Q re Measuring windlass (and other!) stresses

[vas]

hello all,

following a discussion in PBO re data monitoring and playing with small computery things (arduinos, raspberries, et al) Rogershaw suggested using load cells to measure the weight of the gas cylinder on board. (http://www.ybw.com/forums/showthread.php?530008-Wifi-boat-data-monitor-what-s-left-to-measure!/page2)

Now this summer I managed to run out of gas twice, once I'd forgotten to get the second cylinder onboard at the start of the season and ended up walking a few miles looking for a refill (which I didn't find in Koukounaries...) The other was easier, I had a spare onboard but delayed dinner a couple of hours as none noticed the oven wasn't doing it's thing

Anyway, a 10 or 20kg load cell together with it's dedicated tiny board that does the 24bit conversion is accurate down to silly values (not needed) but costs under 5euro. So, plan is to get a couple (for good measure) and set it up in a way that the cylinder with the regulator are resting on a base which is held (actually hung) from this sensor, effectively weighing the cylinder (case+content) as well as the regulator (ok and a bit of the flexhose going down) Reasonably easy to do in my setup with cylinder being in an open custom box on the f/b by the helm. Values after conversion can go on NMEA2000 as oil level and a warning setup when goes down to 10 or 5%. Further my 3 gauge screen setup on the 4inch Garmin GMIs will be configured to 4 so that I have diesel, water, black tank and gas levels shown.

load cells look like this:
https://www.ebay.co.uk/itm/Diy-Load...Hx711-Weighing-Sensor-Ad-Mod-ZSH/293302984978

Thing is that since I'll get two load cells, I might as well get a few more
Problem is I've no other things to measure
yeah I know it's like when you hold a hammer everything looks like a nail case.

So, thought that it would be nice to see what load the windlass is getting when anchored in a blow or with a tight stern line and a bit of a side blow, or whatever.
I have a horizontal windlass Lofrans Tigress best drawings with dims I've found is this:

Thought that I can easily place the load cell in the two rear bolts holding the windlass down under deck (not much point doing the fwd two as the only work in shear and not tension) and see what type of tension the thing places on the deck.
Not planning to compromise the whole setup by slacking the fwd bolts (or even removing them!) so that the rears do all the work with no friction/shearing forces placed on the other two, but was just looking for the experts' views on this and what sort of loads I'd expect to get.
I'll obviously pre-stress the load cells to some sort of value (undetermined, say 200-300N ?) and then I need some "space" for measuring.

So effectively the question is what cells should I get 50kg, 100kg, (or 200kg, 500kg which I very much doubt!) for the described setup on a 12ton 43ft f/b boat (you can then measure the double as there's going to be two of them!)

All safety disclaimers yada yada. Please don't really need preaching that this is dangerous, the windlass is going to detach and end up in the water - the full washers/double nuts will be there just 10mm slack on the bolt so that the cell gets its bending and measuring space.
BTW, also don't need a lecture on releasing stresses from the windlass, it's already 40yo and during the rebuilt all were perfect inside, just had to replace the keys and seals.

cheers

V.

 

[MapisM]

delayed dinner a couple of hours as none noticed the oven wasn't doing it's thing

Urgh, gas oven?
As you might remember, I'm a fan of gas onboard, along the lines that food quality ranks higher than safety in my personal priorities list.
But in your boots, I'd rather replace the oven with an electric one, leaving gas dedicated to the cooktop alone.
The scenario which you mention is in fact one case where gas ovens are known to be very dangerous.
What can happen when the bottle is nearly empty is a momentary lack of gas, very short but long enough to turn the flame off.
Then any residual gas still left in the bottle keeps flowing, filling the oven, with potentially nasty consequences.

Back on topic, gut feeling tells me that the load on the two rear bolts could be higher than 100Kg.
I'm saying this because I've seen the deck of my previous boat slightly flexing, when anchored in a blow.
That was actually many years ago, because that gave me another reason to use snubber lines attached to the cleats, so I only experienced that once.
Anyhow, I never saw that very same deck flexing, also with 2 or 3 people standing in the same area...
Isn't there a way to attach the load cell to the chain? I'm not sure I would fiddle with the bolts.
Btw, if it works with the chain, it could be interesting also for mooring lines, as a sort of early warning for strong winds while the boat is docked.

 

[vas]

P.

I see what you mean, but not at all interested in running generator to cook and turns out that we do use the oven a lot!
Oven is fairly high up with a fancy "window" / windscreen opening next to it and a hatch above it. Bottle is just a tiny 3.5lt one, when it empties, it is empty fullstop, hope I wont get such issues. Further I *think* that it has this security thing, no flame stops gas but not too sure on that. So, looks like that by installing this system I'm going to improve safety on board at least

Re weight/forces, it's easy to get 200kg ones -minus pretension of say 20-30kg leaves 170 each or close to 350kg combined (which I find A LOT).
Should be enough for any snatch loads I'd guess. See what other opinions (if any) and go from there!

cheers

V.

 

[vas]

Isn't there a way to attach the load cell to the chain? I'm not sure I would fiddle with the bolts.
Btw, if it works with the chain, it could be interesting also for mooring lines, as a sort of early warning for strong winds while the boat is docked.

oops, missed that bit!

P, the device works by loading and flexing (where the hole(s) are) On flexing the two sort of plastered areas measure deflection and with the small board next to it that's translated to load.
Cannot think of a way doing it, other than devising a reasonably complex chain lock which doubles as a force load counter with the "lock" part sliding over the deck with the load cell mounted on the one side on the deck and the other side on the chainlock. That could be done relatively easily, not sure how long the load sensor is going to last on the deck (rather than under the deck!) though.

Interesting thought, will try and design something for this, give me some time to think and sketch!

cheers

V.

 

[rafiki_]

Vas, rather than tinkering with load cells, is there a way of converting current draw to load? I’m sure Lofrans would have a view on current to torque?

 

[MapisM]

Wouldn't that work (assuming it does) only while actually recovering the anchor?
I understood that Vas aim was to measure load while statically anchored in a blow...

 

[vas]

Wouldn't that work (assuming it does) only while actually recovering the anchor?
I understood that Vas aim was to measure load while statically anchored in a blow...

correct P.
Paul, main issue is when anchored and windlass not in operation.
Thinking about it again, a chainlock with integrated load cell(s) is v. appealing. More on it tomorrow if the weather plays ball and it's not pissing down

V.

 

[rafiki_]

correct P.
Paul, main issue is when anchored and windlass not in operation.
Thinking about it again, a chainlock with integrated load cell(s) is v. appealing. More on it tomorrow if the weather plays ball and it's not pissing down

V.

Yep a locking link with a strain gauge would be better than the mounts V.

 

[BruceK]

Your endless tinkering amazes me. One day they will launch your boat into space as a fully fledged space station!

 

[gordmac]

Are you planning on slackening the two rear bolts then anchoring in a blow? Brave! The two remaining bolts will take some of the load.

 

[vas]

Yep a locking link with a strain gauge would be better than the mounts V.

yes P, I'm working on this direction now, issue is what do I expect the forces to be, thinking of getting 2X300kg sensors, so capable of measuring up to 600 snatch on the chain. Very much doubt it's ever going to go near that, but really have no data to support my impression.

Your endless tinkering amazes me. One day they will launch your boat into space as a fully fledged space station!

I'm not planning to die out of sheer boredom (that's my excuse at least) and I don't like heights, so spacestation is out of the question
not keen on depths as well, so submarine is also out!

Are you planning on slackening the two rear bolts then anchoring in a blow? Brave! The two remaining bolts will take some of the load.

I'm not very brave and never anchor in a blow if I can afford it...
Idea scrapped, now working on a chain lock thing where the strain gauge will fit.
Other than the basic problem of keeping the sensors dry, I also have another issue to think or rather ask:

Do the chain locks self release when one hits the up button on the windlass or one must physically go there and undo something?
I'd rather they do, but then again I could live without it.

cheers

V.