Submarine driven by kites

Dualism in project realisation

At Pogo,

Although it was my own idea that I posted three years ago, I am sceptical about the application of this submarine driven by a kite as well.

These are the advantages:
I stated this several times: it's for speed records. like for the World Sailing Speed Record Council (WSSRC) of 500 meters.
http://www.sailspeedrecords.com/500-metre

And I don't mind if this idea ends up as a world speed record gimmick.
It's original. But...

Safety is a the big contra:
Safety reasons are more important to perhaps final abondment of this high speed kiteline that cuts through the water at 50 + knots. (which I believe is technical obtainable).

Is it wishfull to make this happen?
No, because it's dangerous to other recreation water users.
Not to forget all the fish that is cut in two for no reason.
And to put people in this torpedo's in murky waters where no obstacles can be avoided in time is also too high risk for myself, thus also for other people.

Not to forget what happens when lightning strikes. Although this also counts for kite surfers, Which I believe is a big revolution for the sport.

Don't do it.

 

Forum posts are an extremely limited means of communication and it is all to easy for conflicts to arise and divert from the thread.

I posted the piece of information that was pivotal in a disagreement to clarify that there was no conflict between statements.

 

Thanks Kerosene: that is the case.

 

Then I'm guilty of the same (unreasonable) reaction upchurchmr had to my own post earlier

 

No worries! - its really easy to miss - take stuff when written, without all the nuance and expression we can bring when we are talking face to face

 

Rastapop,

I should apologize publicly.
Nothing you said was wrong that I know of, I just took it wrong.
Nor do I think you were trying to call BS.

Just me having a not so rare off day.

Sorry to everyone.

The rolling took place over ~3hours as I recall.

Shakeal,

Speeds of 50kts apparently have been reached by Russian Nuclear subs in the past.
The problem is control and the dangers of breaching (coming out of the water) or exceeding crush depth while loosing control and porpoising. Breaching can cause structural failure due to structural loads when out of the water.

 

I agree with you on the safety case. And as far as the influence of waves in relation to depth between the surface they are not for a speed record a concern;
Neither are big waves and Tsunami's in scope.

And which roll over? This one?

 

No, safety is not the biggest drawback at all, as you will see.
Let's do a quick reality check of your idea:

For a streamlined submarine with a round cross-section and L/d ratio of 8, one can assume a preliminary CD equal to

CD_sub = 0.1
​

The cross-section area is:

A = pi/4*d^2 = 50.3 sq.m
​

The speed in SI units is:

V = 50 kts = 25.7 m/s
​

So the drag of this submarine at 50 kts is:

D = 1/2 rho V^2 A CD_sub = 17000 kN
​

The drag will have to be equilibrated by the horizontal pull of the kite, so:

H_kite = D = 17000 kN
​

The kite will pull the sub at an angle of approxim. 30-35° to the horizontal, so an upwards-directed vertical force will be exerted too, equal to:

V_kite = 1/3 * 17000 = 5700 kN
​

The total cable tension will be then (rounded to 2 significant digits):

T = sqrt ( H_kite^2 + V_kite^2) = 18000 kN
​

A RAM-air kite typically produces the maximum force at approx. 20° AoA, the resulting force coefficient being:

CL_kite = 0.8
​

Assuming a wind speed of 25 m/s (48 kt), the required minimum kite planform area is:

S_kite = (2 T) / (rho V_wind^2 CL_kite) = 58800 sq.m
​

That corresponds to an elliptical kite with AR=3 and span equal to:

b = 420 m (or 0.26 miles)
​

The high-strength steel-wire cable has to be dimensioned with a safety factor of at least 5. Hence the minimum breaking load of the wire rope is:

MBL = 5*18000 kN = 90000 kN.
​

That can be achieved with either one of these:

1) single rope with d=300 mm
2) two ropes with d=215 mm
3) 4 ropes with d=150 mm
4) etc.
​

In each case, the overall linear weight of such wirerope arrangements would be approximately 420 kg/m. Hence, 100 meters of pulling cables will weigh some 40000 kg or 40 t.

You will need at least 500 m of control cable, so we are talking about 200 t of cable only, without considering the weight of drums, pulleys, motors, gears and hydraulic systems necessary to operate the stuff. We are talking about some 300-350 t of machinery, mechanical parts and structural reinforcements to be added on board. That's something like 20% of the original displacement of the submarine (taking the german Type 212 as reference).

You can think about substituting the steel-wire rope with a carbon-fibre rope and save 20t of cable weight, but will have to pay a considerably higher price (if anything similar is available at all).

I'll stop here because these numbers are already very harsh, no need to go further into this direction.

Sorry for this, but don't give up thinking of alternatives to current technologies.

Cheers

 

I appreciate your calculation based on a full scale submarine but as you pointed out the submarine you are talking about has the internal area of:
A = pi/4*d^2 = 50.3 sq.m

I talking more in pi*0.25*0.75^2=0,44 sq.m
The diameter of a torpedo that can be manned.

The safety of this manned torpedo is my biggest concern. For reasons as explained above.

I recalculated the drag for this diameter and the quotation is:
For rho=1027 kg/m^3
A = 0,44 sq.m
Drag = 0,5 x 1027 x (25.7)^2 x 0,44 x 0,1 =14,9 kn = one and a half ton.
Dyneema for 3 ton is 6 mm in diameter.
https://www.alletouw.nl/producten/50-154-dyneema-sk75-liertouw-d-6-mm--32-ton.html
Skysails, The towing kite for oiltanker provided 16 ton with good wind.
Area 300 sq.m

Source:http://www.ship-efficiency.org/onTEAM/pdf/Brabeck.pdf

 

I had missed the part where you were talking about the torpedo-size sub.

Well, along the same lines - for a cross-section with A=0.44 sq.m at 50 kts, the drag will be:

D = 14.5 kN​

and the cable pull will be approximately:

T = 15.0 kN​

The required kite (Vwind = 15 m/s = 30 kt) has an area of 135 sq.m. That's approximately a span of 20 m. That's big.

You would need an anti-rotation cable with a MBL of 75 kN - which could be, for example a 10 mm VS10 model.
100 meters of that wire rope weighs 46 kg and the rest of the winding mechanism and structures will be no less than 60-80 kg. Unless you use a constant-length rope, with no drums and motor gears for kite deployment. That's a big concentrated weight for such a small sub.
I am talking about structures dimensioned with common saferty factors used in shipbuilding industry (4.5 or more).

Cheers

 

Aha, We made the same calculation.
I re-edited the calculation above before I read yours.
And indeed, just like in the video, I was planning to use fixed length of dyneema 100 meter.
Even with safety factor of 4.5 of 1,5 ton , the force on the line will be around 7 ton.
7 ton dyneema will have 1 cm in diameter.
http://www.rainbownets.com/Product/Dyneema-SK-62--10mm/e_tdg6210

 

Ok, but I wouldn't use the 6 mm dyneema. The 3 t working load stated in that site is probably calculated with a safety factor of 2.5, which is the standard in the yachting industry. Since you are talking about an application in which too many things are unknown, I would use a more hefty SF of at least 3.5-4 and would opt for a 8 or 10 mm rope. It will add just 3-5 kg to the overall weight, but will increase the probability of not snapping by a factor of 2.

 

Our calculations crossed each other again. 8 or 10 mm rope will be fine.
Still we have the safety issue. A secluded area where there are no other recreants or wildlife can be found.
But what happens when the torpedo hits something or is being pulled out of the water. And how much fun is it to sail in a coffin?

Too much doubt about this project.

 

If it is indeed a record-breaking attempt, then speed runs will be performed in a reserved and controlled area, with sufficient depth beneath. The torpedo being pulled out of the water - well, that's a part of the game. Speed-record breaking is always a risky job and many persons have been hurt or have died trying to become a legend (well, they mostly did, though not the way they had imagined it). It's up to you to decide how much risk are you ready to accept.

As about the question about fun - well, to me personally it would be no fun at all. I go out at sea because I want to see wide open spaces and nice costline, to run away from the crowd, to smell the delicious scent of the sea and to be lulled by the sea waves.
But I guess someone might find your idea funny too. Being towed at 50 kt in an ambient with reduced visibility and a possibility of hitting something head-on is such a nice and inviting alternative to my vision of sailing.

Now seriously, I don't understand how do you intend to control the kite without being able to maintain a constant visual contact with it.

 

The kite can be self steering just like in the video of the french.
But still.. I am not going to realise this project for obvious reasons.
Nice to make some calculations though.

See you.