting boats in and out, there's no special equipment here. Because the water's always low at the end of the season (it's WAY low this year) All the sailboat owners pick a day and get craned out, and split the bill. Works out to about $30 each. I could crane mine out, but it would be a 3 day job removing and reinstalling the party top and hardware, plus 2 crane hours at $600 per. Nah. I've thought renting a dump truck to pull it, that would be perfect, and my guy with the semi may have access to one (he buys and resells heavy equipment) To be perfectly honest, I'm certain my motorhome would pull it, but I'd just as soon use something else.

--I've thought about slick bunks, I even have almost enough 1/2" thick HPDE out in the garage to do that- my concern is the possibility of dropping the boat on the ramp. It happens...

I'm dead serious about air bags- I might even be able to rent or borrow some from Jim Cross. (He removed all the sunken boats from Lake Powell when the water got 100' down, and he's local to me) Floating the back of the trailer would fix a LOT of issues with trailering this boat, including getting the boat on the trailer straight- Procedure would be get the trailer half in the water, air up the bags to float the back (I always have someone holding ropes), back in the rest of the way, get the boat on the trailer, align the back of the boat and trailer, add more air so they stay aligned, pull out until the trailer tires are well on the ramp, empty the air bags, then up and out-- Actually sounds pretty do-able to me...

 

[H20Rat]

I'm dead serious about air bags- I might even be able to rent or borrow some from Jim Cross.

Pics of the trailer? To go along with smoke's idea above, 55 gallon plastic barrels. Each one is good for about 450 pounds of bouyancy, and if you can stack 4 on each side of the trailer, you are going to have almost 4000 pounds of lift. Should be enough to float half the trailer. You don't need it to float on the surface, you just need it light enough it clears the bottom.

(or you could find some old pontoons and weld them to the sides of the trailer...)