Moving axles; inches vs % need help

[harringtondav]

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..

tpenfield Ted, my earlier calculation was pure scat, and I withdraw it. I've been trying to solve this to no avail. I used a different method of calculation of CG, and basically got the same as you. The problem is there are additional loads at the rear of the trailer, 5.29" rear of axle CL that need to be included in the calc. And with the engine(?S) and out drive(s), they are significant moments. Our similar CG shows the entire boat load forward of the axles. Can't be.

I shot a pic of the new and want diagrams to my masters in structural engineering son to see if he can solve it with the info the OP gave. It's the least he can do considering the $$ I spent to set him up.

 

[sam am I]

Since our given data is the boat on the trailer and weights/distances are given as such. Also, the proposed change will be to move the axles (fulcrum) point about the tongue, I believe then, modeling has to be done as a single entity and is the best/easiest (less given different sets of parameters [y vectors, trig and the like]) approach......And now I have a headache!! I think we're all in the ball park here. Well, at least we know which way to move the axles, right?

 

[alldodge]

Sorry and apologizes to tpenfield and sam am I and any others if this offends.

In the right corner wearing Blue and a Thunderbird we have Ted the man with a number 2 wood pencil and a one, I say one sheet of copy paper and a dimension of 11.9 inches

In the left corner wearing Blue and Black and a SSN-21 sea wolf insignia with a mechanical pencil and three sheets of engineering drafting paper and a dimension of 10.69 inches

Who will win in this final no holds bar battle to the ruler. With only 1.21 inches between them just who will win.

The referee Wave34 will be judge jury and pencil breaker, stay tuned
Better hope his original dimensions were correct or there could be a flag on the play

 

[sam am I]

LOL....0.5mm Pentel Super Hi-Polymer Fine 2B if you please.

 

[tpenfield]

I used a pen . . .

 

[sam am I]

I used a pen . . .

Dodge used his keen observation.......Sorta

 

[harringtondav]

sam am I I reviewed you calcs. OP reported db as 63.5", with dc of 330.75". Doesn't matter. Your free body diagram doesn't recognize an fc load. It assumes point loading at fb. My I/O (assuming the OP's boat is and I/O) has >30% of it's weight in the last +-4' of it's length, plus overhung load for the out drive. This is evenly distributed along db, resulting in a load behind fb at the end of the trailer-fc. Without more information from Wave34 regarding his boat's weight, engine(s?) model and out drive model(s?) - weights are available- I don't think this one is solvable by calculation.

Edit: Front bunk support distance from the trailer tongue would help 'we the obsessed' dial it in, and compare results.

 

[sam am I]

sam am I I reviewed you calcs. OP reported db as 63.5", with dc of 330.75". Doesn't matter. Your free body diagram doesn't recognize an fc load. It assumes point loading at fb. My I/O (assuming the OP's boat is and I/O) has >30% of it's weight in the last +-4' of it's length, plus overhung load for the out drive. This is evenly distributed along db, resulting in a load behind fb at the end of the trailer-fc. Without more information from Wave34 regarding his boat's weight, engine(s?) model and out drive model(s?) - weights are available- I don't think this one is solvable by calculation.

Edit: Front bunk support distance from the trailer tongue would help 'we the obsessed' dial it in, and compare results.

Yes, my model assumes the entire 6250 is linearly distributed across the 26' (dc). And its not, agreed!

Dang it, if we only lived in a purely linear world. Thinking, thinking, thinking. Cob webs are sooooooooo THICK, need more paper. :smash:

 

[tpenfield]

Oddly enough, if the OP ( Wave34 )were to try to move the boat backwards on the trailer to reduce the tongue weight, using my analysis, I come up with moving the boat backwards 10.69" . . . Same value as sam am I calculated to move the axles forward.

Of course moving the boat backwards that amount does not seem to be an option, as I believe the OP said he has only about 3" that the boat could/should be moved backwards, if at all.

 

[ahicks]

So, if we were to move the boat back as far as practical on the trailer, and the axles forward the 3-4" the OP mentioned he was thinking, that would leave us pretty darn close to the calculations, and we could all stop thinking about this!

 

[tpenfield]

So, if we were to move the boat back as far as practical on the trailer, and the axles forward the 3-4" the OP mentioned he was thinking, that would leave us pretty darn close to the calculations, and we could all stop thinking about this!

Yes, if the boat could go backwards 3", then the axle would only need to come forward 8.5" . . . by my calculations.

 

[harringtondav]

tpenfield , sam am I Wave34 A third set of calculations to throw into the fray from my SE son. He works in feet., but his result says move the axles fwd 7.5". He also reminded me that weight distribution is irrelevant. So I eat more previous words.:facepalm:

 

[Scott Danforth]

sorry and apologizes to tpenfield and sam am i and any others if this offends.

In the right corner wearing blue and a thunderbird we have ted the man with a number 2 wood pencil and a one, i say one sheet of copy paper and a dimension of 11.9 inches

in the left corner wearing blue and black and a ssn-21 sea wolf insignia with a mechanical pencil and three sheets of engineering drafting paper and a dimension of 10.69 inches

who will win in this final no holds bar battle to the ruler. With only 1.21 inches between them just who will win.

The referee wave34 will be judge jury and pencil breaker, stay tuned
better hope his original dimensions were correct Or there could be a flag on the play

lmao.....

 

[tpenfield]

tpenfield , sam am I Wave34 A third set of calculations to throw into the fray from my SE son. He works in feet., but his result says move the axles fwd 7.5". He also reminded me that weight distribution is irrelevant. So I eat more previous words.:facepalm:

Looks to me like he said to move the axle forward 0.989 ft (22..221'-21.232') or . . . 11.868"

 

[harringtondav]

Looks to me like he said to move the axle forward 0.989 ft (22..221'-21.232') or . . . 11.868"

He did. I don't know whether to quit drinking beer, or have another.......to wash down more of my words. For sure I need a stronger pair of reading glasses.

 

[harringtondav]

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.

You may have fallen asleep during all the chatter here. I wouldn't blame you. But the verdicts are 11.9,10.7, & 11.9" forward. All calculated by competent people. I'm just the messenger here.

 

[tpenfield]

Full disclosure: I have an engineering degree

 

[alldodge]

Mic drop eep: