Posted 2008-08-17 10:50 AM (#89856 - in reply to #89383) Subject: RE: Trailering ( Chad's Questions)
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Posts: 5870 Location: western PA
Boats and boat trailers include many variables not found in the horse industry. The trailers are built with two criteria in mind, the length of the load and the weight it will carry. Within these parameters are many variables that will effect how a pontoon boat will ride on a trailer.
In PA, the largest motor that can be used on any state lake is 9.9 HP. A four stroke motor of that HP rating weighs approximately 100#. In NY state where we have our summer home, there are no HP or speed limitations on most of the lakes. Instead of a 9.9 motor, a 22' pontoon boat would be fitting with larger motors. In our marina, several can be found with twin 175 HP motors, larger yet when singles are specified. An E tech motor of that HP weighs somewhere around 425# +, or doubled, 850# + The larger motors require more fuel, so larger tanks will be installed, adding further weight to the transom.
You and I buy the same trailers and same pontoon boats. I have the small motor, you have the twins. My boat is loaded and the CG is pretty good. There is a 10% tongue weight, everything is working well.
Your boat is loaded and the skegs hit the ground, the tongue is pointed into the sky. A bunch of guys grab the tongue, pull it down, sandbagging and tying it to a hitch. The boat is pushed as far forward onto the trailer as possible, but it's still too light on the tongue. The trailer is jacked and the axles are moved into a more rearward position to carry all the weight of your big engines. The point is found where the CG is achieved, the axles are slipped a little father aft and now your tongue weight is at the prescribed 10%. Now you're good to go. Same boat, same trailer, different results.
Another scenario: A 19' boat and a trailer. A 19' boat can have many types of propulsion, outboard, Inboard outboard drive, or center mounted inboard. Their overall weights can vary greatly, and their CGs will be dictated by the location of their heaviest component, which usually is the power plant. The same trailer used under the same length boat, will have its axles placed at different points on the frame to effect the proper CG.
Because of these differences, boat trailers commonly have adjustable axles, winches and tie downs to effect the proper CG necessary for a proper towing trim. On multiple axle trailers, all of the axles are load bearing, and balance most of the load's weight among them. A proper tongue weight is mandatory on all towed vehicles, but loading the front axle excessively by placing the weight between the hitch and front axle is not desirable or safe.
If the CG were placed between these points, the hitch weight will increase drastically with a load, the front axle would be overloaded and the tracking of the trailer will be adversely compromised. BP trailers are designed to carry most of their weights on all of their axles, except for the necessary 10% tongue weight.
This differs from a GN trailer, that is designed to be loaded at each end. Their axles are found at the rearward end of the frame, pushing the CG far forward. Compare this to the BP trailers which have their axles located more forward, almost under the center of the box. The hitches extending past the box usually add enough forward weight bias to effect some of the necessary forward weight.
BP horse trailers change their load to effect the proper CG, boat trailers change the mechanical equipment to attain the correct balance.
When we hauled two horses in our BP, the heaviest one went in the front stall, the second one went in the rear most stall. This effectively helps to balance the trailer, without incurring a very heavy tongue weight. The center stall was left unused.
Posted 2008-08-17 11:35 AM (#89858 - in reply to #89788) Subject: RE: Trailering ( Chad's Questions)
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Posts: 1391 Location: North of Detroit, MI
Originally written by Reg on 2008-08-15 6:51 PM Campgrounds ? Right as you get under the coupler one rear wheel mounts a bump and now you're 3 inches off to one side - THAT sort of campground problem ? This might work; A couple of short lengths of 2 x 4, maybe 3ft long. Drill a hole near each end, say 3/4 or 1 inch around and 4 inches from the end. When you unhook and BEFORE you drive the truck away, place one behind your truck's left rear tire and one beside it (touching). Drive tent pegs through the holes. This is where you need to come back to and this is how far you need to come back. Paint 'em orange to look "OFFICIAL" if you like. {patent pending} (-:
WOW. that's more than using my yardstick with a clamp. LOL... thanks. That is a good idead too. I think there are probably a couple of hundred year old threads that mention placing blocks on the ground when unhooking so that you know how far back to go.
I've put in crushed limestone at home after leveling - so at least that part is easy. : )
Posted 2008-08-18 7:15 AM (#89885 - in reply to #89855) Subject: RE: Trailering ( Chad's Questions)
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Posts: 2689
Ho hum, this is getting tiresome - the sort of thing that I decided to save my time from a few years ago by not posting here.
So much for the sabatical (-:
Sample arithmetic;
(Check it all you want, measure your own trailer & repeat with your exact dimensions}
axle to axle distance: 36 inches
center point of tandem axles to coupler: 160 inches
(More about this and equalizer bars later)
15% of (whatever weight) at the coupler
85% of (whatever weight) at the center point between the tandem axles
C of G at... err, umm, lets see, calc reqd here;
136 inches back from the coupler
160 - 136 = 24 inches forward of the tandem axles' mid point.
Golly Gee, that is actually 6 inches AHEAD of the front axle.
{Boring, ain't it)
Repeat for 10 % tongue load
160 - 144 = 16
Gee, that is 2 inches BEHIND the front axle's center line.
I think that most of us with more than just a few tens of thousands of miles of pulling agree that 15% is more stable than 10%.
These are actual measurements taken from a 2 horse bumper pull trailer, quite a short one. The greater the distance between the axles and the coupler the farther forward the C of G will be to achieve the 10% to 15% tongue weight.
About that "center point between the tandem axles" thing.
MANY folk in other forums have converted single axle trailers to tandem axles. It is "good practice" to take tongue load measurements as part of the design process and to arrange the axles so that the mid point between them is where the original single axle had it's center line.
The anecdotal evidence is that this results in approx the same tongue load.
Way back ago (pre Dexter Torq-Flex) tandem axles were on leaf springs with an "equalizer bar" between the front and rear springs.
A simple study of this device will show that within some reasonable range of motion it "compensates" quite well for either wheel being slightly higher than the other and distributes the load fairly evenly between the two wheels.
It can be taken that the mid point between the tandem axles is the effective rear point of support when calculating the location of a trailer's C of G and that it is the point at which 85% to 90% of the weight is (effectively) supported - for the purpose of this arithmetic, etc.
EDIT: I forgot to pick up on the boat trailer tangent.
Yes, my I/O sits farther forward on it's trailer than my inboard does (relative to axles), they each have ~15% of the total load on the ball.
END EDIT:
Posted 2008-08-18 8:28 AM (#89890 - in reply to #89885) Subject: RE: Trailering ( Chad's Questions)
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Posts: 5870 Location: western PA
Originally written by Reg on 2008-08-18 8:15 AM
Ho hum, this is getting tiresome - Repeat for 10 % tongue load 160 - 144 = 16 Gee, that is 2 inches BEHIND the front axle's center line. :
My quote was:
"Except for a minimal amount of tongue weight, necessary for proper tracking, a 3 horse bumper pull trailer does in fact, balance on the two axles. This is why the loading is so critical. By having the CG slightly behind the front axle, the tongue is weighted and any loads are still shared by the two axles. "
My example illustrated a three horse BP, but as you have now so eloquently proven, it applies to most tandem axle trailers as well. Thank you for corroborating my statements.
You made the previous statement: "The location of the C of G should actually be AHEAD of the front axle, a popular misconception is that it should be slightly behind the front axle, but that is almost impossible with most designs if an acceptable tongue weight is to be achieved." This differs completely from your voluminous calculations.
Now you are stating: "It can be taken that the mid point between the tandem axles is the effective rear point of support when calculating the location of a trailer's C of G and that it is the point at which 85% to 90% of the weight is (effectively) supported - for the purpose of this arithmetic, etc."
Which is correct? Were you wrong then or are you wrong now?
Gee, you're absolutely correct, this has gone way beyond being tiresome. HO HUM
Posted 2008-08-18 10:34 AM (#89898 - in reply to #89885) Subject: RE: Trailering ( Chad's Questions)
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Posts: 5870 Location: western PA
Originally written by Reg on 2008-08-18 8:15 AM
I think that most of us with more than just a few tens of thousands of miles of pulling agree that 15% is more stable than 10%. :
The least amount of tongue weight that is necessary to effect a proper towing trim and stability, is the correct weight. The industry average of 10%-15% on a BP is just that, an average. In actual usage, the tongue weights will vary greatly by usage and loading. Using any heavier tongue weight than necessary, is detrimental to the increased wear on the towing vehicle's rear tires and suspension, and the resulting loss of fuel mileage.
A well designed trailer will not need a great deal of tongue weight to effect proper tracking. To artificiality add more is unnecessary and wasteful.
GN trailers are often advertised as having 25% of their weights on the hitch. Again this is an average, and will greatly vary from trailer to trailer. A GN with a four foot DR, will have less percentage of its weight on the hitch, than a GN with a long LQ, center tack, tip out and a mud room. Yet each one is calculated to have the same percentage of its weight on the hitch.
By the way, my mileage figure was for that one trailer. I've been pulling for 47 years, many different rigs, many more miles. You only need one mile to know when a trailer is tracking well or not.
Posted 2008-08-18 11:57 AM (#89904 - in reply to #89890) Subject: RE: Trailering ( Chad's Questions)
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Posts: 2689
Originally written by gard on 2008-08-18 8:28 AM
Originally written by Reg on 2008-08-18 8:15 AM
Ho hum, this is getting tiresome - Repeat for 10 % tongue load 160 - 144 = 16 Gee, that is 2 inches BEHIND the front axle's center line. :
My quote was:
"Except for a minimal amount of tongue weight, necessary for proper tracking, a 3 horse bumper pull trailer does in fact, balance on the two axles. This is why the loading is so critical. By having the CG slightly behind the front axle, the tongue is weighted and any loads are still shared by the two axles. "
My example illustrated a three horse BP, but as you have now so eloquently proven, it applies to most tandem axle trailers as well. Thank you for corroborating my statements.
You made the previous statement: "The location of the C of G should actually be AHEAD of the front axle, a popular misconception is that it should be slightly behind the front axle, but that is almost impossible with most designs if an acceptable tongue weight is to be achieved." This differs completely from your voluminous calculations.
Now you are stating: "It can be taken that the mid point between the tandem axles is the effective rear point of support when calculating the location of a trailer's C of G and that it is the point at which 85% to 90% of the weight is (effectively) supported - for the purpose of this arithmetic, etc."
Which is correct? Were you wrong then or are you wrong now?
Gee, you're absolutely correct, this has gone way beyond being tiresome. HO HUM
Gard
My sample arithmetic ONLY corroborates your position for 10% tongue load on a very short trailer, even then it is only 2 inches behind the center line of the front axle. The more desirable case of 15% has the C of G 6 inches AHEAD of the front axle's center line. I suspect that this apparently insignificant 5% may be a large part of the reason that some folk get unstable trailers and others don't, i.e. they dismiss it as insignificant and thereby overlook it as a possible cause of instability.
None of this means that the rear axle is in any way not carrying it's share.
Short-cut; wherever the C of G is both axles are carrying the same load if the trailer is level.
You seem to be reading and/or comprehending very selectively.
There is no inconsistency between my posts, if it helps you to think of it a little differently, the coupler can be considered as one end of a bridge, the mid point of the axles as the other end (review an equalizer bar to see why this works), the C of G (mythical point at which ALL the load would be concentrated to produce the same loading at the points of support) will be 85% to 90% of the distance between the two, measured from the coupler end.
Alternatively, consider a single axle trailer (not for horses) where the axle and coupler are the bridge supports.
Hopefully it is clear where the C of G must be for any given tongue load ?
Again, folk who have converted trailers from single to tandem axles have put the axle mid point where the single axle was and finished up with the same tongue load.
A 3 horse slant load is typically 6ft or so longer than my sample and very little of that length is behind the axles. By extension the C of G is even farther forward on a 3 horse slant for either the 10% or 15% case.
I don't like to haul around with only 10% on the ball, having experienced the result (home built, but a significant learning experience, especially when I stacked pallets all the way back JUST so they would be easy to unload at the tailgate).
Simple subtraction, one multiply, one divide - hardly "voluminous" ?
(-:
Trailering ( Chad's Questions)
