Ive been given a 470 class dinghy and it needs a new rudder and centreboard. Can someone tell me what the best timber to use in is in this application.
Ive done the tiller in sheoak as Im not bothered by weight. Ill not be racing it at all.

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"Entia non sunt multiplicanda praeter necessitatem"

Howdy - While a lighter timber like cedar or paulownia is best for performance foils (rudders and centreboards) you can go a lot cheaper than cedar.

I would recommend glassing them as this adds so much to durability and trouble free operation (no warping) that it is worthwhile - it also means that the timber doesn't have to be the best.

We used fingerjointed radiata for the foils on the OZ PDRacers. You could on the 470 but will need to take account of the higher loads.

You do this by making sure that the section where the centreboard comes out of the hull has all the defects (fingerjoints count as defects) a reasonable distance away. At least 250mm.

Also make sure that the defects don't line up across the board but are randomly spread through its length.

As well as glassing the whole board (6oz glass - 200 gsm grams per sq metre)
I would recommend a second layer to go a foot above the point where the centreboard goes through the hull to around a foot and a half below that point.

The glass will add less than 2mm thickness to the finished timber board and you would need 2mm clearance on the width of the case in the boat.

The rudder doesn't need this extra reinforcing and can also be sized to the same thickness as the inside of the rudder housing. No need for 2mm clearance.

The most important thing you can do to make the boat handle properly is to spend some time shaping them correctly.

See
http://www.woodworkforums.ubeaut.com...775#post268775

Best wishes
MIK

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Or you could see all the pics in one thread HERE.

Cheers,


P

It's a better woodie than I (which isn't hard) to pick the timber in used for these if it's any help to you. Course-ish, blond grain.

See this thread

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Geez Hybridfiat I am good to you!

I dug up the website for the 470 and attached below are the measurements of the rudder and centreboard for the 470.

They are somewhat legalistic but they give the basic measurements for something that should fit in the centrecase and behave properly.

Do you have the rudderbox that the rudder swings up and down in? If you don't there is a better and simpler way than having a swinging rudder so it would be better to start from scratch if you don't have the housing.

The full document is here.
http://www.sailing.org/tools/documen...-%5B390%5D.pdf

Of probably more use is a tuning guide. It tells you where things have to be set up for the boat to perform well. If you get most of your settings around the average of these values the boat will work really well from the moment you drop it in the water. In other words it saves a lot of guess work when you are putting the boat back together.
http://www.470.org/Tuning-Guide-Ullman-Sails

MIK

Attached Files

470 rudder and centreboard.pdf (128.8 KB, 62 views)

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Thanks fellas. Ill get some paulownia if I can. I didnt know if it had to be some specky timber that was difficult to locate.
Ill glass it. Shaping isnt a problem Ive been making rifle stocks and other freehand shaped bits for years.

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I've used a neat trick to protect a rudders vulnerable leading edge. I've carved a shallow cove dead straight along the leading edge, soaked a length of single or double braid polyester line with epoxy, then attached it with thickened epoxy and a brad or two to hold things while the goo cures. Of course it needs to be faired to a reasonable shape, but the result is very tough and I've not seen a single one seriously damaged yet.

Howdy PAR,

It does add extra processes and fairing to keep a nice leading edge shape compared to just going ahead and glassing.

With a dagger type board most of the damage seems to happen on the trailing edge anyhow - the leading edge seems to take care of itself quite well with the standard glassing even under the higher loads of impacts of a dagger setup.

Here where the swinging board makes the impacts less I don't think it will make enough of a difference to be warranted.

As the boat gets bigger and heavier it starts to look quite interesting as a way to absorb energy - and also starts to make more sense as the overall labour of making the boards gets larger and the labour of what you suggest stays about constant.

For performance boats the rope diameter would have to be roughly the calculated leading edge radius or a bit smaller - makes a lot of difference with cruising boats too.

Is the polyester/epoxy reasonable easy to shape and fair in with the rest of the board? I would expect the 'pox to stop it from going furry when fairing?

Interesting and useful idea.

MIK

Attached Files

Michael Aclass rudder.pdf (13.0 KB, 59 views)

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Yes, the epoxy does keep it from going fuzzy, and it wets out surprisingly easily. I've done several centerboards and kickup style rudder blades this way and frankly stole the idea, from someone else I saw use the technique. It is wise to base the leading edge diameter on the size line you use, less some fairing compound. I just use the next size down and fair up to suit.

I usually use a brad at the top of the board to hold it in the cove, then stretch it along the length and tack it at the bottom, usually just around the tip. I try to glue and get a fairing coat on at the same time with reasonably small boards.

I live in shoal waters and beat boards and blades pretty good, with amazing regularity. This technique saves the board, the saturated line is very tough and though you may have to touch up the leading edge every so often (what's new) at least the board proper is in good shape, just some more thickened epoxy and shaping is all that's needed to make it good again.

Hybridfait,
Sorry I did not pick up on your interest in Paulownia ealier. Try High Point Ttimbers in WA for a source of Paulownia, over there, if that is the way you wish to go. Check their prices against www.paulownia-timber-sales.com.au which is me in Northern NSW. I think the freight differential will work in favour of Highpoint but you'll get your Paulownia. Freight costs to WA are more economical from here if the length of the timber is less than 1.8 metres. If you need more information from me send an email to the address shown on my web site.

For dinghy foils, there seem to be two schools of thought. One well known commercial manufacturer of foils made them of tassie oak with just a polyurethane or mirotone finish, the other used a soft, easily worked timber like WRC or balsa and relied on many layers of GRP or carbon fibre epoxy to give the required stiffness. I've used both methods and don't have a preference.
Cheers
Graeme

I do have a preference and that is for inert materials on all boards, dagger, lee, center and rudder blades. High modulus plastics, GRP, fabric set in epoxy over honeycomb or other inert core, etc.

I've had too many centerboards swell up and split or jam the case, repaired to many edges, tried in vain to keep a pretty mahogany board looking pretty 20 years after original assembly. No thanks, I'm done trying to keep up. Yep, they look pretty for a while, then they get enough dings a paint job is needed to hide the battle wounds and wood butcher's friend used to fill them. Inert materials don't rot, can be neutrally buoyant, don't swell, are generally much tougher, hold attachments better and the list goes on.

I might make a pretty set of boards that get installed for a show and never see water. A static set of appendages so to say, for display when I've got a tent up at a swap meet or something.

Hi PAR,

Australia has some nice hardwoods that can cope reasonably well and are used without glassing.

However they do weigh a lot - which can make them a bit inconvenient to move around outside the case (if dagger) and get up and down under control.

But it is not a biggie until the boards become quite large or thick.

MIK

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is there a good reason not to use ply with a coat of epoxy and maybe some glass?

cheers

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Most powertools have sharp teeth.
People are made of meat.
Abrasives can be just as dangerous as a blade.....and 10 times more painfull.

Thanks that is great info.
Ive got a fair stash of timber in the shed so I dont have to locate an esoteric wood. The same cannot however be said for my katana, I still havnt found a source of Magnolia Hypoleuca for the saya (scabbard)

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