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I am not a hydrodynamic engineer but with two models of the Nautilus 4 ft. and 7 ft. and with numerous speed modifications to both in my attempts to re-create the bowwave effect, as seen in the original movie with the Nautilus in ramming posture to rip the hull out of a surface vessel I can make the following observations. As others have noted the design of the Nautilus characteristically makes it want to nosedive from a surface running position. There are a number of variables related to this not necessarily in direct proportion i.e. non-linear relationships.
First the sub wants to dive in relation to its size and speed. These relationships are not necessarily proportional or direct. Taking for example a relative speed of say 50 knots the larger sub is less likely to nosedive. And while I do not believe this is a directly proportional relationship my feeling is that at some theoretical size this effect is minimal or nonexistent. So that the full scale submarine probably would not experience the effect unless of course the speed was very great.
Conversely a sub i.e. the Nautilus, at any given scale or size will not exhibit this tendency to nosedive until some theoretical speed is reached and the speed is not a relative constant but somehow varies in accord with hydrodynamics way beyond me.
This is why I believe that a full-scale Nautilus at the speed shown in the movie would nosedive. I realize of course it was a 22 ft. model towed at great speed. Also the point of thrust I believe makes a difference in the nosedive effect. A propeller at the tail is more likely to induce the nosedive effect than jets located somewhat forward of the traditional propeller. In fact if the Jets were placed very forward there probably would not be a nosedive effect. Similarly another way to look at this is to think of a propeller located completely forward at the nose and in this case there would be no dive effect either.
What I don't know is whether this diving effect persists once the sub (the Nautilus) is submerged. I think not. The reason being that there is resistance from the alligator eyes and the wheelhouse in general which would tend to overcome the downward effect once the entire submarine is underwater. Resistance at the alligator eyes would tend to raise the nose upward thus canceling the inherent tendency of the sub to submerge when on the surface. I just wish I had clearwater to observe this.
So what does this mean to the modeler? It means that for a smaller sub at a faster speed on the surface it will tend to nosedive as opposed to a larger sub at the same relative speed. (as Bob and others have noted) What does this mean for a large submarine such as Pat's mini sub? I don't think it's relevant until really really fast speeds are obtained. What does this mean in terms of trying to duplicate the bow effect with the model submarine? Well it's just one more variable that needs to be considered and adjusted.
In other words the bowwave effect without having the model actually towed is a tough endeavor. This brings me back to my original thoughts about this and that the only real way to duplicate the Disney special effect is to actually tow a model with the water cannon. However in spit of all this I think I have come close to the effect. The last time I had the sub out I was able to use the full speed of the sub in conjunction with the water cannon. But this is no easy task. Should post new video later.
Edited By Carcharadon on 1086200967
First the sub wants to dive in relation to its size and speed. These relationships are not necessarily proportional or direct. Taking for example a relative speed of say 50 knots the larger sub is less likely to nosedive. And while I do not believe this is a directly proportional relationship my feeling is that at some theoretical size this effect is minimal or nonexistent. So that the full scale submarine probably would not experience the effect unless of course the speed was very great.
Conversely a sub i.e. the Nautilus, at any given scale or size will not exhibit this tendency to nosedive until some theoretical speed is reached and the speed is not a relative constant but somehow varies in accord with hydrodynamics way beyond me.
This is why I believe that a full-scale Nautilus at the speed shown in the movie would nosedive. I realize of course it was a 22 ft. model towed at great speed. Also the point of thrust I believe makes a difference in the nosedive effect. A propeller at the tail is more likely to induce the nosedive effect than jets located somewhat forward of the traditional propeller. In fact if the Jets were placed very forward there probably would not be a nosedive effect. Similarly another way to look at this is to think of a propeller located completely forward at the nose and in this case there would be no dive effect either.
What I don't know is whether this diving effect persists once the sub (the Nautilus) is submerged. I think not. The reason being that there is resistance from the alligator eyes and the wheelhouse in general which would tend to overcome the downward effect once the entire submarine is underwater. Resistance at the alligator eyes would tend to raise the nose upward thus canceling the inherent tendency of the sub to submerge when on the surface. I just wish I had clearwater to observe this.
So what does this mean to the modeler? It means that for a smaller sub at a faster speed on the surface it will tend to nosedive as opposed to a larger sub at the same relative speed. (as Bob and others have noted) What does this mean for a large submarine such as Pat's mini sub? I don't think it's relevant until really really fast speeds are obtained. What does this mean in terms of trying to duplicate the bow effect with the model submarine? Well it's just one more variable that needs to be considered and adjusted.
In other words the bowwave effect without having the model actually towed is a tough endeavor. This brings me back to my original thoughts about this and that the only real way to duplicate the Disney special effect is to actually tow a model with the water cannon. However in spit of all this I think I have come close to the effect. The last time I had the sub out I was able to use the full speed of the sub in conjunction with the water cannon. But this is no easy task. Should post new video later.
Edited By Carcharadon on 1086200967
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