Axle Choice

[Spence]

I'm ready to install my running gear to the trailer frame. There is no axles under the frame now and the frame sits on blocks. The load is 3500, and trailer when complete I would guess would be 900-1000lbs with axles.

The first concern is the use of a drop axle or straight. I would be concerned with clearance especially under the rudder which will overhang the rear of the trailer. The trailer frame has two cross members that are manufactured with a bend under the keel. I think the drop here is 3inches or whatever is standard. I could build in a rear overhang on the trailer which will look odd, and I will have the DOT on my back all the time thinking my load is not proportioned properly. Besides, it will interfere with hauling out. I could undersling the springs
on a straight axle, but that would rule out using softer spring capacities as the frame may bottom out on occasion which may damage the hull.

Second is road shock to the hull plastic. With 3500lb axles and matching springs, road shock(pot holes,speed bumps,unexpected gouges in road,etc) doesn't affect the trailer as such, but the stiff springs may affect the hull above them. One option is to use 4 2500lb springs with the 3500 axles which will provide some give. Perhaps this is the best option.

Any help is appreciated.

Thanks.

 

[centerline]

in your first paragraph you state the load weight is 3500lbs and the trailer weight as upto 1000lbs.... that is almost 4500lbs total that will be carried on the axles.

does this take into account all the gear, gas, groceries and personals you will have loaded in it when heading out to the boat ramp?.. is the motor carried on the boat or in the bed of the pickup?
you need to size the tires accordingly also...

over loading the trailer by setting it up with too little spring capacity is far worse than having too much spring.... and if the trailer bunks are matching the boat and its tied down properly, you dont have any worries about hull damage as it rides down the road on the trailer, although it could shake up the contents inside the boat if they arent stowed secured.

if you know the normal weight that you will carry, set the spring capacity to carry 500-1000lbs more, it wont be too much, and it wont be stressing anything, and you will still have capacity when you need it....
too little capacity and the springs get over worked and will "spring out", which means sag and lose carrying capacity.

and im not sure about the DOT rules or enforcement there where you are, but in most states, as a passenger vehicle, they dont have a care about us. they usually deal with commercial traffic.....
and at any rate, the formula for overhang is measured from the front steer axle to the rear most axle of the vehicle or combination.... you are allowed up to 1/3 of this length behind the rear most axle. it seems like a lot, and it is, but its legal, so hang a red flag of the proper dimensions, or a red light at night on the end of it and hammer down...

its usually the state patrol who governs the passenger vehicles and they are looking for the missing red flag or light on the long loads, or for vehicles exceeding the maximum overall length or width, which in most states is 75ft and 8'6" respectively, unless running with a permit....

 

[Sumner]

....over loading the trailer by setting it up with too little spring capacity is far worse than having too much spring.... and if the trailer bunks are matching the boat and its tied down properly, you dont have any worries about hull damage as it rides down the road on the trailer...

I agree, our Mac S a water ballast 26 footer, is suppose to weigh about 1800 empty. I've never weighed our combination....

....but I'm guessing it is 3500-3800 total (load and trailer) going down the road. I added a second axle ....

http://purplesagetradingpost.com/sumner/macgregor/trailer-mods-index.html

.... and have 3500 lb. springs on both axles (7000 total) and the boat and all of its contents have been just fine in thousands of miles of towing around the country. I read of people trying to create this cushy ride for their boat like what we demand in our vehicles. It just isn't necessary in my opinion.

I'm having a hard time envisioning all you are trying to accomplish. Photos would help ,

Sum

[FONT=Arial, sans-serif]============================[/FONT]

Our Endeavour 37

Our MacGregor 26-S Pages

Our Trips to Utah, Idaho, Canada, Florida

Mac-Venture Links

 

[Spence]

I agree, our Mac S a water ballast 26 footer, is suppose to weigh about 1800 empty. I've never weighed our combination....

....but I'm guessing it is 3500-3800 total (load and trailer) going down the road. I added a second axle ....

http://purplesagetradingpost.com/sumner/macgregor/trailer-mods-index.html

.... and have 3500 lb. springs on both axles (7000 total) and the boat and all of its contents have been just fine in thousands of miles of towing around the country. I read of people trying to create this cushy ride for their boat like what we demand in our vehicles. It just isn't necessary in my opinion.

I'm having a hard time envisioning all you are trying to accomplish. Photos would help ,

Sum

[FONT=Arial, sans-serif]============================[/FONT]

http://purplesagetradingpost.com/sumner/macgregor/macgregor-links-1.html

Sum, thnx for the help. I'll go with the 3500's and the same for the springs. Is yours a drop axles or straight.? If drop, how was the clearance and did you get any scrapes on occasion?

BTW: Watch that tie down. They can crank down hard, and they don't stretch. I had my brother load the boat on his log trailer and with good intentions strapped it down hard as he would his logs. You could play the strap like a guitar. Then I looked at the jack supports and noticed the hull convex at the pads. I jumped in right away and had the gang screw them down real quick. No damage thank heavens but I learned my lesson. i don't think they could take much more. I'll need to look at the laminate this spring when I do the fouling, but I think it's OK.

 

[Spence]

Center, good info, thanks.

I intend to put the stock in the truck, even the grub. I may put the light stuff in there that's all.

 

[Sumner]

Sum, thnx for the help. I'll go with the 3500's and the same for the springs. Is yours a drop axles or straight.? If drop, how was the clearance and did you get any scrapes on occasion?....

The axles are straight...

http://purplesagetradingpost.com/sumner/macgregor-trailer/trailer-mods-10.html
...and I made the second one since our trailers are a little oddball in width and it was cheaper than having one shipped to us. I think the clearance issue is going to depend on your trailer and boat combination so no set answer. The Mac's set very low on the trailer and are...

http://purplesagetradingpost.com/sumner/macgregor-trips-1/2009 Powell Fr-Mia.html

...extremely easy to launch, such as above with no ramp.

The trailer originally only had one axle and on our trip to Idaho/Canada I had to raise ...

http://purplesagetradingpost.com/sumner/Macgregor Trips-2-Priest/08-09-8-priest-koot.html

...the bunks in Canada one day as I felt the boat was too close to the axle. Since I added the second axle and extended the frame and added a third bunk back at the back. All of that can be found here...

http://purplesagetradingpost.com/sumner/macgregor/trailer-mods-index.html

Sum

[FONT=Arial, sans-serif]============================[/FONT]

Our Endeavour 37

Our MacGregor 26-S Pages

Our Trips to Utah, Idaho, Canada, Florida

Mac-Venture Links

 

[HEINZIR]

I agree, our Mac S a water ballast 26 footer, is suppose to weigh about 1800 empty. I've never weighed our combination....

....but I'm guessing it is 3500-3800 total (load and trailer) going down the road. I added a second axle ....


I did have my Venture 23 weighed on the way home from the HPCC in Arizona last winter. Sales brochure says the boat weighs 2000 lb.
Rigged for day sailing with trailer, 6hp 2-cycle motor, and all rigging but no food, fuel, or water, actual weight was 3700 lb!

 

[centerline]

I agree, our Mac S a water ballast 26 footer, is suppose to weigh about 1800 empty. I've never weighed our combination....

....but I'm guessing it is 3500-3800 total (load and trailer) going down the road. I added a second axle ....


I did have my Venture 23 weighed on the way home from the HPCC in Arizona last winter. Sales brochure says the boat weighs 2000 lb.
Rigged for day sailing with trailer, 6hp 2-cycle motor, and all rigging but no food, fuel, or water, actual weight was 3700 lb!

my 25 with a 10hp honda 4stroke, loaded for about a three week+ cruise, drinking water, rum, coke and everything else included, on the trailer is 3900, plus what ever the tongue weight is, maybe 250lbs.... it adds up quick

 

[Sumner]

my 25 with a 10hp honda 4stroke, loaded for about a three week+ cruise, drinking water, rum, coke and everything else included, on the trailer is 3900, plus what ever the tongue weight is, maybe 250lbs.... it adds up quick

Oh, then maybe we are over 4000 lbs. :cry:. Going down To Florida the boat was loaded ready to sail, 19 gallons of gas and 40+ gallons of good mountain water, two outboards and probably a lot I forgot but minus ....

food, pop and beer .

When I painted the bottom...

http://purplesagetradingpost.com/sumner/macgregor2/outside-39.html

... I raised the waterline 1 inch above the top of the old waterline strip and ...

http://purplesagetradingpost.com/sumner/FL-fall-2010/FL-Fall-10-4.html

... as you can see at the beginning of the trip we were right at the top of it.

If I remember right a number of the X/M owners report weights of around 4500 for boat/supplies/trailer,

Sum

[FONT=Arial, sans-serif]============================[/FONT]

Our Endeavour 37

Our MacGregor 26-S Pages

Our Trips to Utah, Idaho, Canada, Florida

Mac-Venture Links

 

[tkanzler]

One option is to use 4 2500lb springs with the 3500 axles which will provide some give. Perhaps this is the best option.

I'm assuming you're talking about leaf springs with an equalizer. The POs added a second axle to my trailer, but used the original springs on the original axle (something like 5000 lb per pair, with very thick leaves), and a 3500 lb per pair set on a new 3500 lb axle.

With the equalizer, the effective spring rate is reduced greatly, as it's equivalent to putting two springs in series, which halves the spring rate, but the ride was kinda harsh based on the chatter coming from back there, and the feedback through the coupler into the vehicle. So I took them apart and shortened one leaf on the 3500 lb pair and run just three leaves on that one, and I run two leaves on the heavy set. They're roughly 1250 lb each now, and the boat rides much softer back there.

3500 lb axles, bearings, and wheels are just right, IMO, when used this way, as 3500 lb on those bearings is really pushing it in the first place. But 7000 lb worth of axles, bearings, and wheels is more like it, with springs sized for the actual load. 5000 lb of suspension on 4000 lb of wheel load, equalized, is maybe a little stiff, but as I said, since they're equalized, there is a reduction in effective spring rate when you do that.

Torsion bar suspension, which is independent, is another story, but those suspension systems have variable spring rates which are 'soft' when lightly loaded, unlike the constant rate of leaf springs when all the leaves are always in contact with each other.

 

[Spence]

The equalizer is a good idea, didn't know about this.

I think this place sells the standard utility trailer springs. At 3500lbs, the 4 2500's should flex the springs no more than 1/3 the travel on a road shock event, and that would still require an over axle mount since I couldn't take the chance with underslung at 1/3 flex which may cause the frame bottoming out.

But I think I'll get a lot of answers once I lower the keel onto it. It'll call for jacking the load to replace the springs back to 3500's, with it's problems like spring length and pivot point adjustments, but that's what happens when your not shop equipped for this sorta stuff.

Thanks for the tips.

 

[centerline]

I'm assuming you're talking about leaf springs with an equalizer. The POs added a second axle to my trailer, but used the original springs on the original axle (something like 5000 lb per pair, with very thick leaves), and a 3500 lb per pair set on a new 3500 lb axle.

With the equalizer, the effective spring rate is reduced greatly, as it's equivalent to putting two springs in series, which halves the spring rate, but the ride was kinda harsh based on the chatter coming from back there, and the feedback through the coupler into the vehicle. So I took them apart and shortened one leaf on the 3500 lb pair and run just three leaves on that one, and I run two leaves on the heavy set. They're roughly 1250 lb each now, and the boat rides much softer back there.

3500 lb axles, bearings, and wheels are just right, IMO, when used this way, as 3500 lb on those bearings is really pushing it in the first place. But 7000 lb worth of axles, bearings, and wheels is more like it, with springs sized for the actual load. 5000 lb of suspension on 4000 lb of wheel load, equalized, is maybe a little stiff, but as I said, since they're equalized, there is a reduction in effective spring rate when you do that.

Torsion bar suspension, which is independent, is another story, but those suspension systems have variable spring rates which are 'soft' when lightly loaded, unlike the constant rate of leaf springs when all the leaves are always in contact with each other.

im not sure if i understand this correctly, or if im reading it out of context, but for anyone who may take it out of out of context, using an equalizer does NOT reduce the load carrying capacity of the spring pack...

what it does is allow the axles to "walk" thru low spots or high spots (over curbs) and still let the other tire remain in contact with the road surface and support some of the weight...

if the equalizer was not there, as soon as you got the one tire off of the level surface, it will quickly and severely change the loading on the axles and tires. if you were to back up on a couple of 2x6's laying flat on top of one another, it would lift the other tire off the ground.... loading the single tire with all the weight on that side....
the equalizer will allow the axles to move in relation to one another (within the scope of their design) and still support their share of the load, equally....

 

[tkanzler]

im not sure if i understand this correctly, or if im reading it out of context, but for anyone who may take it out of out of context, using an equalizer does NOT reduce the load carrying capacity of the spring pack...

I'm not saying it does. What I'm saying is, for two spring sets of equal spring rate (force increase per unit distance of deflection), as with two axles with the same springs and an equalizer, the net spring rate when deflecting just one axle, as when hitting a bump at high speed, will be half what it would be with just one axle. When that single spring compresses, the equalizer rocks, loading the other spring also, which causes a deflection in that other spring, too.

Dynamic effects do come into play at high speeds, where the trailer essentially stays still while the wheels take a pounding and deflect upward, and all the bits do have inertia, but the springs themselves have relatively little inertia and will deflect rapidly without a huge additional load. And each axle hits the same bump, so it all happens twice instead of once.

Elastomeric suspensions definitely have the problem of no being equalized, so a larger bump can put a proportionately greater load on one axle while unloading the other. But the elastomerics also have a progressive spring rate, as the rubber rods get squished as the load increases, making them stiffer because they're 'wider' as load increases. And the faster you deflect them, the higher the instantaneous spring rate.

So no, I'm not saying using an equalizer decreases the capacity of a given spring pack. It remains the same, but adding another axle of the same type with the same springs essentially doubles the capacity, but the spring rate (force increase per unit height of the bump) decreases, as they're both being deflected by a single bump, but at a theoretical deflection of only half as much. And they're both deflected twice by the same bump. Since they're equalized.

Which is why I softened all my springs, as their total capacity was way higher than needed, and I wanted to reduce the shock load into the boat.

 

[centerline]

I'm not saying it does. What I'm saying is, for two spring sets of equal spring rate (force increase per unit distance of deflection), as with two axles with the same springs and an equalizer, the net spring rate when deflecting just one axle, as when hitting a bump at high speed, will be half what it would be with just one axle. When that single spring compresses, the equalizer rocks, loading the other spring also, which causes a deflection in that other spring, too.

Dynamic effects do come into play at high speeds, where the trailer essentially stays still while the wheels take a pounding and deflect upward, and all the bits do have inertia, but the springs themselves have relatively little inertia and will deflect rapidly without a huge additional load. And each axle hits the same bump, so it all happens twice instead of once.

Elastomeric suspensions definitely have the problem of no being equalized, so a larger bump can put a proportionately greater load on one axle while unloading the other. But the elastomerics also have a progressive spring rate, as the rubber rods get squished as the load increases, making them stiffer because they're 'wider' as load increases. And the faster you deflect them, the higher the instantaneous spring rate.

So no, I'm not saying using an equalizer decreases the capacity of a given spring pack. It remains the same, but adding another axle of the same type with the same springs essentially doubles the capacity, but the spring rate (force increase per unit height of the bump) decreases, as they're both being deflected by a single bump, but at a theoretical deflection of only half as much. And they're both deflected twice by the same bump. Since they're equalized.

Which is why I softened all my springs, as their total capacity was way higher than needed, and I wanted to reduce the shock load into the boat.

I understand what you mean now... you are correct. 4 springs (2 axles) traveling down the road at 50% load is a softer and easier ride than 2 springs (1 axle) traveling down the same road with a 50% load on them...

and, a spring that is loaded to 3/4 capacity will produce a softer ride than one loaded to 1/4 capacity. (but, it will also take more abuse and be more prone to early failure) but in normal highway operation, at speed, there is little difference in ride quality between the two. at slow speeds or off road travel (or rough parking lots) it does make a difference, but there we usually want to go slower to compensate....

I am not a proponent of over "springing" a trailer, but i am a proponent of getting enough spring under it to last the life of it. too little spring and they are prone to break, and there is a wide margin before it would be considered too much spring for the load.... road conditions dictate to some degree, also travel speed, but still the margin is wide for those with a desire to re-spring their trailer.