Trailer Mod Complete

[RobertB]

Finally finished adding the second axle to my factory trailer.


I moved the original axle 18 inches forward, added the second 36 inches behind.
Fenders are all aluminium: Had custom supports bent to get the right angle against the fender and added a middle support with two large angles and a straight bar.
All hardware is stainless steel - even the trailing arm bolts (replaced the stock galvanized ones and greased the splines so corrosion will not totally lock-up and prevent disassembly).
Used a small dock edge protector along the top edge to keep the hull from hitting the fender. Now to remove the black marks the stock fender left on my hull

Fortunately, was able to do mod with the boat on the trailer - after I figured out the boat does not rest on the axle cradle if the boat is all the way forward on the trailer and supported at the rear crossmember - had to purchase a right angle air drill to drill holes for the bunk outboard support in the top of the trailer i-beam.
Have yet to try it out since the tarps are up for the winter.

UPDATE: Checked MD State regulations about brakes - must have brakes on all wheels of a single axle for gross trailer weight of 3,000 to 10,000 pounds. So, having brakes on only the front axle appears to be legal.

[Phil M]

What year is your factory trailer?

Phil M

[RobertB]

Trailer and boat purchased new late summer 2010.

[Doug W]

Nice looking job!

I may have missed a previous post. Did you have to move the original axle forward or backward?

[Crikey]

Hey Mastreb, I think I found your missing boat!

[seahouse]

Hey Doug!

I may have missed a previous post.

Yup. Ya did...

I moved the original axle 16 inches forward, added the second 32 inches behind.

[roril]

Nice Job!
I want to do the same mod before we start making some long trips. Right now I make sure that I have excellent tires on the ground.

[Hardcrab]

I'm on the fence for adding a second axel on my trailer.
Good, logical Pros and Cons for either method.

The thing I wonder about is the "weight" rating of the axels.
The factory one is 42 or 4700 lbs, (can't remember).

If you duplicate that rated axel, isn't the trailer sprung for 8000 plus total weight?
And if so, will the boat ride hard on the bunks due to so much spring?
That seems to be a pretty rough ride?

With that in mind, if you reduce both axels to say 2500 each, 5000 total for a smoother ride, what happens if a tire blows, and only one underrated axel takes the load?
I'm confused.

As to the single axel version swerving all around with a blowout, that dosen't make sense to me.
It's a "trailing the truck" load.
The added friction of a blown tire just acts to keep the trailer straight back and not swerving around???
I've been told by someone who had a single axel blowout that they did not know the tire was flat, only a strange vibration was felt.

Then there is double the bearing maint and double the tire cost.
Turning radius issues and good tongue height/weight versus axel/tire loading issues.

I'm still on the fence, confused by it all.
Any further insights???

[RobertB]

I agonized over these same issues.

Reason for adding axle: Single axle setup was close to maxed out with boat loaded with all the absolutely essential stuff I cram into it . The car I use, while it can pull easily, has a wierd tounge load rating of only 5% (about 150 pounds) so I wanted to take some load off the rear suspension (the total cost of the upgrade costs less than replacing my rear struts (total cost was around $1000)). To avoid swaying, I had to be real careful about weight distribution while trailering - this is a pain. Most my trailering is at highway speeds and wanted to minimize impacts of a blowout.

As far as the rating of the axles: I did not downgrade (1) because I am cheap and only wanted to buy one new axle and two wheels (2) in the event of tire failure, remaining stub axle/tire is rated for full load (3) when going over a bump or pothole, each axle will be loaded close to full.

Also, the total angular deflection of the axle between 1/2 load and full load is not that much different so it should not really affect launch/retrieve.

I even asked UFP if I needed to change the indexing of the trailing arm on the spline going to the axles and they said keep it the same (about 29 degrees).

As far as bearing maintenance - I believe that as long as bearings are kept greased, bearings should last as long as the trailer. Tires - I can push tire life longer having the second axle than I would if only a single axle.

Big thing to keep in mind: this is not a traditional dual axle tandem setup where the suspension between axles is linked - it is a four wheel independent suspension. Bumps are experienced by each wheel independently if you have one axle or two.

All the figuring aside - I will tell you how it pulls this spring once Luna Sea emerges from hibernation.

[2BonC]

..just another improvement for the use of a Mac-trailer...
Sometimes during the lauch or storing of the boat I was forced to move to the top of the bow of my . As long as the mast and spreaders are still in their storing position it´s quite incomfotable to walk there all the way from the rear on top of the cabin. And it´s even harder to climb there via steering pole/car. I think something had to do about it so I installed a small ladder on the towing bar of the trailer.

I hope this will do it´s work next time I give the boat back to it´s element.

rainer

[RobertB]

The newer versions of the Mac trailer have the bow ladder - very useful.

[bscott]

The load carrying capacity of the trailer is determined by your tire rating--not springs.

Bob

[RobertB]

The stock tires are speced a bit higher than the torsion springs (if I remember correctly) - I did check the load ratings. That is why I refer to the load rating of the springs. And yes, the limiting factor on many cars is the load rating of the rear tires - this is the reason that when I am pulling the boat with my Vovlo XC70, no rear seat passengers and limited cargo (we often will drive a second car to the ramp).

Also, if one were to momentarily exceed the load rating of the tire (within reason), no big deal. If exceeding for a distance constantly, you will heat up the sidewalls and this can cause sudden tire failure (same with underinflated tires).

[raycarlson]

using that logic with four load range "E" tires at at 2500lbs each for a total load rating of 10,000lbs youre saying its safe to haul a 10,000lb boat on a trailer equiped with two 1500lb axles(torsion style like late model M).i dont think so. what you meant to say is your load rating is the lowest rated component be it tires,wheels,springs,hitch, or trailer frame.its not governed by any one item for sure.

[RobertB]

Where in the world did a 10,000 pound boat come into the discussion? That is a bit of extrapolation that was never intended. My analysis meant to support the scenario that if I lost a tire, the remaining tire on that side could support the load. I call that a factor of safety of about 2 instead of close to 1 as a single axle trailer has.

The loaded with trailer is about 4,000 pounds. The axles each rated for about 4200 pounds and the tires speced a bit higher (if 2500 pounds each, that makes 5000 pounds per axle). Never in this thread did I state that I was going to load the boat up to 5 tons total weight! My main intent is to reduce tongue loading on the car hitch, make weight distribution of gear less critical, and make safer if a tire should blow. My engineering analysis and the experience of others doing this same mod justifies the placement of the axle and the choice of components to accomplish this.