How I built a new rudder from scratch

[heron237]

Thought I'd go through the process I used, maybe someone will find it useful.


The rudder post broke off during a sail and the rudder was itself was lost, so I didn't have a pattern to copy.


The boat was of British construction, and I got the rough dimensions from a kindly soul on an owners' website. I also had pictures of the hull and rudder on the hard.


The rudder didn't have any compound curves. So was able to use a naca 0015 profile for a template. I printed it out at the appropriate size and transferred it to a quarter inch piece of plywood-- shaped it to use as a template.


I purchased grade 316 stainless for the rudder post and flat stock for the armature.



I asked the local yard if they could give a name of a local welder they could recommend, and he did a pretty good job, except he didn't switch back and forth on his welding that resulted in a bit of a hook into the post, but since it would be down in the rudder it wasn't critical.


Built a "coffin" sized slightly larger in dimension of width and length. Drilled a hole to fit the post through and used wood blocks to center the post and armature in the coffin, as well as position fore and aft. Filled it with two part urethane 10# foam.


Used a pull saw to take off the worst overages, and then a power plane and angle grinder with a flap disc for the rest. I used my template to maintain the shape.



Fiberglass consisted of one layer of knitted fabric and three layers of 6oz. cloth, extra layers at leading and trailing edges and where the post enters the rudder, which on this boat is normally above the water line (a very good thing!)



Faired with West System fillers and System 3 epoxy. Sealed with two coats of Interlux 2000 Barrier coat.

[MicHughV]

looks like you've got it all figured correctly....

[Fore and Aft]

Heron 237 my first question is what stops the stainless steel tangs from crushing the foam when the rudder turns? Second question I would have thought that the fiberglass cloth layup was very light. 6oz cloth for me is only a sheathing cloth for plywood. Third question where the stainless steel shaft enters the foam did you make a fiberglass channel and then fill it with Sikaflex afterwards? This area is always an issue with dissimilar materials and I have found a channel of sealant works best to seal it properly.
Keep us updated on how it looks after 12 months of use.
Cheers

[heron237]

The foam density is high enough to prevent crushing the tangs, I omitted that I did use a caulk where the rudder stock exits the rudder. I didn't make a channel. I did use two layers of thick cloth in addition to the multiple layers of fabric. I forget the weight.

[coopec43]

I think your rudder will fail in time (just as my rudder will too)

I had three tangs welded to a 316 rudder post (2 inch?). The welder warned me the rudder post would bend because of the uneven heat from welding. I removed that using a hydraulic pipe bender.

I used a marine ply sheet with cut outs for the tangs (filling any gaps with epoxy bog)) Then I used epoxy glue to attached 3 sheets of marine ply each side of the tangs.

I then shaped the ply with planer and belt sander. The I carefully epoxied 3(?) sheets of glass cloth over the ply. Finally I sealed the epoxy/SS rudder post with Sika 291(?)

I think it will, in time, fail because seawater will eventually leak into the interior of the rudder and will corrode internally. You won't have any problems with seawater corrosion of the rudder stock but where the corrosion is internal the oxygen build up increases corrosion rapidly. (There are excellent article on the subject online but here is a start:

How does oxygen affect corrosion rate?
It is found that the corrosion rate increases rapidly with the increase of dissolved oxygen content in different corrosion environments, and there is a positive correlation between the corrosion rate and dissolved oxygen content[3-5].

My next rudder will be a SS rudder post, ss tangs and 316 SS sheet folded and welded to the tangs. I will drill holes in the SS sheet to allow seawater to flow freely inside the rudder to avoid any oxygen build up.

If I can find a link to the article on se water corrosion I will upload it in a later post.

[coopec43]

Maybe this is the link?

https://www.boatus.com/expert-advice...-corrosion-101

[boatpoker]

Originally Posted by coopec43

How does oxygen affect corrosion rate?
It is found that the corrosion rate increases rapidly with the increase of dissolved oxygen content in different corrosion environments, and there is a positive correlation between the corrosion rate and dissolved oxygen content[3-5].

My next rudder will be a SS rudder post, ss tangs and 316 SS sheet folded and welded to the tangs. I will drill holes in the SS sheet to allow seawater to flow freely inside the rudder to avoid any oxygen build up.

If I can find a link to the article on se water corrosion I will upload it in a later post.

You have completely misunderstood the last article you linked.
SS corrodes in the absence of oxygen. Stagnant water inside a rudder is what corrodes the SS. "Stagnant" water is deoxygenated water.

From your "link" ... "An all too common type of corrosion that affects stainless steel. Simply put, stainless steel is not particularly stainless unless it is exposed to oxygen. Only in the presence of oxygen does an oxide coating form on the surface of the metal; it's this coating that mitigates rust or corrosion. In situations where stainless steel gets deprived of oxygen but moisture is still present, crevice corrosion will occur. This can happen, for example, when a chainplate starts to leak, introducing water into the space where the chainplate passes through the deck — an area where there is very little oxygen." https://www.boatus.com/expert-advice...-corrosion-101

[coopec43]

Originally Posted by boatpoker

You have completely misunderstood the last article you linked.
SS corrodes in the absence of oxygen. Stagnant water inside a rudder is what corrodes the SS. "Stagnant" water is deoxygenated water.

Maybe this is a better link which explains the problem in more simple terms. (This is the link I was looking for)

Why crevices can corrode To work at its best, stainless needs free access to oxygen. Crevices are wide enough to permit entry of moisture, but narrow enough to prevent free circulation.
The result is that the oxygen in the moisture is used up. In addition, if chlorides are present they will concentrate in the stagnant conditions and, by a combination of reactions, the moisture can become acidic.
These are all conditions that can lead to the breakdown of the passive film on the stainless. Attack can then progress rapidly.

https://www.assda.asn.au/stainless-s...-and-corrosion

[boatpoker]

Originally Posted by coopec43

Maybe this is a better link which explains the problem in more simple terms. (This is the link I was looking for)

Why crevices can corrode To work at its best, stainless needs free access to oxygen. Crevices are wide enough to permit entry of moisture, but narrow enough to prevent free circulation.
The result is that the oxygen in the moisture is used up. In addition, if chlorides are present they will concentrate in the stagnant conditions and, by a combination of reactions, the moisture can become acidic.
These are all conditions that can lead to the breakdown of the passive film on the stainless. Attack can then progress rapidly.

https://www.assda.asn.au/stainless-s...-and-corrosion

As I said, deoxygenated water is the issue not too much oxygen.

[RaymondR]

Nice job.

[coopec43]

Originally Posted by boatpoker

As I said, deoxygenated water is the issue not too much oxygen.

Thanks boatpoker.

It is so long since I made my rudder I got it screwed up.

[Secondshift]

Thanks for sharing your process.

Our rudder post required key way slots for our radial steerer and emergency tiller attachment.
Did you outsource these steps as well?
Also wondering what your total cost and time spent was.

I am a professional welder and a fair hand with fiberglass but I decided to have our rudder made by Foss Foam of Fl.

The total cost was $3000.00 plus about a tank of gas to drive and pick it up.

This allowed me to continue using our boat right up until I swapped it. It was in useable (inshore) condition.

I changed the rudder while it was in the water resulting in additional savings of yard/lift fees.

Best Regards

[heron237]

Hi Second, I live near New Bedford, so there's a substantial amount of marine related services available. I had to have a marine machine shop drill out the tiller mount and retaining ring holes for me. The lack of a rudder and other priorities left the boat on the hard for two years. I researched as best as I could on-line, but I found solutions that didn't seem appropriate for my application, (mostly like the poster above using a plate and plywood, etc.) The weight of the two part foam at ten pounds made it almost rock hard for instance, and without the original rudder as a template it seems like a reasonable way to do it. I spent in total around a 1,100.- for materials.

[Secondshift]

Well done!!

I believe the Foss foam rudders are very similar to the style you created.

High density foam and metal skeleton with a fiberglass skin.

They had the mold for our boat (every Hunter model , every year) so saved me lots of time and research.

Ours had a lot of visible corrosion on the post and I had repaired areas of missing / delaminated skin early on. No telling what the skeleton looked like.

Hope yours and mine both last forever.

Best Regards