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Flatfendershop 11-26-2009 11:42 PM

Rudder construction
 
Greetings all. This winter I intend to build a new rudder for my 1968 Venture 21. It currently has a fixed rudder and I would like to make it retractable. One design I'm considering would use a piece of 1/2 inch thick aluminum 6061-T6 for the lower section (basically the part below the water line) instead of wood. I already have plans to build the top section out of 6061, it will match up to the 6061 tiller I built last winter. My experience is in metal working, so I have the resources to do a professional quality job in cutting, fastening, fitting, etc.

I only question this in wondering if the lack of a foil shape on the rudder will really be that noticeable (I know, the fanatical purists are cringing at this point:rolleyes: ). Do you think it will flutter in the water at 5.5-6 knots (hull speed)?
I think strength will be ample, does anyone disagree?

My original rudder is teak and wrapped in fiberglass and is in very good shape. I intend to save it and don't care to use it for a donor. My only source for teak is on-line, wow! Its very expensive!

Please notice what I'm sailing, I'm not made of money. I can do the aluminum set-up for about $150 total. I only sail on fresh water, so I'm not too worried about corrosion.

Thanks for your thoughts. Flat.

SVPrairieRose 11-27-2009 01:58 AM

Any reason you can't work the aluminum into a foil shape?

mitiempo 11-27-2009 02:18 AM

Flat
Good thing you're not having to replace much of your boat - by the time you finish it would all be aluminum:D
Do you mean the blade will pivot up and aft?

pedcab 11-27-2009 02:47 AM

The only inconvenience I forsee in your plan is that the ocurrence of corrosion in the friction area might cause the rudder to seize or weaken in a very significant manner.

I would consider using large thin teflon or nylon shims between the ruder blade and casing and would fit both with a couple of sacrificial anodes.

Regards!

Faster 11-27-2009 09:38 AM

Putting a 1" or so taper on the leading and trailing edges and leaving them slightly rounded would probably be close enough for the type of sailing you'll be doing. Or perhaps radius the leading edge and put a longer taper in the trailing edge.. either measure will probably get rid of any "flutter" you'd otherwise feel.

Ped's idea of shims/bushings is good, but be aware some nylons and plastics will swell when kept wet. I don't think anodes would be required, just store the rudder dry between trips.

Flatfendershop 11-27-2009 08:15 PM

Thanks for the ideas, there's no reason I can't work the "slab" of aluminum into a foil, I think it would not be hard at all. Yes, the idea is that the lower half of the rudder assembly will pivot up and aft. Since my keel retracts, it only makes sense the rudder would too.

I like the teflon shim idea, I wondered if the marine grease I put in my wheel bearings on the trailer would work but it would be nice to put in something that wont wash away. If there is some corrosion over time, I may have to rebuild, but maybe I'll be rich by then.

mitiempo, I have completely restored (rebuilt) this old boat (separated deck from hull, new paint, fixed gaping hole in hull, new interior, new rigging, new sails, -the whole nine yards (or 21 feet as it were)). One of my efforts was to rid her of wood that would need to be varnished ( I like the look of the wood, but not the maintenance). I've built cabin hatch sliders, companion way doors, and tiller out of aluminum so far. Its all worked out quite well. I'm not talking about scab and gob type work, but real nice looking parts. I think its a viable option. Anyway, its worked for me!

Here's another option I discovered today in the shop. I found some white pine that is very nice and in 3/4 x 1 inch slabs. Would it be better to use a couple of layers of that instead of the aluminum? Should it be painted, varnished, or glassed over if I do use it?

Flat.

SVPrairieRose 11-27-2009 09:02 PM

I know that glass wrapped cedar is fairly common, I see no reason that wouldn't work for pine.

mitiempo 11-27-2009 09:12 PM

3/4" x 1" slabs?

paulk 11-27-2009 11:47 PM

Getting all the 3/4"x1" pine to lie flat,stay together, and not warp when it gets wet (and it will get wet, regardless of any varnish, paint, or fiberglass) will make you much happier with the aluminum. The time saved will more than make up for any cost difference for the materials. The rudders on Lightnings are essentially sheets of mahogany plywood, radiused at the leading edge and tapered on the trailing edge. If that was good enough for Olin Stephens, it should work for you in aluminum too.

Flatfendershop 11-28-2009 11:27 AM

Sorry about that, I should actually read my post before posting it. The boards are 3/4 inch thick by 1 foot wide, several feet long. I would laminate two together and then shape it into a foil.

My teak rudder is wrapped in glass, I'm sure it must get wet in there since there is not any sealant where the pintles are bolted on. It apparently doesn't swell enough to crack the glass. Any idea if pine would swell more than teak?

I'll check out some cedar pricing. As I remember it's fairly rot resistant, so is redwood. I used redwood for the bunks when I built my trailer. Maybe there are some options besides teak.

Flat.


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