Thread: 70 mph with less drag?
03-27-2010, 05:29 PM #1
70 mph with less drag?
Isn't a stock pro 785's top speed around 63 ? If you trued the hull, sharpen the strakes, polishing the plate and grate and polishing the tunnel,prop, and stator, waxing,then teflon over the hull, how much additional speed is obtainable?. not counting props or head work or any mods.
03-27-2010, 05:51 PM #2
.2-.5 Polishing will loose speed. The trick is to break water tension. Also the back of any surfice should be a 90*or more to break the tension.
03-27-2010, 06:41 PM #3
- Join Date
- Oct 2006
- Cleveland OH
03-27-2010, 07:30 PM #4
This is my reasoning for polishing the plate and grate.
Fluid-object interactions are often illustrated using flow lines to represent flow behavior. Prior to the interface, the approaching flow is a pattern of smooth parallel flow lines. This is called rectilinear flow. Velocity along each line is constant (although different lines may have different velocities). At the front surface of the object, the flow lines part to move around it. For a smooth ((polished and gotten rid of pits,or bumps))streamlined object with its axis aligned with flow (e.g., a thin plate situated parallel to flow), the disturbance in the flow lines is minor, and they quickly retake a rectilinear pattern after leaving the trailing edge of the object. This flow is considered one-dimensional, because all of the velocity vectors remain virtually parallel. Mathematical analysis becomes considerably more complex when two- and three-dimensional flow fields are considered.
Consider the flow lines for a flat plate situated perpendicular to flow. They approach the plate in rectilinear flow and then are forced widely apart upon impact. They move across the plate surface (where the boundary layer forms), but are unable to make the sharp turn following the plate edge. The boundary layer separates from the plate surface and plunges into the free-flow area. An area of extreme turbulence occurs directly behind the plate, characterized by swirling eddies and vortices (i.e., a wake). The eddies dissipate their energy with increasing distance from the plate and eventually flatten out into uniform flow lines again.
Flow within the boundary layer along the plate surface can be laminar (uniform) or turbulent. This is important because the shear forces (and thus the drag forces) ((this is why)) are higher in areas of turbulent flow. For the parallel-flow plate, flow is usually laminar near the plate's leading edge, and then becomes turbulent at some point along the surface. Quantitatively, this is represented by the dimensionless Reynolds Number (NRe). For any distance x along the plate, NRe,x= xv/, where v is the bulk fluid velocity, is the fluid density, and is the fluid viscosity. The NRe,x value at which flow becomes turbulent varies between 10,000 and 3,000,000, depending on the smoothness((Theres that word again!)) of the plate and the turbulence of the approaching flow ((you mean that polished hull in front of the pump NOT creating any disturbance?)). If the transition from laminar to turbulent flow occurs nearer the plate's leading edge, then the total drag is higher than it would be for a transition located farther downstream. ((So it is important to have the hull smooth right before the pump area!)).
((Shows ya in that last couple sentences why its important to have the ride plate flush and smooth to the hull.))
I got the info from here. http://www.bookrags.com/research/hydrodynamics-wom/
Interesting reading anyway for all you hydrodynamics geeks out there! lol I'm interested in it.
03-27-2010, 07:36 PM #5
03-27-2010, 07:38 PM #6
03-27-2010, 07:44 PM #7
03-27-2010, 08:21 PM #8
Applying something to the hull that helps keep an ultra thin film of water against the surface will yeild the fastest results. Above all else, water slides best upon itself ...hint hint (a little known speed trick)...man, brings back memories of the good ole days with the slip-n-slide!
Last edited by 32DegH2O; 03-29-2010 at 11:56 AM.
03-27-2010, 08:26 PM #9
03-29-2010, 09:41 AM #10
On a full size boat (outboard) it adds about 2mph or more. It seems like on a 55mph ski mine runs the same with a big gash out of the bottom, a broken intake grate or smooth.
My Lavey has sharp edges and a special primer on the running surface that has been sanded.
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