sanding the hull for speed

mixmkr

mixmkr

Well-Known Member
Reading another thread, it was suggested that some #220 sandpaper to scuff the hull, actually was faster than a waxed hull. Knowing a bunch of J22 racers and such, they always wet sand with #1200 or so and would only use 220 to sand out scratches. I can't see the Americas Cup boats using such a course grit either.

That said, the dimples on a golf ball are there for distance(speed) and Dennis Connors did affix some "rivlets" on his old 12 meter...stuff that replicated shark skin and had a texture. It was proven to be faster but was illegal for racing Amer Cup.

I think wax somehow might "grip" the water so to speak...but I think a smooth bottom is preferred. What are some of you racing guys doing?
 
mixmkr said:
I think wax somehow might "grip" the water so to speak...but I think a smooth bottom is preferred. What are some of you racing guys doing?
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Dunno, but your question suggests that an unwaxed "flat" paint would be an improvement over "gloss". :oops:
 
im also intrigued, i cant recall when and where but i have also read a rough surface is better than a smooth one for sailing

maybe this doesnt have any relation but the "dimples" in golf balls are there for faster and longer distances.

quote:
Dimples on a golf ball create a thin turbulent boundary layer of air that clings to theball's surface. This allows the smoothly flowing air to follow the ball's surface a little farther around the back side of the ball, thereby decreasing the size of the wake.
 
I'm hoping someone with some science background has an opinion n this that they post here before I start sanding and worrying, lol !!!!!
 
Letitflow said:
I'm hoping someone with some science background has an opinion n this that they post here before I start sanding and worrying, lol !!!!!
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No serious racer sands their hull with 220 as their final finish. I'd search online but suspect you'll find perhaps 1000 grit is recommended. In any even there must be better info available on the web than what you will find here.
 
Charles Howard said:
One bad tack or missed wind shift and any benefit is lost.
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That is not really true. When leaving the starting line, a bit of extra speed in the first 3 minutes of the race can get you bow out on the boats near you, so you can hold your lane. On the other hand, if you are slow, fall behind and cannot hold your lane, you will be forced to tack to clear your air and you will sail the whole race trying to come back. That bit of extra speed can also give you the two inches you need to clear a starboard tacker, meaning you can keep going to your preferred side of the course without being forced to tack- a potentially huge benefit.

With that said, I am not sure that a wetsanded hull will give you that speed anyway, but every tiny bit of speed can make a huge difference in the final score of a regatta.
 
You're speaking of the surface effects of Boundary Layer air/water flow and it's relation to surface roughness. Here's a link to
research done by the Rand Corp.

http://www.rand.org/content/dam/rand/pubs/research_memoranda/2009/RM1129.pdf

There is also drag reduction in squaring off the trailing edge of a Dagger board and Rudder although I don't know
exactly how much to take off although racers have done this. Removing a small amount of drag can make a difference over
the course of a race and through many races. The One-Design rule is set up to reduce this as much as possible, hence you can't
remove the Bailer and still race.
 
Back in the 70's when I was covering The America's Cup I asked Ted Turner about sanding. He said it allows the hull to better grip the water but declined to go into details as what to use and how to use it. I am pretty sure the Aussies sanded don't know about Baron Bic. Turner who was racing for the N.Y Yacht Club which hated his guts..won . and celebrated by being totaly drunk at the NYC news conference.
 
beldar boathead said:
No serious racer sands their hull with 220 as their final finish.
I'd search online but suspect you'll find perhaps 1000 grit is recommended. In any even there must be better info available on the web than what you will find here.
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Googling "sanding the hull of a race boat" got this:

" After spraying, he says, sand with 600 or 800 wet-dry paper and then burnish the entire area...He says the best way to get a smooth finish on the bottom of your boat is to spend the proper time filling and fairing first, and then move to the sanding.

"We once brought a 12-year-old Beneteau First 8 back from the graveyard with a new bottom job. Basically we used orbital sanders to take all the paint off and take the bottom down to gelcoat. Then we gridded the bottom with four-inch squares using a wooden yardstick. After that we used a straight-line sander that's 12 inches wide :eek: and worked from the waterline down to the keel; we kept this up until we sanded off the surface layer and we found the low spots. Then we abraded those spots with 80-grit paper and filled them with a marine-surfacing compound made by 3M.

Much more at:
http://www.sailnet.com/forums/racing-articles/20783-hull-preparation-performance.html "

The bottom of my most-used Sunfish is so "bendy" :( I'd stay with a 3" sanding block. (Or just use a "flat" paint finish instead of "gloss"). :cool:
 
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Many thanks for posting the piece. Sunfish Hulls have alot less fiberglass than the boat he is talking about,,thus the flex . The older ones alot less then new ones. Like people...each one is an individual with its own set of problems. . I would be hesitant about sanding too much of the hull off on older fish.
 
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