Inqism-01: 3 Guesses. First 2 don't count.

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Jimmyt
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Re: 3 Guesses. First 2 don't count.

Post by Jimmyt »

That looks good!
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Re: 3 Guesses. First 2 don't count.

Post by Inquisitor »

finding41 wrote: Sun Oct 25, 2020 9:57 am Nice design. I may have to copy that for my 26D. It is pretty heavy coming up.
The biggest problem I have when raising the DB is the safety rope getting caught between the DB and the trunk. I'm not sure there is a quick fix for that.
One thing I've noticed with my DB is that it changes position when ever I tack. One tack it's / in the trunk, the other tack it's \.
I wonder if that takes away from the pointing ability. I think I could design a set of rollers that would go inside the DB to keep it strait and still allow it to be raised and lowered. (That seems like a lot of work...)

Marty
Safety Line
On the M, the D/B sinks and people who intentionally weight it more... it sinks faster. I'm going the other way. I plan to seal the D/B and add just enough concrete so that it floats about an inch out of the water (obviously the elliptical bottom will point down). That way, when I add a safety line, its just to keep from sailing off without the board. I can turn around and pick up the bobbing board. I'm also considering using a smaller line. I have some of the Spectra 300 lb fishing line. Its only 1mm in diameter. It can flop around all day long in the D/B case and not catch anything.

Flopping D/B
Actually, I've been scratching my head on that one for a future project. Take this with a grain of salt... I'm not a fluid dynamicist.

Its my contention that the crabbing any sailboat has to do to create a positive angle of attack (AOA) on the D/B to generate lift to counter the leeway creates a lot of drag. Check your wake... it doesn't go strait back. For our boats, I can stall the D/B which according to theory is around AOA >= 10°. Thus at high load (trying to go faster) the boat is crabbing near this 10°. Now if you add a flap to the daggerboard so it creates lift without an AOA the hull will point true and has less drag. Another way without a flap... if the D/B rotates so it creates an AOA, you also reduce the drag on the hull.

Point being (that you've observed) if the D/B is pivoting about the trailing edge (a good guess if its wedged in the V) and flops to one side or another of the D/B case, then you're getting a FREE AOA that your boat hull doesn't have to rotate to achieve. IOWs the large (one might say sloppy) manufacturing tolerances with Macs actually works to your advantage. On mine it rotates +/- 1.5°. Not much, but its free. A future project was going to try to push that number up so the daggerboard pivots closer to +/- 5° or maybe even +/- 10° number. At some point, I'll try to calculate an optimum AOA for "spirited" sailing.

VBR.
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Re: 3 Guesses. First 2 don't count.

Post by finding41 »

" Now if you add a flap to the daggerboard so it creates lift without an AOA the hull will point true and has less drag. Another way without a flap... if the D/B rotates so it creates an AOA, you also reduce the drag on the hull." VRB

A flap? so the DB changes shape to more of a airplane wing for better lift? I've thought of this before when developing my "Whale Fin Rudder" (The whale fin was all about the Tubercles and not so much about the one sided lift.)
For both ideas the DB would have to be perfectly inline with the center of the hull.
You have me thinking now.
Thanks
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Fluid Dynamics 101

Post by Inquisitor »

This may make some people want to puke, but its the kind of stuff I like playing with for fun. Yes... I'm not right. :)

This is the foil shape of the D/B on the M. At least... it seems "kind of close" if you cross your eyes and use your thumb for measuring. :P
Image

This is how the foil should behave in water at a range of speeds under 8 knots. The main take-away (left graph) is the curve bends over about the 11th point (11 degrees). This is the AOA when it stalls. The Cl on the left size shows how much lift the D/B is generating. It peaks just under 0.7. The drag (on the X axis) peaks goes to crap after stalling, but is around 0.06 at stall.
Image

If you add a flap (that'll bend both ways) and deflect it 15 degrees...
Image

And here is the behavior with the flap. The very first point (AOA = 0 degrees) generates about the same amount of lift at a slightly lower drag of 0.050. But the main thing is the hull would also be at AOA = 0 and thus making the minimum amount of drag.
Image

This is all academic... cause I couldn't come up with a bullet proof way to control the flap. Anything involving pulling cords will just pull up the whole D/B. Anything else... gets real complicated, real fast.
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Re: 3 Guesses. First 2 don't count.

Post by Jimmyt »

Maybe not. Bell crank at the deck with a torque rod in a sleeve allowing the up and down without moving the bell crank...
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Re: 3 Guesses. First 2 don't count.

Post by finding41 »

That would work Jimmy.
I've been working on a design loosely based on the 0012 shape. (Loosely because I'm shaping this by hand!)
I'm almost ready for glass. Just have to make the pivot hole and the raising / lowering holes. I want to make them larger than needed so I can bolt through without any wood being exposed to water.
I have another rudder now that is the same shape except it doesn't have Tubercles and has a 3/16 flat trailing edge. It handles great! I can turn on a dime but... I get this crazy vibrating wiggle that happens in waves. (Not water waves. Time waves.) Drives me nuts! I have to wear anti vibration gloves if I'm sailing for more than an hour.
Here are some shots of the whale fin rudder.
Marty

Image

Image

Image
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Re: 3 Guesses. First 2 don't count.

Post by Inquisitor »

Damn! That's a work of art. I couldn't put that on the boat. I'd put a clear coat on it, mount to a pedestal and display it in my living room.

You know... if someone could CAD that up once, you could 3D print them.
Do you have any links on the theoretical background of that shape? I'd be interested in reading it.

VBR
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Re: 3 Guesses. First 2 don't count.

Post by Inquisitor »

Jimmyt wrote: Sun Oct 25, 2020 4:19 pm Maybe not. Bell crank at the deck with a torque rod in a sleeve allowing the up and down without moving the bell crank...
Well... If torque rod was rigidly mounted to the rudder it would come up and fowl the boom/sail. So... it would have to slide in/out of the rudder. In that case the sliding joint is at the bottom getting coated with water (salt water) sea growth, etc. Any joints I had to contend only had to deal with a vacuum and usually worked only once. All that mechanism sliding, rotating in a relative cesspool is out of my comfort zone.

Hmmm... Damn it. Just popped into my head. I hate it when a challenge is thrown down. Maybe a square SS tube and a 3D printed Nylon sliding "nut" with a PVC pipe to receive the SS tube inside the rudder. Might work. I'll add it to the list... :D

Inquisitor's Project List
1- Fix Motor
2- Clean Boat
3- Make elliptical D/B (this project)
4- Extend V-berth
5- Move Head
6- Re-do water pressure system
7- Re-do Saloon / Galley project
8- Radar, StarLink and other antennas, solar panels, main sheet traveler arch.
9- Extended boom 5+' to aft arch (get all the damn lines out of the cockpit)
10- New, extended main sail
11- Rock'n Bowsprit like Highlander's 8)
12- Segregate/move helm
13- Hull extension
14- Tubercles D/B with articulating flap :D

Oh and lots of sailing to places unknown (by me). These are winter only projects... I might get to 14 before the next life. :(

VBR
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Re: 3 Guesses. First 2 don't count.

Post by Jimmyt »

Inquisitor wrote: Mon Oct 26, 2020 4:58 am
Well... If torque rod was rigidly mounted to the rudder it would come up and fowl the boom/sail. So... it would have to slide in/out of the rudder. In that case the sliding joint is at the bottom getting coated with water (salt water) sea growth, etc. Any joints I had to contend only had to deal with a vacuum and usually worked only once. All that mechanism sliding, rotating in a relative cesspool is out of my comfort zone.

Hmmm... Damn it. Just popped into my head. I hate it when a challenge is thrown down. Maybe a square SS tube and a 3D printed Nylon sliding "nut" with a PVC pipe to receive the SS tube inside the rudder. Might work. I'll add it to the list... :D


Oh and lots of sailing to places unknown (by me). These are winter only projects... I might get to 14 before the next life. :(

VBR
Not a challenge, my friend. Just a reminder that very few things are impossible if you've got enough game. You seem to have plenty.

It would be a pretty significant prototype fab project. Your point regarding fouling concerns of the mechanism is spot on, and would drive design decisions.

I'm not sure how much performance gain to expect from it, but I would want it to be easily noticeable. The fab project and having one more thing to tune during sailing are significant cons.

Try to save time for sailing between projects - as your climate allows. I've had my boat pretty much dry since the start of the galley project. My buddy with the Potter 19 can't go sailing with anyone because he keeps his grandson regularly and doesn't want to risk exposure. Plus, we've been in the hurricane cone about half of the summer (and again today). I haven't been to the ramp to see if it's damaged yet. Just as well, I guess. It will likely have storm surge again this week. All that to say, I've had a long dry spell and I'm ready to be on the water again. Boat projects are fun, but boating is more fun.

Can't wait to see how your new, improved dagger comes out. Great project!
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Re: 3 Guesses. First 2 don't count.

Post by Jimmyt »

finding41 wrote: Sun Oct 25, 2020 7:22 pm That would work Jimmy.
I've been working on a design loosely based on the 0012 shape. (Loosely because I'm shaping this by hand!)
I'm almost ready for glass. Just have to make the pivot hole and the raising / lowering holes. I want to make them larger than needed so I can bolt through without any wood being exposed to water.
I have another rudder now that is the same shape except it doesn't have Tubercles and has a 3/16 flat trailing edge. It handles great! I can turn on a dime but... I get this crazy vibrating wiggle that happens in waves. (Not water waves. Time waves.) Drives me nuts! I have to wear anti vibration gloves if I'm sailing for more than an hour.
Here are some shots of the whale fin rudder.
Marty
Marty,
I'm with Inquisitor. That thing is a work of art! Anxious to see how it performs, but agree that it would look great hanging on my living room wall!

On your flat trailing edge rudder, you could add bondo and bring it to a sharper point as an experiment. It would probably peel off without too much work if you didn't over prep it, so it might be a way to do a quick test.
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Re: 3 Guesses. First 2 don't count.

Post by Jimmyt »

Image
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Re: 3 Guesses. First 2 don't count.

Post by finding41 »

Thanks guys! That degree in Fine Art is really working out well for me. LOL! (I did study Fine Art in College and University.)
I plan to glass over this rudder and test it next year on the Mac26D. Im not sure I can keep a point on the end of this one as I trailer this boat a lot. I know it will get damaged when I throw it in the V berth with the anchor, fuel cans and boom. I hope to round it at about 1/8".
The other rudder with no Tubercals I hope to sand down and fair the trailing edge the same way. (It's wrapped in a heavy weave glass. That could be the cause of the vibrations. But I doubt it.) The pattern of the weave is present on the outside. I did paint one coat of gelcoat on it to lessen the bumps / divots but there still there. I was thinking of how a golf ball travels strait through the air. The science should transfer to the rudder... Right?
Ive never seen a study of the vibration that a golf ball though...
As for Whale Fin Rudders and Tubercals. If you Google you will find some stuff I've written on another forum and some other peoples testing on fans and wind turbines. You can also look into the air disrupt strip (Not sure what it's called.) on the top of airplane wings.
Beware the Rabbit in that hole!
Marty
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Re: 3 Guesses. First 2 don't count.

Post by Inquisitor »

Jimmyt wrote: Mon Oct 26, 2020 6:17 am (a) Not a challenge, my friend.

(b) I'm not sure how much performance gain to expect from it...

(c) ... we've been in the hurricane cone about half of the summer (and again today). I haven't been to the ramp to see if it's damaged yet.
(a) Didn't take it anything but a normal Blue Sky Design Session. I miss the collaborative "positive" attitude design sessions of my career.
(b) Twin Sons of Different Mothers - I'm right there with you. I don't need another single-handed thing to pull. Besides, hull speed is a <expletive>! You can do and/or spend a bunch on carbon this, carbon that, Kevlar 3D sails, etc... and what... buy a 1/2 knot?!
(c) I noted your location early in the interactions... but didn't really rationalize the living in the hurricane's sites. I feel it for you. :|


But... I'd trade my six hours to the coast and any real sailing for your... what 10 minute commute and hurricanes in a heart beat... as long as that workshop came with it. :wink:
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Re: 3 Guesses. First 2 don't count.

Post by Inquisitor »

finding41 wrote: Mon Oct 26, 2020 11:28 am Thanks guys! That degree in Fine Art is really working out well for me. LOL!

The science should transfer to the rudder... Right?
Creativity comes in many forms and many backgrounds. :)

I don't want to squelch your enthusiasm... but I also don't want you to go down a path of that's not valid. A dibit'd (is that a word :o ) golf ball doesn't fly further because of less drag... it because it spins and the spinning cause a Bernoulli affect similar to a wing and thus creates lift... that causes it to fly further. Now... "mainly using spoons..." we can make the rudder spin. :D

I've seen but never read about shark skin and Tubercals and theory behind them. Like Jimmyt said... you can throw a lot of great idea at the problem and they won't bear fruit simply because of wave drag at Hull Speed. It wasn't because they're bad ideas... just...

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CAD and Raw Prints Complete

Post by Inquisitor »

Just finished the final printing.

Image 1 - All ABS daggerboard foil sections. I used more plastic than I initially thought. I printed them more robust than they really have to be as simple forms for the fiberglass. Large, thin ABS prints tend to oil can and warp easily.
Image 2 - The aft/top portion of the daggerboard where the lifting line mounts. Include custom Nylon sheave and bolt (untightened) for 2:1 lifting.

Current Outlay
20 hours of CAD work - That is a one time thing. I'll publish the models on Thingiverse.com and anyone wanting to give it a go can make one.
84 hours of 3D Printer time. But that's mostly un-supervised. So I don't really count that as effort or cost.

2.8 Kg - ABS 3D Print Filament - $28.00
12 g - Nylon 3D Print Filament - $0.50
(1) 1/4" x 5/16" x 3/4" Bronze Bushing - $2.80
(1) 1/4" x 2.5" SS Course thread bolt - $0.74
(1) 1/4" SS Flat Washer - $0.13
Total $31.36

Image

Image
Last edited by Inquisitor on Tue Oct 27, 2020 2:32 am, edited 2 times in total.
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