building a rudder replacement

[Bob Cronin]

In heavy winds last Sunday (7/22) my rudder snaped at the water line - the broken off part disappeared as my C&C 24 was blown in circles until I got the sails down. A replacment was quoted at $2900. The construction was fiberglasss mats over two sandwiched mahogany planks. I am looking for advice on rebuilding it. Would marine grade plywood be stronger? I thought I would cut the general shape out of mahogany or plywood sandwiched together and then over lay it with fiberblass mats. Any suggestions?

[Canoeyawl]

Plywood rudders are not as strong as a solid plank of the same thickness. ( About half of the grain is contrary)

[Bob Cronin]

Thanks

[seo]

The advantage of plywood is that it is more dimensionally stable than solid wood. Which means that if you put FRP sheathing on it, it's more likely to stay adhered and do it's job. If you build up the sheathing thick enough, what's inside isn't critical to strength. Many rudders have foam cores...
If I were building a rudder out of solid wood, I wouldn't sheath it at all for an outboard hung rudder. If I wanted it sheathed, I'd use plywood.
The old-fashioned oak rudder hung on outboard pintles & gudgeons is still very practical. Drift the planks of the rudder together with bronze rod, use cheek pieces at the top for mounting a tiller. Old fashioned but easy to make and very practical.

[David G]

Roughly what size will your rudder be, when finished ? That $2,900 quote sounds like it may be a very large or very complex rudder?

I've built small boat foils for my own small boats (for experimental purposes) out of plywood, solid lumber, staved lumber, fiberglassed foam core, and metal plate.

From my experience, colleague's experience, and from everything I've read... I'd be inclined toward solid timber put together with drift pins for large cruising boats. For my own purposes, and for most client's small boats, I go with staved lumber sheathed in fiberglass/epoxy. I make the bulk of the staves out of western red cedar, with something tougher/harder at the nose and tail staves.

[kc8pql]

He says the boat is a C&C 24. I would think that ply and glass is the most appropriate and simplest to build.

[David G]

Ply and glass would likely work - if you went heavy on the glass/epoxy, and built in some solid lumber attachment points. Since he's already broken one... I'd be inclined to upgrade to a staved construction, with glass.

[wizbang 13]

Did the shaft break or did the blade break?

[Ron Williamson]

If you are anywhere near southern Ontario,you might try to find and modify a Shark 24 rudder.
Being an active racing class,there should be piles of old,but heavy rudders around places like Hamilton and Toronto.

Here's a recent-ish post;
http://www.sailnet.com/forums/c-c/71...-c-24-a-2.html
R

[JimConlin]

I'd go with staved mahogany or DF.
Inlay a strip of 1/8" x 1" G10 in a saw kerf at the trailing edge.
You can't do much better than a NACA 00xx foil. There are calculators out there.
When shaping the board, sand enough to reveal some of the G10 for the glass to bond to.
Glass it with maybe 16-20 oz. of cloth, laid on the bias.

[seo]

Wiz, I don't think those rudders have shafts. They're straight outboard hung,
It's amazing how many old Pearsons there are around that still have logged-up wooden rudders. It seems that even a FRP builder like Pearson didn't immediately see the advantages of a solid wood rudder.

[wizbang 13]

Thanks seo , i just noticed the drawing.
So, I guess I am wondering anyway, how and where it broke? On the fitting, did the blade tear off the pintle bolts, did it get rotten, did it snap going backward?
The few rudders I have built to non specs, I make the front silly strong , and the back of the blade silly weak, that if it breaks from grounding or whatever, the strong part may still be attached.
bruce

[willin woodworks]

I'm wondering the same thing; how and why it broke? In any case I'd crawl inside and check the bedding of the hardware. Assuimng it's transom mounted pintles and gudgeons, I'd want to check the backing plates etc, in fact I would take them off and re-bed them for peace of mind.

I'm not sure it matters much whether you go with solid or ply unless you want to finish the upper portion bright. I would use ply and have a layer of glass between the plies. Cover with glass laid on the bias and go sailin'....

[kc8pql]

I'm wondering the same thing; how and why it broke?

From the OP's post:

In heavy winds last Sunday (7/22) my rudder snaped at the water line - the broken off part disappeared...

I'd take that to mean that the submerged part snapped off more or less at the waterline. That makes me suspect that the glass sheathing had been breached, or maybe a poorly bedded rudder fitting, allowing water into the wood core, it rotted over time, and the heavy lateral load did the rest. Op doesn't say how old the boat is, but a lot of them are 35+ years old now.

[Jay Greer]

There is no reason you should not build your new rudder out of marine plywood. Just be sure to book match the two profiles out of the same sheet of stock in order to balance any warping tendencys. The glassing will add the needed re-inforcement if the original was foam cored. Your new replacement will be much stronger and cheaper if you build it yourself.
Jay

[Bob Cronin]

I measured the rudder on another C&C24 - It is 72" high - 10" wide to the waterline then then angles under the stern to a width of 19" then narrows to 14" at the bottom. The plan I am considering is to epoxy two 6 ft pieces of mahogany then add two more for the extension under the stern - held in place by bronze rods. Plane and sand to the approximate final shape and over lay with fiberglass and epoxy mats. Sound reasonable?

[Bob Cronin]

A few years ago I noticed a crack in the spine of the rudder - and the sound of sloshing water inside. I assume water got in - froze and expanded. I paid Brunswick Boat Works (now out of business) $475 to reglass it and put in a drain (that was 18 months ago). The boat is a 1976

[Bob Cronin]

http://i485.photobucket.com/albums/r.../IMG_0013a.jpg Here is what the piece I have looks like -

[kc8pql]

[JimConlin]

I measured the rudder on another C&C24 - It is 72" high - 10" wide to the waterline then then angles under the stern to a width of 19" then narrows to 14" at the bottom. The plan I am considering is to epoxy two 6 ft pieces of mahogany then add two more for the extension under the stern - held in place by bronze rods. Plane and sand to the approximate final shape and over lay with fiberglass and epoxy mats. Sound reasonable?

Sounds good. Don't use mat. It's cheap and bulky, but not strong. Instead, use a couple of layers of glass cloth, laid on the bias, if practical.

[MiddleAgesMan]

The picture shows the layup is woven roving followed by mat. I would trade the mat for glass cloth but stick with woven roving for the first layer of the layup. Of the three products, woven roving is the strongest. Use glass cloth to get a final smooth surface.

[wizbang 13]

I would strip plank it. as large as possible of hardwood the forward 6or8inches,then taper to half an inch of cedar.no glass . galv casing nails

[David G]

Your present plan is making me nervous on two counts.

First - the fg mat has been addressed. I agree with the notion of straight s-glass cloth - or with MAM's notion of starting with woven roving - then glass cloth.

Second - the core of epoxied up slabs, drifted together before glassing. You're combining a technique for the rudder body that is designed to expand & contract... with a glass skin that will try and keep it from doing so. That worries me. Something's gotta give. Now - keep in mind - I've never tried that particular schedule, and can't say for certain that it will fail. But I'd very much suspect that it will fail. I'd go with Jay's idea of a bookmatched plywood blank before I'd do what you propose - even though it's true that plywood construction has almost half of the material strength running the 'wrong' way. It'll still likely be stronger than the original. But overall I still prefer the staved construction.

Quarter-sawn central staves of western red cedar are light, relatively stable, and rot-resistant should there ever be moisture intrusion. A nose and tail stave or two of something tougher/heavier (ipe, jatobe, iroko, teak, black walnut, black cherry, african mahogany, honduran mahogany, etc.) will strengthen the areas most likely to be subjected to impact.

[seo]

I think if you're going to glass the rudder, use plywood instead of solid wood. Solid wood expands and contracts to much to coexist well with FRP sheathing.
I'd advice against foam core, because it takes a lot of planning to get solid material for fastening the mounting hardware.
It will sound kind of quaint and old-timey, but an old-fashioned logged-up hardwood rudder works really well. First, it's quick. A few years ago I built a rudder for a Herreshof H-28, which has a considerably bigger rudder than yours, in a morning. Put on sealer at noon, primer below the WL, varnish above, that afternoon. Second coat of varnish at 5pm. Bottom paint went on the next morning, hang the rudder, go sailing.
In comparison, building a sheathed rudder takes a lot of time. Glue up the plywood, wait for the glue. Shape the rudder, seal with epoxy. Wait for the epoxy to kick. Apply a coat of epoxy/glass, then hot-coat with a second layer four hours later. Post-cure? couple of days. Then paint. The point is that Solid wood is quick, waiting for glue to kick is slow.
Finally, if you have a solid rudder, you can fool with the shape after the fact. If you've sheathed the rudder, there you are, if you want to change the shape you have to grind away the sheathing, and re-do it.
With the H-28 rudder I made the leading edge of the rudder the same thickness as the trailing edge of the deadwood, went straight back 1/3 chord, then a straight taper to the trailing edge. First I brought it back to a square edge on the trailing edge, but it vibrated. so I rounded it over a little, and got rid of the vibration. As an experiment I brought the trailing edge of the rudder down in a straight line that met the line of the bottom of the rudder which extended straight, just pitched up a little (maybe 8º) up from the line of the keel. This "square-shinned" rudder was not at all like what the master, L. Francis Herreshof, designed for the boat, but I was curious as to what would happen, and was prepared to round off the bottom of the rudder if my little inspiration didn't work.
I did notice a little flutter in the steering that seemed to match with fluttering of telltale streamers that I attached to the bottom trailing edge, so I put a very slight round in the trailing edge, and VOILA! it disappeared! What fun.
The point being that if you're curious about how your rudder works, then an easily modified construction is a lot more fun, because you can fool with the shape, try it out, change it if you like, This is much more difficult with FRP composite construction. This is of no interest to the manufacturer, just as the fact that the process of making a rudder goes on over several days (waiting for the glue to cure) is of no concern. They can manage their production line easily so that the rudder is ready on time. This isn't the same for a person who isn't sailing because their boat has a broken rudder.
In terms of weight, unless you're going to go with foam/epoxy/carbon, the difference in weight between one construction and another is maybe 10%, and with a short-ended boat like yours, it will have no effect on performance.

[Roger Cumming]

+ mahogany. Skip the fiberglass sheathing. If the wood is of proper thickness the fiberglass is superfluous.

[rudderSpek]

Replacement composite Rudder

We had a similar problem on O'day 22 this July.
We made a replacement solid core composite rudder from 1” stock.
Check the thickness of your rudder under the pintles. If it is the same as ours 1” it will cost you
around $550-$700 to make a new piece.
We installed it and ran the boat, could not be more happier.
Cannot attach pictures, but if needed can e-mail them.
Good luck.