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Re: New Trailer Needed -- Help

Posted: Tue Jul 28, 2015 11:47 am
by C Buchs
rszobel wrote: in order to calculate tongue weight how do you go about it ---- I would take total weight and apply at supports (bunks) based on area of each bunk (distribute total weight in accordance with support areas - reasonable assumption) and then apply each individual bunk load at the centroid/center of each bunk, then simply sum moments to determine what the tongue weight would be - is this your approach as well??
Don't forget that you need to find the center of mass of the boat. I'd bet it's not evenly distributed across the boats length.

Jeff

Re: New Trailer Needed -- Help

Posted: Tue Jul 28, 2015 11:53 am
by rszobel
that could be a bit tricky to say the least. how would you suggest finding CG of boat when loaded ?

once you find CG of boat and estimate tongue weight, again, how would one adjust it - by moving around items stored on boat would be one way but not sure how much of an influence that would have unless I move gas tanks around for trailering as tanks are probably the heaviest item i store on the boat - maybe my water supply as well - other heavy items would be batteries, but that is a PITA to move around just for trailering boat!

suggestions on how to adjust tongue weight other than moving axles ??

Re: New Trailer Needed -- Help

Posted: Tue Jul 28, 2015 12:08 pm
by RobertB
Center of mass can only be determined by measuring weight at the front and rear (or at the wheels) of the trailer. But, this is highly variable based on your loading (gear, water, fuel). Recommend you measure a factory trailer in relation to the boat on it. How far back are the axles from the bow? Then have the new trailer designed around this. I personally installed my second axle so the two axles were the same distance fore and aft of the original axle position. If you want to change tongue weight, then your trailer builder can figure out the offset you need.

Re: New Trailer Needed -- Help

Posted: Tue Jul 28, 2015 12:10 pm
by rszobel
RobertB -- you are not very far away from me. do you know of a trailer dealer locally that i could consult??

Re: New Trailer Needed -- Help

Posted: Tue Jul 28, 2015 1:07 pm
by RobertB
No, I did my own work. Recommend an internet search and some phone calls.

Re: New Trailer Needed -- Help

Posted: Tue Jul 28, 2015 9:31 pm
by Phil M
rszobel wrote:I see that the trailer has longitudinal bunks as opposed to transverse as is the case with the original trailer. I've heard that this can cause deformation of the hull. Have you had any such issues??

Also what specific mods did you do to trailer as you mentioned and also what did you do to insure correct tongue weight??
No issues with hull deformation. But with longitudinal bunks the Mac is not always perfectly centred.

Specific mods: http://www.macgregorsailors.com/modt/in ... ?view=2017

And

http://www.macgregorsailors.com/modt/in ... ?view=1678

There was a thread in this forum on how to measure tongue weight. My best estimate with crude equipment was that the tongue weight was too much. I moved the axles forward a small amount, I think it was two inches. Measured again and the weight seemed about right. It was a lot of effort.
Whoever it was I dealt with in sales knew nothing about Macgregor sailboats. :? So I did everything the hard way - myself. :)

Re: New Trailer Needed -- Help

Posted: Wed Jul 29, 2015 7:54 pm
by rszobel
So I was looking at the loadrite brochure online and it looks like the axles are bolted to the frame making it possible to move the axles if needed. Is this correct?

Re: New Trailer Needed -- Help

Posted: Wed Jul 29, 2015 8:08 pm
by Phil M
rszobel wrote:So I was looking at the loadrite brochure online and it looks like the axles are bolted to the frame making it possible to move the axles if needed. Is this correct?
That is how I was able to slide them over a small amount.

Re: New Trailer Needed -- Help

Posted: Wed Jul 29, 2015 8:12 pm
by rszobel
Phil M wrote:
rszobel wrote:So I was looking at the loadrite brochure online and it looks like the axles are bolted to the frame making it possible to move the axles if needed. Is this correct?
That is how I was able to slide them over a small amount.
How much work was it and how long did it take you?
How did you figure out where to move them to?

Re: New Trailer Needed -- Help

Posted: Thu Jul 30, 2015 12:04 am
by Phil M
rszobel wrote:
Phil M wrote:
rszobel wrote:So I was looking at the loadrite brochure online and it looks like the axles are bolted to the frame making it possible to move the axles if needed. Is this correct?
That is how I was able to slide them over a small amount.
How much work was it and how long did it take you?
How did you figure out where to move them to?
There is a thread in this forum somewhere about calculating the tongue weight using an ordinary bathroom scale. I measured the tongue weight, moved the axles a small amount, and measure the tongue weight again. There was a noticeable and satisfactory weight adjustment. you can only measure the tongue weight when the boat is on the trailer. You can only move the axles when the boat is off the trailer.
Everything takes time and effort, and a little more of each when you're lacking experience. :?

Re: New Trailer Needed -- Help

Posted: Thu Jul 30, 2015 8:58 am
by Tomfoolery
rszobel wrote:that could be a bit tricky to say the least. how would you suggest finding CG of boat when loaded ?
That can be done, but the more information you have, the more accurate the estimate will be.

Do you have the original steel trailer?

Do you know what the boat and trailer actually weigh, equipped as it normally is?

Do you know what the tongue weight is as it's normally set up for towing?

Re: New Trailer Needed -- Help

Posted: Thu Jul 30, 2015 11:33 am
by RobertB
If you want to find the CG (the CG of every boat is unique since it is dependent on how the boat is loaded):
1. Load the boat as you would expect to trailer it (gear, fuel, water, etc.)
2. Tow the boat to a business with a scale - e.g., one that sells bulk yard materials like gravel, stone, and mulch. Get a weight with only the trailer wheels on the scale.
3. Weigh the tongue at home using methods already outlined on the forum.
4. Contact UFP to get a weight of the axle assembly and wheels (including the tires) since this mass is what you will be moving. You will need the serial number of your axle for this.
5. Pencil/paper/calculator to calculate the current CG and how far to move the axle to the desired tongue weight.

Or, do as many of us have done and fake it.

Re: New Trailer Needed -- Help

Posted: Fri Jul 31, 2015 11:21 am
by Tomfoolery
Phil M wrote:There is a thread in this forum somewhere about calculating the tongue weight using an ordinary bathroom scale.
Since I had to get an updated tongue weight anyway, and since we're on the subject anyway, I snapped a couple of pics for posterity, for anyone who doesn't want to go looking.

The tongue weight was too high for the scale, as it's brains got scrambled when I tried (digital load cel type), so I used a 2:1 mechanical disadvantage. A 2 ft 2x4 on its side, a thin spacer on the scale to be sure flex in the 2-by didn't end up contacting the scale surface in the wrong place, another bit of 2-by to keep the beam level, and yet another 2x4 as the post. The post had 45 degree miters on the ends, which was a happy coincidence, as contacting the beam along a transverse line removes some potential error.

The post contacts the beam mid-span (I even drew a line across), although it doesn't look like it in the pic due to the miter being one-sided. Absent any outside influences, the scale will then support exactly one-half of the tongue load, and the fulcrum at the other end will take the other half. Since I didn't use pipes for fulcrums, a little error will creep in as the actual effective length is a little variable, but I kept the beam contacting the two fulcrums by only a small amount to limit that. Not that a high level of precision is required, but just keeping the contact small at least reduces the potential magnitude of error. Using a longer beam also has a positive effect, though the load a 2x4 can support on its side is, of course, limited.

Since most bathroom scales can handle at least 300 lb, a 2:1 measurement is fine unless you're carrying gold bars in the bow. In which case, a 1/3 - 2/3 arrangement can be used to reduce the scale force by a factor of 3.

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Re: New Trailer Needed -- Help

Posted: Fri Jul 31, 2015 9:44 pm
by WASP18
rszobel wrote:RobertB -- you are not very far away from me. do you know of a trailer dealer locally that i could consult??

This one is in Delaware. I've done business with them over the phone. I live in Mass.
http://www.easternmarine.com/?gclid=CL_ ... HwodWnUFAg

Re: New Trailer Needed -- Help

Posted: Mon Aug 03, 2015 5:42 pm
by Tomfoolery
C Buchs wrote:Don't forget that you need to find the center of mass of the boat. I'd bet it's not evenly distributed across the boats length.
rszobel wrote:that could be a bit tricky to say the least. how would you suggest finding CG of boat when loaded ?
The original trailer had a tongue weight of about 160 lb, and an empty (tare) weight of 710 lb. For an :macx: loaded up to the GVW of the trailer, which is 3500 lb, the boat and engine and contents would weigh about 2790 lb. So the tongue weight would be that of the empty trailer, plus whatever proportion the boat puts on it, with the rest going onto the wheels.

The distance from the hitch ball to the center of the axle is 225 inches. So the location of the CG of the boat that adds another 190 lb to the tongue (for 10% of the gross trailer weight) would be 190 lb x 225 in / 2790 = 15.3 inches forward of the center of the axle.

The pointy end of the raccoon stripe on the side, where it ends at the rub rail, is pretty much right over the axle, so 15 inches or so forward is just a hair forward of the mid point of the sliding hatch. But it's easy enough to measure from that raccoon stripe end.

That's all based on a 3500 lb boat with 10% tongue weight. The standard OEM trailer doesn't change, but the boat contents and equipment do, so to get an accurate location for your circumstances, you need the actual gross weight, and the actual tongue weight. From there it's some easy cipherin' to determine where your actual C of G is.

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