Swap my old foam rudder for a INOX steel rudder

[Nobody]

I'm pretty sure a if a hollow rudder fills with water it will not weigh more

after all if you fill a steel bucket with water then place the bucket in water

the weight will be that of the bucket not more

[blubaju]

Great, I'll eat 100 �� plus 100 �� and I will still weigh the same ��

[CombatDiver]

Thanks for give me your opinion

But that I want is a formula which gives facts or removes

Sorry but I dont understand you when you stated that a steel ruder can not have positive bouyance at all. I will depend on the total volume (or equivalent quantity of water which is displacing what would be above that the total weight in wood , steel or ever rocks which the rudder are made of) right?

Thank you anyway

Originally Posted by BillKny

Yes, you will have problems...

Your current rudder is designed basically to be (about) neutrally buoyant. Your proposed metal rudder will be very heavy, and when the boat is heeled will constantly be tying to sink, resulting in significant helm force to avoid the boat falling off. It will feel like a serious case of weather helm, but not one that sail trim can fix.

You are replacing a significant volume of foam and fiberglass with metal that is significantly denser. There is nothing you can put back that will weigh less than the foam and restore proper buoyancy. No math is needed to see this. That is not an opinion, it's just a fact.

Your new rudder should weigh the same as your old one, and ideally have its mass distributed in the same fashion. I just don't see anyway for this to happen given the design changes you are suggesting.

[BillKny]

Read this paragraph again:

You are replacing a significant volume of foam and fiberglass with metal that is significantly denser. There is nothing you can put back that will weigh less than the foam and restore proper buoyancy. No math is needed to see this. That is not an opinion, it's just a fact.


It likely that you have already decided to do what you are going to do, and are just looking for someone to tell you it is ok. Lots of people post on the internet looking for affirmation, not information.

There is NO WAY you can remove foam from the rudder. replace it with stainless steel, AND end up with a rudder with the same buoyancy. There is nothing you can add to the rudder to reduce the weight back to what is used to be if you add stainless steel.

There is no magic "formula" that can change that, unless you make the rudder bigger and use the larger volume to reduce the overall density.

I would suggest that you would be better off trying to understand WHY you have so many rudders failing. Under what conditions are they failing? grounding? Just sailing? Other issues?

[CombatDiver]

Originally Posted by RaymondR

If you build it using SS tube for the stock with light steel formers and say 2 mm SS outer cladding and seal it it should be sufficiently buoyant to not weigh much when immersed.

Hi RaymondR and thanks for your contribution

Yes, I want to know a way to make the calculations
I want to know what is the weight of my current rudder in foam + the SS tube

By the way, with the SS tube, you mean the rudder shalft right?

I will reuse the shaft, so this weight is the same, but I will replace the foam body by the steel cocoon that would be soldered to the former shaft.

So the calculation should be some like this:
- The weight of the steel cocoon ( steel formers + oulter plates) should be equal of the weight of water displaced by the volume of the cocoon or new rudder
- Or the weight of all foam should be equal or above the weight of water displaced by the volume of the rudder

I guess I can calculate all this "x" or unknown, using specific weight of standard foam, but maybe there is a more direct method

Sure I can remove all the foam and put in a weighing scale, but before start to get out the rudder, I want to make the calculations to be sure the project has a good future

thanks!

[CombatDiver]

HI raahell

Many Many Many thanks for all the info you have given

It is gold for me. Particulary the one refering to put inside oil. Aslo to reduce weight with holes in the frames as in air industry.

About the book, I'm sure it will be all the keys to finish my project, so I will try to find it. The problem is I'm crusing my boat, in a remote country, remote place, and we don't have amazon available. We will also have to proceed to the "old way" , I guess the nearest waterjet cutting machine is 200 miles away. I guess your project will be successful with no doubt keeping in mind the care you put in the matter!!

Besides, with this forum, I'll try to find pre-project main questions, to be resolved before to go or not go to further investigations and project design, and finally get out of the water and start to work

That's why I asked for the formula, a simple calculations before be immersed a complex book material.

Thanks a lot !!

Originally Posted by raahell

Hi Combat Diver,

I'm in the middle of a similar project but I'm replacing a steel rudder with another steel rudder. I'm using the existing SS shaft as well. Everything else will be new. I was going to do it in 316 SS but the price was prohibitive, so I'm going with regular carbon steel, properly protected with 2-part epoxies of course. It will last longer than I will as long as I inspect it every few years and touch up as req'd.

I get the impression that you're thinking to design and build it yourself so my advice is based on that.

The earlier comment about weight is very important. Weigh your existing rudder and that's your design goal. If the new rudder is a bit heavier (say 10%) it's no big deal, considering the overall weight of the vessel. I question the earlier comment that a steel rudder is automatically heavier than a GRP rudder. Read on about that.

Since you want math and science (always good) I refer you to the books by Dave Gerr. "Boat Strength for Builders, Designers and Owners" is an excellent resource to help you determine the structural layout and thicknesses of the rudder's ribs and skin. It was selected by the USCG as their primary text on boat construction so that speaks to its utility and veracity. Gerr's other book, "Boat Mechanical Systems Handbook: How to Design, Install and Recognize Proper systems in Boats" has a very complete section on steering systems and rudders that will give you an excellent understanding of the design and engineering options as pertains to your boat. This book is also just an awesome reference in general. Both books available on Amazon.

I used both books extensively to design my new rudder. Now that I know what I didn't know previously I thank the heavens I decided to purchase and read these books. BTW I've nothing to do with Gerr or his publisher, just a satisfied customer.

Rudder shapes done in GRP are not always easily translatable to steel. Be careful there. You may end up with a less effective rudder shape/profile if you don't do your homework. You could also end up with a MORE effective rudder if you read up on your options. Gerr's "Boat Mechanical Systems" will help you there.

As for rudder weight, in order to reduce the weight of my rudder I added as many lightening holes to the ribs as possible. See pic of my rudder design as an example. When done correctly, it does not affect the rudder's strength. This is used extensively in the aeronautical industry where strength-to-weight ratio is even more important. As a result, my new rudder will be considerably lighter than my existing and is a more effective shape and profile, so I'm expecting a marked improvement in performance (my reason for the effort).

I had all the pieces of the rudder cut with a waterjet. There are companies all over North America that can do this for you. You get high precision and huge savings in work. Properly designed, the pieces fit together with holes and tabs like a jigsaw, then just need to be welded together. Of course you can always do it the old fashioned way with drawing the parts out on the steel and cutting with acetylene torch or plasma.

My other advice to you is to have threaded holes installed at the top and bottom of your new steel rudder. This way you can fill it with vegetable oil to prevent corrosion from the inside. Also, once every 5 years, drain the oil and install a compressed air quick-connect to one of the holes - plugging the other - and blow air into it to check for leaks. Best way to ensure your rudder isn't getting compromised.

PM me if you're interested in progress on my rudder. I'm picking up the waterjet cut parts today

[CombatDiver]

Hi VictorLucas. I'm not sure to understand you. Inside the rudder will be air (with oxigen), and anyway, if I leave vacuum, I'm not sure to understand you that the rudder is not going to work?
thanks anyway

Originally Posted by lvictorlucas

A problem you did not mention is that most "stainless" Requires oxygen to work. Unless you use a very expensive type you will need tp protect the inside.

[RaymondR]

You have what is a fairly large sail boat.

The small difference in buoyancy or weight between a foam filled rudder and a sealed atmosphere filled rudder will be of absolutely no consequence to the handling or motion or stability of your boat.

However a properly fabricated all metal rudder with be far more durable than a foam filled fibre glass cased rudder.

If I were building a carbon steel rudder I would use a minimum of 1/8" (3 or 4 mm) plate to provide a corrosion allowance but not for structural purposes.

However if I was building in stainless steel where corrosion is unlikely to be a problem I would use 2 mm or even a lighter gauge material.

Your model for the build is an aluminium aircraft wing with the rudder stock being the main wing spar. The "ribs" only need to be 2 mm SS and you can drill a line of holes along where the "skin" bears against the ribs and spot tig weld the skin onto the ribs by filling the holes.

I would not worry at all about the slight difference in weight of the two designs, just go ahead and do her mate. When it comes to rudders being comfortable that it is going to stay in place in one piece and do it's job in the most adverse of circumstances is the most important consideration.

[CombatDiver]

Thanks TrentePieds, I will keep in mind all your remarks!!

Originally Posted by TrentePieds

Quote: "Mainly this question is focused to know if there is a standard formula to know what would be new weight..."

There is no standard FORMULA that I know of. There is, however, a standard PROCEDURE that you would be well advised to embrace.

1) You measure the dimensions of your existing rudder and commit those dimensions to a properly scaled 3-view drawing of the rudder.

2) You make copies of that drawing, but you do NOT draw upon it. You draw upon the copies so you can scrap them when you make mistakes or go up dead ends, as you will.

3) You design the structure of the new rudder and depict that design upon a copy of the 3-view.

4) You list all components of that new rudder as depicted in the 3-view.

5) On the list you note the scantlings (dimensions) of every component part, and calculate the volume of each component part.

6) You look up the "weight of material" (which you can find on line), and calculate the weight of each component part.

7) You total all the weights. That total is now the weight of your new rudder.

Whether your new rudder will be "mass balanced" or not is a separate question entirely.

Whether your new rudder will be dynamically balanced or not is a separate question entirely.

The anticipated "time till failure" of your new rudder is a separate question entirely.

As raahell has pointed out, there are books - dozens of them - dealing with ship design and with mechanical engineering generally. I recommend that you get some of them under your belt before you undertake this project. One important matter when discussing such things a this is to use the relevant jargon with precision. You will be better able to do that after reading some of these books.

May you have success in your endeavours :-)!

TrentePieds

[CombatDiver]

Thanks aagain raahell

Yes, in the initial title I set "INOX" or 316, but of course the project is in its beginings, so everthing is subjected to be modified

It can be normal carbon steel, as there are version stronger than Inox with the same volume, what ultimatelly equals to gain bouyancy. I can suggest to paint the plates inner faces, to avoid or reduces corrosion. And outter faces will be covered with fiber

Even I got the idea that to use the holing technique you show me in the cover plates to reduce weight, and a surface with more gripping to stick the fiber, and use the final layer of fiber to gain the waterproofiness, i.e., use the steel cocoon like exosquetum rather than skin

Thanks also fo the idea to use compressed air and let me know that the SS is hollow ( but I don't know how much and what is the thickness to know an aprox weight)

Thanks

Originally Posted by raahell

316 Stainless Steel is widely used for marine applications including encapsulated steel assemblies. A SS rudder is hollow and will be left full of air so it is protected. I would add oil in the case of a carbon steel rudder. sorry for not being clear on that.

In my own rudder project I compared the pros, cons and prices of using 316SS, W44 Carbon Steel and doing one in GRP. In the end, despite my perfectionist tendencies, I couldn't justify the 316SS version as it will considerably outlast the vessel itself, which doesn't make sense. Carbon steel, well protected and inspected at every haul-out, made the most sense for someone with limited funds.

To be precise, the costs of the rudder parts in 316SS were 4x that of W44 carbon steel. Add to that the additional costs and complexities of welding 316SS. In my case I'm using MIG so that means more expensive 316LSi wire and tri-gas mix. The welding environment and tools used also have to be cleaner/better to prevent contamination of the SS weld pools. It just wasn't worth it.

[CombatDiver]

Hi adjo, first of all thanks for your contribution

For me this is out of the question,as I adviced in the original post, anyway I will explain here not to have again the same discussion and to clarify to anyone who has the same thinking

When you are cruising the world like me, since 4 years ago, 365x24 all time the boat or anchored or sailing, and living in it like your house,it happens things, specially in certain locations, where there is no charts available.

If you are passing by a place deepless, or almost, very low speed as you know most of the times you are in a dangerous place, or even you know you are in a bad places with coral risings everywhere and imposible to chart, you will touch with your keel first as I did several times. After that the boat will stop. Not big deal because I touched with the keel, and it is very strong.And then, you would try to go backwards to leave this place for the same way you enter. When you do that, or even with no movement at all, the boat stern will move a little to stardboard or portside, just a little.., for the current, for the propeler or whatever, just a small movement between rocks both sides. If you have a rudder like my rudder, the small tip , lowest tip of the rudder will touch sideways to something. It will brokes like a biscuit, because it is little strong and it is connected to several tons, the boat, and only this part, as there is no steel "squeleton" in this part, will be broke, almost like if I kick it with my leg.

There is no big deal with this. I made thousands of NM with this small part of the rudder broken. Mine has 2 hingles. A guy with only 1 hingle (above in the hull) must not make this project using a steel rudder

Every time it is broken entail go out water, get out of the boat (remove all the mechanism), carry with the rudder to some place, repair, 1500 to 2500 USD, and set again backwards

It is very uncertain that my rudder can be broken with a frontal collision that will be very catastrofic for its integrity and the hull itself. THere will be always the keel before it. By the way my keel is done in the original maker with steel, 10mm of plates and with enforcements.

So with the steel rudder, I want to preserve the integrity of the botton tip, as
I guess it will survive to a colision as I described above, with this kind of forces I already felt and saw ( not more like if Im making some kind of "skid" at full speed and touch laterally a big rock, not a coral)

THanks

Originally Posted by adjo

Personally I would be concerne0d about making a rudder that is significantly stronger than the original.

It is one thing to damage the rudder. Not good but usually not a disaster.

If the same impact does not damage the rudder (because it is so much stronger) but, instead, tears out the stern of your boat the situation might be catastrophic.

I know of a Moody 54 that this happened to when it got entangled with a drifting meteorological buoy. The crew survived but the boat was lost.

[CombatDiver]

You are replacing a significant volume of foam and fiberglass with metal that is significantly denser. There is nothing you can put back that will weigh less than the foam and restore proper buoyancy. No math is needed to see this. That is not an opinion, it's just a fact.
Reading you again I guess you are thinking that my original plan was to use a rudder of steel, with no air inside, totally soild of steel, I'm right?

It likely that you have already decided to do what you are going to do, and are just looking for someone to tell you it is ok. Lots of people post on the internet looking for affirmation, not information.
You are wrong, I was asking for maths not to someone like you that told "it is a fact". A sentence , whatever who is saying it, the Papa or US President, or Einstein, is not a fact. A mathematical expresion will tell what is a fact and what is not. I asked someone for this prior to make my project go ahead or not

Wou will think that there is no boats made by concret and can not have bouyancy, because it is a fact that concret is more dense than fiber?

I wish to avoid this such of discussion. This is only waste of time
tahnks anyway

Originally Posted by BillKny

Read this paragraph again:

You are replacing a significant volume of foam and fiberglass with metal that is significantly denser. There is nothing you can put back that will weigh less than the foam and restore proper buoyancy. No math is needed to see this. That is not an opinion, it's just a fact.


It likely that you have already decided to do what you are going to do, and are just looking for someone to tell you it is ok. Lots of people post on the internet looking for affirmation, not information.

There is NO WAY you can remove foam from the rudder. replace it with stainless steel, AND end up with a rudder with the same buoyancy. There is nothing you can add to the rudder to reduce the weight back to what is used to be if you add stainless steel.

There is no magic "formula" that can change that, unless you make the rudder bigger and use the larger volume to reduce the overall density.

I would suggest that you would be better off trying to understand WHY you have so many rudders failing. Under what conditions are they failing? grounding? Just sailing? Other issues?

[AKA-None]

Originally Posted by Nobody

I'm pretty sure a if a hollow rudder fills with water it will not weigh more

after all if you fill a steel bucket with water then place the bucket in water

the weight will be that of the bucket not more

The point is it definitely will not float in any manner shape or form.

[blubaju]

Sorry if this sounds rude: why does it cost thousands of $?

If you live on board, in remote countries I do all these repairs myself.

But first of all, invest in a forward looking sounder, doesn't help in open ocean, but great for motoring SLOWLY into unknown places in brown water.


With some LOCALLY purchased LOCALLY produced laminating epoxy you will repair your rudder for less than 100$. Ask local fishermen, someone will help you sourcing, for this repair you do not need the world-best highest grade US epoxy. Urine smell is not an indication for bad epoxy, once cured the smell is gone

Reading this thread one might think you are designing for the next Admirals Cup.

And once again, you want your rudder to brake, not your yacht, and a broken rudder is much much better compared with a bent one. This will usually jam when turning the wheel. Forget steel or inox. Make 3 jigs as sanding guides for minor repairs and 2 half negative forms.

I sail Philippine waters, plenty of uncharted coral heads, rocks and unlit oyster farms here, but good Epoxy too ;-)

[Searles]

If you build a verry strong rudder with no safety breakaway at the bottom ,you will probably break the stock at the lower bearing or tear out the whole rudder and steering assembly’s,plus unless the new rudder ir the same shape and similar weight,you will have LEE helm as the vsl heels to looward, think this through some more.⛵️⚓️