Undergrad How to weigh a car topped boat?

[pbuk]

Yes, that would be the "saw horse" approach. A 2 by 4 (nominal dimensions -- actual is normally about 1 and 3/4 by 3 and 5/8) could be used as the top of a saw horse.

I think using saw horses would be both less convenient and less accurate. Put the scale on the ground and the 4x2 directly on top.

 

[Andy Resnick]

I can't visualize what you mean.

I am suggesting you rig up something like this to lift the boat:

 

[russ_watters]

I bet the OP is sooo glad he came to PF for this question.

 

[HRG]

Yes, that would be the "saw horse" approach. A 2 by 4 (nominal dimensions -- actual is normally about 1 and 3/4 by 3 and 5/8) could be used as the top of a saw horse.

Yes, I will use sawhorses when I weigh the boat.

The boat will be slightly less than 4 feet wide. I'll have two sawhorses with 5 feet long 2x4's screwed to the tops which I'll be using to build the boat on. So they will already be available. I'll just set the ends of the boat on the sawhorses, then put a bathroom scale below a horse and barely lift that end of the boat off the horse while standing on the scale. Ditto for the other end. The measured weight will be way close enough to verify the loading on the roof racks.

 

[HRG]

I am suggesting you rig up something like this to lift the boat:

View attachment 285872

Wow, way more complex than what I have in mind. But I appreciate your contribution to my question.
Thanks.

 

[HRG]

I bet the OP is sooo glad he came to PF for this question.

 

[berkeman]

I bet the OP is sooo glad he came to PF for this question.

But wait, it gets better...

@HRG -- Do you have any truck weighing stations near you? If so, there is a good (but expensive) way to get the data you need.

-1- Drive through the truck weigh station at the speeds posted, and drive off. You will quickly be pursued and pulled over by the Highway Patrol officer assigned to that truck stop. You can try pleading ignorance about drving through a truck weigh station, but with the warning/ticket you can ask for a copy of the weight record as part of the evidence of the crime.

-2- Then load your boat on your vehicle, and drive through the same truck weigh station again (preferably within the same hour), again obeying the posted speed limits. You will again be pursued by the same Highway Patrol officer and pulled over, and best case you get a ticket and can again request a copy of the weigh record that will show you the delta weight to give you the weight of your boat.

-3- Then, assuming you didn't get arrested for -2-, you can drive through the truck weigh station one more time with the boat on your vehicle, this time at highway speed. You will almost certainly be arrested, but if you can get the weigh record for your 3rd pass, that will show you how the aerodynamic forces are acting on your boat at high speeds. You can adjust your tie-down strategy from there. (Well, after you get out of jail)

 

[russ_watters]

The only real open question/complication with your method is make sure you lift it from the point it touches the ground on each end and lean in such a way as to get your feet/scale directly under that point*. That ensures the weight registered(minus body weight) is the weight held up by that point when it is resting on the ground. Otherwise this is as easy-peasy as you thought when you first entered this nightmare joined PF.

*or, depending on the type of scale, just rest the ends of the boat directly on the scale and avoid 2/3 of that pesky math.