Carmichael low drag bulb

It might work. Or the boundary layer might separate at the join of the elliptical bow and middle section, or near where the middle section joins the tail.

Here's another paper for your burgeoning collection

MATTNER, T.W., TUCK, E.O. and DENIER, J.P. " Optimal nose shaping for delayed boundary-layer separation in laminar plane-symmetric and axisymmetric flow ", 15th Australasian Fluid Mechanics Conference, Sydney, 13-17 December 2004. Proceedings edited by M. Behnia, W. Lin, & G. D. McBain, The University of Sydney, 2004, paper AFMC00078.

http://internal.maths.adelaide.edu.au/people/etuck/pdfiles/AFMC00078.pdf

Good luck!
Leo.

 

Leo/Tom
The referenced paper has a couple of qualifications concerning angle of incidence. For example:
< Another important factor is sensitivity to
angle of incidence. The optimized forebody geometries exhibit
rather sharp corners. We expect that such features would pro-
mote separation in the presence of small angles of incidence.
This is also the subject of future work. >

This supports my understanding that it will be difficult to retain or promote laminar flow over a large portion of the hull if it is intended to do high speed gymnastics.

Irrespective of this the axis-symmetric shape is interesting as it does not exhibit the same shape as the Carmichael body. I need to take it in a bit more and understand the differences here.

Rick W

 

You guys are awesome. I was about to give up on outside help and just start experimenting. I know I sound like a wealthy man from my life experiences (all my bragging) but I am not. I wasn't even going to build a working test model, but am now reconsidering. Can radio control be used underwater? I'm thinking not. OR, is the range just reduced?

Rick, what is your background? If in a previous post, please direct me.

Leo and you have made me think about this transition (drift) and angle of incidence. This is angle of attack? One reason I'm leaning toward a spherical leading "edge" (nose) is angle of attack. When manoeuvring,
or performing my gymnastics, flow direction will change over the "wing" and the apparent shape will become chubbier. I'll bet you're loving the technical terms here! A sharp pointed nose, like what you attached Rick, would be disastrous with eddies popping up an the lee side of the nose, no?

Okay, what is snap roll? I can find lots of references to it but no definition.
I'm assuming it is a sudden, negative effect of a cumulative affect of turbulent flow around protrusions on a submerged hull form making way.
Am I close?

In my last closing I mentioned I was going to try and get it up. What I neglected make reference to was my drawing. So, stand-by...

 

Radio - do not really know but I think Mermaid has knowledge on it.

Background - boats for hobby and recreation since as long as I can remember. I am the fifth generation of a sea-going family but my older brother is the only one in the current generation working on boats. I play with them. I am an electrical engineer by profession and get paid to be the devil's advocate and work out how things will fail before they do with the objective of preventing failures.

Incidence - A pointy nose is most streamline in-line but a small angle of incidence will cause detached flow. A rounded nose is more tolerant. JavaFoil is a very useful tool for playing with these things and getting an understanding. It only gives wing sections rather than bodies of revolution but I believe it will give insight:
http://www.mh-aerotools.de/airfoils/jf_applet.htm
The shape I gave you in wing section form has detached flow on the low pressure side from about 1.5 degrees of incidence. This will increase drag over a hull with rounded nose. Maybe a beneficial aspect is that it will help the hull turn as the turning moment will be lower than if you had nice attached flow. I expect a rounded nose will produce a large moment that counters rapid turning. So my proposed shape might actually turn a lot easier. Might be Dolphins have a pointy nose for good reason. There are certainly a lot of cues in nature that you can learn from with these things.

This is the sort of area where Tom Speer or Leo might be able to comment meaningfully.

I also expect there are simple relationships for drag on a body of revolution with respect to a wing of the same section. If you had this then JavaFoil would be very useful for analysing shapes and forces imposed with some angle of incidence.

Rick W

 

Rick, thank you once again for your input.

I am the first genertion to make a living on the water. However, it only lasted 12 years. About seven years ago, I found work in earthquake research here on the west coast, (Canada) in earhtquake country.
That ended two years ago and I am primarily a stay at home Dad that dabbles in boat sales, woodwork and gardening.
I just got off the water from demo-ing a high speed Zodiac replica (made locally) to a German police agency. It was great to be out on the water again. Especially at 52 knots!!

Thanks for the JavaFoil tip, should prove interesting.

I'm not able to get my silly drawing up. I have a MAC and don't know how to use it I'm affraid... Can I post it somewhere else on this site?

Tom, Victoria BC

 

If you can get a drawing on the screen then you can post it. To get a screen image of the drawing you have follow this:
http://www-rohan.sdsu.edu/~scc/web/screencapt.html
It will produce a png file that can be posted.

Just follow the logic of the window that comes up when you click on the paperclip icon on the Reply to Thread screen.

This is being done on a MAC.

Rick

 

JPG of drawing.

 

Rick I get the F*£@%^!*^@!! image up on a JPG.

But get a Invalid File response from the "Manage Attachments"

paper clip window.

 

I have to go break something now before I piss all over this computer.

 

Imgp4552.jpg

 

Is there a webmaster that can hold my hand through this infuriating process?

 

I have attached an image of the Manage Attachment window.

You <Choose File> the file. Then <Upload> it. If it is a large file it will take time. The window looks like the second image when it has uploaded. Simple as 1,2 and 3.


Rick W

 

Thanks Rick, but it wont do it.

I'd love to be able to show you what happens, but that would require me getting the image up, and well that's not working now is it...

Would you please email me directly and then I can send it to you and, if you would be so kind, post the f-ing thing for me.

Thanks

 

All
These are thoughts on paper, but you get the general idea.

This is page 21 of the process. Page 19 follows, showing the elevators only idea.

A hard, clear ballast tank in the nose. Likely, a bunch of lead shot as a drop-weight (so it can flow out a small hole). The little rectangles are 2" X 6" X 4", 2 kg batteries. If room allows, I'll add more.

I think the rest is obvious. If not, please let me know.

Tom

 

Well, that went over like a lead balloon.

"A picture tells a thousand words" and silenced everyone...

I have researched all the references kindly given above

and am no further ahead with my hull form.

Surely, someone out there has some feedback to offer.

Again, my design objectives are zero to twenty knots,

great handling and manoeuvrbility, fun to drive, low drag,

minimize cabin volume (buoyancy, and therefore, mass).

If no further critique, could anyone suggest where else I look

for assistance with this hull form design?

Thanking you once again in advance,

Tom.