Gernby

Now that I study the mounting points for the hitch and location of the receiver, it looks like the forces on the ball will probably be evenly distributed between the trunk pan and bumper beam. If it takes 1000 lbs of pull to get the boat up the ramp, the bumper beam may only have to support 500 lbs of it. Since the tow hook is totally supported by the bumper beam, it can probably do quite a bit more than that.

BlitzSRM

can you measure the bolt diameters, and the mounting plate (on the hitch) thickness, I'll try to idenitfy the mounting locations on the car and get the thickness. which ever is thinner is were i will start the calculation.

Looking at the picture, we can break down how the designers distributed the forces.
-it looks like the 2 legs extending foward attaches to the bottom of the trunk am i correct? each leg has 2 bolts. These legs handles the horizontal loads, starting and stopping.
-the other 2 vertical legs handle vertical loads, the tougue weight. i assume, since you can lift the trailer hitch, load isn't more that 4 rims, & tires you previously mentioned you loaded. So this will not be the weak link.

Assuming, the 2 legs extending fwd attached to sheet metal under the trunk, sheetmetal will be thinner than the mounting bracket. I can get an ultra sound reading for the thickness of the sheet metal on my trunk. Please verify that the attachment point.

gernby, Note: if it is found that failure mode is the sheet metal will shear, we have a few options. such as intalling a plate, attaching more fasteners on the legs etc.

for now I can start to work out the forces assuming a 30 degree incline, accel to 5mph in 5 secs, and 2500 lb boat. do you agree with these assumptions?

Blkturbos2k

the car is now made for a turbo. I break stuff because Irun 18lbs of boost on the street. The motor is 9-1 comp Ive replaced 1,2,3, and 4th. Now the new diff is going in. I will soon have the Drive Shaft shop axels in and I hope there drive shaft. The car is made to go fast. I work at a very large body shop and the rear rein. may take it for some time but the day will come. The s2k dont do all that great in a crash. The rear are mad to smush. Good luck?

mikegarrison

Have you ever crashed one? I have -- hard. Put the back end of the car into a concrete wall at about 80 mph. The car was fully repairable. The car is damn solid, but the parts are so expensive that it is easy to total it.

There is no question the frame rails could take the load of the boat -- the only question is the load path from the frame rails to the trailer hitch.

Legal Bill

(In the voice of comic book guy from the Simpsons)

Worst post ever!

Anyway, no hard feelings pal.

Gernby, I still say you should first try to pull it up a hill that approximates the ramp. It doesn't have to be some monster long hill that will get the boat going 30 mph if the bumper pulls off, and it doesn't have to be anywhere near houses and stuff.

Oh, and If you really think it might break (and I'll bet money that it won't) you might want to take off your bumper cover first. That way, if the bumper pulls off, the shop can just weld it up and you can reinstall the cover and probably avoid an expensive body shop visit.

Gernby

I can't measure all the bolt diameters easily. The bolts that mount the hitch to the car are really large ... large enough that the mounting points would fail first. I think the weakest link (even in the horizonal direction) is going to be the 3 OEM bolts that hold the bumper rail to the car. The bumper rail is made of sheet steel, and there are only 3 14 mm bolts holding it to the car. The bumper rail will definitely share some of the horizontal forces of pulling and stopping the boat, since the ball will be several inches above the horizontal plane of the mounts that attach to the bottom of the trunk (the 2 legs that extend forward with 2 hole each). I seriously doubt the 4 attachment points below the trunk would fail, since the TL's hitch ONLY has these same 4 mounts that handle ALL the load of the trailer. I expect that the TL's trunk bottom is made from the same type and guage of steel that the S2000's trunk has.

I think adding backing plates to the bolts that extend through the trunk bottom is a really good idea. The TL's hitch does have really thick backing plates inside the trunk, and the S2000's hitch does not. The S2000's trunk bolts just have large fender washers.

As far as your assumptions, I think you should use a 20 degree incline and 3000 lbs total trailer / boat weight.

Something else that I've been considering is that if my engine puts out ~100 ft-lbs of torque (at the RPM I would be using while pulling the boat up the ramp in 1st gear), and my total gearing is 17.3:1 in 1st gear (with 4.77s), then my max horizontal pulling force will be about 1700 lbs (assuming a 24" diameter tire), right? Wouldn't that be the number that should be used to calculate load on the hitch regardless of the weight of the boat? If the boat weighed less, then I would just accellerate up the ramp faster, right?

BTW, your help is GREATLY appreciated. Your response is the intent of this frickin' hellaciously stressfull thread.

Gernby

I just realized that the 1700 lbs of forward force generated by the engine would be distributed between the car and the trailer. If the total weight of the car is about the same as the total weight of the trailer, then the maximum force on the hitch would be only 850 lbs of pulling force.

Gernby

[QUOTE=Legal Bill,Sep 2 2004, 08:57 PM] Gernby, I still say you should first try to pull it up a hill that approximates the ramp.

Gernby

Something that I just thought of is to do some WOT accelleration runs in a wide open parking lot with the trailer attached. That would put the maximum amount of stress on the hitch with very little risk to the boat. If it holds without disturbing the hitch or bumper mounts, then all I have to worry about is the clutch being able to pull it up an incline.

BlitzSRM

the max force can be calculated with F=ma, mass of boat x accelaration, (which you control). I mentioned earlier i'm assuming 0 to 5 mph in 5 seconds is that too slow? gotta try it out and see how long a slow take off takes.

The other way you mentioned is kinda complicated. lots of dynamic elements. maybe someone with that kind of experience can ring in if they know how to approach it that way.

You have a good point if the trailer is angled the hoizontal and vertical forces will be split, can you provide the angle the trailer approaches the hitch take the angle from a level plane. also if the horizontal legs are off level give me that too. I also need the lengths of the vertical, & horizontal legs. I'm assuming the vertical and horizontal legs are 90 degrees from each other.

as far as three OEM bolts after we get the forces, we can check that. gotta leave, won't be able to check this till tomorrow.

O'yeah, glad to help. it's a challenge.

************froze on me***************