Reducing hull friction

[syotr]

Anyone used special coatings to reduce friction between the hull and the water? I am building a kayak to race in whitewater and would like every advantage.

[jehardiman]

Starving and purging for two to three days before to get your weight down 5-10 lbs will have more effect than any hull coating in whitewater conditions.

[rturbett]

What would happen if you sanded horizontally on the front half of the hull, and sanded vertically on the back half? Wouldnt that create an magnetic field that would help propel you through the water? Of course, if I got the directions reversed, it might send you backwards!

Seriously, I posted the thought of putting a graphite finish on my boat. (harder finish, smoother wet sanding) Knowledgable people shot that idea down.
Rob

[syotr]

Originally Posted by jehardiman

Starving and purging for two to three days before to get your weight down 5-10 lbs will have more effect than any hull coating in whitewater conditions.

I normally weigh about 150. I try to get down to 140 by the day of the race by special diet and exercise the month before.

[syotr]

I have seen some coatings advertised that you paint on regular motorboats which is supposed to reduce friction, improve speed and gas mileage. I wonder if they would have a measurable effect on a human powered craft?

[jehardiman]

Originally Posted by syotr

I have seen some coatings advertised that you paint on regular motorboats which is supposed to reduce friction, improve speed and gas mileage. I wonder if they would have a measurable effect on a human powered craft?

Not in whitewater. There is some effect on HPV propeller torque, but in the hulls Renyolds regime any effect is lost in surface disturbance flow loss noise.

However, "Fast is as Fast thinks", so if you want to apply a hydrophobic teflon wax and think you're faster because of, so be it. Note that this assumes that the hull is already fair within +/- 0.05mm and 800 grit sanded ready for a filler wax. If not, get out the long board.

[longliner45]

vinal coat ,,it will reduce drag,,dont know how much,,,,,we used it on our fishing boat once ,,it made some economic sence,,longliner

[nordvindcrew]

I recently had a conversation with a person that had done design work on 12 meter keels and he said his research indicated that sanding with 1200 grit wet paper to get a finish where water disperses rather than beads is the way to go. His explanation is that then the shear is water to water rather than water to solid finish surface. Can't back it up, just an idea I heard from a pretty smart guy

[frosh]

I see two possible methods, the first being more preferable and easier. Use the highest quality yacht hull graphite finish. Whether it works or not actually doesn't matter in reality. Psychologically it will work and maybe give you up an extra 1% in performance.
The other one I don't know a lot about personally, but you could investigate the full suits that elite swimmers now use in races. They are not ultra smooth as logic might suggest, but mimic the surface skin of a shark somehow. This theory has been tested and works for swimmers for sure.

[Bergalia]

Frosh isn't far out with the idea of mock sharkskin - the fabric is available here down under (expensive) but I believe it's used in the modern swimming wear with which the Aussie swimmers make the US team look silly....
But - I also believe there is a 'wax' used by surfers (like skiers) to give a better 'grip' on the waves. Worth researching ?

[Frosty]

--smooth and glossy is not fast, glass like surfaces is not good.

Egg shell is the type of surface to go for thats why an egg is the fastest thing in the sea.

If you paint an egg and drop it into the sea it will reach the bottom---- eerm-- hang on a minute.

No ---if you drop an unpainted egg along side an painted egg you get,-- eerrmm.

Oh my dinner is ready. goody goody

I think I should get some neg points for this. Dam!!!

[Bergalia]

Originally Posted by jack frost

I think I should get some neg points for this. Dam!!!

Negative points on the way Jack, for misspelling 'damn....'

[Delane]

A: Because of water tention. That best sums up the wax theory.

Another example is Golf Balls. Break up the laminar flow and extend the shot.

I beleive 3M developed a special coating years ago for one of the Cup races. Yes, not silky smooth, but like a shark skin finish.

Bubbles pumped out of small holes at strategic places around the hull. Something about this is in the forum somewhere? The Chinese are or have developed a Torpedo that uses a bubble generator at the head to basically allow it to travel through mostly air verses water at tremendous speeds.

[Bergalia]

Originally Posted by Delane

....Bubbles pumped out of small holes at strategic places around the hull. Something about this is in the forum somewhere?.

Some time back now Delane - you'd probably have to 'Search' it. Another system which I saw in practice was the hull 'plated' with small overlapping 'tiles' - not unlike roof shingles. The motion through the water caused air ripples to flow back from the 'tiled' surface. Impressive - but relied on speed in the first place. Bit like the ram-jet. Needs high speed to go even faster.

[Bob Bird]

Thirty years of canoeing here. I have learned to wax my canoes regularly. Sometimes before each trip. Makes a big difference. Mother's California Gold seems to work best.