Weighing a large boat

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fallguy1000
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Weighing a large boat

Post by fallguy1000 »

Oof. Lotsa work trying to weigh the Skoota.

Not sure the weights are right, but feel like they are close.

Design displacement. 8540 as adjusted for width, 8643 with beaching keels
Dry weight. 8254
Wet weight at 50%. 64 gas @6=384 plus 25 gallons water = 400 for total of 784
Add more batteries. 126
Add more anchor mass to port side. 100
Steps in each side 100

Added weights 1110

Total = 9364
Versus displacement
8643

721 pounds over no passengers when 50% wet

BH1 port weight 1327
BH1 star weight 1848
BH5 port weight 1980
BH5 star weight 3100

Additional weights to middle of hull.

Steps both sides 20kg
Batteries to port middle 58kg


Might be some errors, gotta check the level. Need sleep.


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Re: Weighing a large boat

Post by narfi »

Why is the starboard so much heavier?

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Re: Weighing a large boat

Post by fallguy1000 »

Well, I expected it to be 300 pounds or 500 pounds more with the helm station, but something seems off so the boat is probably not level enough. Inaccurate reading..
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Re: Weighing a large boat

Post by Jaysen »

Are you running the 4 scales simultaneously?

Assuming that there is a measurement error, it seems that the BH5 star is likely "out of plane" with the other measure points. The total weight would still be accurate but the distribution of weight would be off (you would have a heavy spot). I'm hoping that it is as simple as that.
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fallguy1000
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Re: Weighing a large boat

Post by fallguy1000 »

Jaysen wrote: Mon Apr 25, 2022 10:52 am Are you running the 4 scales simultaneously?

Assuming that there is a measurement error, it seems that the BH5 star is likely "out of plane" with the other measure points. The total weight would still be accurate but the distribution of weight would be off (you would have a heavy spot). I'm hoping that it is as simple as that.
Likely right.

I just went out with my laser level and the star aft corner is way high, so it is carrying a disproportionate amount of the port side as the lifting picks up the entire hull.

I have level references, but we did not have time to use them and now it seems like things are way off on my individual spots.

The system is not ideal. But I believe we got a pretty good overall load... Putting the feet under each corner and getting the levels precise was not our goal yesterday. The beam scales were bending down the way I had them mounted. They were bending the 1/4" hot rolled steel 8" c channel. I, of course, mounted them in the middle and once we realized they were bottomed, we moved a couple of them beams scales to the edges of the channel. Keep in mind, we are teetering thousands of pounds on a single furniture foot like 2.5". And the boat wanted to move a bit.

The hull stands were made with green treated 2x8 and one of the boards cracked in half from the boat moving/uneven loading.

I'm not sure the guy who was helping me had the patience to do more as he works 8-4 and was here on his weekends and 3 hours away. So, he left just when I realized we were not level enough. That was around 1pm Sunday. I was at midnite church this weekend, so also pretty tired yesterday.

I have another guy I can enlist help from this week, but also having Mom come to help me sew a cover for the helm. Might reweigh in a week. The weather here sucks, too. High today is 38F.
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fallguy1000
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Re: Weighing a large boat

Post by fallguy1000 »

The scale is a converted livestock scale.

Each foot is on the end of a beam scale and is mounted upside down on 8" c channel.

The method requires teetering the boat stands on the single rubber foot.

And it would require making the boat level to her reference level along with the teetering...
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fallguy1000
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Re: Weighing a large boat

Post by fallguy1000 »

Here are pictures of the scale.
30B21F99-54EC-475E-B900-E74AC06B86C1.jpeg
588909C2-E43B-423D-ABF7-FC480322CEB4.jpeg
B9E33A82-01B4-4106-AF62-DA3955717EFF.jpeg
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Re: Weighing a large boat

Post by APLJaK »

Just a thought from a former measurement technician. Did you check each load cell with a test load? The junction box contains trimmers that allow the "corners" to be set. If the four cells were calibrated together with a single load and the corners were not trimmed first, you could easily have a bias in the cells. Since you are relying on accurate cell outputs, this would not be desirable. In other words, a four load cell scale can be accurate for a center load (shared by all four load cells), but still inaccurate as the load moves towards a corner. The first step in calibrating an electronic scale like this is to ensure the corners weigh the same, regardless of this being an accurate weight or not.

Of course, its going to be very difficult to test individual load cells mount in this manner. You could run an experiment, change the location of the cells and see if the indication changes or stays the same (relatively)

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Re: Weighing a large boat

Post by APLJaK »

One further thought to reduce the sketchy/scary loading of a boat on individual loading points like this. There is no reason you couldn't bolt the assemblies that you have built to a beam, tying them together. The original scale used a "bridge" to do the same thing. Large scales typically use pairs of load cells in sections which is what you would also be doing. You would want to continue to load as close to each load cell as possible as it is corner balance weight that you are interested in, not so much total weight.

I wouldn't trust overall accuracy too much on a setup like this without being able to test it (compare it to a known weight), but you might be able to get some good relative readings that are arguably more important for balancing a boat anyways.

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TomW1
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Re: Weighing a large boat

Post by TomW1 »

fallguy don't you have a truck scale near you? Get it on your trailer and take it to it. Whether it be a quarry or a highway or something else. I am not sure you are going to get an accurate weight with what you are using. Tom
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