sailorman
Well-Known Member
RUsure
he mention the "drg of the Olson 30", did he actually say, he had one ???
Building a rudder - materials advice?
- Thread starter Foolish Muse
- Start date
he mention the "drg of the Olson 30", did he actually say, he had one ???
Triassic
Well-Known Member
I would suggest you take a moment to research who Foolish Muse is......
vyv_cox
Well-Known Member
My instinctive response is that a wooden rudder post would be nowhere near strong enough, not only in resisting the bending stress that is inherent in a spade rudder (plenty of steel and carbon fibre ones have broken) but also in the attachment of the rudder to the shaft, which is often a weak point even in a welded construction. The design in the plans does not look like an expensive one to have made, any decent welding shop will do it for you.
Wrapping the timber with GRP or carbon fibre is an option but I am aware that it is all too easy to do this incorrectly. I read only the other day of attempts to make spars in carbon fibre that were unsuccessful after huge inputs of cash and time. Better to go with the tried and tested methods I think.
Wrapping the timber with GRP or carbon fibre is an option but I am aware that it is all too easy to do this incorrectly. I read only the other day of attempts to make spars in carbon fibre that were unsuccessful after huge inputs of cash and time. Better to go with the tried and tested methods I think.
Triassic
Well-Known Member
The Olson 30 has a spade rudder so the single most likely point of failure is the stock where the rudder meets the hull. The original design as I understand it uses a 2" stainless tube for the stock. If you want to replace this with another material you are obliged to keep it with the same OD as it will still need to fit the tube through the hull. Wood is a great material as it is very strong for it's weight and it can be quite forgiving, however it's yield point will still be lower than an equivalent stainless item. You also need to bear in mind that wood will not have the same resistance to wear, so if you were to use it you would have to fit some kind of bearing collar around the stock (either metal or nylon) and this would effectively reduce the diameter of the structural wood right at the point where you need the most strength. All this on a rudder that you are proposing to make even longer than the original that potentially could be placing even greater forces on the point of weakness.....
I took an interest in this thread because I'm in the early stages of building another rudder for my boat, although my parameters are completely different from the OP. I did however carry out a little research into self built rudders, including speaking to people who have built them, and they came up with the following.
Start with a stainless stock that extends about two thirds of the way down the proposed new rudder. To this you weld two frames that ideally are the profile of the finished item, although they can be simple plate if necessary if you're not sure at this stage of the final shape. One of these needs to be several inches below the top of the rudder (not right at the top as you don't want to be welding to close to the point of maximum stress), the other near the bottom of the stock which is still about a third above the bottom of the proposed rudder. Depending on how heavy you want the final item to be you can then build up between, above and below the frames with marine plywood or high density foam and shape until you achieve the desired size and profile. If using foam and the frames were simple plates then it's important to remove any between the frames and the outer skin of the rudder and replace with hard infill. Once you have the shape and size you want you simply cover the entire thing in GRP and finish as desired.
The strength comes from the stock and frames so the GRP process is less critical than might otherwise be. The reason for stopping the stock short of the bottom is that the tip becomes sacrificial so in the event of an accidental grounding it should snap off rather than bend the stock.
I took an interest in this thread because I'm in the early stages of building another rudder for my boat, although my parameters are completely different from the OP. I did however carry out a little research into self built rudders, including speaking to people who have built them, and they came up with the following.
Start with a stainless stock that extends about two thirds of the way down the proposed new rudder. To this you weld two frames that ideally are the profile of the finished item, although they can be simple plate if necessary if you're not sure at this stage of the final shape. One of these needs to be several inches below the top of the rudder (not right at the top as you don't want to be welding to close to the point of maximum stress), the other near the bottom of the stock which is still about a third above the bottom of the proposed rudder. Depending on how heavy you want the final item to be you can then build up between, above and below the frames with marine plywood or high density foam and shape until you achieve the desired size and profile. If using foam and the frames were simple plates then it's important to remove any between the frames and the outer skin of the rudder and replace with hard infill. Once you have the shape and size you want you simply cover the entire thing in GRP and finish as desired.
The strength comes from the stock and frames so the GRP process is less critical than might otherwise be. The reason for stopping the stock short of the bottom is that the tip becomes sacrificial so in the event of an accidental grounding it should snap off rather than bend the stock.
Kukri
Well-Known Member
(edited to add - this was written whilst Triassic was posting and I agree with Triassic's comments)
I am also thinking about a new rudder, in my case for an Ohlson 38, which is a late sixties fin and skeg cruiser-racer and no relation at all to the Olson 30!
My rudder has developed the problems common to many old GRP rudders, that is to say it is full of water and has serious osmotic blistering, to the point where Martin Evans, the well known surveyor said, quite bluntly, "That's OK for round here, but I'm not letting you cross an ocean with that!"
I have been thinking of using carbon fibre and epoxy, on the stainless steel rudder stock and webs, taking the opportunity of stripping the GRP off to check these over, and I am just starting to read up on what may be involved.
If the stainless stock and webs are at all suspect - and the inside of a foam cored GRP rudder is just the spot for low oxygen content water to permit crevice corrosion cells to set up in way of the welds - I am contemplating a silicon bronze tube and webs, and have located a firm that can do this, but have yet to establish whether personal bankruptcy would inevitably follow...
Which leads me back to Foolish Muse's rudder... since the boat is a (an?) ULDB I wouldn't use wood as most of the weight is doing nothing. Incidentally I have twice in my sailing career broken a solid wood rudder stock - the more recent one was five inches in diameter...
I would think that carbon fibre is the way to go, if permitted by the Class Rules. I recall that there have been "issues" with carbon fibre tubes for rudder stocks on racing boats in the past but I am out of date. If these have been solved then I would definitely think carbon fibre is the way to go but using a bought in two inch carbon tube for the stock and building onto that, rather than making the tube oneself. If carbon fibre is problematical I would go with a stainless tube with webs welded to it and build the rudder blade (again preferably carbon, but failing that high tech glass,) onto that.
There is rather a good discussion on rudders here:
http://www.wavetrain.net/boats-a-gear/400-fiberglass-boatbuilding-rudder-construction
I am also thinking about a new rudder, in my case for an Ohlson 38, which is a late sixties fin and skeg cruiser-racer and no relation at all to the Olson 30!
My rudder has developed the problems common to many old GRP rudders, that is to say it is full of water and has serious osmotic blistering, to the point where Martin Evans, the well known surveyor said, quite bluntly, "That's OK for round here, but I'm not letting you cross an ocean with that!"
I have been thinking of using carbon fibre and epoxy, on the stainless steel rudder stock and webs, taking the opportunity of stripping the GRP off to check these over, and I am just starting to read up on what may be involved.
If the stainless stock and webs are at all suspect - and the inside of a foam cored GRP rudder is just the spot for low oxygen content water to permit crevice corrosion cells to set up in way of the welds - I am contemplating a silicon bronze tube and webs, and have located a firm that can do this, but have yet to establish whether personal bankruptcy would inevitably follow...
Which leads me back to Foolish Muse's rudder... since the boat is a (an?) ULDB I wouldn't use wood as most of the weight is doing nothing. Incidentally I have twice in my sailing career broken a solid wood rudder stock - the more recent one was five inches in diameter...
I would think that carbon fibre is the way to go, if permitted by the Class Rules. I recall that there have been "issues" with carbon fibre tubes for rudder stocks on racing boats in the past but I am out of date. If these have been solved then I would definitely think carbon fibre is the way to go but using a bought in two inch carbon tube for the stock and building onto that, rather than making the tube oneself. If carbon fibre is problematical I would go with a stainless tube with webs welded to it and build the rudder blade (again preferably carbon, but failing that high tech glass,) onto that.
There is rather a good discussion on rudders here:
http://www.wavetrain.net/boats-a-gear/400-fiberglass-boatbuilding-rudder-construction
Last edited:
rogerthebodger
Well-Known Member
I don't know why wood/GRP rudders are still made when you consider the leakage you where the GRP and metal rudder shaft connects.
This is the internal structure of one of my rudders. This was subsequently covered in stainless steel sheet tig welded to the shaft and plug welded to the internal webs.
The only problem is its floats so must be held down.
This is the internal structure of one of my rudders. This was subsequently covered in stainless steel sheet tig welded to the shaft and plug welded to the internal webs.
The only problem is its floats so must be held down.
macd
Well-Known Member
+1 for Triassic's suggestion, which is a proven, well-tested approach. Fabrication of the steel parts should be straightforward for a metalwork shop; much of the rest should be simple enough for someone used to working in wood, like the OP. I'd suggest cloth and epoxy for the GRP work, partly because it's stronger, but equally because it should result in a more watertight structure (cf Minn's experience, and many more like it).
Not nylon for any bushings though: takes up water and expands too much.
Not nylon for any bushings though: takes up water and expands too much.
sailorman
Well-Known Member
I had added Troll to my post but removed it
BobPrell
Well-Known Member
I would love to see the whole rudder. Is it a lovely fair shape? I do not see many welded sheet shapes that are really fair.
IMO, the OP proposal to use a wooden shaft is silly. To have the equivalent strength as the SS tube specified in the plan it would need to be much larger, and so it would not fit into the existing rudder tube.
BobPrell
Well-Known Member
Your mind must have been put at rest considering your lengthy and sensible post #25
rogerthebodger
Well-Known Member
Don't have a pic of the full rudder but I used quite thin sheet stainless and being fully welded it does have some distorsions.
This rubber is an auxiliary rudder for my wind vane, my main rudder is built the same way but from thicker mild steel (oil filled). this one I wanted light so I could lift it when not using the wind vane.
Pic of main steel rudder and skeg.
BobPrell
Well-Known Member
Aha! Now I see how floating would be a problem - I was mystified how a bit of extra buoyancy would not be ok.
Thanks for prompt reply.
TQA
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A guide from West System
http://www.westsystem.com/ss/rebuilding-a-rudder/
They finished up building a new one. Note the use of a stainless steel stock.
Carbon fiber rudder stocks are widely used but building one is not something that an amateur working in a drafty garage can do and expect success. Either buy a ready made tube or leave it to the experts eg http://www.jefa.com/
I am a cruiser and would not trust a spade rudder with a carbon fiber stock, too many have failed. OK for round the cans racing or inshore cruising with help a call away. Where I cruise the 'rescue' services often do not bother monitoring the VHF and may not have any fuel in their rescue boat which may not be running anyway due to lack of essential maintenance.
http://www.westsystem.com/ss/rebuilding-a-rudder/
They finished up building a new one. Note the use of a stainless steel stock.
Carbon fiber rudder stocks are widely used but building one is not something that an amateur working in a drafty garage can do and expect success. Either buy a ready made tube or leave it to the experts eg http://www.jefa.com/
I am a cruiser and would not trust a spade rudder with a carbon fiber stock, too many have failed. OK for round the cans racing or inshore cruising with help a call away. Where I cruise the 'rescue' services often do not bother monitoring the VHF and may not have any fuel in their rescue boat which may not be running anyway due to lack of essential maintenance.
Triassic
Well-Known Member
Even with my fairly limited time on this forum I knew exactly who Foolish Muse is, and what boat he has. I was quite surprised that Sailorman with over 71 times my experience needed to ask, especially when it was so obvious in the original post. Still, life goes on.
Joker
Well-Known Member
I can tell you all about broken rudder shafts:
... earlier this year.
... earlier this year.
Foolish Muse
Well-Known Member
Thanks for all the comments guys. I don't know how many times I've heard in the past that "Material X is "pound for pound as strong as steel." So I thought it would be worthwhile to consider wood. But I think the quote earlier is apropos:
Yesterday I sent this question off to designer/builder Paul at Riccelli Yacht Design. Here is the answer he gave, that echos most of your thoughts:
I wanted to do this as a project of my own, but metal work is beyond my ability. My granddaughter is taking a welding course next year. Perhaps she could make this her class project.
Yesterday I sent this question off to designer/builder Paul at Riccelli Yacht Design. Here is the answer he gave, that echos most of your thoughts:
I wanted to do this as a project of my own, but metal work is beyond my ability. My granddaughter is taking a welding course next year. Perhaps she could make this her class project.
lw395
Well-Known Member
I suspect the 1/4 wall stainless tube is somewhat over specified, but does that matter?
You might reasonably get away with alloy or carbon tube of the same section.
I think I would go with stainless, then make the blade from wood, foam, glass and carbon.
I 'd guess the stainless stock would not be overly expensive?
I would think it possible to avoid much welding?
There was some good info on making carbon blades on the Cherub dinghy website a while back.
Do let us know how it goes.
You might reasonably get away with alloy or carbon tube of the same section.
I think I would go with stainless, then make the blade from wood, foam, glass and carbon.
I 'd guess the stainless stock would not be overly expensive?
I would think it possible to avoid much welding?
There was some good info on making carbon blades on the Cherub dinghy website a while back.
Do let us know how it goes.
vyv_cox
Well-Known Member
I assume that the weight in this boat is important? Just for comparison, the shaft in the skeg mounted rudder on my Sadler 34 is 1.5 inch solid bar with two bearings in the hull and one in the shoe at the foot of the skeg.
Triassic
Well-Known Member
Yes you can, and there are two easy ways.
The first is to cut slots in the stock tube and make the webs out of flat plate that is inserted through the stock projecting both sides, obviously only a little on the leading side and six to eight inches on the trailing. When the stock is bonded/built into the rudder this prevents the webs moving fore and aft.
The second is to drill a hole in the stock and cut vertically up from either side of the hole for several inches. You then pull this tang of metal out until it is at 90 degrees to the stock. You do this several times down the stock. This method probably isn't suitable for a boat the size of the Olson 30 as it isn't as strong and it's best suited to long high aspect ratio rudders where weight wants to be kept to a minimum.
William_H
Well-Known Member
I doubt you could screw up the original rudder to any significant degree. Compared to fitting a replacement rudder that may fail. Adding area to a rudder can also be seen as a frangible addition which can be broken off such that you are back to original. Removing some areas should not be too difficult to repair over the cut. Even if you get frustrated it should not take much to get it back to usable condition.
However of course if you have doubts about the integrity of the original rudder then you must replace although I still think repair is a better option. Assuming you will have the boat out of the water for winter. good luck olewill