Hypothetical question

[jimi]

If the sea were made of heavy water, would your boat sail faster or slower?

 

[Evadne]

Well, displacement would put the wl very slightly lower down the hull, reducing the waterline length so you'd sail slower. Friction is identical. Stowing extra beer and FB pie tins would compensate.

 

[john_morris_uk]

[ QUOTE ]
If the sea were made of heavy water, would your boat sail faster or slower?

[/ QUOTE ]Faster: as few atomic particles would be hitting the keel and exciting it!

 

[Cutter]

You would glow in the dark

 

[jimi]

[ QUOTE ]
[ QUOTE ]
If the sea were made of heavy water, would your boat sail faster or slower?

[/ QUOTE ]Faster: as few atomic particles would be hitting the keel and exciting it!

[/ QUOTE ]

That's what I thought, wonder if the length of wave constraining displacement speed would be affected?

 

[Salty John]

If the sea were made of heavy we would all sail slower due to the drag created when refilling the glasses.

 

[catmandoo]

Deuterium is about 10% denser than water so a ship would displace less and hence would ride higher in the water .

The coefficient of friction would probably be affected too as density is a parameter in Reynolds No and I also suspect the viscosity might be less and so the friction factor would be less and so with the wetted area being less then the boat would go faster

 

[Wunja]

I think Newtons laws come in to play though, as the heavier water would require more force to move it out of the way. More force = more energy = less speed.

But I'm not a physacist

 

[catmandoo]

Bit late to night but methinks mass displaced is just the weight of the boat so no change

 

[LymingtonPugwash]

Eh? /forums/images/graemlins/confused.gif

 

[Wunja]

Vince slaps forehead. Archimedes strikes again!

 

[catmandoo]

I used to have a canoe when a boy and used it at the mouth of the river Nairn . Sea water is denser than fresh so when I hit the boundary from sea to fresh there was a sudden sinking feeling as well as more drag

 

[Guest]

[ QUOTE ]
I used to have a canoe when a boy and used it at the mouth of the river Nairn . Sea water is denser than fresh so when I hit the boundary from sea to fresh there was a sudden sinking feeling as well as more drag

[/ QUOTE ]

The approx. rule of thumb difference salt to fresh is 1/48th of draft change.... so where's the sinking feeling come from ?

Canoe draft ... maybe 10cms ?.... + 1/48th = 10.21 cms

Oh and on your previous about vessel will displace less ... suggest that be qualified with "displace less volume" ... as someone may confuse your unqualified post with vessel displacement - which is weight of water displaced so that vessel floats !

/forums/images/graemlins/wink.gif

 

[sailorman]

one would need a good look-out for them Mosquitoes /forums/images/graemlins/smirk.gif

 

[catmandoo]

Its straight Archimedes . Vessel weight balances weight of water displaced so with denser water less volume of water displaced by the ratio of fresh water density to sea water density . Sorry don't get your point ????

I also have no doubts about the feeling when I hit the fresh water . The change was definitely felt . Why not try it yourself some time ?

 

[Searush]

Density affects flow, imagine sailing thro' treacle! I would expect a slower speed thro' a denser fluid, regardless of the very small amount less of boat in the fluid.

 

[Danny Jo]

It may be a hypothetical question, but the more important issue is whether the answer is hypothetical (i.e. one based on what we think it is, based on our incomplete knowledge) or empirical (i.e. based on experiment).

There are too many variables (known density higher by about 10%, known viscosity higher also by about 10%, hydrogen bonding effect perhaps stronger [judging by higher melting and boiling points], surface tension, etc.) for a hypothetical answer to have any meaning. And the cost of the D2O for a tankful large enough for a speed trial of Jimi's yacht would make the experiment impossibly expensive.

Mark

 

[catmandoo]

However how about a canoe trip across a river mouth .

Theory may be one thing but a practical demonstration puts all the doubt to bed .
It may not be perceptible on a large boat but in a kayak where the occupant is one with the vessel the difference is certainly felt .

I know because I have done it .

Science is based on experiment as you rightly indicate