Like Tree0Likes

Blistered, dimpled, smooth--Which is faster?

Reply
Old 08-25-2002, 08:51 PM
  #1
Registered
Platinum Member
Thread Starter
 
Join Date: Jan 2001
Location: PA and MD
My Boats: fuel injection, superchargers
Posts: 1,449
Default Blistered, dimpled, smooth--Which is faster?

After reading the thread on the Donzi and the blister problem I was wondering which surface is faster?

1)Blister-- and the tiny little bumps
2)Dimpled-- and tiny little dents like on a golf ball (less wind resistance and more distance)
3)Smooth--speaks for itself
4)Waxed smooth--some say is slower
5)Bottom paint--rough surface, slower

What do you think? Has any manufact tried different hull surface textures and how they effect speed?
cobra marty is offline  
Reply With Quote
Old 08-25-2002, 09:48 PM
  #2
Registered
 
Mark in So. MD's Avatar
 
Join Date: Mar 2002
Location: Solomons Island, MD
Posts: 885
Default

Wouldnt it seem that the dimpled golf ball with less wind resistance is kinda like the step bottom with less water resistance.

And without a step, like you said, smooth, it speaks for it self. I have also heard some say wax is slower, but then you have "Hydrocoat"(sp), but does it really work?

And you would think there would be a simple answer to this.
Mark in So. MD is offline  
Reply With Quote
Old 08-25-2002, 10:05 PM
  #3
DJD
Registered
 
Join Date: Oct 2000
Location: Greenwich CT. U S of A
My Boats: 38' Cigarette, 42'Post, Driver:F2-07 Wild Child
Posts: 1,839
Default

When hit properly, the spin of a golf ball with the dimpled surface gains altitude giving it farther distance.
The bottom of a boat is not spinning (aside of a few that go too fast into a turn) and dimples create more drag.
Wax also creates drag.
speed gain???.........Wet sand the bottom of your boat with 800 grit paper.
DJD is offline  
Reply With Quote
Old 08-25-2002, 10:10 PM
  #4
Banned
 
cuda's Avatar
 
Join Date: Sep 2001
Location: Deland, Florida
Posts: 25,191
Default

I think the boat with the most horsepower will go the fastest!
cuda is offline  
Reply With Quote
Old 08-25-2002, 10:21 PM
  #5
AT Cult Member #3
VIP Member
 
R Addiction's Avatar
 
Join Date: Oct 2000
Location: Pa.
My Boats: '99 Active Thunder Tantrum
Posts: 20,687
Default

Sand the bottom of my high dollar boat for, maybe, 1 MPH!!! I don't think so.

R Addiction is offline  
Reply With Quote
Old 08-25-2002, 10:34 PM
  #6
Registered
 
Join Date: Aug 2001
Location: Gainesville Fl.
My Boats: 93Avanti 27' 502
Posts: 573
Default

The bottom of my wake board is dimpled Sand the bottom of a good hull I don't think so eather
FloridianSon is offline  
Reply With Quote
Old 08-26-2002, 12:44 AM
  #7
Charter Member #232
Charter Member
 
Audiofn's Avatar
 
Join Date: Oct 2000
Location: Carlisle, MA USA
My Boats: 1979 Formula 302, 99 Formula 353, 81 Donzi 18 2+3 with 454
Posts: 18,379
Default

Ok guys do not shoot me but the blow boaters sand to a perfectly smooth finish. They go up to 4000 grit on the sand paper and make it perfectly smooth. If you ever get a chance to take a look at a high dollar racer thake a look. The finish is nothing short of amazing.

Jon
__________________
Put your best foot forward!
Audiofn is offline  
Reply With Quote
Old 08-26-2002, 05:20 PM
  #8
Registered
 
Racing_Fan's Avatar
 
Join Date: Mar 2002
Location: Alexandria, VA
My Boats: 2004,Formula,292 FasTech
Posts: 64
Default

I recall from my Fluid Mechanics course (don't quote me here, I fell asleep alot in that class ) that a dimpled golf ball travels farther because the dimples allow the air flow around the ball to become turbulent, rather than laminar, resulting in less drag. My only fear about creating turbulent flow underneath a boat would be that the flow of water would be aerated, and that situation might cause a handling nightmare.

As for Hydrocoat, there was a thread on OSO earlier this year about this product. I seem to recall that wax slows a boat down because the waxed surface creates more drag because you have the water surface flowing against the wax layer. The Hydrocoat product is supposed to allow the hull to pick up a layer of water, so that you have water flowing against water, reducing drag and increasing speed slightly.

Fluid Mech guru's, please correct me if I'm way out of line on this one

Last edited by Racing_Fan; 08-26-2002 at 05:26 PM.
Racing_Fan is offline  
Reply With Quote
Old 08-26-2002, 06:06 PM
  #9
Platinum Member
Platinum Member
 
CigDaze's Avatar
 
Join Date: Jun 2001
Location: St. Petersburg, FL
My Boats: Cigarette 35 Cafe Racer
Posts: 21,346
Default

Racing_fan, you're really close with your statement. The dimples work twofold on a golfball. One, they do disturb the airflow and allow a greater boundary layer to form around the ball. This allows some air to stick to the ball creating air-to-air drag, which is much less then air-to-solid drag. Secondly, as DJD eluded to, it is this same adherance that allows the ball to generate greater lift while spinning and thus allowing is a longer range as it counteracts gravity pulling it to return to earth.

How, this translates to boats?...Well, a lot of paralells can be drawn and this also applies to aircraft. Next time you are flying near a wing seat, notice the little triangles along the leading edge of the wing right along the spar(also the center of lift). These are called vortex generators and that's exactly what they do. Turbulate the air and disturb laminar flow. Once again, this reduces the boundary layer drag. The motion of the air is not always paralell to the surface, some of it is rotating and away from the surface. The vectoral flow being in different directions changes the components of drag and ultimately reduces the sum of all drag.

Same goes with boats. You want a certain amount of the water, on the order of a few microns, to adhere to the hull. This eliminates water-to-solid drag and induces water-to-water drag. It's bordering on hysrostatic loading(like a film of oil on a piston), and helps lower the friction. Theoretically, this would lend itself well to sanding or some sort of irregularity. However, the reynolds number and density of water is orders of magnitude different than air and boating velocities are realms apart, relatively speaking. To notice the same kinds effects as aircraft, boats would have to be in the 400-500mph range.

Like most racers will tell you, the speed cotes, snake oils and sanding will barely account for a single mph...Worth it, not really?
CigDaze is offline  
Reply With Quote
Old 08-26-2002, 06:16 PM
  #10
Registered
 
Frequency's Avatar
 
Join Date: Aug 2001
Location: Peoria, IL & FMB, FL
My Boats: '91 Carbon 70 Cafe, 3370 Pursuit
Posts: 1,008
Default

Laminar flow is a good thing, allowing the boundary layer of water to remain attached to the bottom of the hull, which in turn reduces drag. Golf ball dimples are effective due to the round shape of the ball. As air passes over the ball at it's maximum diameter, the boundary layer tends to be pulled away from the ball due to the significant pressure differential. Dimples keep the boundary layer attached to the ball further back, reducing overall drag.

Consider the shape of a bullet. Very different from a golf ball. I don't recall ever seeing a dimpled bullet. Anyway, we're talking about boat hulls. Laminar flow is difficult to maintain, and it is difficult to design a surface that will maintain laminar flow in a resistive medium (water). Flow of water over the hull will turn turbulent very quickly. Of course, this means sanding a stepped hull beyond the first step is a waste of time as the flow is already turbulent.

My $0.02
Frequency is offline  
Reply With Quote
Reply

Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
kennyo
Baja
3
08-16-2006 11:15 PM
SCOPEwebmaster
General Boating Discussion
46
08-14-2004 02:26 PM
Payton
General Boating Discussion
2
03-17-2003 10:47 PM
puder
General Q & A
8
03-17-2002 04:52 PM



Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 07:52 AM.


Copyright 2011 OffShoreOnly. All rights reserved.