Moving axles; inches vs % need help

[Wave34]

I just bought a trailer for my 26' cruiser. The axles are adjustable.

The boat sits flush at the transom and rear of trailer.

I went to a public scale (multi plates) and found that I have 14% of tongue weight.

I would like to reduce it to 10%.

Can the distance the axles need to move forward be calculated or it is a trial and error process?

Distance between the ball and center of axles is 267.25''.

Boat and trailer are 9250 lbs (full of gas).

 

[alldodge]

Calculating tongue weight

http://www.continuouswave.com/whaler/reference/trailering/trailerCalculations.html

In most cases it doesn't take a lot to move weight from the tongue. This all depends on the center of gravity of the boat.

If your tow vehicle can carry it, then might be easier to install a class V hitch (17000 load, 1700 tongue) which will give you more room

 

[harringtondav]

What is the distance from the axle center back to the rearmost bunk support? A simple FxD calculation with this info would get you close.

 

[Scott Danforth]

I just bought a trailer for my 26' cruiser. The axles are adjustable.

The boat sits flush at the transom and rear of trailer.

sitting with back end of trailer or transom is on end of bunks?

 

[tpenfield]

Yes, it can be calculated if you have good measurements for weight and distances. I did it for my sailboat many years ago. I'll see if I can dig up my notes on the calculations.

 

[tpenfield]

http://www.tpenfield.com/Catalina22/Tongue_Wgt.html


I found my notes on my web site . . . (link above)

my rough calculations, using your data, say to move the axles forward about 11" from where they are now. I'll double check the calc's when I get home from work.

Big trailer, right ?

 

[alldodge]

Don't forget that he probably has a tandem trailer

 

[tpenfield]

Here are my calculations . . .


EDIT . . . Fixed the arrows on the tongue and axle weights . . .

 

[Wave34]

What is the distance from the axle center back to the rearmost bunk support? A simple FxD calculation with this info would get you close.

I measured 63-1/2'' from the center of the axles to the rearmost bunk support which is the rear crossmember, inline with the transom.

 

[Wave34]

sitting with back end of trailer or transom is on end of bunks?

Yes, withing 3''. There is an indentation in the transom where the sterndrive is mounted. Maybe 7''. At that point the center bunks are 3'' passed the vertical. The outside bunks are maybe 5'' front of the transom.
But that will change, I plan on moving them to be equal to the transom.

 

[Wave34]

http://www.tpenfield.com/Catalina22/Tongue_Wgt.html


I found my notes on my web site . . . (link above)

my rough calculations, using your data, say to move the axles forward about 11" from where they are now. I'll double check the calc's when I get home from work.

Big trailer, right ?

Thank you for the calculation.
I was hoping for less than 11'', I thought that maybe 4-5'' would be enough.
I will have to check with the cross members if I have enough room to move them.

 

[Wave34]

Calculating tongue weight

http://www.continuouswave.com/whaler/reference/trailering/trailerCalculations.html

In most cases it doesn't take a lot to move weight from the tongue. This all depends on the center of gravity of the boat.

If your tow vehicle can carry it, then might be easier to install a class V hitch (17000 load, 1700 tongue) which will give you more room

Thanks for the link.
Very complete.

 

[harringtondav]

I measured 63-1/2'' from the center of the axles to the rearmost bunk support which is the rear crossmember, inline with the transom.

I calculated differently than tpenfield. I used your 330.75" trailer tongue to rear bunk distance with the same goal of shifting 370# off the tongue back to the rear of the trailer, not to the axle CL. Lots of weight rear of those axles. Same 8325# goal. This would require you to move your axles forward to 66.45" (call it 66.5"), 3 inches. The sum of the tongue weight and the weight at the trailer end must = 9250#. Your axles/tires will carry 370# more, the hitch less the same #s.

 

[tpenfield]

I’m good with the calculations as I have presented them. Keep in mind that you can move the axles forward, or the boat backwards, or even a little bit of both to reduce the tongue weight.

if you do move the boat backwards 2-3”, you may want to check the tongue weight before making any adjustments of the axle, because the distance they would need to move would need to be re-calculated based on the new CG location.

 

[ahicks]

Thank you for the calculation.
I was hoping for less than 11'', I thought that maybe 4-5'' would be enough.
I will have to check with the cross members if I have enough room to move them.

I would likely be willing to go for the trial and error method. The 4-5" plan sounds good to me. I would do that and see where it leaves you. It could easily be "close enough"!

 

[NYBo]

I think those calculations are based on the CG of the boat being exactly centered along its length. That is undoubtedly not the case. The stern will be heavier, so I would use the minimum number calculated, then recheck tongue weight.

 

[tpenfield]

I'm still good with the calculations that I posted.

Wave34 You mentioned that you may not have enough room to move the axles forward far enough to bring the tongue weight down. You may want to see if you can move the boat backwards and still have the bunks supporting the transom notch upright, then check the tongue weight, and then move the axle assembly forward to achieve the 10% tongue weight.

By moving the boat (bow stop) backwards, you can reduce the amount that you have to move the axles forward.

 

[Wave34]

I will try to make the changes before winter and report back.
My brand new trailer is leaving this weekend for a major repair, (welder that thinks he's an engineer = bad design) and should come back the following week.
Thanks again for the help.

 

[sam am I]

I think those calculations are based on the CG of the boat being exactly centered along its length. That is undoubtedly not the case.

Yup!!

Thinking though, how to from here? On way might be, is once he moves the axles, he will re-measure, if it's not quite right AND if he gives us that second remeasured amount, we could then use his first measurement and his second measurement to get a delta per distance (d), It should just be a set of linear equations from there.

Should be able to then find his boat's specific CG based on the above delta/dist, once CG is found and placed/marked, could calc (similar to tpen's method) distance(d) to move the wheels aft (or boat relative to the trailer based on boat's CG) of the CG to get desired tongue weight........

Or

With a known weight centered port/starboard on the deck of the boat (say 100lbs sacs of potatoes because I live in Idaho) and move it about the deck relative to the center of the axles are as they sit now. Watch the scale on the tongue as the weight is moved forward or aft about the axles. Move it aft or forward such that the desired tongue weight is achieved, measure that distance (delta distance potato [ddp]) and translate that weight/distance to the amount the axles are required to moved....Should be close, I think.

Or

Sit at the scales and move axles etc till it's close enough....


Which ever is easiest!

 

[tpenfield]

Keep in mind that I did calculate the Center of Gravity (CG) for the combined boat/trailer as being at 229.85" from the coupler, based on the weights and distances that were provided by the OP.

Given that both the trailer and the boat have their own individual CG's and if the axle assembly is moved, it changes the CG of the trailer to some extent, it is not a perfect science, but generally good enough to make the desired adjustments.

My experience in adjusting my sailboat trailer using this type of analysis got me spot on my desired tongue weight .