Power Required

I've decided to code name this project “Tadpole” for the little Blue Whale in us all.
But I have a question relating to waves.
This little boat will end up spending a good bit of her time frolicking in nonbreaking waves, and maybe a little in some breaking ones, things don’t always work out as planned.
So how would that influence the design?

 

If you are within 4 hull diameters of the surface then you need to take into account wave drag. If you are aiming to do 4 to 8kts then the lowest drag hull will get considerably more slender.

Post #54 on this thread compares a surface hull and a submerged buoyancy hull:
http://www.boatdesign.net/forums/boat-design/10-foot-swath-28081-4.html
There is a chart showing drag. The surface hull gives you an idea of the shape of the lowest drag hull for 4kts and whatever the displacement was - you need to backtrack to find out.

The submerged buoyancy hull gives you an idea of how deep you need to be to get negligible wave drag.

Rick W

 

I'm not sure what you are getting at. When elliptical cross-sections are appropriate, people use them. If not, they use some other shape.

Leo.

 

Yes I have come to that conclusion, mostly it was a bad choice of words.

 

Thanks Rick,
You are refering to drag due to bow and stern wave fromation. Is there any additional considerations for surface wave action having an effect overall.

 

That's very similar to the disign I have in mind.

 

Hi,

Have you already made a choice of the motors types ?
In streamed waters, near the ground, many motors are not almost compulsory ?
So, Pod, pan cakes, 1, 2, 3, 4 ?

No tiller just motors fixed or passive pitched position modulated to do a fish like propulsion by a succession on unbalance laminar movements ?
3 or 4 EM real time synchronized give a security if one is dead
You test randomly, wait, get a good vibration !
Just an idea among 1000 other

This can deeply impact the shape and design



Why so small turbines ? (Or why making noise)
If my mission was to collect informations i would remain silent to ear better informations I'm looking for. A tiny audio detail can help.
Also, vibrations will modulate your measures and than may lower resolution ?


The extra drag from bigger prop + fairing can be fully compensated by an advance magnetic design of the motor.
If the only purpose is civil protection, the you should have no problem to have access to this magnetic pumping (OU) technology. Even if a solar surface for refill is needed, the main problem will be the weeds and bernacles on lenses unless you already tested an ultrasonic like device ?

 

Not certain if you understand the influence of wave drag.

The craft does not need to be on the surface to make waves. The pressure disturbance caused by the movement through the water extends many hull diameters from the actual hull. If the surface is being influenced by the pressure disturbance then it is forming waves and energy is lost in making the waves. The hull is providing that energy. The waves are not generated by the bow or stern as such but by the pressure disturbance of the entire hull.

Since you have looked at JavaFoil you can use the flowfield visualisation in it to see how far the significant pressure disturbance extends for a 2D body.

The yellow hull I made was set 1 diameter bellow the surface. It is 300mm diameter and was set to a draft of 600mm. I achieved 6.5 knots on it. At that speed the wave drag on the submerged hull was roughly the same as the frictional drag on the hull. Despite being well below the surface it still made waves.

Rick W

 

I don't think this boat will have much need for extended surface operation, It will be under way at depths to deep to consider the induced wave. Mostly it will only be station keeping when surfaced.

Hence the question about surface waves, I should have said surface conditions or maybe surface piercing capabilities.

 

Does 2 counter rotating separate pods have the same efficiency loose than in axial serial design (like volvo dual prop by example) ?

About buoyancy (gravitation) propulsion are there any practical vehicle using it, efficiency should be terrific ?

 

See comments.

 

Nice
Very impressive work using cop effect of gazes compression.
Thanks

 

hey i am looking for a pair of hering performance boat props or mercury props email me at uvcoatings@sbcglobal.net i am also looking for a hotdog or convincer power boat email me if you got on thanks!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1

 

Here top speed is 8 Knt
m46, Did you try in Dubaï ?

Joe, Rick, is this a normal Quantum effect of talking about OU magnetic design ?

 

Do you have a drug problem?