Bent rudder stock- repair vs build new rudder

[kayakerChuck]

On our last sail of the season, I grounded my O'Day 30. We beat around on the hard sand bottom for a bit, and were able to return home without much drama, or much steering.

The boat is now on the hard until April. I've removed the rudder. The rudder stock is bent ~7 degrees, just above the rudder blade.


The existing rudder seems to be in good condition. The grounding pushed the aft edge of the rudder blade into the hull and split the rudder a bit at the trailing edge. That is an easy fix. I see no other apparent damage to the rudder or hull. We have LOTS of local marine machine shops and I imagine straightening this is well within their capabilities. The rudder stock is 2.35" OD, with a .200" wall thickness.

But- we are not fair weather sailors and we like to sail some of the lonelier places in the Great Lakes. From the factory, the rudder sits about 2" lower in the water than the keel (stub keel with centerboard). This makes me nervous. The more I think about this, the more I'm leaning toward making a new rudder.

The proposed rudder would have a sacrificial, and easily replaced, bottom 6 or 8" piece. If we mash it, I should still have good control of the boat and will be able to bolt on a cheap replacement bottom piece at our convenience.

I've got a pretty good selection of tools, including a 4x8' CNC router and access to a wide variety of skills. If I can figure out WHAT I want to build, actually building it should be relatively easy.

Does this sound like a reasonable plan?

My biggest question now is where can I find the loads on the rudder? The sacrificial piece needs to be strong enough for use, but weak enough to break before the loads get high enough to hurt important parts.

[barnakiel]

imho replace, but wait and see what others say


new shaft, the rudders skins can be very likely reused


get Q steel for the shaft, today there is a lot of poor steel around, source the good stuff, not the vanilla stuff



b.

[donradcliffe]

You have a boat with a very poor rudder design. If you want to take it to remote areas, redesign the rudder to be shallower than the keel. If you aren't happy with the tradeoffs (control, helm) from the redesign, sell the boat.

[markxengineerin]

https://www.cruisersforum.com/forums...ck-289240.html a similar recent thread you might find interesting

[kayakerChuck]

Agreed- poor rudder design.

Ours is a 1979. I'm lucky enough to have a few of the same model boat on the hard near me. The 1978, the first year of production, has a shorter rudder. It's approximately the same depth as the keel. The next year, they seemed to have changed to a slightly deeper rudder. My thinking is she's price point boat and they didn't want to do this, but had to based on the boat's actual performance. A permanently shorter rudder seems like a bad plan unless I can get the same turning forces from a shorter one.

The O'Day 30 actually checks most of the boxes for us. I had a handful of other boats on my shopping list, and I bought the first boat I found that checked most of our boxes and was in a condition I was willing to accept. It was a year of looking at boats. We'll keep her. ;-)

But- the rudder definitely needs a re-design. Is there a design that might give me similar turning force in a shorter blade?

Also agreed- If I build a rudder, it will be with parts of known pedigree.

Mark- thanks for the link!

[TrentePieds]

kayakerChuck said: "But- the rudder definitely needs a re-design. Is there a design that might give me similar turning force in a shorter blade?"

There may not BE a design, but surely you can devise you own?

"High aspect ratio" is all very weel, but it is NOT essential for a rudder as all the "barn door rudders" we've seen over the ages testify..

What I would do is design a rudder that is 4" shorter than your keel draft, but has the same AREA as the existing rudder and is balanced in the same ratio as the existing rudder, e.g. 30% area afore the stock and 70% abaft.

It'd be a piecacake to laminate up the blade from 2x lumber and profile it with a plane/sander, grinder. At the semi-finished stage you could even mount it and do a test sail, then, if you've got it right, dismount it and finish it with cloth, resin and paint. If it's not right, figure out why not before you spend the effort and money on the finish.

That you need a new stock goes without saying.

All the best :-)

TrentePieds

[kayakerChuck]

TrentePieds-

I should have thought of that, but I didn't. Thanks! The forums are great for getting more brains involved!

That sounds like a very practical solution. Our O'Day 30 is definitely built for comfort, not for speed.

[Dennisb2]

A book: Rudder design for sailing yachts. — ayes #79. Search Amazon it will lead you to a source. The book provides guidance on rudder design. You should be able to use you existing shaft in a new build with a wider width and shorter span.
A good winter project

[Lepke]

I'd build a new one shorter than the keel, but longer for more control.

[TrentePieds]

Sudden thot - thanks to Dennisb2 :-)

If the stock still turns freely in the well-tube even after it was bent, then you might not even need a new stock!

Just be careful when laminating up the new blade. Plot the actual runs of the tangs carefully before you rout for them. Then the boat will never know that the stock ain't "as designed" :-)!

Best!

TP

[kayakerChuck]

Sadly, the stock does not turn freely. I LOVE the idea of adjusting the rudder to fit the stock, but I think my stock is done. (pun intended)

Not only did I find a way to ground my boat with 3.5' draft in 7' of water (I found a hump on the bottom- yay!), I bent the rudder back AND sideways.
[IMG][/IMG]

[ashmun]

Two choices, since the original steel might be 304 depending on the age of your boat:
1) Buy new from Foss Foam (assuming they already have that mold)
2) If you have time and handy, split it open, replace the 304 with 316 steel and epoxy it open (barrier paint, bottom paint, etc.). There are plenty of posts on the forum and off on rebuilding the rudder.

Unless you have naval architecture or naval engineering knowledge to redesign the rudder, I’d leave it or hire one before modifying the rudder.

[Goodxcharly]

I did the same thing a few years back. I had a boat yard repair it $3000.
I watched some of the process and it looked quite easy.

- Split the rudder in 1/2 using a saws all. Just saw in till you reach the support stainless grid. Carefully separate the 2 1/2’s from grid. Cut out old pipe and weld in new one to grid.

- Clamp and Epoxy 2 1/2’s to grid.

- New rudder!

There is definitely skills involved when doing this. The above is a simple picture of how it was done.

-

[Mike Burch]

Yes,, you could straighten that bent stock, but it will not be as strong if you do.

Design and build a new rudder, using the appropriate profile for the different aspect ratio you will finish up with when you knock a few inches off the height but retain the same area. (In fact, if you want the same steering efficiency you will need to increase the area slightly, since a long skinny rudder has a higher lift-to-drag ratio than a short fat one.)

[Cheechako]

Originally Posted by kayakerChuck

Agreed- poor rudder design.

Ours is a 1979. I'm lucky enough to have a few of the same model boat on the hard near me. The 1978, the first year of production, has a shorter rudder. It's approximately the same depth as the keel. The next year, they seemed to have changed to a slightly deeper rudder. My thinking is she's price point boat and they didn't want to do this, but had to based on the boat's actual performance. A permanently shorter rudder seems like a bad plan unless I can get the same turning forces from a shorter one.

The O'Day 30 actually checks most of the boxes for us. I had a handful of other boats on my shopping list, and I bought the first boat I found that checked most of our boxes and was in a condition I was willing to accept. It was a year of looking at boats. We'll keep her. ;-)

But- the rudder definitely needs a re-design. Is there a design that might give me similar turning force in a shorter blade?

Also agreed- If I build a rudder, it will be with parts of known pedigree.

Mark- thanks for the link!

It ain't rocket science, some makers have changed their rudders over the years. What you need depends on how much you are heeled for one thing. You might consider making the new rudder shorter as you suggest but simply add more rudder area at the aft bottom instead of a break off piece on the bottom. Or IF you have good control as it was it may be fine a bit shorter.