Scale Model Testing of Sailing Rigs, ...Outdoors

[sharpii2]

The easiest way would be to support the sails on a rolling platform on marbles or ballbearings in a big table with edges.

Then, attach pulleys at the most useful vectors ( from the stern, from windward etc ) and hang measured weights and see what they platforms pull.

I'd use rubber bands or springs instead of weights.

The amount of stretch for each can indicate the amount of load on them.

 

[rwatson]

Are rubber bands linear in stretching ?

ie The first 2 inches is easy , the last two inches is hard.

Also, the thickness of manufactured rubber bands is not very precise, so you would need to use weights to calibrate each new band used, and possibly re-calibrate every now and then.

 

[brian eiland]

If you are interested in comparing two rigs under identical conditions you could test them against each other by putting them on the same platform. For example, take a floating circular disk, put rig A on one side and rig B on the other and set them so that they are working against one another. The rotation and movement of the disk should give you some insight into how the rigs behave relative to one another.

That's an interesting idea,...I'll have to take that into consideration.

(waiting for my head to clear up after really bad case of the flu)

 

[brian eiland]

Comparison Testing Method

If you are interested in comparing two rigs under identical conditions you could test them against each other by putting them on the same platform. For example, take a floating circular disk, put rig A on one side and rig B on the other and set them so that they are working against one another. The rotation and movement of the disk should give you some insight into how the rigs behave relative to one another.

I'm liking your idea the more I think about it,.... now some thoughts.

I do realize that my rig is going to be the higher drag rig of the 2, if nothing more than its a 'ketch' with 3 sails rather than the sloop. So if I were to place the two experiments at an equal distance from the center of rotation of that big disc you suggested, its no doubt which one would win....not mine.

But what if I could make it so that the distance from the rotation center of the big plate could be varied,....then I might find a balance point that should be a good indicator as percentage of difference in the 2 by way of determining the difference in the radial arm of each rigs location on the plate :idea:

And that 'round plate' need not really be a big circular one, but rather could just be a 'rotating/swinging beam' connecting the 2 experiments.

In the end I might be able to show visually that my rig will point as high, at least, as the sloop (if it is commanded to do so). And I will have some good idea of the relative drag/propulsion forces between the two without having to physical measure those individually and then scale them up, all of which can suffer in mathematical scaling problems.

 

[brian eiland]

More Photos of the Model

I posted some more photos of that boat model I took to the Miami Show...

http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-46.html#post733497

http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-46.html#post733498

 

[brian eiland]

Interesting test rig set up displayed in this video...

https://www.youtube.com/watch?v=z91al4uBm9g

 

[markstrimaran]

Any one know a wind speed to sail area = horsepower formula. Say at a 90' too the wind. Thanks I don't have much time to research. As most of my free time is spent trying to get my boat in the water.

 

[brian eiland]

Mark has just posted a photo of his latest experiment over on this other subject thread:

A new picture. Aft mast 2 sails up.
Added mast head stays. The boat is 30% faster with both sails. Verse the single head sail.

Perhaps we could term this a larger outdoor 'model test'

 

[brian eiland]

Wind tunnel and CFD investigation of unconventional aftmast rigs

Not exactly an 'outdoor' test , but here is a pretty detailed model test that gives some credence to my claims pertaining to the acceptable aerodynamic performance possibilities with this dbl headsail, aftmast rig.

I posted this study and some pics over here:
http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-52.html#post748462

Several unconventional configurations have been tested, all characterised by an “A” shaped stern mast without mainsail in single-jib and double-jib configurations. Aerodynamic data available from experiments have been used to perform some performance prediction at full scale by means of a VPP code.

Both experimental tests and VPP calculation show that the double jib configuration with overlap gives the best performance and also the same configuration without overlap gives better results in comparison with the standard sloop solution.

 

[brian eiland]

J24 testing sessons

http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-52.html#post748931

 

[Jammer Six]

The problem is not building or sailing the models, the problem is measuring the results.

 

[markstrimaran]

mast bend above the hounds. how much?

Well the mast is my next week link. Went sailing in 15 mph gusting to 25. Actually went out to see if I could break it. I did destroy a 25 pound rated snap shackle. The mast held up, after about a mile of this. I was satisfied that 20 mph gusts is a good upper max. As any harder the windward outrigger starts flying. With me in the center hull.
The 150 Genoa blocks my view to leeward. So I can't see if the outrigger is going pitch pole.
I was too busy looking at my airborne hull to check out the other side. I am sure I had very little freeboard as water was coming in over the bow gunnel. My single Lee board was lifted out of the water. I was steering too leeward but the boat followed the weather helm until it lost power and steering was restored. At 1500 pounds with outriggers drafting over 3" Normal a very flat heel.
I was hoping that it would get up on a plane. Then again I was on the very rough down wind side. With white caps and opposite direction ground swells. Top speed was 7.9 mph in a 14.6' ama x 18 aka hulls.
Spent the rest of the day with just the inner stay sail. On the other side of the lake.

 

[brian eiland]

Sails for Test Model

Been thinking back about this model test project (in between a lot of other honey-do projects ). When I get time I still am interested in performing a few relatively simply 'comparison test'.

The question arises, 'What to make the sails of?"

For that model I took to the boat shows, I simply heated up plastic sheeting with a hair dryer and rolled it over a circular form.
http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-46.html#post733497
http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-46.html#post733498
That was certainly a lot simpler than cutting and sewing up small scale, soft sailcloth sails.

Perhaps I should chose to make some sort of 'form' akin to the manner used to make 3D sails?

I'm thinking the sails themselves might just be thin metal bent to shape of plastic sheet as I utilized before.
(BTW, I'm thinking of an approx 6 foot tall mast model)

Any other ideas??

 

[Earl Boebert]

There's a ton of information on the Web pertaining to model sailmaking. I recommend the "Claudio Gadget." Google on the words

claudio gadget sailmaking

for a start.

Since you're not worried about them getting wet, I'd use ripstop nylon from Goodwinds:

www.goodwinds.com

Cheers,

Earl

 

[David Cooper]

Are you sure you want to test outdoors where the only useful results you produce will be relative ones between two rigs? Have you considered using a long hall and an electric-motor-driven trolley to replicate the main functions of a wind tunnel. It won't produce wind shear, but the air flow should be constant and smooth. You'd only need to run the rig far enough for the air flow over the sails to settle down and then get a measurment of the force it's applying to electronic scales, the readout of which could be recorded throughout by a video camera. The rig itself would be attached to a second trolley sitting in a hole in the of the main trolley (to prevent it from adding its own drag), and it would have rubber wheels to ensure it can only move in one direction without rotation or sideways slip. You should then be able to measure the forces developed by the rig in any direction: you'd measure how much useful lift it produces by aligning the upper trolley in the direction the hull would be pointing (or at a variety of other angles to find the maximum lift), or else measure the drag by aligning it in the same direction as the main trolley underneath.