Submersible hulls

i stand by what myself and r watson are saying, efficiency is the biggest gain from the least expenditure of energy and speed is a natural outcome . i say again if underwater is more efficient why are yachts racing on the surface instead of underwater.

 

yes the best gain from the least expenditure-agreed

but your copmparison is not analagous to efficiency--if speed correlated to efficiency then we would all have 300 MPH boats that used 1/2 litre per hour...


--whats the difference in efficiency between tavelling 1000 miles @ 3 knots with 1 hp and 1000 miles @ 300 knots with a 1000 hp?? you tell me; which will expend more energy??


and thus: speed does not mean efficiency...if you could go 300 knots with 1 hp burning 0.5 litres of fuel -now that(!) would be efficient...!!

more speed = more power = less efficiency..that simple. sorry i dont make up the laws of physics..i wish i could..

 

ef·fi·cien·cy
   [ih-fish-uhn-see] Show IPA

noun, plural -cies.
1.
the state or quality of being efficient; competency in performance.

2.
accomplishment of or ability to accomplish a job with a minimum expenditure of time and effort:

3.
the ratio of the work done or energy developed by a machine, engine, etc., to the energy supplied to it, usually expressed as a percentage.

 

This is the whole point.

You cant compare submarines and rubber ducks - compare like for like.

If you make a model submarine, and a similar size model boat, and do the 'bathtub test' - the sub will slow down long before the surface vessel -
because their is more friction from the water.

I don't know how you can keep implying there isn't.

If subs were more efficient - all the supertankers in the world would be running mostly submerged.

 

I love this thread, it's like watching a dog chase it's tail!

Lol!

-Tom

 

you make me laugh watson!:

--have you ever tried it??? thats not what happens... the sub will gain much more momentum than the surface vessel..
in fact be careful in the tub--the ballasted sub will almost go through the tub if you shoot it too hard--of course- depends too on size..remember to make sure they are equal in mass...the sub is by far more effcient than a surface vessel. like i reiterated--it will need 1/4 or less the propulsion to gain efficeint speed..remember --i have delved into all this before...built ferro-cement submarine models, compared them to boats etc ad infinitum...

you will be surprised(as i was) when you push your neutrally bouyant model sub at how easily it moves compared to the boat model of equal proportions and displacement on the surface...

btw -they did think about running cargo submerged-the idea has been around for a while ...too many logistical problems though so it was abandoned.
so hows your project coming along? should be a nice boat when you are done...

 

too FUNNY!!!!

 

Yes, I have tried it - in a proper tank.

If the two vessels are of equivalent weight, they will both have the same momentum, the sub cant magically 'gain' extra momentum.

The surface vessel CAN be designed to run further from the initial 'push' due to lower viscous resistance.

The big issue isn't if current commercial surface ships DO have more efficient hull shapes than submarines - most don't, due to operational and construction limitations.

The big issue is if a surface vessel hull CAN be designed to be more efficient than a sub hull - and they can.

http://www.scribd.com/doc/39037779/Drag-Boundary-Layer-and-Hull-Roughness-on-Ship-Hull-Surface

The other issue is that hulls are designed around a desired maximum speed. The subs that look for 70+ knots underwater sacrifice a lot of other advantages ( like load carrying capacity, etc)

Consider - the high performance offshore power boats can exceed 70 knots on 500 HP - compared to the 15,000+ HP of a nuclear submarine. - and the submarine has no weight burden !

 

alright i admit it! -i just couldnt let this one slide--came back here to repost --this needs to be said: why is it people who disagree about what i have to say , like spoiled children, try to give you a bad reputation as though its going to change my mind or get in some last parting shot...? whats the point?? really whats the point?
hey- if you want to live in bizarro physics world...so be it..



as far as this project --like i said--i hope it works out -i'd like to see the result of this...out of curiosity.

 

.....

 

adhoc allready posted the hybrid swath stability boats i now see
more legs give as much drag as a small contineus waterline i once read ?
and yachts with fload torpedo's sticking out but best wavepiercer sample yet is the incat rite ?
small one below without stabiliser i guess..

 

That's what I'm talking about. Under press of sail, the boats would be even more even in rough conditions. So let's build one and win some races

 

here's a sailing submersible hull i found at Marin http://www.youtube.com/watch?v=35-x...DvjVQa1PpcFPqtE8Kj6mo8jCC1igH9X6yF4qvNMILtH4=
looking why they build a big new depressurised test tank http://www.marin.nl/web/Facilities-Tools/Basins/Depressurised-Wave-Basin.htm
they even have a contest and open day in oktober, eh, guess i might be rather on holliday at the med than

 

This is a pretty cool application of a submersible hull pod that uses flooded air space to aid buoyancy:

http://www.cyclekarts.com/XBoats2.html

Scroll down about half way.

-Tom

 

Great link Yipster, thanks!

-Tom