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Riv View Drop Down
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Posts: 352 		Post Options Post Options   Quote Riv Quote  Post ReplyReply Direct Link To This Post Topic: Lugger rudder
    Posted: 01 Aug 20 at 5:50pm
Yesterday I dropped our club's Drascombe Lugger rudder on my toe.
It's made from welded galvanised steel. Blade is 6mm thick.
I would like to make it lighter so I don't drop it again.
Does anyone know of a composite sheet material that in 6mm thick form will be strong enough and sink?
Mistral Div II prototype board, Original Windsurfer, Hornet built'74.
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JimC View Drop Down
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Posts: 6625 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 20 at 7:05pm
carbon/Foam sandwich ballasted with lead [grin].
More seriously perhaps aluminium might be lighter and hopefully strong enough
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Sam.Spoons View Drop Down
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Posts: 3370 		Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 20 at 8:00pm
I'd probably be considering taking more water with the rum ration.....  Wink

More sensibly why did you drop it, was it simply 'cos it was too heavy? As Jim C says ally is roughly ⅓ the weight of steel and should be plenty strong enough for a rudder blade.


Edited by Sam.Spoons - 01 Aug 20 at 8:00pm
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Rupert View Drop Down
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Posts: 8956 		Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 20 at 8:57pm
They are a hell of a weight. Not hit my toe, but laying them flat can go out of control if you aren't careful.
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Sam.Spoons View Drop Down
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Posts: 3370 		Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 20 at 9:27pm
I'd look at an aluminium blade then, much lighter and reasonably cheap and easy for a local engineering company to make.

If you need it to sink under it's own weight then I'd think it needs a density of at least 2.0 g/cm3, aluminium has a density of 2.7 g/cm3, steel is around 8.0 g/cm3.


Edited by Sam.Spoons - 01 Aug 20 at 9:46pm
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Guests View Drop Down
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 20 at 10:33pm
Anything with a density over 1g/cm3 will sink in freshwater...
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Do Different View Drop Down
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Posts: 1312 		Post Options Post Options   Quote Do Different Quote  Post ReplyReply Direct Link To This Post Posted: 02 Aug 20 at 6:04am
Aluminium comes in many grades with varying properties of strength and corrosion resistance. Metalsupermarkets are an excellent source of information on all metals or any engineering firm capable of doing the machining should be able to suggest the correct spec.
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Riv View Drop Down
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Posts: 352 		Post Options Post Options   Quote Riv Quote  Post ReplyReply Direct Link To This Post Posted: 02 Aug 20 at 9:26pm
The offending article.

This is as it would be hanging under the boat. You can see the top bearing bottom left of the picture and the narrow slot the stock will slide down,
Mistral Div II prototype board, Original Windsurfer, Hornet built'74.
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Brass View Drop Down
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Posts: 1143 		Post Options Post Options   Quote Brass Quote  Post ReplyReply Direct Link To This Post Posted: 03 Aug 20 at 5:02am
Originally posted by Riv

The offending article.This is as it would be hanging under the boat. You can see the top bearing bottom left of the picture and the narrow slot the stock will slide down,

What a fearsome piece of ironmongery.
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Brass View Drop Down
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Posts: 1143 		Post Options Post Options   Quote Brass Quote  Post ReplyReply Direct Link To This Post Posted: 03 Aug 20 at 5:05am
Originally posted by JimC

carbon/Foam sandwich ballasted with lead [grin].
More seriously perhaps aluminium might be lighter and hopefully strong enough


Do you think the top bearing engineering needs that weight to keep the rudder and its post properly seated and immersed?

What would be the effect on fore and aft trim if you replaced it with alloy? Would you have to remove the half hundredweight CQR from the forward compartment?
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