Physics simulation of a weighted daggerboard mast raiser

[mastreb]

I'm testing some educational physics simulation software for my Son's class, and, needing something to simulate, I decided to do a weighted daggerboard setup in a connected system with a mast.

Pivoting on a 5' tabernacle, the end of the mast is directly connected via a chain to the top of a weighted dagger-board. Everything on the boat is made of "wood" excepting the dagger-board, which is made of "steel" for physical properties (which is why it doesn't "float" the way the rest of the boat does).

Dropping the dagger-board causes the mast to pop-up, and pulling down the mast (as by using the halyard) creates a lever that raises the weighted dagger-board.

http://www.flickr.com/photos/68241682@N07/6379697869/

In a real system, you'd pin the daggerboard in the up position at the cabin deck, relieving tension on the system and making it safe. Once in the water, you'd pull the pin, dropping the daggerboard and raising the mast. Pinning the mast in place will subsequently allow you to raise the daggerboard if you so desire, although the pulley mechanism to do that is an exercise left to the reader.

Now imagine pivoting the tabernacle at the location of the current mast-foot so that it folds down forward, taking the mast forward with it for the trailering position. This would eliminate the disconnect and reconnect at the bow-pulpit and would ensure that the mast movement is controlled at all times. The tabernacle would be held in place by SS baby stays at the locations of the for and aft chain-plates, which would be shackled when the tabernacle is put in the upright position.

Just a thought.

[Divecoz]

Couple questions... Just For Fun
Isn't the "Dagger Board" too , short in the trunk with no room at the top in the raised position, for more length..... to be of use, on your model?
How do you lift the D.B. if the mast is in use?
How do you release tension on the pin to release the D.B.?

[mastreb]

Couple questions... Just For Fun
Isn't the "Dagger Board" too , short in the trunk with no room at the top in the raised position, for more length..... to be of use, on your model?

Yes, because I just eyeballed these sizes. The system could be sized correctly to work. Essentially the Tabernacle pivot needs to be exactly the length of the dagger-board line above the deck, and the dagger-board line needs to be the exact length that the dagger-board should drop from cabin-top to the bottom of the dagger-board trunk.

How do you lift the D.B. if the mast is in use?

The mast would be pinned in place, and a separate DB raising line would have to be used from either a pulley with enough purchase to lift the weight or a 12v DC Gearmotor. Yep, not fantastic, but the same situation as with a weighted DB today.

How do you release tension on the pin to release the D.B.?

The right answer is not what this simulation shows. The correct way to go would be to keep the system in balance such that when the mast is down, the dagger-board does not weigh enough to pull it up. The crew would have to push the mast up to at least the half-way point, at which point the levered weight of the mast is overcome and the dagger-board can now pull it up the rest of the way to vertical. This is both simpler, less unbalanced, involves much lower forces, and is inherently safe. But not what this simulation shows.

Given that you've done this, the pin is trivial to remove because the mast is pulling the DB up by a few pounds, not down. This also means that you have to use the halyard to pull the mast all the way down, and that the system is proof against mast falls in the event of a fore-stay failure, which would be a great additional safety feature.

I'll try to get the simulator showing this mode by reducing the weight of the dagger-board.

This would be done by precisely controlling the weight of the dagger-board, which would need to vary any time you added hardware to the mast. That seems rather unlikely to be realistic.

By the way, I really like this physics simulator. Google Algodoo if you're interested in having a look--it's $20 or so to purchase and works really well for 2D simulations. Very simple to use and it comes with great in-app tutorials.

Thanks for the great questions!

[pokerrick1]

I was JUST about to ask those same questions

Rick

[arknoah]

Kinda cool....

[Divecoz]

$20 !!!!! Go Figure...I would not do well on The Price Is Right.. Guessing The cost of outboards I'm always under.. Living in the past I guess and for tech stuff I am always .........high.
Remember how much those first crude Cad Programs were? hahaha I received a Watch as a gift from a Contractor.. Nice case and band. and it was one of the first Electronic Watches ... If you pushed..... The Button.. It lite up and told you the time in a digital display..It was 1975 and cost about $100.. 10 years later they were giving the full plastic versions away, For free at a local gas station for a fill up haha..
Very Cool Mastreb Very cool.. $20.....

[Mic]

I'm testing some educational physics simulation software for my Son's class, and, needing something to simulate, I decided to do a weighted daggerboard setup in a connected system with a mast.

I tried to post a drawing being, new to this forum I don't know how to.

Are you doing your son's home work ????

Being a retired bush mechanic this is my suggestion, san drawing.

Anchor a line on the deck at the side of the trunk. Pass the line down to the DB and through a pulley on top of the DB. bring the line back on deck and through a turning pully, go to the fwd stay anchor through another pully then up to the mast fwd stay and fastetn it. When raising the mast the DB will not move much in the last 40 degrees. Need a computer and nerd to work out the math ratios. Or on paper with string and pins.
Have fun
Bush Mic

[Mic]

PS if there is too much mast movement of the mast put a block and tackle in the system. The hoisting line cannot be lowererd below the fore stay and sail to reduce the traveling distance of the mast. A block and tackle will also give more leverage on a heavy DB

Bush mech Mic

[mastreb]

So I'm not going to bother doing another video, but I balanced the weight of the dagger-board with the mast, and I kind of like the mechanics. There are two forces in opposition: The weight of the dagger-board pulling up the mast, and the increasing friction and buoyancy of the daggerboard as it goes into the water. This means that the system is actually in equilibrium at about a 70 degree angle, and not at either the top or bottom. What makes that nice is that it doesn't ever "bang" or have culminating forces on either end-rather it tends towards the middle, and you add a little pushing force to get it all the way up or down. Very, very safe. The whole assembly is essentially a catapult, so by reducing the weight to be in balance, the entire assembly moves... very... slowly...

It does not go all the way upright in my balanced simulation because I haven't correctly modeled friction (of the dagger-board against the trunk) and friction begins to dominate when the mast is coming up. When you release the dagger-board pin, the mast slowly rises to about the 11 O'clock position and stops. You'd have to push it to vertical and pin the mast foot. This effect may be exaggerated in the real world because I'm also not modeling the buoyancy of the dagger-board, and as it slides into the water it will have decreasing pull on the mast bottom.

To put the mast down, you'd have a few pounds of pull on the halyard after unpinning the mast foot. The dagger-board comes up and you get increasing resistance as you pull the mast down. It will likely be easier to pull the dagger-board up using the secondary hoist line, letting the mast drop as it comes down. The lift on that hoist line will be easy because the mast is actually doing most of the work to lift the dagger-board.

Once the mast is down and the dagger-board is up, pinning the dagger-board up ensures that the whole system is free of tension and the mast will stay down. At this point, the A frame tabernacle can be unshackled from its aft stays and the tabernacle and mast can fold forward, taking the mast most of the way to the pulpit position controlled by the A-frame tabernacle for final trailering position.

I like all the inherent safety in this system. I might actually consider doing this. I'd make the A-frame tabernacle exactly the way the spreaders are connected to the mast (I have an M and still want the mast rotation) and use aluminum tubing to go down to the side shrouds, ending in a custom machined cap that can bolt to the chain plates for the side stays. I'd use two sets of baby stays to hold the aluminum tubes in place connecting to the fore and aft chain plates. This would make this a very simple mod, and most importantly completely removable if it turns out that something is seriously amiss.

I'm going to keep studying it.

And Dive, My 3D Solid CAD modeller is $7000/workstation. So yeah, I wouldn't go on Software Price is Right either

[mastreb]

PS if there is too much mast movement of the mast put a block and tackle in the system. The hoisting line cannot be lowererd below the fore stay and sail to reduce the traveling distance of the mast. A block and tackle will also give more leverage on a heavy DB

Bush mech Mic

Hey Mic--Yep, I think you're spot on about the pulleys, and a B&T can be used to compensate for the fact that the lengths and forces may be imperfectly matched.

Being a math nerd, I'll figure it out. And no, I'm not doing his homework, just helping his teacher come up with some simple physics experiments for the whole class.

[Mic]

Hi Mastreb
Glad to read you are making them think. Don't give them too many clues.

Its a stimulating idea. When they made me a mechanic they forgot to do the labotomy much to a few bosses distain.

Another project, when you have structured this one. A spinnacker raising cone shaped drogue in the water astern. Line going from the drogue to the crows foot then down to the spinnacker head.

Just a thought
Mic

[mastreb]

Hi Mastreb
Glad to read you are making them think. Don't give them too many clues.

Its a stimulating idea. When they made me a mechanic they forgot to do the labotomy much to a few bosses distain.

Another project, when you have structured this one. A spinnacker raising cone shaped drogue in the water astern. Line going from the drogue to the crows foot then down to the spinnacker head.

Just a thought
Mic

So... What's a crow's foot? Haven't found a reasonable definition in Google.

[K9Kampers]

How to Tie a Crow's Foot

Not to be confused with a Camel Toe

[Mic]

So... What's a crow's foot? Haven't found a reasonable definition in Google.

It used to be crows nest then became chicken foot or was it turkey or crow's. Now a camels foot.

All this for the "mast head fitting" with pulleys in and on it plus in this area bird @#$% and bent wind vanes.

[mastreb]

Ah--Crow's nest I know. I don't have any good way to determine how much pulling force a drogue will provide or how much a spinnaker requires to haul up, but my guess is that the drogue isn't going to be enough without a force multiplier, and then you're talking about a really long line to be storing aboard for that function. Is setting a spinnaker that difficult? (I've never done it, and I'm almost certain I'd go to a drifter before a spinnaker as a second headsail after my Genoa 150).