How to Build a Sailboat Rudder From Scratch




Introduction: How to Build a Sailboat Rudder From Scratch

About: I know my name suggests I'm a female, but I assure you, I'm not. I just thought the name was funny kind of like Ivan the Terrible, but a play on Ellen Degeneres' name.

This particular rudder is built off of the original rudder for a ~20' Bayliner Buccaneer sailboat.  The original had cracked and rotted pretty badly.  The owner of the sailboat cut the top of the rudder off and made a wooden 'boot' to cap the rudder.  However, it wasn't water sealed with fiberglass, and over time more and more moisture got in until it became so flimsy that it wasn't reliable.  

While this instructable is specifically for this Bayliner sailboat with a tiller-style rudder, the instructions should be general enough for you to modify it to work for many sailboats.  With that said, there are many many nuances to fiberglass/composite marine construction, so this type of build will require more research beyond what is covered here.

Step 1: Previous Rudder

In these photos you can see the extent of the damage.  

The rudder was foam-core/fiberglass sandwich.  Think of it as a Big Mac; the three buns of the Big Mac were layers of fiberglass, and the meat was the foam (the yellow stuff).  The only difference was that the buns would have all been connected and fully enclose the meat.

First, I cut apart the rudder along its perimeter with an oscillating saw, so that I could use the pieces as templates for the build.

In the fifth image you are seeing a piece of balsa (I think) at the edge of the rudder where the mounting hardware was located so as to provide compressive stability for the tightened hardware.

In the last image, if you look at the top of the image you can see where the previous owner had chopped off the top of the rudder.  There was a rudimentary wooden cap on that, so you can see how easy it would have been for water to get in.  

Step 2: Rebuild

Because of the difficulty of rebuilding the rudder the same way, I chose to use two sheets of 3/4" solid plywood.  While this increased the overall weight of the rudder, it ensured maximum strength and stability.  There is a good reason that I chose to do it in two pieces:  I wanted to be able to sand the exterior faces of the rudder in order to get a tapered surface, and by doing it in two pieces allowed me to have the piece be level on one side.

In the first image below, you can see the old pieces of the rudder all stripped of foam next to the new plywood pieces.  In the background you can see the middle fiberglass 'bun' of the whole kit 'n caboodle.  I scraped away all of the foam because I had originally wanted to save the exterior pieces and reuse them, but the Big Mac style construction made it more difficult to reuse them.  

Simply place the old pieces on your sheet of plywood, trace, then cut out with a jigsaw.  

If for some reason, you only have one template to work with, and you are using two pieces of ply that will later get glued together, be sure to flip the template over before tracing, so you have mirrored pieces.  

The customer asked for a little more material at the top of the rudder, as you will see in the last images of the Instructable.  It ended up making it look a little strange, however.

Step 3: Sanding

Unfortunately, I only took one image of the sanding process, shown below.

As I mentioned, it is good to sand the two pieces separately, although this picture is of the two already glued together.  A handy trick is to imagine your surface and the lines of ply as the lines on a topography map.  The curved edge of the rudder closest to us in the image is the narrowest edge, from the little notch all the way down the side to the very bottom of the rudder.  This is because it is the edge of the rudder that points forward when it is on the boat.  

I started by using a disc sander, but it was too slow, so I switched to a grinder.  The grinder worked well, but it was a bit too fast, so if you decide to use one, be very judicious in your use of it, otherwise you will end up with big divots.  

Step 4: Fiberglass Layup

As I already alluded, there are many many variations to fiberglass construction.  For this project I used chopped strand mat (which you can see in the first image), and a woven fiberglass cloth on top of that, with vinylester resin.  Later on in the project I switched to West Systems Epoxy 105 and 205, because it was on hand.  This type of layup requires you to use both the mat and the cloth in one process.  The general idea is that you cut your mat to about the same size as your rudder, pour your resin on top, spread it and around, then immediately lay on the cloth (that you have also already cut to size), and the resin underneath should be enough to saturate the cloth.  Often, however, it wasn't, and I had to mix more up really quick and pour it on top of the cloth to get it fully saturated.  This is where you will need to conduct more research on mixing ratios of resin, temperature, amount per surface area, etc.  Generally, I was able to get about 30 minutes of working time out of each batch.

In the back is a finned roller that you use after you mix and start pouring the resin to remove the air bubbles from under the chopped strand mat and to spread the resin around.  After a while the roller gets all gummed up, and I ended up using just my gloved hand to push out the bubbles, and I found that a simple plastic spreader worked best for spreading.

Don't worry about the stuff that hangs over the sides.  Originally I wanted to have it fold over and seal the edges at the same time, but this was near impossible, as we will see soon, and I just let it hang and harden from any of the spilled over resin.  I dealt with it later with a lot of sanding.

Step 5: First Layer and Sanding

The order I used was as follows:

Glass one side of the rudder, let cure.
Cut off excess edge stuff and rough sand/grind.
Glass other side of rudder, let cure.
Cut off excess, sand until flush.
Glass edges based upon which were generally 'up' when clamped in a mostly horizontal way (images 4 and 5).
Glass the remaining edges.
Sand the nasty edges until flush.

The first image is after the glass on the faces have cured, showing the excess.  The third image was after sanding the excess from the faces.  The following  images were taken doing first layers of the edges, after the faces.  

Step 6: Additional Layers and Difficult Spots

I don't remember exactly how many layers went on total, because after sanding where necessary, sometimes more wood gets exposed, and all that's required is a simple patch.  The first image is after fully sanded face and edge layers.  

There are some really difficult spots that you need to pay attention to.  Generally, corners are the spots you need to look out for.  It's like trying to wrap a piece of paper over a 3D form without letting any edges lift.  They will tend to lift up one end of your saturated cloth and allow air to get right in there, which means you'll have to sand that air bubble out and re-do it later.  The very bottom tip of the rudder was one of them.  Although the second picture is after I had drilled the holes for the hardware, it's useful to see the method for tackling those difficult spots.  

Visibile at the tip of the rudder is a bit of blue painter's tape.  For that spot and others, which I will mention later, I basically taped the heck out of it, making a small well, and poured in enough resin to cover it.  You can also see in this picture, how it has started to get thick/bulky.  That's normal as layers build, you just need to sand it down flush later.  Sometimes the tape gets sealed in there, so I just left it in.

Step 7: Notes of Caution

If, after a good amount of sanding, your rudder has patches of white at the surface and you can feel a clothy texture when you run your fingers over them, it means the cloth did not get fully saturated and means the surface is not fully sealed.  When this happens, it is sufficient to mix up a new batch of epoxy/resin, and spread it over the surface(s) without the need for another layer of cloth.  The entire surface is sealed when all of it feels smooth/looks glossy and hard, although some spots may still be bumpy.

After you think you've sealed the whole rudder and you go to sand it smooth, you may uncover more white patches or air bubbles.  It's extremely frustrating to think you're almost done and find another one of those, but it pays off to patch them properly.

If there are some air bubbles or pockets that just don't seem to patch up and keeps reappearing after you sand this product is really helpful:  It's a putty-like marine epoxy, so it serves the same purpose as regular epoxy, but it is much more workable and can be packed into a hole to completely seal it.  The is the best product for repairs of deep scratches or small punctures in a fiberglass surface.  

The notch at the top of the first image was one spot that I taped significantly in order seal every spot with epoxy.  This is the point where I switched to epoxy from resin, as I had run out.  The purple is the natural color of the epoxy after it hardens.  

Step 8: Hardware Holes

This step is extremely important and tricky.  If, by chance, you have the previous hardware which mounts the rudder to the transom of the boat, great.  Use them as guides as you don't want to make your rudder thicker than the original and not fit into the hardware.  If you don't have previous hardware and your boat needs a very specific bracket, go buy it early so you can make sure to construct your rudder to fit into those, otherwise, just buy some to suit.

Use this tutorial to help you get the holes right:

Basically, you need to drill your holes bigger (1.5x, I think.  The tutorial with specify this.) than the hardware needs.  You then fill the hole with epoxy and let cure.  Then you drill your holes again with a bit sized for your hardware.  After painting, get some sealant (specified in the tutorial) and coat the bolts, holes and the inside face of the bracket immediately before placing them on the rudder.

It's really important to drill your holes square through the rudder.  If you don't, you'll find when putting the bolts through, that they won't meet with the bracket holes.  If you're slightly off (like I was), you can just enlarge the hole at the problem end.  If you're really off, you'll have to sand the paint away, drill the new hole, fill with epoxy again, re drill, then paint.

Step 9: Painting

Painting a boat or any underwater surface is another realm that has a large amount of nuance, specificity, and also varying opinions.  It is still a bit unclear to me, but the most ideal situation is to find a marine paint that actually bonds with your fiberglass/epoxy surface.  Interlux makes really good products and they have tutorials on which paints to buy and how to apply them:

Before painting, you must 'cut' the surface (a light sanding), so there is surface for the paint to bond to, and you will need to remove any oils or chemicals that are on the surface with acetone or a similar product.  

The paint will usually specify a total thickness of paint required to be considered sealed, and will allow you to calculate the number of coats from the average thickness per coat.  

Next use a top-side paint (I think we used an auto-body paint) to cover the surfaces above the waterline to make it look nice.

Lastly, apply a bottom paint (also called anti-fouling paint) below the waterline of the rudder.  Bottom paints, especially, vary greatly by geographical location, type of water, EPA legal restrictions, etc.  Their purpose is to prevent organisms from attaching to the submerged surfaces, so naturally, they will contain certain chemicals and/or metals.  Copper is a common ingredient in anti-fouling paint, as it slowly leeches from the paint, preventing any organisms from attaching permanently.

Step 10: The End!

Attach the hardware and tiller, and you're ready to put it on the boat!!!

(That's my pops holding the rudder.)

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    5 Discussions


    4 years ago

    Thank you so much for the excellent article and pics. It has been very very helpful as I built my rudder. I do believe that there was one small error. I believe that you knife edged the wrong side. Though it seems counter intuitive, the tapered edge should be on the back side of the rudder to be most efficient, and the front side simply rounded, like a wing shape. Maybe I just looked at the pictures wrong. If you wanted to be extra efficient, you would sand to a specific airfoil shape number(I didn't do this either...) I built my first blank and started planing on the wrong side (front) first (just not paying attention!) and had to laminate another blank and start over. Again, don't want to come across as nitpicking your nice work, but others will undoubtedly want to use your guide in the future and if so, can make a more efficient boat my shaping the rudder like a wing. Thanks again for posting this!


    7 years ago on Introduction

    Nice job !…
    It's too bad that you let some spots unsaturated. Especially since you worked on a flat surface and it was not that large. I you have any demise from your rudder it will come from these spots.
    What you should have done to be more than perfect (but it pays on the long run !) was to impregnate the wood with epoxy before putting the fiber glass. This is done by heating the wood with a heat gun, or better a hair drier). It goes loke this. You heat up the wood on a manageable surface (this one finds by himself depending on tools, location, type of spar, etc…) so that the space between fibers opens and you spread epoxy which is sucked by the wood : resin is inside the material not on it's surface only. A word of caution though : do not "reheat" the wood surface you've just impregnated as you will heat the epoxy resin and depending on its formulae its qualities may well be ruined.
    Once you're familiar with the technique it goes pretty smoothly and a large surface can be done pretty fast.
    It took me 3 days to make hull and deck of my 10m (33') cruise boat (then I applied 7 coats of epoxy with different additives on all surfaces bellow and over water line and that was an other story !!…) That was 17 years ago and all the surfaces did not show any sign of wear. Except for a soft spot that ruined one plywood panel on the deck, but that was due to to a hammer that fell from the mast and we failed to care properly for the dent it made… before noticing rain water had seeped under and rotten a somewhat large area that we had to replace … A case of overconfidence !).

    PS. I should add that the surface heating process was not a personal invention but a recommendation from the epoxy manufacturer.

    Ellen the Generous
    Ellen the Generous

    Reply 7 years ago on Introduction

    Thank you for your suggestions! The heating to increase the space between the fibers of wood makes a lot of sense. I did go back and re-saturate all those areas of which that you can see in the pictures before moving on, so I am pretty confident is is sealed.

    Thanks again!


    Reply 7 years ago on Introduction

    I'm sure you have plenty of time for uneventful sailing (regarding rudder I mean !) ;)
    Anyway, this vital spar has to be checked quite often just to be on the safe side : attachments (nuts, bolts, forks, etc… can be very prone to electrolysis
    The problem with electrolysis is that it's full of mysteries : you never know why a bolt here is affected when another 20 cm from the 1st is not… 
    I doubt fix a zinc anode on the rudder.
    If both forks do not connect do the connection with a copper braid. Works perfect.

    Enjoy sailing !…
    (the most wonderful pleasure in this world !…)


    BTW : one way to check that wood has sucked enough resin is that it should slightly "overflow" from the wood : surface shines a little bit. However do NOT re-heat the surface once it is covered with resin. If you feel that patches are more shiny (where the epoxy "overflows" - sorry my english is not perfect) than others leave it at that. I wouldn't want ruining epoxy properties by blowing heat directly on it.


    7 years ago on Introduction

    Nice job. If you go through a hurricane, you might want to strap yourself to the rudder. It is probably stronger than the boat now :-)

    Regarding building in two layers: Besides the construction advantages you mention, having two layers will decrease the tendency to warp, because warping in the two layers work against each other.