Re: Tricky math?

If you lower you and your boat into the water you will displace water.
I am sure you will find if you roll up and down your single without
moving you will create a small wave
through altering your position in the boat in relation to the
stationary water beneath you.

With these combined you will have something that you can then relate
to propulsion and the displacement
whilst moving.

I am neither physisist nor mathematician so am simply posing the
question...

On 29 Feb, 17:03, paul_v_sm...@xxxxxxxxxxx wrote:
On Feb 29, 8:00 am, "donal.ca...@xxxxxxxxx" <donal.ca...@xxxxxxxxx>
wrote:

I think the math would also be complicated by the fact that there will
be a certain amount of roll as even the best singles/crews will not
necessarily balance the boat. Also of course the rise and fall of bow
and stern in and out of the propulsive phase will have an effect.

Rather than doing complex Math on the curve could a more relevant
experiment be to place the hulls in an archimedes type measuring tank
and see how much water is displaced by the boat with crew or sculler
inside and perhaps the crew whilst stationary rating various rates...
28...34...38...42. You would still be missing the element of
propulsive power but you would measure the actual displacement volume
with the force of a weight moving up and down the slide which surely
would equate reasonably well to a less theoretical and more actual
effect?

Would the total displacement really change, without the mass of the
Crew or density of the water also changing?
I keep telling my crews to not row in the same place for too long, but
it looks like that's what the protocol above would be.  [;o)

- Paul Smith



Donal
On 26 Feb, 21:54, paul_v_sm...@xxxxxxxxxxx wrote:

On Feb 26, 10:22 am, marco.b...@xxxxxxxxx wrote:

I need some clarification no a table published on the Vespoli Website:

http://www.vespoli.com/content/view/285/182/

In this table they compare displacement and waterline measurements of
the latest Vespoli 8+ design with the one of some of the major
competitors.

I'm trying to understand how they came up with few numbers.  I
understand that shorter waterline doesn't correspond with lower
displacement but I don't understand how the with Resolute shorter
water line (16,791 m. vs 16,891 m. for Vespoli), shorter beam (0,573
m. vs 0.586 m.), smaller depth (0.183 m. vs 0.182 m.) end up having a
larger wetted surfice?
Isn't the wetted surface the product of these measurements?
Also how come the Wetted Surface is the same to the Hudson in square
feet but it's different in square meter?
Can someone explain me that?
Marco

Seems like once we get to a normalized mass displacement we're dealing
with a +0.1 to 0.2 square meter difference in wetted surface, or about
1%.
Not very much, and as has been discussed before, the wavemaking
characteristics will vary with the targetted speed of the hull,
unfortunately the hull speed can vary considerably from the Avg system
speed and that may result in chasing a phantom "optimal shape" for the
desired "Gold Medal Standard" avg speed.  At least if efficiency is a
primary concern, which I'd suggest, it is not; at the top levels of
competition.

Even the wetted surface must change during the stroke cycle, at least
as it appears from watching the boats, there seems to be varying
degrees of planing and sinking as the hull speed goes through it's
variations.  Or does a "displacement hull" not have any properties of
a planing hull?

Maybe the answer would be to come up with a hull shape that takes into
account the variations in speed to achieve the best balance of small
wetted surface and small wave making, as it could "Appear to the
water" to be morphing fluidly between displacement and planing
conditions.

- Paul Smith- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

.

Relevant Pages

  • Re: Tricky math?
    ... necessarily balance the boat. ... Would the total displacement really change, ... Also how come the Wetted Surface is the same to the Hudson in square ... unfortunately the hull speed can vary considerably from the Avg system ...
    (rec.sport.rowing)
  • Re: technology changes?
    ... skis - it's astonishing that it was not done years earlier. ... For centuries, if not millenia, it's been well understood that a long narrow hull will move through the water faster than a short, wide hull. ... Part of the reason is that a wider hull must push more water out of the way as it goes by, but there's also the concept of "hull speed" which says that the max speed a boat can travel is proportional to the square root of the length at the waterline. ...
    (rec.skiing.alpine)
  • Re: Water Usage in Locks
    ... The larger the displacement, ... the water level drops significantly. ... The same could be said of a lock. ... > the boat has direct impact on the water volume within the lock. ...
    (uk.rec.waterways)
  • Re: Actively variable deadrise
    ... boat so it makes more sense to have a different boat design for ... above the surface of the water because of the hull’s buoyancy and by ... At a point called hull speed your boat will be traveling in a trough ... variation in dead rise angle measured at different points from bow to ...
    (rec.boats)
  • Re: Water Usage in Locks
    ... The larger the displacement, ... the water level drops significantly. ... The same could be said of a lock. ... >>> the boat has direct impact on the water volume within the lock. ...
    (uk.rec.waterways)