Underwater speed?

[NickMu]

Avionics,

I can not explain the duplicates of your suggestions in your earlier posts other than I started my input to this topic late and I did not carefully read the posts before my question to Ed about the RC system.
I felt that I should share the little information I had but the last thing in my mind was to take credit for something that you already posted. Ed asked for a possible formula and, without reading the earlier posts, I gave him the best I could find just to repay his generous information exchange about RC system.
Please accept my apologies for that.
If one positive thing will surface from this is that it could be Ed’s best solution since two separate people thought the same solution which is an “engineering nonsense”. You will always have n+ 1 solutions from n designers. Each one has a different solution and the +1 is the one that should be used.

Again, it was just my superficial attention to this topic and I’m sorry for it.

Best regards,

Nick

[Ramius]

Thanks Nick!
If it is 1" is that the body of the paddle wheel or the pipe inlet size? The reason I am asking and trying to keep everything as small as possible is that the bow are is starting to become very crowded as this is where the torpedoes and missles are plus a mechanism to deploy and retract the bow planes!

Ed

[NickMu]

Hi Ed,

The sensor I used does not have your traditional cylindrical shape.
Just to have an idea of the way it looks go here:
http://www.jets24.com/bombardier-brp...m_store=german
Also if you search Sea-Doo part 278001998 you might find more pictures to get a better idea. A view from the oposite side will give you more information.
The paddle wheel is about 1 ¼” diameter. The mounting plate is about 2”x5” but you can cut most of it off. With a little creative engineering you can hide most of the body and expose only the tips of the paddles.
It is used but in working order. I will send you pictures in a few days when I will get back to work.
My offer still stands but it will take few more days until I will be able o mail it to you.

Regards,

Nick

[AvionicsMaster1]

Sorry. I was just ecstatic someone agreed with me. You're right I should have done a better job of that.

Anyway, the downside is I finally got hold of an engineer I know who has a maritime background. He said paddle wheel thing is about your best bet as you wouldn't have to compensate for density: an inch of water is an inch of water. You could have inlet in forward facing torpedo tube and outlet in aft facing tube. You could also shift it to a non watertight compartment, creating room in bow, if you can find one that is submersible.

He also suggested a way I havent' seen posted and that is to use and accelerometer. True it would only work in still water but there are several phones that have internal accels built into them. Just a thought.

[NickMu]

The paddle wheel I used is completely sealed and, after finding the right spot for it, all you have to do is run the three wire cable inside. There will be only one time calibration required (determine the “active diameter” of the wheel) and after that just use your favorite method (frequency or period of the pulses) to calculate the speed.

Regards,

Nick

[languer]

I agree the paddle wheel is a good, simple idea. But I don't think the paddle wheel by itself can tell you the speed of the boat. If I remember my dynamics class, the paddle wheel will tell you the flow in the wheel. Which will be a function of two forces; (1) thrust of the sub, and (2) thrust of the water. In other words if the sub is travelling against a strong stream, the paddle wheel (I think) will incorrectly state the sub travelling at higher speed. If the sub is travelling in the same direction of the stream, the paddle wheel (again I think) will incorrectly state the sub travelling at slower slower speed. If the sub is travelling in still water, the paddle wheel will correctly indicate the speed. I believe you also would need to know the thrust of the sub (i.e. propeller movement) to properly calculate the actual speed of the sub (or maybe I am all screwey - which happens quite often).

[NickMu]

Hi Languer,

40 – 45 years ago these things were much clearer in my mind.
I can safely say that you are correct. And to add to the injury when checking the speed with paddle wheel in a stream not only that your readings are shifted with ± stream’s speed but they will be different depending on your position within the stream’s body: the closer to the walls and bottom the slower the water speed.

So the only accurate way to check the speed will be counting the time spent between two telegraph posts (LOL) or GPS based. Any other of the suggested methods will require some sort of calibration before each use if the environment changed.

Let’s look at the bright side: I recall some posts ago that Ed’s answers to various questions suggest that he will be using his sub only in fresh steady water.

Regards,

Nick