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darryl
05-27-2012, 06:20 PM
Was thinking today about rigging up a mold for making pontoons. Then I'm reminded about the textured surface on golf balls making it fly farther. I wonder if there's a texture which would make a boat hull glide through water easier?

Beyond that, might there be a surfacing material which could be added to the gel color coat to do the same job? I know there are paints which help prevent stuff from sticking to the hull, but that's an after-the-fact additional coating. It might be good to mold the hull with any such additive included directly into the finish coat, which in the case of fiberglassing would be in the gel coat.

I'm not up on anything which might be a recent advance in fiberglass and resin technology, so I really don't know if there is any material or method which would result in a lower friction hull. Anybody more clued in than me?

Maybe I just build it smooth then rub a dead fish all over it-

customcutter
05-27-2012, 06:55 PM
Get as much of the hull out of the water as possible. Use the lightest building materials/techniques possible. Years ago I had a soft spot in the floor of my bass boat. I stripped it down, ripped out the bad floor, replaced the rotten stringers and transom, also ripped all the hatch covers out. Replaced everything with divinycell(sp) except the transom. Replaced all of the foam also, a lot of it was water logged. I though it was fast before, all the weight reduction lifted the hull 3-4 inches when sitting in the water. It was "scary" running on the pad and running the trim up to "break it free". It was more like flying than boating.:eek:

I've seen several video's where the entire boat rises up out of the water and runs on "foils". That would be interesting a pontoon on foils.:D

Good luck.
Ken

loose nut
05-27-2012, 07:57 PM
I don't know about boats but they have good results by putting a pebbly surface on the front of a car to reduce friction/air resistance.

Mike Burch
05-27-2012, 08:36 PM
Darryl, there have been literally millions of dollars spent in researching this, and the general conclusion still seems to be that smooth is best.
Without going too deeply into Reynolds numbers and other mysteries of naval architecture (and I do recommend that you read a good book on the subject), let me just say briefly that there are two basic types of hull, displacement and planing.
A displacement hull's maximum speed is governed by its length—it is a function of the square root of the waterline length. With a clean bottom at normal cruising speeds the majority of the resistance comes from wave-making. At slower speeds the frictional resistance can be a significant proportion of the total.
With a planing hull, there is a dynamic lifting effect from the water, and at full chat very little of the hull is still immersed. A hull designed for displacement will never plane, no matter how much power you feed it.
Putting little dimples all over the hull has been tried and generally found to be a waste of time and effort (and money).
There is a product which mixes copper dust with epoxy as a first layer of gellcoat, but although it lasts a while, it's nowhere near a permanent solution to fouling. The job of a gellcoat is look good above the waterline and keep the water out of the layup below it, and anything which compromises the latter and promotes the dreaded osmosis must be avoided.

darryl
05-27-2012, 08:42 PM
That's kind of like a golf ball, the pebbly surface. I would think something similar would work for water, but with different magnitudes involved because water is much more dense.

I've always liked the hydrofoil idea, and it would be fun to experiment with that on a model. We have a much better power/weight ratio these days, in terms of electric motors and batteries, so the result could be 'electrifying'.

I would like to build myself a two-hulled two person craft to replace my stolen canoe. The idea is to create a seat structure from fiberglass, which would have 'wings' on it to fasten each pontoon to. Two seats would be made, and it could be rigged with only one, or with both. Mounting points would be available on the pontoons to accommodate either way. It could be left assembled and put on a roof rack, or taken apart for more compact storage. I would also consider making the seats so they can be turned sideways and still mounted to the pontoons, so the pontoons are close together. You would probably not use it like that, but it might make for more compact storage with all the parts together.

I'd like to keep the total weight under 75 lbs or so, which is still less than what my canoe was. Lots to consider here.

elf
05-27-2012, 09:40 PM
75 pounds is rather heavy. I think you need a baidarka instead of a canoe :)

Gazz
05-27-2012, 09:57 PM
I believe I have read that the roughness of a sharks skin gives it considerable hydrodynamic qualities. But I don't know how that would apply to a boat hull. I do know that removing any algae growth or other living organisms from the hull will increase the speed. I once had a very old fiberglass boat (made in 1959) and the gel coat had basically decayed from the hull leaving it kind of furry with the actual strands of fiberglass. That boat was real pig.

darryl
05-27-2012, 10:21 PM
I will make it smooth, then.

My canoe weighed 85 lbs, and I portaged it many times. I liked the canoe but not the weight.

A friend and I set out to build our own canoe with weight saving in mind. To this end we were planning to keep the skin thinner, but add ribs to keep the strength and shape throughout the hull. We started by building a mold around an existing canoe. Our efforts on the mold were a bit of a disaster, as my friend failed to take into account the factors involved with the resin. Basically, he put in too much hardener, the resin was black, and we were working in the sun. Long story short, the mold didn't turn out, but the skin was intact, so we added the ribbing inside of that. It became a canoe, 14 ft in length and weighing 25 lbs. You could reach down below the level of a dock and lift it out of the water with one hand. He used it for years like that.

I intend also to use ribbing to help a thinner skin keep its shape. We developed a method of making the ribs in place, which meant that every rib was a custom fit for its placement and bonded as well as it could be. I would plan to fabricate the hull inside the mold and add the ribbing as I go, for the best bonded structure possible.

Anyway, I know that my design of having fiberglass molded seat structures will be heavier than just adding wooden board seats to an existing hull, but I will try to take advantage of every weight-saving measure I can.

One concern I have for the design is that I don't want to raise a wake between the pontoons because of forward motion. I had enough of that when we lashed two canoes together and raised a sail. We had water rising up higher than the sides of the canoes. I suppose the inside surfaces of the pontoons will have to be straight and parallel, regardless of what curvature might be on the outside surfaces.

I also plan to totally avoid the use of threaded fasteners. I don't want to deal with corroded threads, or need to use screwdrivers, etc to put the thing together.

Astronowanabe
05-28-2012, 03:55 AM
something like this might be interesting
http://www.fastcoexist.com/1679878/mits-freaky-non-stick-coating-keeps-ketchup-flowing

there are two routes to try one a hydrophilic surface so a layer of water sticks to the surface and does not move with the water flowing over it so your hull is effectively painted with a layer of water.
another approach is a hydrophobic surface that discourages water from contacting in the hull at all.
my bet would be on hydrophilic surface cause fish are slimy.

Mike Burch
05-28-2012, 04:23 AM
If this vessel is to be man-powered your chances of getting it up to hull speed (when the speed in knots equals 1.3 times the square root of the waterline length in feet) and keeping it there for any significant length of time are remote, unless your middle name is Silverback.
At hull speed, the hull is supported fore and aft, with a hollow in the middle. And the poor boat is trying to climb up its own bow wave, which it simply can't do, which is why a displacement hull just can't go any faster.
The vast majority of the resistance to forward motion at that sort of speed is caused by wave-making, and there is very little you can do about it. The frictional resistance at that speed is a very small percentage of the total, so don't waste your time worrying over-much about it.
And if you want the boat light, use carbon fibre and epoxy.

Mike of the North
05-28-2012, 04:50 AM
Are you trying to make something like this but for two people?
http://tufox.com/hobie/index.html

johnnyd
05-28-2012, 11:19 AM
Here is a link to a "super hydrophobic" coating that recently came on the market.
I don't have any first hand knowledge of how well it works, I just saved the link.
Hope it helps. John




http://www.neverwet.com/

Forestgnome
05-28-2012, 11:42 AM
Lowering hull resistance falls into two realms, planing and non-planing hulls. The difference is defined by where the bow wave ends up, in front or behind the bow. Yours would be a non-planing hull. The best I've seen in non=planing hulls are surface-piercing designs. They minimize the bow wave and therefore the energy needed to push the wave. The earliest designs were on native canoes of Alaska and the Pacific Northwest. Golf ball dimples shape the air around the ball creating lift. This was used to some success in Nascar in the 70's to reduce drag. As far as planing hull surfaces go, roughing up the rear third of the hull using coarse sandpaper has been noted to improve speed by creating small channels for air bubble traveling rearward thereby breaking the hull-water interface. Breaking loose from the friction of water has been the goal of most high speed hull designs. According to a hydroplane speed record-holder I know, the sandpaper trick only starts working above 85mph. Below that glass-smooth is the ticket.

Void
05-28-2012, 12:10 PM
Many years ago I used to clean sail boats (therefore displacement hull) of fouling. We used scuba tanks, full wet suits, (SF Bay is pretty cold) and mainly used big green scrubbies with plastic handles. Very hard work. It did rack up dozens of hours for my dive log book though.

The skippers said the difference was immediate in that it could add 1-2 knots to the speed of the boat. They also wanted their boats scrubbed the morning of the race to obtain maximum benefit. 24 hrs after a scrub the film of microbial life would again be noticeable.

The two types of boat bottoms that were easiest to clean were the type that had a coating that would easily scrub to a matte (think wet sanded primer) finish. Gel coats below the water line were very difficult to clean (my experience) and not the fastest (skippers experience.) Of the two types that would scrub easily were the blue colored anti-fouling and the copper based (maroon/brown colored) anti-fouling. The copper based anti-fouling was the most effective but it was also the most expensive. At the time (late 1970s) there was talk of restricting the use of the copper based anti-fouling in the Bay Area.

I got quite a bit of experience and feedback from some skippers because we did their boats at least once a week for an entire season.

That's about all I remember that is relevant. It was a long time ago and much may have changed in the technology and techniques since then.

-DU-

RWO
05-28-2012, 02:02 PM
During one of the US based America's Cup races some years back, I seem to remember that someone( might have been 3M) came up with a textured plastic film for application to the hull of the US yacht that reduced the hydrodynamic drag.

RWO

Googgle found this:
http://www.nasa.gov/centers/langley/news/factsheets/Riblets.html

http://www.kisspolymers.com/Science/dragreduction.htm

http://books.google.com/books?id=iq4YLNE2D7UC&pg=PA60&lpg=PA60&dq=drag+reducing+film+for+racing+yachts&source=bl&ots=qOaky0ypHc&sig=mw3N1fiiODPcChulnUrUaxJKHKo&hl=en&sa=X&ei=TK3DT5X6C-qa2gXntpCNAQ&ved=0CFIQ6AEwAg#v=onepage&q=drag%20reducing%20film%20for%20racing%20yachts&f=false

darryl
05-28-2012, 04:57 PM
Thanks for all the input gentlemen. Never-Wet was particularly interesting, as was the swimming motions of fish. The hobie cat is pretty close to what I have in mind, though a slightly drawn-out lengthwise version of the pontoon would be closer.

Imagine taking a 14 ft canoe and cutting it in half lengthwise, then put a flat wall up each one to restore the hull to a floatable condition. These would be separated by the seat structures and the result is the hobie cat. The difference would be that the inside walls of the floats don't force a wave of water up between them during forward motion. That's what I'm looking for.

In actuality, the inside walls of the floats would not be flat- they would curve upwards starting from the bottom of the floats, but they would be straight front to back, not bowed out like the sides of a canoe. The upwards curve would be just enough to give it rigidity.

It seem apparent that for the low speeds I'd be moving at, the surface finish would not affect things much. Smooth is easiest to produce, and then if I really wanted to, I could apply one of the slick coatings.

Each float would have generous flotation compartments, but a large center opening would remain. That should be enough room for one child and/or gear, if that should be needed.

Getting it up on plane would not be a problem- it won't happen and there's no need for it. I could never get my canoe up on plane either :)