bottoms, foils and finishes

One of our newest advertisers, Waterline Systems, shares some pretty good bottom and foil info right here.

Why does my boat need fairing?  

When resins cure, they shrink. This is an inescapable fact of composite boatbuilding. Of the preva lent resin systems, epoxy shrinks the least, polyester the most and vinylester is somewhere in the  middle.  

The mold can be perfectly fair, but as the resin shrinks within the matrix, some areas end up low  and others slightly high. This is not a manufacturing defect, but an unavoidable property of the  materials used.  

Fair vs. smooth  

Many sailors mistake smoothness for fairness. We see people at regattas compounding, buffing and  waxing their bottoms. They may be pretty proud of their obviously un-fair bottom. Fairness and  smoothness are different things, with fairness being by far the more important in terms of speed.  

Water flowing around a hull does not like to change direction. Highs and lows in your hull surface  force the water to make a rapid direction change. This leads to a dramatic increase in drag. We  aren’t making this up! Julian Bethwaite, the designer of the 49er ran full-size in the water tests  between a faired 49er and a 49er fresh from the mold. Incredible as it seems, he found a 14% differ ence between the faired and un-faired hulls. He published his findings in Seahorse Magazine.  


Sailors grossly over-estimate the value of smoothness. At the speeds we deal with on keelboats a  400 – 600 grit finish is all you need. It is not until speeds roll into the 30 and 40-knot range that  smoother finishes add any benefit. Even at high speeds it’s good to note that the BMW Oracle AC  Cat actually spent vast sums to carefully introduce roughness to the hulls via the 3M Riblet film.  

Keel and Rudder fairing. Science and art  

Keel and rudder fairing is substantially more complicated than bottom fairing. With the bottom we  are only concerned with drag reduction. Keels and rudders both need to generate lift as well.  Highs and lows are still vitally important, but now we add the need for a very precise shape.  

Choosing the proper foils shape is the science part of the equation. Waterline Systems works  closely with some of the world’s foremost hydrodynamic engineers and Naval Architects to help us  determine the correct shape. We need to balance lift/drag, pressure distribution and the limitations  imposed by class rules.  

With the science in hand, art takes over. Actually getting the foil to the designed shape is pure art.  Our team will fair more keels in a year than most yards do in a lifetime. Even with that level of  experience, Company founder/President Randy Borges is still hands-on with each keel fairing pro ject. 

Club Racer’ / “Grand Prix’ – What’s the difference  

Waterline Systems offers 2 basic levels of fairing service. Time is the difference. Block sanding is  the time consuming part of the job. With every block-sanding pass, the surface gets a bit fairer. In  a Grand Prix job, we do an additional few steps; filling with epoxies, and spend additional time  block sanding.  

The Club Racer bottom is really, really good. The Grand Prix bottom is better!  

What is the ‘maintenance/ scuff and shoot’ bottom?  

Over time, bottom paint loses its potency and epoxy primer gets a bit tired. Boats with our bottoms  tend to get wet sanded a lot and eventually the paint just gets thin. The scuff and shoot is a re fresher. Since we know what is on the bottom, we can block sand the existing paint, re-shoot and  then wet sand. The scuff and shoot gives you an extra fairing pass, and your bottom comes out bet ter than ever!  

What is the ‘Cruising / Daysailor’ Bottom?  

We’ve heard from plenty of customers who don’t race but still want a higher quality bottom paint  job than they can typically get at their local boat yard. We sand, apply Interprotect 2000, sand and  prep that then spray your choice of anti-fouling. The bottom will get a bit fairer, but we aren’t  spending our time or your money aiming for fairness. A sprayed application of bottom paint is a  whole lot smoother than a roller job!  

What’s up with the hard line at the waterline?  

There is a definite line, almost a ridge where the bottom job ends. We position this several inches  above the static waterline. This really bugs some people but it shouldn’t. Even immersed, this line  is in the very top layer of the water. This area is really turbulent and actually mostly bubbles. The  smart guys tell us that it makes zero difference to boat speed and may actually create lift going up  wind like a chine. Hum? Maybe that makes sense? Anyway live with it.  


The materials we use are expensive. We occasionally hear from clients inquiring if we can use less  expensive stuff. There are a few good reasons that we don’t: First, in the overall project, materials  are a small percentage. Labor makes up the vast majority of the total. Second, we know they work.  We stand behind our work and our suppliers stand behind their products and in the end, you win.  

What products do you use?  

Below the waterline, we exclusively stick with the AkzoNobel line of Interlux products. This in cludes solvents, epoxy fillers, barrier coat, primer and anti fouling coatings. Our manufacturing  reps all shy away from the word paint these days. Modern coating systems (that’s what they call  ‘em) are all designed to work together on a chemistry level. While most of us muddled through re medial chemistry classes. They have PhDs. It’s smarter for us to do what they say works! And they  stand behind our applications.  

Above the waterline we use Awlgrip, which is also from the AkzoNobel product line. After about 25  years, Awlgrip has really earned our trust. It can be difficult to work with, but we have the experi ence needed and it simply gives our customers the best finish and is the most durable product on  the market.  

  Bottom Paints  

What are our options on bottom paints?  

Dry sailed Boats  

For dry sailed boats we specify VC Performance epoxy. This is a white epoxy paint, which cures  extremely hard. For our purposes, harder is better. A hard paint allows us to wet sand to the very  best possible finish. The label on the can says “With Teflon!” This can confuse people into thinking  that it has some anti-fouling properties— it doesn’t!  

VC Performance epoxy is legal in both the US and Canada.  

Wet sailed boats- Salt Water  

Baltoplate – Baltoplate is our default choice for a racing antifouling paint. We feel that it cures the  hardest and gives the best wet-sanded finish. It comes in one color and honestly; it’s not the best  anti-fouling going but it sands smooth.  

VC Offshore – Interlux claims this is essentially the same paint as Baltoplate. Our wet sanders  swear it is just as hard as Baltoplate. It does come in different colors (Red, Blue & Black) both are  legal in Canada.  

Even though these products are “anti-fouling” Most racers find that they need to clean the bottom  weekly or bi-weekly.  

Wet sailed boats- Fresh Water  

For boats to be wet sailed in fresh water we like VC-17. It seems to have the best anti-fouling prop erties in fresh water. VC-17 is an extremely thin film. This makes it difficult to wet sand without  burn through. It also makes it single season paint.  

Legal in the US and Canada  

I want a white racing bottom.  

If you really need a white antifouling racing finish, Interlux “Trilux” is about the only thing we will  recommend. We have used Petit Vivid with limited success and experimented with all the E-Paint.  Trilux provides good antifouling characteristics Ever since tin was banned in the 80’s there simply  isn’t a white anti-fouling paint that is great for racing. Truth be told, no one misses Micron 33. It  was plain nasty stuff.  

Ablative paints 

Waterline Systems does not recommend any ablative paints for a racing finish. These paints work  by being really soft, and effectively slowly ablating off during the course of a season. Because they  are soft, they don’t sand well. That and the fact they need to go on thick, just can’t add up to a rac ing finish.  

For a cruising or day-sailing finish, they’re just fine. 

Maintaining your Waterline Systems finish  

Dry sailed boats  

VC-Performance epoxy is the hardest and most durable paint we use. Still, you can mess it up! The  most important thing is to keep it clean. Every time you haul, go over the bottom with a hose and a  soft sponge, cloth or one of the soft brushes made for topsides. Don’t ever use a scrubber pad or  abrasive cleaners. Use dish soap to clean.  

After a road trip you may find little hunks of tar, or diesel soot. The bug and tar remover available  at you auto parts store will take this off with a soft rag.  

Polishing – Don’t do it! Don’t put any type of wax or polish on your bottom. It will not make you  faster, but may prevent us from being able to do a proper ‘scuff and shoot’ somewhere down the  road. Epoxy sticks to lots of stuff, but not wax or Teflon!  

Wet sailed boats  

Bottom Cleaning  

We see divers using abrasive cleaning pads or sandpaper on a perfectly finished WLS bottom.  “Hint” don’t hire that guy. Whether you do it your self, or hire a diver, make sure that the only  thing that touches your bottom is a soft rag or sponge nothing more abrasive than the 600grit it  was polished with. More frequent light cleaning is far preferable to letting things get out of control  and then falling for the temptation to use something abrasive. If this happens go back to the section  on (Scuff and Shoot)  

Seasonal Maintenance  

The hard anti-fouling paints we use need to be immersed to keep their effectiveness. When they’re  exposed to air, the very top layer oxidizes and ‘locks in’ the poison. We apply the paint nice and  thick and it’s nice and hard. This means that if you wet sand the boat right before spring launch ing, you remove the oxidized layer and expose fresh poison. Most of our clients get 3-5 seasons be fore needing to re-spray.  

Wet sanding  

If you are going to wet sand your own bottom here are some tips to keep you from wrecking your  investment:  

Equipment needed:  

Sanding BlockYou need an 8-inch rubber sanding block. These are available at you local auto body  supply store. They take 1/3 of a sheet of sandpaper, lengthwise.  

Squeegee An auto windshield squeegee with a sponge on one side and the squeegee on the other is  just the ticket. (Auto body supply or at your local gas pump)  

Big Bucket You need a bucket big enough for the squeegee to fit in. (5 gallon)  

Dish Soap We add dish soap to our sanding water. This both acts as a lubricant and keeps the  water film on the surface longer. 

Sandpaper- Cheap sandpaper is really expensive. Buy it by the sleeve and plan on using lots more 

than you think.  


Like a lot of things, there’s a lot more to wet sanding than you think.  

Fill your bucket with CLEAN water (We only use Perrier) and add a good squirt of soap. Dunk  your squeegee in and wet down the hull using the sponge end. Always wet sand fore and aft and  use full strokes. Hold the block with both hands. The objective is to remove a tiny, uniform layer of  paint. If you sit and whale on one spot, you are just making a hollow!  

Use the sponge side of the squeegee to wet the hull, and then use the squeegee side to wipe the wa ter and floating dust away. This will help you determine where you have been and what you still  need to hit.  

Change your paper frequently. I see amateurs with 4 or 5 scraps of paper laying under the boat at  the end of a session. At the shop, there is a blizzard of paper. When you drop your block, don’t just  pick it up and start sanding with it! Take the paper off and rinse it well. A tiny piece of gravel will  make mincemeat of your bottom.  

Stay an inch or two away from any edges; stem, transom corner, the centerline ridge and keel trail ing edge. It is way too easy to apply too much pressure on the edges and burn through the paint. If  you burn through, you need to touch up with more paint and that is going to be a big hassle. Come  back to all your edges and delicately hand sand and follow with a couple quick/light passes with the  block.  


Remember a few paragraphs ago when we were talking about wetsanding your Baltoplate or  VCOffshore to expose fresh poison. We weren’t kidding. Antifouling paint is considered a pesticide.  Keep the stuff off you. Gloves, goggles, tyvek suit. Don’t eat lunch, drink a beer or even smoke be fore you’ve cleaned yourself up completely. Material Safety Data Sheets are available online.