Hull Speed

If the design will save me fuel, I'll buy it.

 

Robert, when you have your patent filed I would suggest you take it a step further and incorporate your analytical methods into a piece of software (e.g. like Michlet). This way designers can import neutral hull model files into your tool and analyze their performance. If you don't do this you may find your theories won't be put to good use in the real world.

Meanwhile, we will rely on the existing analysis tools out there and wish you all the best

 

Robert, you have to excuse folks who have replied so far and to understand their frustration. For you the 2035 conference might be just another past experience, but the rest of us will have to wait for 23 long years before seeing the papers from that event...




Cheers

 

Sorry to nit-pick, but technically you mean Intact or Initial Stability.

Intact stability relate to a vessels ability to stay upright. It is considered t be in "equilibrium", ie all resultant forces (and moments) acting on the vessel are zero. When inclined to some small angle from its position of rest (or equilibrium) it returns back to that position. It is the first thing to check when doing a new design. Does it float (hydrostatics) and does it float upright, basic curves of statical stability!

Dynamic stability is the amount of work done to heel a vessel to a specified angle. Usually taken very slowly and constant displacement in order to ignore work done against air/water resistance.

You need to have positive Intact stability taken from the statical stability curves generated for the vessel first before you can establish its dynamic stability. Although it can also be done in a similar manner to statical, via the CoB ~ CoG differences and its displacement, but takes longer to calculate this way.

 

What is the "hull speed limitation"? What is the connection between hull speed and boundary layers?

 

I remember the HULA, used by Newzeland. If I remember correctly, they made a shell to organize the BL at stern, avoiding separation and making the hull "virtually" larger, reaching a little bigger Fn. They earned something like 80 mts. for each 1000 sailed against the twin-boat without the device (wich was a lot, considering the parity showed in the finals). Anyway, they weren't planing hulls.

 

No, I did not mean initial or intact stability, or even the amount of work needed to slowly heel a vessel to a specificed angle.

I was talking about the tendency of a craft to return to an upright, stable position when disturbed while being traveling at high speed. The term "dynamic stability" is used to describe this, and an example of such use is in the paper published in Marine Technology, Vol 29, No 1, pp 4-12 by Blount and Codega: Dynamic Stability of Planing Boats.

An example of dynamic instability at high speed http://news.google.com/newspapers?n...MYgAAAAIBAJ&sjid=c2oFAAAAIBAJ&pg=1359,5256064

 

A clue?

http://www.google.com/patents/US5992465 This patent is for internal flow, but let's see where it goes...

 

I am struggling to understand how can that device be related to the wave drag of the hull.

 

As I read the patent, the claim is that rotational flow induces what he calls "quasi-laminar" flow. Periodic vanes in a pipe promote this rotational flow. The terms that were used by the OP in this thread (e.g., chaos theory, laminar flow) show up in the patent, which makes me think that he is considering an external flow variant of this idea.

IF you believe the claims are capable of the behavior presented (which I do not for a variety of reasons), then one can see how he might get the idea that external vanes could reduce turbulence and perhaps even change the wave system (like a bulb might).

Of course, external flow is nothing like internal flow - not to mentioned that flow in a pipe is very well behaved as compared to that of a ship that sinks, trims, pitches and rolls.

 

DCockey made a good observation (after Leo Lazaukas opened my eyes) by mentioning what the "hull speed limitation" was
and asked for the connection between hull speed and boundary layers

as i learned frictional resistance, blue in the graph below, only rises slowly with speed till "hullspeed" is achived
its the wave drag curve in red you see rising steeply over the blue friction curve were "hullspeed" creates a hump bow wave
there are more drags like formdrag, resudual etc as jehardiman for example wrote here

you can download the java hullspeed calculator applet as zip from link above, still works and think its appropriate here
everybody with winrar and java can use freds calculator, a simple hullspeed calculator made by fiona sinclair
its an aproximation and only the sample hull can be LB and Cp modified but gives a good visual idea of these drag forges and where to find "hullspeed"
to be clear: planning and other boat designs are not included here

try it out, download 2 secs, dont have to instal this java applet, it still runs from the winrar line shown below in bleu
set your hull dimensions and observe the generated graphs, they show frictional drag (boundery layers) have little to do with "hullspeed"

 

oops, while i was making a sandwich i now see DMacPherson's reply
and realise fionas calculator and my story above was beside the point?
it was a bissy day, i got to pay better attention and be faster

 

The connection between frictional resistance rising more steeply above hull speed is coincidental. Frictional resistance is almost proportional to velocity squared. The small difference from velocity squared is due to Reynold's number effects.

 

This is utter nonsense. If you look at the flow graph in the patent paper, you will notice that the loss is not following the rules for Newtonian fluids. You will find that the loss in this case is roughly: H=3.1*Q-17,9; which certainly is far outside turbulent Newtonian flow. The test is most probably done with a fluid velocity close to the critical Re number. In this transient zone there are a few surprises in the fluid mechanisms.

For instance, if the flow is changing from a laminar profile into a turbulent one, the balance between the static and dynamic pressures is changed. In fact, you may see an increase in static pressure downstream, since the total dynamic pressure (integrated over the diameter) of the laminar flow is higher than the corresponding pressure of the turbulent flow. In the case with a spiral flow, there will be a radial pressure gradient due to the peripheral velocity induced by the vanes.

All in all, introducing a secondary flow, with the corresponding increase of dynamic pressure loss is not reducing any losses. This example shows the importance of knowing what you do when dealing with empirical experimenting, otherwise chaos is waiting around the corner.........

There are cases, where a change of degree of turbulence may lead to a loss reduction, f.i. the flow around a cylinder (rough surfaces on sectors of a mast profile), but that is only working within a specific flow environment. Naah, someone said something about snake oil, huh?

Sorry DC, you were just ahead of me here, same reasoning on losses; look at the patent text.

 

Thats the internal screw patent discussed I belive as OP has not disclosed even what "hullspeed" gain is claimed

@ DCockey, point I made with graph and calculator above is its wave drag, not frictional that limits "hullspeed"

For sortof "normal" hulls and waters that is