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 Post subject: Re: Weighing a boat with bathroom scales
PostPosted: Tue Nov 01, 2016 5:43 pm 
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Joined: Thu Nov 19, 2009 11:53 pm
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Location: Cheshire, UK
Boat Name: Frances Ann
Hi Mike and Steamboating colleagues

Thank you so much for the suggestions so far. I have been contemplating Mike's proposal this afternoon (only found that folk had answered the post at lunch time) and wonder if I should add some information and some thoughts.

As the boat is in the garage which has a gravity leveled concrete floor we have a nice level platform on which to work. The trolley is a wooden frame that has three significant cross members in the centre of each is a nylon roller that is proud of the cross member by about 1/4" (Measurement mistake on my part during construction). The boat has two bilge keels that are arranged so that they are at the same level as the keel over part of their length. Thus if placed on a flat surface she would sit horizontally level which is what happens on the trolley. At the rear of the trolley is a V cradle on the cross member which ensures that the boat stays level if the bow is raised thus removing the support of the bilge keels. There is also a V cradle on a 'loose' cross member slotted into the trolley frame at the front. This is the 'string' bit of Belt, Braces and String.

If one had (say) some two inch square section steel tube, it would be possible to slide this under the boat but over the longitudinal frame of the trolley. Taken at a point as far as possible forward where the bilge keels and keel are in line crossways the risk of tipping would be zero. There would be no problem building up supports from my stock of 8 X 2 offcuts and other stuff and that could be topped by a bit of 2" angle iron to give a 'pivot' point from which to measure. As the boat is on one side of the garage the bar could project out into the body of the garage allowing plenty of space for the positioning of the scale. Given that the stern hangs a fair way off the trolley and is or can be lined up with the door into the garden, there is scope for doing a second weighing with the bar at that point. I would imagine that in all cases the boat would not be lifted by more than an inch or so. For additional safety it would be possible to use the engine hoist gantry that sits over the boat to support a safety sling.

Since I have CAD drawings of the cradle and the boat kicking around somewhere I will try bringing them together and show what I was thinking.

Regards

Pete


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 Post subject: Re: Weighing a boat with bathroom scales
PostPosted: Tue Nov 01, 2016 5:49 pm 
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Joined: Wed Dec 07, 2011 6:41 am
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Location: Lopez Island, Washington State, USA
Boat Name: S.L. Folly
I think you have it under control. Let us know what numbers you come up with. Hard data is in scarce supply.

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 Post subject: Re: Weighing a boat with bathroom scales
PostPosted: Thu Nov 03, 2016 9:41 pm 
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Joined: Thu Nov 19, 2009 11:53 pm
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Location: Cheshire, UK
Boat Name: Frances Ann
Hi Folks

Here are a couple of pictures. One gives a reasonable view of the stripped down boat on the cradle along with the engine hoist. The second is a cross section drawing on which I have done a few calcs.

Image

Image

For the calcs I started with the fact that the bathroom scale has a limit of 150kg so I would need to be working on a loading on it of between 75 and 120kg. Given the boat's position, the length of 'short leg' is about 2ft (622mm) as a given. If we then assume that the stripped boat at the forward end has a guessed weight of 1,000lbs (450kg) we can do some calcs. The 1,000lb figure is based on the 1,200 displacement calculation for Rose hulls and the knowledge that Frances Ann floated about on the planned waterline. It was then a case of putting some numbers into the formula. 2511mm was arrived at simply by 'stretching' that bit of the drawing until it was roughly 2,500mm. The weight on the scale at that point would be 111kg (246lbs) which is within the desired bounds. As the 1,000lb guestimate is probably too much, the scale should be working at a lower level with the real weighing. From the drawing it looks as if we ned a bar of about 3.25m in length. So all I have to do is see which friend happens to have any 2 X 2 steel tube in more than 3m length!

Regards

Pete


Last edited by PeteThePen1 on Fri Nov 04, 2016 11:27 am, edited 1 time in total.

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 Post subject: Re: Weighing a boat with bathroom scales
PostPosted: Thu Nov 03, 2016 10:43 pm 
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Joined: Wed Dec 07, 2011 6:41 am
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Don't forget to subtract the weight of your steel bar and anything else that is resting on the scale and not part of your boat.

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 Post subject: Re: Weighing a boat with bathroom scales
PostPosted: Fri Nov 04, 2016 12:17 am 
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Joined: Sat Aug 13, 2011 6:41 pm
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Boat Name: B.N.Y.S.
Pete, why not just 2488, a straight 4X?

I think I'd go with 50 x 100mm steel box , on edge, not 50 x 50mm. To keep the flex down.

I had a 4m length of 100 x 100mm, this time last year, but as you know it's now a fence post! :lol:

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 Post subject: Re: Weighing a boat with bathroom scales
PostPosted: Fri Nov 11, 2016 4:37 pm 
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Hi Peter
I think I have the sq tube you need, i go and measure it later

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