this Cat needs new RUDDERS

This is the better one of the pair. The other is in even worst condition. The foil is not that good, plus it looks like I can not trust the structural integrity.
So far the progress is:
- Western cedar planks laminated into the thick blank, and roughly cut into the shape of the original boards
- West epoxy and some fiberglass cloth ordered.


I am playing with some NACA 0012 shape on the paper and planning the working order.
First, using the router to make the cuts at intervals to start forming the foil, then more shaping with the planer, finally, some sanding.
When the wooden core is sanded, I intent to glass it.
As somebody suggested on another thread, 2 layers of cloth, 4 Uni Carbon, one cloth to cover, filler, sanding, epoxy primer then bottom paint.
I would appreciate some help in estimating the thickness of the laminate (the rudders are rotating, so they should fit snuggly into the alum cassette).
Any other advice/suggestions are very welcome

 

You really don't need a lot of glass when you use miracle fiber w for the core, the cedar on its own will be strong enough for most rudders, the wood is the unidirectional fiber, I would use 1 layer of 12 oz double bias with epoxy to protect it and give it the hoop strength it is lacking. Any more is just added weight. Where you would need a laminate schedule would be if you were to use foam as the core which in itself contributes nothing to the strength of the blade.

Steve

 

Oh, I forgot to mention, if you have not already bought your cedar you might want to look into Perfect plank, I believe they make cedar blanks in various sizes for sign boards, nice stuff, exterior bonded , stress relieved, knot free, straight. Saves a lot of work. If you glue up your own make sure you stress relieve it by ripping the planks into strips and rotating every 2nd piece and gluing it back together. Also I like to cut a slot in the trailing edge and glueing in a strip of G10 which gives a nice strong and straight edge to shape to.

Steve.

Steve

 

If using solid wood, I prefer to strip plank (vertically). This eliminates the cross grain strength issue and I too would sheath in biax, possibly with an external skin of Xynole for abrasion. Leading and trailing edges can be reinforced several ways.

A cored blade needs to have a reasonable schedule, so it can stand.

Lastly what's this going on, because NACA 00 series shapes are fine if the boat is fairly slow? If she's able to get up and scoot, you might want to consider other shapes, likely a combination of sections, along the length of the blade.

 

What is a G10?

It is a Seawind 24, so I would expect it to be rather slow.

 

G10 is a dense, pre cured fiberglass sheet made out of many layers of fiberglass fabric and epoxy resin, very useful in many places on a boat, makes great backing plates for deck hardware, thru hulls etc, its not cheap and you can certainly make your own. It is available from Mcmaster Carr and im sure other places. A cheaper version made with polyester resin is also available. BTW, i just checked the perfect plank website and the WRC sign blanks are still available in many sizes and is better than I thought as it is all full length strips and glued with resorcinol, perfect for rudders and daggerboards. I have only used their Honduras mahogany and sugar pine perfect plank and it beats the hell out of making your own unless you are able to select your own stock.

Steve.

 

A Seawind 24 is not exactly slow but a 0012 foil would be fine, it was used on the Great Barrier Express cats which are a lot faster.

Steve.

 

The cedar alone is probably as strong as a SW24 stock rudder. No need to go overboard with too much glass. While you are messing around at that end of the boat take some time to align the pintles correctly, typically they are out of line on a SW24 and it results in a heavier helm than needed.

 

Thanks a lot for all the advice!

Steve,
I already got the wood for the rudders, but my next project will be the daggerboards. I will check the Perfect plank products.

 

Looking closely at the rudder in the picture its same as what was made years ago
The gel coat is thick !! theres chopped strand matt and just maybe a woven roving in each side !! then a great mix of filler and then the two halves are clamped together till they go hard !! So in reallity theres not much strength there at all , the top and where its fitted inside of the housing there nothing added to make that stronger at all !.

 

Tunnels, ive seen so many rudders made as you describe, its criminal, a nice cedar/epoxy/glass blade will be much stronger and lighter.

Steve.

 

Yeah i know what ya mean ! jUST TAKE CARE OF WHAT GLASS YOU USE TO COVER THE CEDER WITH !! NOT WOVEN ROVING !!

 

I used to believe that Steve, but now prefer inert materials. Less trouble, lighter, stronger, no rot, no absorption, etc. Metals and plastics seem to out preform any of the wooden versions in durability. Carve a blade out of HDPE and see how long it lives. It's neutrally buoyant, self lubricating, tough and easily machined. A metal armature with a foam and 'glass skin is nearly as durable. Wood works in smaller craft, just because it's a material folks can understand, but isn't my first choice any more.

 

I havnt built a wood rudder myself in years either, I just built 2 new rudders this winter using proset epoxy/uni s glass/epoxy foam, I don't consider them superior in any way to a well made wrc/epoxy/glass blade. I had the opportunity of examining a rudder and skeg on a cold molded 26 ft sailboat we built in the early 80s, a couple of years ago and it was as good as new, no other material would have been better.
I cant imagine using HDPE for a rudder regardless of durability, its way too heavy for me and not very stiff which is important in foils.

Steve.

 

HDPE has been and still is employed by several outfits as direct and upgraded replacements for many production craft. They are generally cheaper then the stock replacement and more durable. Yes, they are heavier then foam cored, but not as heavy as you might think, plus it's all but neutral in water. A 30' boat doesn't usually see as much damage as an 18' boat's blades, but breaches in sheathed wooden blades can lead to troubles.