By Mark Sloan
Click here to see the actual dimensions of many San Francisco Santana 35s
I have written these notes because there seems to be some interest in fairing the foils of Santana 35s around the country.
I have completed the foils on my Santana 35 with excellent results. My boat has won the summer championship season the past two years as well as the past two nationals. I do not attribute all of our success to the foils however, they have made a significant contribution.
I started work on the foils for two primary reasons:
1. I was sailing in a very competitive One Design fleet where the top boats had faired their foils.
2. I read an article by Peter Isler detailing Dennis Connor’s 3 priorities for preparing his CF27.
· Fresh sails
· Lighten the rig and boat
·
Fast foils and
bottom prep
Disclaimer:
I am an amateur sailor with no formal training in fluid dynamics. I also have no professional training in boat maintenance and/or performance modifications. I have written these notes without, (or the promise of), compensation. They are merely my personal experiences that I am offering to other amateur boat owners considering the task of fairing their foils.
Flaws:
Determine the flaws in the foils so that you can make a decision on how to prioritize the work and how much you are willing to do. These are the flaws found on my keel:
1. Keel has a flat spot between the leading edge and maximum width. This is not a fast hydrodynamic shape. This should be the section that develops maximum lift and instead it is flat.
2. The area of maximum width is too radical a shape, (the turn is too sharp and steep), and may cause early separation.
3. The aft section of the keel is not flat. It is rounded like a hooked leech to windward. The aft section should be flat or hollow.
4. The trailing edge is too fat. It should be 1/16” to 1/8”.
5. The bottom aft corner is rounded. This corner should be a hard 90 degree angle to reduce drag.
Work Required:
Doing the complete job on your foils will require a significant commitment. Even if you could work on the foils during the week and if your crew offered to help, there is always the overnight downtime waiting for the epoxy fairing to cure enough to sand. A large bulk of the work is sanding, filling, coming back the next day and then doing it again.
I will detail the steps, technique and materials I used below. If this seems to be more work than you would like to commit to, then please go to the last section where I have identified a few things you can do to improve performance without a major commitment.
I dry sail my boat. I started dry sailing so that I could work on my foils over an extended period of time. Dry sailing has allowed me to work at my convenience making this project much more enjoyable. Instead of bottom paint, I use a white epoxy which is designed as a barrier coat. It is a hard finish but sands well.
Fairing to
templates:
This will correct all of the flaws except the aft bottom corner.
Templates: I paid a well known Naval Architect $300 for full size Mylar drawings for the keel. There should be 3 drawings. Each drawing is created for a specific horizontal position on the keel usually measured from the top of the keel down. Please be aware that Santana 35 class rules state the shape of the foils must conform to the NACA shape of 63A012.
Take the drawings to Kinkos and have a copy made. They have copiers that will give you exact copies. Place the copies over the originals to confirm they are accurate.
Some of the drawings will come in two sections with marks to line them up.
Glue the copy to plywood making sure you have at least a six inches spare at each end. I cut mine out with a simple jig saw. Do not saw directly on the inside line of the shape. Leave a 1/16 inside the line and use a sander to get to the line. This will make a more accurate shape.
For those of you who have not seen templates before, you use only one half of the drawing to make a template. Use it on one side of the keel and then flip it over for the other side. This makes it easy to use and ensures symmetry.
Absolutely essential: Once the template is finished, make sure that you create a mark from the drawing at the center of the leading edge on both sides of the template. This will be a constant guide during the grinding and fairing process. Do the same for the trailing edge.
Before you can apply the templates you need to draw the appropriate horizontal lines on the foil. The placement of the lines will come from the Naval Architect.
In addition, draw a vertical line on the foil, in the center of the leading edge. When the center line on the template meets the line in the center of the leading edge you have taken enough material off the keel.
Once the lines are drawn, apply the templates and mark the high spots on the keel. I found that the templates were significantly longer that the chord of the existing keel. I called the naval architect and he told me I could either lengthen the chord or leave the keel as is. The fwd 1/3 of the keel is the most important surface for lift and extending the chord would just create additional wetted surface, (not to mention lengthen the amount of work required), so I left it as is.
Now is the time to don protective gear, especially respirators. Do not use a surgical mask. Spend the extra money and get the real thing because very shortly there will be fiberglass dust and fibers in the air and they are very dangerous. Protective eye glasses are a must.
How to take down the fiberglass? Yes, you can grind it but you will be there for a very long time. 36 grit on a grinder is potent but small potatoes for the job at hand. I used a portable electric planner with carbide blades. Buy an extra set of blades. The planner was designed for wood but it will go through fiberglass and lead like a hot knife through butter. Time savings is at least 5 fold if not 10. This process took me two days. If I had help or more stamina it could have been done in one day.
Caution: The class rules state that you can take lead off but not replace it. You are not allowed to use the original lead shavings either. I stopped planning when I reached the lead. The keel was still too fat but I made the decision that I would rather have a fair and slightly fat keel at maximum weight than a thinner and lighter keel.
As you will find out, there is a lot of fiberglass to be removed. It is not structural so don’t worry about it.
After the keel has been reduced to the desired shape wipe it clean with acetone and wet the whole keel with epoxy. This assumes all paint and debris are gone.
After the epoxy has cured and the lead and exposed glass sealed, redraw the lines as required.
Fairing:
Mix the epoxy, (please use pumps, it’s much easier and accurate), and add filler till it is the consistency of peanut butter.
You will be surprised how much filler you can keeping adding to the epoxy in order to get the right consistency. The filler is going to have to hang vertically so don’t be shy about making it thick. It will take a couple of batches to get the consistency right so don’t worry about it because if you need to, it grinds off easily.
Starting with the top horizontal line, use a stiff putty knife and apply filler to the entire length of the line. When you apply the template to the foil, you will notice a gap between the foil and the template. Use enough filler to fill and then exceed that gap.
Lay saran wrap over the filler and then press the appropriate template into the Saran Wrap. Press the template until the marks on the template match up with the line on the leading edge and trailing edge. If the chord length of the templates is longer than the chord of your keel, you will have to guess. The leading edge is the critical measurement. (I could not get the marks to line up perfectly because I choose not to grind the lead down. In my case, I missed the leading edge by 1/8 inch).
Pull the template off and tape up the saran wrap if needed. This will leave an impression in the filler. Do not take the saran wrap off until the epoxy has cured.
Repeat this step for the remaining two templates on the same side of the keel.
After the epoxy has cured, (next day), remove the saran wrap and sand almost down to the impression. Leave about 1/16 of an inch of filler above the impression. This gives you a margin for error when you fill and sand the rest of the keel.
After sanding to within 1/16 of an inch of the template impression, lay a straight edge perpendicular to all three impressions. Hopefully the straight edge will lay evenly across all three. If not, make a judgement call on where to sand. When using the straight edge, remember that it must be parallel to the leading edge and then gradually stand up straight as it moves aft, making it parallel to the trailing edge. This is true for measuring, finding high spots and applying filler.
This is a good time to make an important note. The templates are a guide to making your foils fair. I don’t believe anyone can make perfect templates and perfectly faired foils. The closer to perfect the better but don’t get hung up on absolutely perfect.
Once you are comfortable with the three horizontal impressions, mix up some more filler to go between the lines. Lay it on with a putty knife and then make it smooth with a straight edge spanning at least two impressions, and pull from the leading edge aft. This will sag unless you’re a pro. I have watched pros and they push the wet filler into the surface with a large putty knife and make good contact with the hard surface. It’s an art but you will get plenty of practice.
When epoxy cures, it creates a shiny, waxy surface. This needs to be roughed up with sandpaper if you want the next layer to stick on top of it. Also, all surfaces should always be wiped down with acetone before applying epoxy and filler.
After the side of the keel is properly filled, you should have that 1/16 of an inch to sand because we left that much above the impression. Use a longboard, 100 grit to 220 grit for the last 1/16. Use the straight edge to find high and low spots.
I had some difficulty with the leading edge, lots of filling and sanding repeatedly, until I got it they way I wanted it. The shape is hard to sand and maneuver straight edges, longboards, etc. But the leading edge is absolutely key to creating lift so I spent the time to get it right.
The final step is the most rewarding. Take your masterpiece and wet it down with epoxy to seal the filler. Sand with 220 and spray on some paint.
Rudder:
My rudder had almost the identical flaws of the keel with one exception. The aft, bottom corner was a proper 90 degree angle.
I removed the rudder from the boat and used a couple of sawhorses to lay it on. This turned out to much easier than leaving it on the boat.
Use the same steps on the rudder as the keel. Drawings for the rudder should be less expensive that the keel, but not much. I did the keel in ‘99 and the rudder in ‘00.
One huge difference between the keel and rudder: The fiberglass is structural. As you grind, (I did not use the planner on the rudder), you will eventually get to the cloth and mat. Every 100th of an inch you grind off will weaken the rudder. Below is the key problem I encountered and how I dealt with it. I am not recommending you do the same. I am just relating my experience.
The rudder post does not enter the rudder parallel to either the leading edge or the trailing edge. It actually angles forward through the rudder. This creates the ugly shape aft of the leading edge. Put a template on it to see how really ugly it is.
I took the grinder to it not knowing what I’d find. As I got through a couple layers of glass a dark shape began to appear underneath the remaining glass. All the advice from the various experts around the yard assured me that it was just wet foam. When the grinder hit stainless steel we realized it was in fact the bottom edge of the rudder post. To make matters worse, the rudder post only extends halfway down the rudder. This was a serious structural problem.
We made the decision to fair the rudder first, and then lay two layers of carbon cloth over it. We decided to fair it first because we didn’t want to risk sanding into the carbon and we wanted a fair form for the carbon to conform to hoping that it would increase the strength. I was advised that carbon did not buy me much over conventional glass cloth because carbon excels in compression and tensile applications. This application could be argued as lacking those requirements.. We went with carbon anyway because it was not that expensive and might add some additional strength.
Laying carbon:
After the rudder is faired, find a way to use the rudder post to support the weight of the rudder so that you can have it hanging in the air, leading edge up.
Wipe it down with acetone and then lay dry carbon on the rudder. Measure and cut. We laid the first layer with the weave horizontal and vertical. The second layer diagonal. Because this is structural, lay it over the leading edge, and cut it at the trailing edge. One piece of carbon from top to bottom, and from trailing edge, over the leading edge and back down to the trailing edge.
After the carbon is measured and cut, wet the rudder with epoxy, lay the dry carbon on top, wet it with more epoxy using a brush. Use a squeegee to get epoxy into every pocket and corner.
For some reason, I had some trepidation about using carbon. I was told it won’t wet out properly, it was easy to get air pockets, etc. Actually, it was very easy to use and wet out perfectly. We bought it for $25 a yard, (I think I bought three yards), at a local marine supply store. (I’m told that kevlar is truly hard to use so you may want to avoid it).
After it cured, a light sanding to remove the waxy substance on the surface, a good washing with acetone and then the final fairing. This stuff is worse than fiberglass so please wear respirators.
Obviously I am not qualified to tell you if this repair is sufficient to handle the high loads of a broach or big seas. Everyone I know thinks it is but I suggest you ask Tom Schock or a Naval Architect if you are concerned. We sailed with it this past summer and put it through the normal strain you would encounter when racing. I only race in the bay so if it did come apart it wouldn’t be catastrophic. Halfway to Hawaii is a different story. Please consult an expert if you plan to sail in weather that will put a serious strain on it.
I did not grind any further after reaching the rudder post so the rudder ended up being fatter than expected. At speed downwind, the rudder hums so we ground down the trailing edge at a 45 degree angle and that solved the hum. It’s still too fat but…… it is fast.
I was surprised by the performance gain from the rudder. I knew the keel would be a big help but I did not expect to see a measurable difference in performance from the rudder. The biggest difference I’ve noticed is sailing to weather. My target speeds went up noticeably.
Other performance
enhancements:
Bottom Preparation:
Filling blisters, sanding and burnishing your bottom paint will give you marked improvement. I know some sailors skip this simple and easy step. Performance coming out of tacks and light air sailing will see an improvement well worth the effort.
Sanding the “orange peel” can be done by two people in less than 4 hours:
1. Longboard with 220
2. Wetsand with 400
3. Wetsand with 800
4. Burnish with a polishing pad
This step alone will surprise you and your crew with the
performance gain. Sprayed bottom paint requires the same preparation.
My bottom is a hard epoxy as stated earlier. If you chose to go this route and drysail, you can compound the epoxy instead of burnishing. I did it once a couple of years ago and had great results.
As you sand with finer and finer grit, you will notice the bottom, (paint or epoxy) will begin to gleam. A reflection is an indication of how smooth the bottom is and can be calculated in microns. Under ten microns is smoother than the boundary layer which is the main goal. I have been told that 800 grit gets the surface under ten microns. I prefer 1000. I can wet sand a Santana 35 with 1000 grit in less than an hour.
After the bottom has been prepped, a 3M scrubbing pad will keep her clean and fast whether you have bottom paint and keep her in the water or dry sail as I do. This should last 6 months to a year before she needs to be prepped again.
Bottom aft corner:
This is relatively simple to repair. If you are able to look at foils on high tech boats, especially rudders because most modern keels have bulbs, you will notice the sharp angle of the corner. This is done to prevent the pressure on the leeward side from escaping underneath the foil to the weather side thereby creating vortices and thus drag. Pressure will always escape from the one side to the other but if you can reduce it, speed increases.
1. Grind to fiberglass
2. Wet bare glass with epoxy
3. Wet out glass fiber filler
4. Use paper folded several times to mould shape, insert the wet glass fiber into the paper and attach to keel. Tape paper with glass inside to the keel. Paper will grind off leaving the glass.
5. Shape, fair and paint
Trailing edge is too
fat and aft section curved:
1. Use a straight edge held vertically on the keel to determine high spots.
2. Grind to just high of desired depth. Do not grind just the trailing edge. Take down at least 1 ½ feet forward of the trailing edge to ensure attached/re-attached flow. This section should be at least flat if not slightly hollow. (see templates)
3. Longboard the section to 220 grit.
This covers both flaws: Trailing edge and aft curved section.
Hull:
I haven’t mentioned the hull yet but it too deserves some attention.
Hopefully you have noticed the longitudinal lines on every Santana 35. This was created by the plug to make the moulds, or so I’m told. The story goes like this.
The plug was made from boards of wood. Schock had them beautifully faired and was building the mould for the Santana 35 when a Santa Anna wind came in and dried the boards. This changed the shape of the boards and is reflected in every Santana 35 ever built.
The longitudinal lines are below the waterline as well as in the topsides. I faired the bottom of the hull too. This is a terrible job. Longboarding over your head is a killer. I didn’t have the skills to use a grinder so I longboarded the whole hull. Sand and fill, sand and fill, forever. I guess if I had 3 or 4 crew members helping it would have been a lot easier.
I mention this because I don’t think fairing the bottom was worth the effort. The impact on boat speed is difficult to measure but I think the real gain is in the foils. After you complete the foils, and you are comfortable with admitting that you are obsessive compulsive like me, then by all means, fair the hull.
Equipment
list:
Planer – Makita Power Planer model N1900B (I bought Craftsman first but couldn’t find carbide blades)
Grinder – Porter Cable 6” variable speed Random orbital sander model 7336 (highly recommended)
Longboard – 3M – hook and loop (2 kinds, flexible and rigid take your pick. 36” long)
Longboard sandpaper – 3M
Epoxy – West System – fast curing
Pumps – West System
Filler – West System 9 (not micro-balloons, the brown stuff – I think 404)
Putty knives
Straight edge
Acetone
Plenty of rags
Respirator
Surgical gloves
Protective eye glasses
Pencils and marking pens
Epoxy barrier coat – if you
need this info call me and I’ll find out from the yard.
Contact
Information:
I’m sure some of you will have questions.
My e-mail is: sloane_mark@emc.com
Or call me at home in the evening at 925 820 4112
My boats name is Bluefin and she is on the hard at Nelsons. Please feel free to have a look. If you call me first, I’ll try to meet you there.