Dual axle aluminum trailer

[u12fly]

I did something similar with a few xhanges.
First, got to buy narrow fenders - really about the width of the tires. There is really no room between the fenders and the hull.
Second, instead of cutting the fenders, I had brackets bent and mounted these to the outer surface of the fender. Had to get custom brackets because the fender was still at a angle at this point and the brackets match it. I also added a support between the wheels for stability - worked real well when the boat rode up on the fenders on a steep ramp - the fenders held.
Did not close out the fenders towards the boat - left them open.
Finally, because the fenders do touch the boat on one side or the other (or at least are REALLY close), I added Taylor dock edge bumpers http://www.sportsmansguide.com/net/cb/t ... x?a=572846 to the top edge of the fenders.
http://www.macgregorsailors.com/forum/v ... rs#p238533

Robert your fenders look pretty good, I know what you mean about clearance, the Mac to Trailer mounting is really tight. I wanted my fenders covered on the inside such that any road debris would not be flinged into the boat. I have very little tire side wall to inner fender clearance, I think it is about 3/4". I want to use 3/4" plywood, but do to the space constraints I had to use 1/2" plywood. I routered the plywood round at the top and covered it with bunk carpet. It acts as the bumper for the boat... I have about 1 inch of clearance between the boat and the covered plywood on the fenders. Even with all these tight clearances I have never had an issue with anything touching. The boat always seems to land onto the trailer in just about the same spot.

I have the fenders very stiffly mounted to the trailer, nothing wiggles (Have you ever seen how much the stock fiberglass fender moves as you go down the road!!!!). My brackets also meet the fenders on an arc, in order to account for that I mounted angle brackets stiff and square to the frame, and then jiged the fenders (with several temporary brackets and clamps) before drilling the front and rear mounting holes. The area of the arc (point where the bracket and fender meet) was later filled with epoxy flox which hardens to fill the void then the screws were fully tightened. I don't have an image - and I'm not sure I've explained well enough to follow. Along with the the two outer support brackets I have a simple center block that attaches the wood inner fender well to the trailer frame, this stops any form of vibration.

The hole assembly is very strong, and you can even walk on the fenders with no issues (Although I do not make a habit of that)


Chris.

[Hardcrab]

Okay, I've got a few questions about all of this that maybe could be batted around here.
It applies to single or double axle trailers.
First, take a look at avrios pictures of his excellent work a few posts back.
See how both covered bunks in the center of the axles are dimpled down due to carrying some amount of boat weight.
The wood has been somewhat crushed to match the hull shape there.

One would assume that the axle is seeing a significant load right in it's middle of span.
Therefore, that load pressing down would tend to change the tire angle (camber?) to the road from a true 90* and end up wearing the insides of the tires.
That can't be good.

Would it be logical and desirable to add some amount of aluminum shim stock between the axle mounting and the aluminum I beam to effectively lower the center bunk thereby transfering more weight to the I beam bunks where you really want it to be?

The old steel trailer bunks carried ALL of the load on the rails due to the spring set-up.

Why can't the aluminum trailer do the same to stop the axle from bending and causing uneven tire wear?
Was the axle designed to actually be a heavy loaded crossmember from the start, or did it just end up so by mistake?
I've seen many Mac M's on trailers with the tires splayed out at the bottom when the boat is on, and true to the road when empty. This can't be a good thing in the long run.
I'd challenge everyone with a single axle to stand back and take a critical look at their tires to see if they are running true to the road as you are normally loaded. Then look again after launch.


I'm thinking that 1/4" aluminum plates (about 5"X12" or so) between the axle and rails will send a huge amount of load to the rails.
That thickness seems to be about half of what the bunks have been crushed.

Comments, ideas??

[Tomfoolery]

Well, FWIW, my steel trailer had a second axle added. This is the OEM trailer, by the way, with leaf springs, so no load is placed on the axle other than through the springs.

The original axle is splayed out a bit at the bottom, and the new axle is the opposite, with the tires tilted the other way. The new axle has some camber built into it, and the old one does not.

What I don't know is how much off square (to the road) either one actually is. The new one, being cambered, and 3500 lb rated, is probably designed to deflect under full load so the tires sit true to the pavement, but it only has about 1/2 it's rated load on it. The old axle may actually be a little bent from carrying the full load for the first three years of its life.

One of these days I'll have to investigate that.

Oh, and to your point, it's entirely possible that axle was made with some camber, as I know it's common to put boat load directly onto it. But I don't know.

It's a good question, though.

[Russ]

Was the axle designed to actually be a heavy loaded crossmember from the start, or did it just end up so by mistake?
I've seen many Mac M's on trailers with the tires splayed out at the bottom when the boat is on, and true to the road when empty. This can't be a good thing in the long run.

You know what, I think you have a point here. The boat shouldn't sit on the axle but it clearly does and probably bows the axle in.
I've noticed some uneven tire wear on the inside and this is probably the cause. Well, hopefully a second axle will help distribute more weight.

[Hardcrab]

Thanks RussMT for the pictures.
I've seen other Mac M trailers just like this.

After looking and thinking some, when (if) I go to dual axles, I will kill two birds with one stone.
I'll bolt a length of the alum box tubing (same stuff as the aftmost factory box tube) right where the current axle location is.

Then I'll transfer all the existing "bunk junk" to place the load on this new crossmember.

Position the old axle( w/brakes) 15" forward and new one 15" aft -- adding thick enough shims to ensure the boat can have no axle contact at all.

These axles will not get any of the "bunk junk", they will just carry the load only at the rails as intended (IMHO).

The boat will not know the difference as the bunks will still be in the exact place as before the mod on the new crossmember.

Until I go dual axle, I'm going to add shims as described to help unload the axle center.

I'm really getting close to being fully convinced that ole Rodger may have scr*wed to pooch by loading the axle center as heavy as he has.

When I bought my new trailer from the factory, Mike Inmon suggested that I add 1/8" shims under the 4X4 riser blocks on the rails to help unload the axle.
(He knew something?)
I did that, along with some other mods before I used the new trailer.
My virgin center axle bunk still showed the crushing from load after the first time I put the boat on it.
And my tires looked splayed out at the bottoms.
More height was needed, hence the 1/4" suggestion, but at the axle/rail bolts instead of under the wood riser blocks.
I may need to add even more after I gage the results.

Again, the steel trailer carries all load on the rails/bunks.
Why can't/shouldn't the aluminum do the same?

Opinions?
Ideas?

[Highlander]

I think u guys r all smoking something bad !!
Th alum trl axle is designed for the way it is installed , thats why it has a V bend in the middle so as when it flexes the camber will ajdust to a near level possition
the reason ur tires r wearing out on the inside is due to eccess loading of the trl 's weight capacity dude believe me I have talked to the factory & they even admit that most trl's r overloaded by the time most people mount their eng, gas & gear , supplies anchors & rode water food & u name it my boat & trl scales out around 5000# - 5500# when fully loaded for cruising just for me . A lightly loaded boat & I mean lightly loaded LOL & trl weigh in at approx 3550# not including gas & start or house batteries UR TRL LOAD CAP is 4200# so their is not much leaway to load up the boat alot of people load up the tow vehical instead & transfer the gear all the time thats a pita

No pun intended
when I do the dual axle thing I will also do dual brk's & bunks on each axle

J

[Bassco66]

I have a question, Why would you tow a boat, or anything with a trailer with no suspension? Your roads in the US must be smooth?

[Tomfoolery]

Torsion axle suspension. The cross bar, which contains the rubber spring rods, is bolted directly to the trailer frame. The trailing arms, which have the spindles on them, rotate against the rubber rods as the wheel load increases.



http://www.pacifictrailers.com/UFP-Trai ... bars-arms/

[Hardcrab]

Highlander,
I quit smokin years ago
My 2011 trailer does not have a "V" bend, as you suggest.
(Maybe it does when it's loaded )

I wish my trailer acted the way you report.
My tires are not pitched out at the top witout load, then bending to true to the road with a load as your model suggests.
In fact, my tires look true to the road unloaded, then noticeably bottom pitched out with a load.

You said the axle mfg engineers for the boat resting some unknown part of the weight on the center of the axle?
Can you expand on that please?
Do they give any max limits for this center of axle span loading?

No other aluminum trailer I have looked at loads the axle center of span the way the Mac trailer does.
Granted, that's a small number of trailers looked at, but they all keep the load on the main rails and cross members.

The moment arm from the rubber torsion insert to the actual axle shaft loading point seems to be very short and very stout in the last picture.
For the tire pitch out that most Macs have, your model suggests that the bending must come from this area due to simple static overloading.
Perhaps some does, but it's hard to imagine all of the pitch out just from axle shaft bending with overload.
Please look at that picture again.
What bends where?

One would think that a static overload condition would just twist the trailing arm and torsion rubber tighter rather then bend, as your model suggests.

I wonder what happens when dynamic bumps are encountered; does the pitch out increase still more or does the trailing arm/rubber torsion insert twist up more?

Taking the weight off of the axle center of span is not a bad thing to do, no matter where the bending actually comes from.
That is just my simple minds thinking; I'm not a M.E.

With your engineering experience,do you see any down side to fully unloading the axle at it's center of span like other trailers do?

[yukonbob]

Personally I'm in the maintain the oem trailer for now and buy a new beefier, better and more better trailer in a year or two. I have a factory steel, and other than regular maintenance I don't intend on putting any more money into something that seems bare minimum. IMO …BUT I have seem some of those factory aluminium tandem axel trailers, and those are a whole different story. I'd hang onto one of those if thats what I had

[Bassco66]

Torsion axle suspension. The cross bar, which contains the rubber spring rods, is bolted directly to the trailer frame. The trailing arms, which have the spindles on them, rotate against the rubber rods as the wheel load increases.



http://www.pacifictrailers.com/UFP-Trai ... bars-arms/
tkanzler
Admiral

OK that explains a lot,thanks

[Tomfoolery]

Your roads in the US must be smooth?

I thought you were messing with me for a minute there. Smooth roads? In the north-east? Ha ha ha ha ha ha




(They're actually far better up here, where it really snows, than down in the NYC area where I grew up, but that's another story.)

[Tomfoolery]

I wish my trailer acted the way you report.
My tires are not pitched out at the top witout load, then bending to true to the road with a load as your model suggests.
In fact, my tires look true to the road unloaded, then noticeably bottom pitched out with a load.

You said the axle mfg engineers for the boat resting some unknown part of the weight on the center of the axle?
Can you expand on that please?
Do they give any max limits for this center of axle span loading?

No other aluminum trailer I have looked at loads the axle center of span the way the Mac trailer does.
Granted, that's a small number of trailers looked at, but they all keep the load on the main rails and cross members.

Dexter's Torflex axles all have positive camber (humped up in the middle), and are designed to carry load. They don't specify in their catalog how much camber, nor the cross tube size and wall thickness, but with that little bit of info, it would be relatively easy to figure the amount of load a given axle can support in order to reduce the camber to zero.

You could also take your existing axle off and have someone cold bend some camber into it. Probably by the same amount of negative camber that's in it now, with the boat sitting on it (pull a string or use a long straight edge). You'd want to space the axle mounting pad to frame interface by the same amount so the center pad ends up in the same place. Now when it's loaded, the wheels won't be cambered at all. This is the same principal used for bridge beams - they're fabbed with camber, and when the deck is completed with concrete and so on, they lay flat (or whatever profile they're designed for) via elastic deflection.

You could also space the bunks up a bit to unload the center pad a bit. That puts more boat load on the other bunks, and I don't know if the boat is designed for that, but it's an option.

Another option would be to reinforce the axle. If it's galvanized, you probably don't want to compromise it by grinding off the zinc, but you could u-bolt another member to the bottom. Clamping another member of the same size and wall thickness to the bottom, without welding along its length, will double the strength and stiffness. Stitch welding along its length will quadruple its strength, but that's more work, and it compromises the galvanizing.

The moment arm from the rubber torsion insert to the actual axle shaft loading point seems to be very short and very stout in the last picture.
For the tire pitch out that most Macs have, your model suggests that the bending must come from this area due to simple static overloading.
Perhaps some does, but it's hard to imagine all of the pitch out just from axle shaft bending with overload.
Please look at that picture again.
What bends where?

One would think that a static overload condition would just twist the trailing arm and torsion rubber tighter rather then bend, as your model suggests.

I wonder what happens when dynamic bumps are encountered; does the pitch out increase still more or does the trailing arm/rubber torsion insert twist up more?

Taking the weight off of the axle center of span is not a bad thing to do, no matter where the bending actually comes from.
That is just my simple minds thinking; I'm not a M.E.

With your engineering experience,do you see any down side to fully unloading the axle at it's center of span like other trailers do?

Putting load on the wheels both twists the torsion component (against the compliant phenolic), and puts bending moment into that axle cross-tube. The leaf spring axles with camber (like the Dexter second axle on my trailer) will only have bending induced by that short moment arm from the wheel center to the spring center on each side. Mine always has positive camber because it's a 3500 lb axle with 2000 lb or less on it - not enough load to flatten the axle between the springs and stand the wheels up straight.

Unfortunately, Dexter gives no information on the amount of camber, nor the materials used, implying that for load bearing applications, they want you to ask them. Which I don't really blame them for doing, since those axles can be used where there is no load applied, and where there is load applied, and in the end you want the wheels to stand up straight (no camber), and they may select different axle tubes based on the exact loading profile, which is the only way to allow for bending from wheel load AND from loading the span (point or distributed).

http://dexteraxle.com/i/u/6149609/f/1-7 ... g_6-11.pdf

[RobertB]

Interesting discussion about loading the center of the axle beams and how this may affect tire angle - also, that realistic loading may be in excess of design. One thought - when adding a second axle, this load is now carried by two axles, the amount on each depending on how thick you make the bunks. Adding a third beam sounds to me as a real good way to add weight to the trailer without adding much value (especially if you are also adding a second axle).

[Tomfoolery]

The nice thing about the load bearing axle arrangement is that whatever load is born by the axle is not carried by the frame, nor the connections of the cross member to the frame. But you're right - if the axle is deflecting to where the wheels are cambered out, something isn't right. Too much load on the axle, or the axle wasn't made with any (or enough) camber, or that particular axle wasn't designed to carry load directly. The Dexter axles are, but who's to say what the axles MacGregor used are designed for?