Replacement rudder blade questions

chriscallender

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As my transom hung rudder blade split a couple of weeks ago, I need to make a new one over the winter. Its for a 22' trailer sailer so about 4 feet x 1 foot to give an idea of the dimensions. I've got a couple of questions, and I'm hoping that someone will read this who has done something similar before...


- What kind of wood would be suitable for making it from. I had been thinking of marine ply but I'm worried about it delaminating on the leading/trailing edges when I sand it thinner to make an aerofoil section. I can't identify the wood that the old rudder was made from other than to say that it is not a ply.

- How critical is the shape of the aerofoil? I'm assuming that any old plank of wood of the same size would give just about as much steerage and the reason for shaping it is to reduce drag. Anyway my plan was to rent a belt sander to sand it down to have an aerofoil cross section constant along its length, which I'd check with a cardboard template. Does this sound possible - I'm not a carpentry expert!

Thanks

Chris
 

Stemar

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Your plan sounds fine to me. The exact right foil shape might be important for Play Station, but is unlikely to be too critical on your boat, as long as it's symmetrical (or it won't steer straight!)

Marine ply should be fine too. You can use thin ply and laminate with epoxy to build up the thickness, but don't clamp it down too tight, or you'll squeeze all the epoxy out, which will leave you with weak bonds.

If you also epoxy some glass cloth over it when you've done, you shouldn't have to make another for a loooong time. If you do decide to cover it like that, you could get away with using cheaper ply, but it must be BWP (boiling water proof) standard, or when the water does get in, which it will sooner or later, it will start to delaminate.
 

tony_brighton

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At least marine ply is cheap. One of the reasons for the aerofoil shape is to generate lift (same as a keel) so any old shape will be disadvantaging your performance and might make the tiller sloppy. Presumably you are thinking of glassing it or epoxy-ing it once the shape is made?
 

chriscallender

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Thanks for the replies. My plan until now had just been to paint it with something waterproof which is how the existing rudder blade was made (but not from ply), but then it clearly wasn't strong enough, so glass/epoxy covering sounds like a good improvement - it was not much fun finding out that the rudder had split into two pieces when entering the Hamble on a beam reach!

Building the basic shape by glueing thin pieces of maine ply together also sounds like a good idea - less sanding and much easier to make it symmetrical than if I start with a single thick piece of ply.

Chris
 

Strathglass

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Use thick ply not thin ply and do the initial shaping with a hand power plane. You will see the shape and accuracy very easily as each glue line in the ply will show up as straight lines. Use an aerofoil section otherwise the performance drop of to windward will be quite significant. Sheathing with epoxy saturated fibreglass is a very good idea and WBP ply would be adequate. After coating with epoxy the blade must be painted to protect it from UV otherwise the epoxy will not last.
 

blue_anchor

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all above is fine..its also worth checking out boat jumbles and saving all the hard work!!i saw quite a few rudder blades at the last one.,which if oversized can be easily cut to fit.
 
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Now thats the idea ..... check out s/hand and also the boat scrap sites like Belsize in Southampton for example !!

Also the point about ply and NOT using laminated ... I am not so sure to dismiss using multiple lays of thin ply. You can still get the 'bands' of different laminates to give good sioght lines etc. But lminating thin ply layers allow the use of epoxy and thin 'tissue' glass-matt between the laminates to add immense strength to the final product. Final thin glassing over can add the final factor.
 

Seapepper

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Beware ply! Remember that the strength of the rudder is needed along its length, so only half of the grain in the plywood is running along the length of the blade. I replaced a solid wood rudder with one of exactly the same dimensions, but in plywood. It snapped in half the first tome the boat ran aground. Needless to say, the next blade was made from solid.
 
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