Weighing a dinghy on bathroom scales

[Chiara’s slave]

If you sail the boat to Cowes, we can weigh it for you with the XOD class load cell. Slightly more seriously, dinghy clubs I have been a member of have had weighing apparatus. Usually a steel h section ‘football goal’ some slings, shackles and a load cell. A few blokes can lift any dinghy, a trolley jack lifts almost any dayboat. Dunno why more clubs don’t do it. Lift the boat, put the slings round it, let it hang.

 

[dancrane]

That's a kind offer. I'd like to get over to Cowes this year if it isn't blowing hard on one of the desperately rare days when I'm not working, so maybe I'll call in.

 

[Mistroma]

We wanted to weigh a large hatch cover. We found a fulcrum, a beam, and a suitable (20kg in this case) weight. Hung the cover off one end, the weight off the other, shifted the weight until we had equilibrium, did the measurements and applied the ratios. The weight can be a container for water which is added and is easily quantified. Or you can use a person of known weight.

Beaten to it by #18 & #29. I thought pretty much the same, pretty easy if there's something suitable to hang it from. Easy enough if there are boats on cradles in a club yard if owners don't mind and there's enough room. A beam between two boats would be quick to set up with padding to the decks. I actually used a similar approach to lifting my old Bukh DV20 out as it didn't have access above.

I knew the approx. weight and had a couple of 56lb weights. Simple enough to work out length of beam to reach in over the engine and min. length on other side to balance the engine with my weights. Same principle but I wanted to work out the beam length from known weight instead of working out the weights.

 

[Thistle]

Any dinghy measurer should have access to a set of scales - and know how to use them. Get in touch with classes similar in weight to the Osprey with a decent number of boats local to you and they should be able to help ... subject to a suitable donation to the measurer's (or measurers') beer fund.

 

[Malabarista]

What bin will you be getting in to?

Well being as how as i was fully ‘laden’ i will let you work it out ?

 

[Daydream believer]

Well being as how as i was fully ‘laden’ i will let you work it out ?

Looking for a burial at sea are we?

 

[Malabarista]

Looking for a burial at sea are we?

??

 

[Malabarista]

just to make things clear …This is my wifes idea and NOT mine. A further caveat she is an architect and not an engineer. She reckons that “reverse displacement “ would work. So basically fill it with a known quantity of water and work out the weight of the water contained within. I scoffed at the idea but I’m not intelligent enough to explain why it wouldn’t work. Or maybe it will. Come on guys I need help ?

 

[Daydream believer]

just to make things clear …This is my wifes idea and NOT mine. A further caveat she is an architect and not an engineer. She reckons that “reverse displacement “ would work. So basically fill it with a known quantity of water and work out the weight of the water contained within. I scoffed at the idea but I’m not intelligent enough to explain why it wouldn’t work. Or maybe it will. Come on guys I need help ?

First of all the water will not displace the volume taken by the bulkheads & the hull itself. So the water will not represent the full volume of the vessel. Plus there will be pockets of air which unless the boat is tipped upside down will not be filled. But then all the water will run out anyway. Then there is the upward curve of the deck. The aft section is lower. So water level will not reach the top.
Typical of an architect she never thinks of the FULL amount always finding reason to add to the final fee.
Better if she sticks to designing recesses at the base of kitchen units-- That way she can get in closer to do the dishes.

 

[dancrane]

My interest in the weight of the boat wasn't a need, only a whim, so I wasn't going to take the boat anywhere or make requests or purchases to satisfy my curiosity. I have bathroom scales so I thought that would be easiest, unless weighing three points separately is so flawed in terms of accuracy that it wouldn't be worth trying.

Anyway, today was fine so I had a try.

I was glad I had used paving slabs to prevent the wheels sinking in the mud over the years, because however bad or good the one-wheel-at-a-time weighing method may be, I'm sure without a firm surface beneath, the scales couldn't measure accurately.

I didn't remove the cover or any of the fittings, and the trolley is heavy - probably over 15KG.

Nevertheless, the results were a real shock, especially as the centreboard, rudder and tiller, (all heavy parts) are in my garage.

Here it is: bow, starboard wheel, then port wheel, in kilos:

I think that totals 214.3KG.
Less 15KG for the trolley, but adding perhaps 7KG for the absent rudder and centreboard.

Appalling to reflect that all the times I hauled the boat up the slipway, I was pulling three times my own weight. I may have made light of it ten years ago and since, but I was that much dafter and I doubt I've grown stronger, nor am I likely to in the next ten.

Food for thought.

 

[Malabarista]

First of all the water will not displace the volume taken by the bulkheads & the hull itself. So the water will not represent the full volume of the vessel. Plus there will be pockets of air which unless the boat is tipped upside down will not be filled. But then all the water will run out anyway. Then there is the upward curve of the deck. The aft section is lower. So water level will not reach the top.
Typical of an architect she never thinks of the FULL amount always finding reason to add to the final fee.
Better if she sticks to designing recesses at the base of kitchen units-- That way she can get in closer to do the dishes.

Oh boy…i said i needed help not another ground for divorce ?. The first bit i get but the second bit may earn you a visit from a violent Seth Efrican

 

[Daydream believer]

My interest in the weight of the boat wasn't a need, only a whim, so I wasn't going to take the boat anywhere or make requests or purchases to satisfy my curiosity. I have bathroom scales so I thought that would be easiest, unless weighing three points separately is so flawed in terms of accuracy that it wouldn't be worth trying.

Anyway, today was fine so I had a try.

I was glad I had used paving slabs to prevent the wheels sinking in the mud over the years, because however bad or good the one-wheel-at-a-time weighing method may be, I'm sure without a firm surface beneath, the scales couldn't measure accurately.

I didn't remove the cover or any of the fittings, and the trolley is heavy - probably over 15KG.

Nevertheless, the results were a real shock, especially as the centreboard, rudder and tiller, (all heavy parts) are in my garage.

Here it is: bow, starboard wheel, then port wheel, in kilos:

I think that totals 214.3KG.
Less 15KG for the trolley, but adding perhaps 7KG for the absent rudder and centreboard.

Appalling to reflect that all the times I hauled the boat up the slipway, I was pulling three times my own weight. I may have made light of it ten years ago and since, but I was that much dafter and I doubt I've grown stronger, nor am I likely to in the next ten.

Food for thought.

Isn't the class weight circa 140Kg?

 

[dancrane]

Slightly under 140.

P'raps I should buy a new example, kept nicely down to weight. It'd feel like a Laser, to me. ?

 

[Chiara’s slave]

You’ll find only a modern one will be down to weight.

 

[dunedin]

Slightly under 140.

P'raps I should buy a new example, kept nicely down to weight. It'd feel like a Laser, to me. ?

Including centreboard but no rig presumably

 

[dancrane]

That's a good point which I'd never considered.
The 2019 Osprey class rules (which I've never looked at before) read:

"The weight of the hull shall be taken in dry condition excluding spars, sails, rudder, rudder stock, tiller and all portable equipment as listed in C.5." C.5 includes gadgets for navigation, bailers and sponges, towing/mooring lines, paddles, etc.

I think my mast alone weighs ten or twelve kilos. The boom isn't featherweight either. I daresay if I took off even just the items that the class minimum weight excludes, my total would drop by over 20KG.

I'm not suggesting mine isn't terribly overweight, but it makes even new examples sound a lot heavier than I'd supposed.

I wonder what those ancient sailing-school Wayfarers weigh, the ones that were overbuilt to survive arduous lives. I think the traditional racing weight under Wayfarer class rules, was 169kg, but the present builder Hartley, quotes 183kg for handling purposes.

I'm thinking of downsizing. Wouldn't be clever to wait for an injury.

 

[Chiara’s slave]

Ospreys are big boats. I used to run a 505, that was almost svelte alongside an Osprey.

 

[dancrane]

I've always felt its enormous presence to be one of the things I liked most about the Osprey, although it's a fact that I can't singlehand upwind in more than a force 3 without reefing.

If I change boats I'm not sure it'd be wise to look for a newer, lighter example of the same thing, which age and idleness will surely make me reluctant to launch and bring ashore.

I kind of like the K1 ballasted dinghy. The owner of one at my club let me haul it up for him lately, and it felt like a doddle after the Osprey. The K1 (even with a 60kg ballast keel) is said to be 140kg, so more or less what the Osprey ought to be. ?

The Tasar always looked good to me, too. Half the Osprey's design weight, and a third the weight of mine.

Why is the prospect of buying, so much more enjoyable than actually owning?

 

[Chiara’s slave]

Personally Ienjoy the owning at least as much. I’m thinking about a dinghy too. Mine has some different criteria. I have to pull it on it’s trolley about 100m by a slightly less than straight route to the beach, and launch and recover though surf, though there is a slipway. The mast must also pass under some overhead power lines across the road. Mostly single handed but occasionally 2 up. Don’t mind it tricky, I can sail a foiling Moth reasonably. But what to buy? If I were you I might look at an RS400.

 

[dancrane]

Interesting recommendation, thank you. I know a few RS400s that sail where I do. They're certainly light for on-shore handling, but whenever I've seen them sailing in a breeze I was impressed, but daunted. Really not a singlehander, was my impression - do you know differently?

What d'you weigh, if I may ask? I gained a spare tyre over Christmas, but I'm meant to be ten stone, barely 65kg. You may picture the trials I have been through, singlehanding the 200kg Osprey on breezy days, and hauling her out, afterwards. ? But I'll be interested to know what dinghy you select. ?