Will golfball dimples make my boat hull, surfboard or sailboard go faster

The problem is that its not just the dimples making the golfball go further – it is the spinning and dimples together.

It works because as the ball rotates with backspin because of the slope of the club’s face it pulls air over the top in the backwards direction and underneath in the forwards direction.
This means the effective air velocity over the top is increased and that underneath is reduced.

Sound familiar?

Yes, it is the same way a wing gets lift.  The faster airflow over the top reduces pressure because of Bernoulli and the opposite happens underneath – the ball is really flying something like a wing .. it is gliding.

The old story about a “wing being longer over the top so the air has to go faster is wrong.  Otherwise sails, bees, dragonflies, paper planes and balsa gliders which have the same distance both sides of the wing wouldn’t be able to fly.

How sails really give lift - link to articles by Arvel Gentry

So if you plan to spin your boat and it is ONLY in Air or only in water without touching the other … you might just be on to something!

There have been numerous attempts to get some “super surface” to work by reducing vortices and keeping the smooth (laminar) flow at the beginning of the hull going for more of the hull length, but none of them have proved practical.

The best solution is a surface that is FAIR – smoothness at the building level and then has a smooth surface as well.

There is not a lot of difference between a nice paint job or a nice paint job plus sanding with about 400 grit wet and dry sandpaper and water using a sanding block – NOT hand held.
This is particularly true for the first part of the hull and the first part of the foils because the water gradually moves from smooth (called laminar) flow to turbulent flow.

You can see the difference if you leave a tap running just slightly faster than dripping so there is a stream.  The first part is beautiful and smooth, almost mathematical, but a little further down towards the sink the stream of water suddenly becomes rough and turbulent.  This is inevitable.  There is less drag on the hull from the smooth flow so it is better to have as much as possible.  So it is a good idea to get rid of roughness.

Practically this means that with foils in particular and maybe the front part of the hull it could be sanded.  They say spend about 70% of your time getting the first 30% of any boat surface smooth.

Personally I would almost ALWAYS sand foils but usually just try to get a nice paint finish on the hull.

I did see that “Mythbusters” found otherwise with a full sized car.  Mythbusters is entertainment and only moves into the area of science occasionally where it won’t spoil the story.  Testing flow and drag with something as complicated as a car is very tricky.  A dimpled car just possible might have some local effect that might smooth some local drag.

For example if the air going over a particular car normally suddenly changes from smooth flow to turbulent going over the  top of the windscreen causing a lot of drag it is possible that just through luck the placement of dimples might reduce that drag enough if the dimples are the right size and just the right position.  That’s why such testing is normally done with much simpler shapes.

If dimples did reduce drag in this way, then Boeing and every cargo carrying ship would have been using it for years.  But it don’t, so they don’t.

At least until I see a properly referenced and scrutinised scientific paper that says I am not correct (along with Boeing).

If you want to get into wing theory a bit more and want to know why it really works, you need to read Arvel Gentry, who I read when I was about 14 and digested over a couple of years.

He caused so many arguments at the time because people were reluctant to give up the old ideas of “flows faster because of longer distance” and the “air accelerates in the slot between the mainsail and jib” which had been held for a considerable time by aerodynamists and others that should have known better.

Start with Arvel’s “the origins of lift” and work your way through it on Arvelgentry.com

Hope this helps.

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9 Comments on "Will golfball dimples make my boat hull, surfboard or sailboard go faster"

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Osbert
Guest

Thanks for that. But isn’t there something about micro-scales on sharkskin reducing drag? I seem to remember something about some Olympic swimmers being disqualified for wearing suits with that effect.

Scot McPherson
Guest
The description of the dimple effect on golf balls is not entirely accurate. The spin of a golf ball is created mostly by the striking force, i.e. where the ball is struck in it’s travel vector…i.e. hitting it close to horizontal, but low. The angle of the club face has a lot to do with _where_ the ball gets hit and how much spin is transfered because of creater surface contact on the striking surface. Consider a basketball. When you bounce it nearly vertical, no spin. Add some angle to the bounce, and the greater the angle the more spin… Read more »
josh
Guest
I always found that mythbusters episode to be flawed, they only ran the car one way, in record setting where wind can change the results you have to run the course both ways, check out the rules for the bonneville salt flats racers, two passes both ways with a strict limit on the time between passes or it doesn’t count, the other example being for the worlds fastest human powered boat, MIT in MA, USA set the record but they had to do a run both ways and then average the times to get the speed. Mythebusters did scale the… Read more »
Bruce Taylor
Member
I guess that golf balls have had an awful lot of scientific measurement on them. Pretty much though, if you wanted to design a golf ball that just had to fly as far as possible, then it would have to be perfectly smooth. It gets complicated, because golfers want control as well, so the size, shape and number of dimples dictate the characteristics that a particular golfer might want on any given day. Your comments on the first 30% of the boat’s surface needing the most work sounds about right. But I just want to make a comment on foils… Read more »