Replacing rotted rudder with marine grade plywood coated in fiberglass

[Shore Footed]

I am in planning stage to rebuild my rudder. I've watched videos on fiberglassing process. My dilemma is in choosing weight if fiberglass and amount of layers for durability. My plan is to sandwich 3/4 " plywood then use original as template. Original is 1 3/4 " thick which leaves room for 1/8" shell of fiberglass. Any help or direction would be greatly appreciated.

Shore Footed is an appropriate Handle since I've owned boat for about a year and have yet to be able to take her out of the slip!!!

[DeepFrz]

I urge you to use high density foam rather than plywood. Any leak and the plywood will wick the water through the whole rudder. Sorry can't help you with the layout but there may be info. on that on the West website.

[model 10]

That is not very much fiberglass. It probably would leak and ruin the rudder. Some 1" foam board from the lumber supply and a 1/4" of fiberglass on each side would be better.

[Adelie]

Is the rudder inboard or outboard?

Marine ply is a bad choice, too much of the wood grain runs the wrong way.

[rognvald]

And how do you attach the rudder post to the plywood? And what prevents torsional twist of the rudder under sail?

[shamrock]

This will never work, Google boatworks today rudder rebuild and there is a great video. You can use the old one as a mold basically and fill with foam. Plywood will get soaked and rot. Dry rudders are a rare thing.


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[xeon_tsd]

Originally Posted by shamrock

This will never work, Google boatworks today rudder rebuild and there is a great video. You can use the old one as a mold basically and fill with foam. Plywood will get soaked and rot. Dry rudders are a rare thing.


Sent from my iPad using Cruisers Sailing Forum

^^^^^^ exactly what I was going to post...

Here is the link well worth following on youtube.

https://www.youtube.com/watch?v=MRXNnFx7DBQ

[Nicholson58]

Originally Posted by Shore Footed

I am in planning stage to rebuild my rudder. I've watched videos on fiberglassing process. My dilemma is in choosing weight if fiberglass and amount of layers for durability. My plan is to sandwich 3/4 " plywood then use original as template. Original is 1 3/4 " thick which leaves room for 1/8" shell of fiberglass. Any help or direction would be greatly appreciated.

Shore Footed is an appropriate Handle since I've owned boat for about a year and have yet to be able to take her out of the slip!!!

Others will suggest foam or balsa fill. Both are NOT water proof materials and both have a positive permeability. Given enough time, they will become saturated. Neither of these materials will maintain a bond to the skins once wet and neither one, especially foam has a great shear strength. I would not use either system for any structure that was meant to be always submerged. We live in the north. One only need walk the yard in the spring as the weather warms to see split & dripping rudders where the freeze expansion has burst the skins & wrecked the fillers.

I researched the problem when I rebuilt my rudder. The blade is 3o X 60 and 5 inches thick. I was able to leave the bare edges attaché while the guts and remainder of the skin was hacked away. New glass was built up using US Composites 635 THIN epoxy resin and 48 oz Fabmat. This was applied to the SS armature and the stock. The rudder was placed on the floor over my lower half form. This form was (starting at the rudder) 7-mill polyethylene release film; 1/8" flimsy plywood; layers of foam rubber & slats of wood. The procedure was to form the above system against the lower surface using the wood slats and foam rubber so that the upper surface where the skin should be would be level.

Next, I filled the rudder cavity with syntactic foam made from the same 635 THIN resin mixed with 3M microballoons also from US Composites. The mix is 3 gallons of epoxy with 10 gallons of balloons. Use large plastic buckets & a drywall mixer in a heavy drill. Hang on to the bucket so it does not spin and start slow. The mix is like Kraft Marshmellow cream. Pour this into your mold and let it cure. The resin noted is extremely slow and even a thick pour will not overheat. It will take 4 days or more to be able to sand or grind without wrecking your media.

The cured strength of the syntactic foam is about 3000 psi compressive. Your skins will bond to this filler better than anything else you can imagine so the final strength of the structure will be massive.

Remove the lower form & film. You may find low areas of void that need to be filled. Use the same stuff. For leveling and fairing, I used a 9-inch right angle grinder & 40 grit disk from Home Depot. For eying the level, I sued an aluminum bar as one would use a concrete screed. As you drag it over you working surface, black marks will be left behind at the high points.

I could have applied the skins myself but preferred a pro job with a vacuum bagger. Instead of buying the stuff, I found my local yard was know for this & could do the job for less than it would cost for me to buy the tools. I furnished heavy carbon fiber cloth. Three layers made for a really strong finish. The syntactic foam is very light weight and will never, as long as we live, become waterlogged.

My photos include a number of shot of this project.
Member Galleries - Cruisers & Sailing Photo Gallery

[Cheechako]

How big a boat? 1/8" fiberglass seems very thin. Non pourous lightweight epoxy filler is a good way to go. Regular foam will soak up water even worse than epoxied plywood.
As mentioned... you need tabs welded to your shaft. Or is it an outboard rudder? If it is I would go with the plywood.... or wood of some sort.

[dpddj]

Same questions as Cheechako - how big is the boat?
DO NOT PUT WOOD internal to your rudder if it is to be submerged most of the time. There is a zero probability that water will not again get inside.
I just rebuilt the two rudders on my cat. I laid up a mold from one of the original ones, faired it better than new and proceeded bit by bit as I had time. Combination of eglass, vinyl ester and epoxy products. Dropped 10# per rudder (more gin tankage available). Contrary to what some posters have stated, there are foams that will not absorb water and are structurally perfect for this application. Stay away from EPS and many urethane foams. Especially foam rubber .
I would have machined direct molds on one of my CNC machines but I was too lazy to create the 3D CAD file needed. Besides, sometimes old techniques are more fun.
Have fun - it's only messy for the duration.

[BriaF]

If you choose to go with ply ?
Despite the above posts then paint the ply
with a epoxy like international everdure
This is a very thin ie. watery consistency
Epoxy that will soak into the ply
Keep painting multiple coats wet on wet
Do not let dry until finished.
The end grain will soak up a fair amount
Keep painting as long as it soaks it up
This will deeply penetrate the ply especially
the end grain, it will be slow to completely harden
but can be glassed over while still wet (best)
Make sure every screw-bolt hole, ALL exposed
Ply is sealed.
If done properly the ply should be sealed for life
& will last even underwater.
Even the interior ie, if using more than one piece
of ply should be painted before glueing
Be a pedantic old granny about complete coverage
I have tinber rudders glassed over that are 15yrs old
with no water inside.
Despite all the nay Sayers it is possible with care.
Rebate the top of the rudder or where ever the shaft exits
About 6mm or 1/4" & seal with long life caulking
Eg sikaflex 295 this should be enough to be able to
flex with any expansion/contraction & stop water
Wicking down the shaft & prevent crevice corrosion
In the shaft

[UNCIVILIZED]

Some tips, as we have no idea what kind of rudder, or for what boat & application you're building it for.

You can directly bond fiberglass cloth with epoxy to a stainless steel, or aluminum rudder shaft. And to this, you can bond various types of internal rudder structures.

The methodology, as well as things to watch out for are well documented in many places on the WEST System site, in addition to multiple other composite resources.
But,... regardless, do yourself a BIG favor & download the (free) classic book, On Boat Construction via the WEST System site, along with their user guides. Also, their other resource is Epoxyworks magazine. Again, free for download, with searchable archives, describing various project builds, just like on the main WEST System site.

Pretty much every composite supplier, & manufacturer have how to publications, as well as videos, & tech help lines. That, & if you get stuck at some part in the process of rebuilding things. You can come here for some answers, or better yet, go to BoatDesign.net Forums
They're all about building, & fixing things which float.

As far as wood, if you're fixed on using it, you're best bet in terms of making sure that it survives for a while, is to use thing stuff. Like thin sheets of BS 1088 Okume plywood. Say 3-4mm, and use a vacuum system to pull the epoxy through each piece, so that there's no air space left in the wood.
Then, laminate them together (under pressure or vacuum) to get whatever thickness it is which you desire.

You can use things like a clear penetrating epoxy sealer, this one for example Clear Penetrating Epoxy Sealer but as long as there are spaces in the wood that water & air can get to, then things can rot.
That's just reality.

To get some ideas as to how some of the "pro's" build/rebuild rudders, take a bit of time looking around on this site. CCI Marine composite fabrication | Competition Composites Inc.
They've been around/playing this game for a few decades, & a good bit of their stuff is pretty decent. I say a good bit, as in/for some applications, you really need to be an experienced engineer to say how well X will work for a specific job.
But being a business, it's in their best interest to keep their customers satisfied, so have a look at some of their techniques.

Albeit, IMO, there are far better ways of building a rudder than to "secure" a stainless steel blade structure in between 2 glass skins, using only high density foam as the "structural attaching" component. Meaning that which is the primary attachment between the rudder stock & blade skeleton, & the skins.

Frankly, there's a LOT which goes into designing & building a quality rudder, but no one here wants to read a (technical) book on the subject, so... that said, I'll shut up, & wish you well on your project.

Good Luck!

[crazyoldboatguy]

I had an older edge glued rudder made of mahogany. It was deteriorating (not rot, just the glue joints opening up in a few spots).

I decided to cover it in fiberglass, knowing that it was not the best. It is a deadwood attached hinged rudder on a Pearson Triton. The original wood rudder is nearly 50 years old. Granted, it lived in fresh water all its life but 50 years is a long time.

Anyway, the key to sealing wood underwater is to do it right. After the old rudder was covered in glass, I made sure EVERY hole in the rudder, along with the total surface area, was coated in the required 6 layers of Interlux 2000e water barrier coating. Every fastener hole was slathered ALL THE WAY IN with this material.

I have used this rudder for over 10 years. ZERO evidence of ANY incursion of water into the wood. Any water getting in would have caused swelling and splitting of the rudder inside the fiberglass. There is no evidence of this.

I wouldn't make a rudder using foam to fill same. Boats in the northern climes are not always stored in a heated building (mine is). Any water getting into the foam will freeze and crush the foam, creating voids and trouble.

I may make a new rudder out of steel and fill same with oil. The oil would prevent corrosion inside the hollow form. Who knows - that may just work.

[nauticalnomad]

Check these guys out...
Jefa Rudder bearings

[Wotname]

Marine ply is fine for a rudder if properly built (and maintained).

FWIW, my ply rudder is still giving good service (touch wood) after 40 years of being submerged.