Shaft material opinions?

[Sindel]

Which is better?

http://woodie.ppworks.com/Shaft-RIP.jpg

A shaft that is made out of "aqualloy".

A shaft that's a little softer, like plain "stainless steel".

"Bronze" shaft or something else...

What is your opinion and why.

[Ad Hoc]

The material choice selection is principally to balance the requirements of:
1)strength
2)Fatigue
3)Corrosion

You can't just choose one for your basis of selection. Therefore you need to address what it is you want from your shaft....sounds obvious, but it is not! It requires a bit more thought to the solution, ie the question.

[apex1]

Duplex 1-4462 Stainless Steel, has a hardness 40% better than AISI 316, and 30% better tension strength. On top it has better corrosion resistance than AISI 316 and Aquamet 17 to 22.

Regards
Richard

[Ad Hoc]

I believe his boat runs in fresh water lakes etc, yes?
Therefore plain normal mild steels can be used, so long as the bearings are made the same. But a popular choice in FW applications is manganese bronze, as it is a good compromise between cost and life.

But as i said depends on what he really wants from the shaft, otherwise we just go around in circles guessing!

[apex1]

You´re right! BETTER is just nothing, better for what, is the question.

[Sindel]

I'm asking for your personal opinions/preferences...

The shaft on the bottom of the picture was my first shaft.
It length was determined by a marina, who then order an installed the shaft and my original prop (don't remember the size)
The shaft was aqualloy something...
Hit a rock, broke the tapered end of the shaft off and lost the prop...

The 4 bent shafts above it are 316 stainless.
I purchased the 12' stick of 1" stainless and machined the shafts myself.
At a cost of less than $300 for all 4 shafts (back in 2000) This I thought was a good deal.

Been busy, had money (2 years ago) so I bought a "aqualloy" shaft.
Quick, easy (lazy), but done...

This year, (lazy again) ordered a new "aqualloy" shaft...
Wow, $200 now!

Is it worth it?

To me, I'm trying to decide if it is worth the extra money?
Where have you seen shaft breaks occur more often - near the coupling, by the taper, above/below strut, just random? (your experiences)

I was lucky not to lose the prop from the top shaft in the picture...
It broke at around 2500rpm and went back and hit the rudder.
I'm thinking about the possibility of losing a prop in this...

The boat is used in rivers, small lakes, also been out on lake erie, tackled 9' wakes on lake michgan, etc.
It runs nearly everyday from june to november...

apex1
Thanks for those specs, that helps a lot.

I had not considered bronze, how does it hold up?
Say compared to the 316 stainless...

Recent events have made me consider going back to a softer material...
Hence the questions...

I guess I should have asked what metals are commonly used, how they compare, there specs, etc. but I was looking for some opinions too...

[Ad Hoc]

"...I guess I should have asked what metals are commonly used, how they compare, there specs, etc. but I was looking for some opinions too..."

Well, the trouble with opinions is that they can be very subjective and sometimes ill-informed. Selecting anything on a boat is never about one simple criterion, there are usually many to consider all at the same time...

The best approach would be to go back to the beginning, to 'design' from fresh using today's methods of analysis and materials. It is not a difficult task, just requires some basic data of the engine and the prop. This then gives you a starting position or baseline, and something to aim for rather than just guessing which material is best when you don't even know what size diameter for each material is best. The two are dependent upon each other. This should also be coupled to the excellent advice from baeckmo on your other thread.

[CDK]

If you've already ruined 4 shafts of 316 SS, I do not think there is anything on the market that will not bend or snap. Manganese bronze or Monel are both softer than 316 SS.
High tensile strength steel, plated with stainless steel is an expensive solution for a shaft that will not bend easily, but when the prop strikes an unmerciful object, blades may snap off and/or you'll loose the end of the shaft.

Perhaps you should adapt the construction so that the prop is less exposed.

[TeddyDiver]

Of course hitting a rock brokes something.. but are all incident with rocks or smth softer also?
How much Hp have you in the other end of the shaft? Maybe you having too thin...
Displacement speeds.. or Planning? Prop diam, rake and rpm?

Ok found some of the details in your other thread :)
http://www.boatdesign.net/forums/props/props-rake-28716.html

[apex1]

[QUOTE]Manganese bronze or Monel are both softer than 316 SS.
Not much Cornelis! The tensile strentgh of Bronce is very much the same (impressively), a bit "softer" yes.
Perhaps you should adapt the construction so that the prop is less exposed.
That sounds like the best solution, not the choice of material. Although the duplex I mentioned above is not easy to destroy.
But we should not forget, that it might be not pretty clever to make the gearbox the weakest point in the drivetrain!?!

Regards
Richard

[Frosty]

No shaft will survive bad driving and hitting rocks . You could modify that old dated engineering of pinch screws. Is that all that stops it coming out in reverse? --- a pinch screw?

Going up a 1/4 of an inch (you have the space) or two with a tapered shaft at both ends would help.

What would indubitably help would be your driving technique.

[Guest62110524]

size for size absolutely nothing measures up to 2205,
tensile is way up corrosion in tepid salt is nothing like that of other ss,s
I use it , every time, it allows me to use smaller dia. for likes rudder stocks, , and prop shafts

[mark775]

"What would indubitably help would be your driving technique."
I agree with Thurston J. Howell lll here but hate the thought of breaking shafts (I have not in near 8,000 days on the water). The best way IS a taper at the forward end of the shaft. (except that the bolt is hidden by the coupling and not easily inspected). I don't know what a pinch screw is.
Especially in this day of aluminum housed trannies, Apex certainly has a big point here, tho. Since I watch where I'm going, I opt for stuff that doesn't break and will eat the $10,000 tranny cost, if it comes to that.
Many breaks happen at the keyway. Your prop/shaft doesn't need a key anyway. The convenience of not having to lap a prop to a shaft is the only reason for having this weak link, as I see it. If one is going to have a keyway, the edges should be rounded, perhaps the end of the keyway spooned, as they used to do, or better, a short, shallow keyway nearer the thick end of the taper.

[Yellowjacket]

There are two areas where you have had trouble, the end by the prop and the end by the coupling.

At the prop end if you have a material with high ductility it will be more likely to bend than break off like your first shaft did. 316 SS isn't very strong, but it has the ductility of taffy (50% elongation at tensile failure) and while the 2205 is better in terms of strength, it has only 25% elongation. Aquamet is three times as strong as 316 but only has 18% elongation at failure. The high ductility of the 316 coupled with the low strength allowed the shaft to bend and not fail. Typically what you gain in yield strength you lose in ductility, so unless you go to something exotic (like Inco 718 nickel alloy which has 170ksi yield strength and still has 21% elongation) and if you are balking at paying $200 for an Aquamet shaft, an Inco shaft would cost a lot more than that for just the material.

The Aquamet 17, 19 or 22 are all pretty good stuff. 17 and 19 have a yield of 105ksi and the 22 is 130ksi. The Aquamet 22 is three times as strong (yield strength) as the 316 that you had and bent. Aquamet 22 is better in both yield strength an ductility than 4340 (normalized) steel so you are probably better off with the Aquamet than going with a high strength steel since you get the better corrosion resistance and as good or better material properties. I'd pick the Aquamet 22 over the other higher strength steels, but your choice is more basic than that.

If you don't want to lose the prop maybe the softer shaft is worth doing again, provided you are willing to replace the shaft every time you hit something. If you go with something like Aquamet 22 you are less likely to lose the shaft, but may bend the prop. But if you hit something really hard you are going to lose both.... Neither is very nice, but you are the only one who has an idea what makes sense for you.

It also depends on what you do for a prop. If you have a softer prop material you will absorb some of the energy in the blades and won't be so hard on the shaft. A soft (bronze as opposed to stainless) prop coupled with an Aquamet 22 shaft may be a way to go.

With regards to the coupling end, as others have noted you should get rid of the coupling that you have now and replace it with an SAE tapered joint with a flange bolt pattern that you have now. The flange can likely be bought off the shelf and the shaft will bolt thru the flange (like the prop does on the other end) and seat on the taper. A keyed tapered coupling won't have the fatigue issues that you have with your current coupling, and most importantly the shaft will be properly centered in the flange.

What you have now is a rotaing fatigue machine. Misalignment of the shaft and engine are creating bending loads in the shaft and that is what is causing the fatigue. It is made worse by the pinch screw setup which forces the shaft off center in the flange, and concentrates the bending under the pinch screws. A tapered SAE flange will fix both of these issues and if you align it properly and use a flex joint you will never have an issue with this end of the shaft no matter what shaft material you chose. Somebody offered to help you get the engine and shafts properly aligned, and you absolutely need to do that.

Lastly don't listen to Frosty, his advice in this case is really bad (as usual). You don't want to increase the shaft diameter at the flange end of the shaft. If you do you will increase the bending stiffness of the shaft and that will increase the stress from any misalignment. If you have enough strength to transmit the torque, you don't need to increase shaft diameter or you will just make things worse. More strength at the prop end wouldn't hurt, but you have to fit the existing prop strut and once you do that the diameter is pretty much set.

I trust all this is helpful, it doesn't solve all your problems, but hopefully it lets you make an informed decision as to what your choices are. You are the only one who knows what you may or may not hit where you are running your boat, and that makes all the difference in the world.

[Frosty]

The dia is not pretty much set. Did you know that you can buy different sizes of cutlass bearings. The shafts are tearing up, and bending, you say that going bigger will make it worse!!!!.

Look at the pics of the prop??? tiny shaft, what is it 3/4.

He 'can' turn out his original drive coupling to an sae. This would improve vibration which must be terrible.

How do you know my advise is always bad?--You have only been on the forum 3 months, you hav'nt been here long enough to know.

[Yellowjacket]

The dia is not pretty much set. Did you know that you can buy different sizes of cutlass bearings. The shafts are tearing up, and bending, you say that going bigger will make it worse!!!!.

Look at the pics of the prop??? tiny shaft, what is it 3/4.

He 'can' turn out his original drive coupling to an sae. This would improve vibration which must be terrible.

How do you know my advise is always bad?--You have only been on the forum 3 months, you hav'nt been here long enough to know.

Here we go again...

Frosty,

No I didn't say that increasing the shaft size at the place where it is bending wouldn't improve the bending problem. In fact I said it would help in that regard. I just wasn't sure that it was worth it, or that it couldn't be addressed with the material change.

And yes he might be able to turn his existing coupling out to a larger SAE size, but if he does he risks increasing the stress in the shaft because, for a given shaft misalignment, the stress will be higher because the shaft is stiffer. Sit down and do a bending stress calculation for a canteliver beam and you will see that for a given deflection the stress will be higher for the stiffer beam. So increasing the shaft diameter will make the bending stress (which was the cause of the failure of the shaft in the coupling the last time) for a given deflection higher. It will also put bigger offset loads on his engine which is not a good thing either. I said he might be able to mod his coupling to fit the SAE format, but not sure if there is enough length to have a sufficiently long taper and the nut within the present envelope for it to work properly. Since I don't have the dimensions of his coupling, don't know the material and haven't looked at it, it is probably less hassle and risk to just go out and buy one. Since he is making a new shaft, a new SAE coupling for his current size shaft is, in my opinion clearly the best way to address the failure at the coupling that he saw without risking a failure due to a change in stiffness that results in higher shaft bending stress.

Sindel seems to want to keep his boat as original as possible. Not sure that he would want to modify his existing cutlass if it wasn't going to make a big difference. And I really doubt that he would want to put a new replacement on that wasn't a duplicate of the original.

As I said, there probably aren't any real simple solutions here since stiffening one part will just transfer the loads somewhere else and push the failure upstream to the next weakest link. Unless he can keep from hitting big chunks of wood at speed, he is likely going to have some damage, the only question is where that is going to occur, and how much collatteral damage is going to happen along with it.

If you are an engineer (as your profile says) do some back of the envelope calculations before you give somebody some advice, or at least give the basic engineering principles some thought before you chime in...

[Frosty]

Might be able to turn out to SAE. Probably are'nt any simple solutions?--Probably. Are you not sure? Off set loads on his engine ??? what rubbish.

Probably, maybe, might???

No I don't work things out on the back of an envelope which a lot of people do and still dont know.

I can only offer experience of doing "exactly" the same thing on the rivers in summer of England. Albatross , Delta, Moon fleet, all shaft drive, and ive owned all of them, thats all the ski boats we had in Uk 40 years ago.

Bent shafts week by week, vibrations, and shear,----ski one day fix the next.

I also imported the first Master craft into Dubai 28 years ago for the first Gulf water ski championships

How many shaft drive boats have you had? It does'nt matter --I don't care.

But you go ahead you tell him what would probably fix it. Its all yours

[Sindel]

Ad Hoc
See opinions are more fun...
I go boating (having fun and enjoying myself the whole time) for the weekend and have all sorts of opinions to generate thoughts for me.
Shaft's are 1" and 32.75" long...
And, I know a lot of the boat could be better designed, but I am happy with its performance with all it's antiquated components.

CDK
I'm not looking for something that I cannot break...
Actually would like to be harder to bend than the ss, but not as hard as to break like the aqua-whatever. The design of where I live on the river would be the most I could do...

TeddyDiver
The bottom 3 shafts are rock hits in that picture.
- Bottom picture was my first trip up the Auglaize River... (choose never to go back that way again...)
- 5 years later...
Wife wants this house on the Auglaize about 600 yards past where we hit before? We chose to trailer the boat for the first month until a neighbor showed us the way through. I also ride back a forth in an aluminum jon boat with a modified outboard (extra aluminum plate beam clamped to skeg) and try to find the rocks... The 2 (worst) bent shafts are from this area of the river...
The top shaft just got tired? (my antiquated stuff contributed this?)
The next 2 are from hitting logs, of which the worst there also tweaked the strut... I bought a new/used/different strut (before I knew they could be straightened)
The engine is supposed to be 105HP (so say the manual?)

apex1
As always, your advice is well appreciated. Thanks
Does bronce bend or is it more likely to break?
How do the various stainless steels on the market compare for strength?

Frosty
Yes, an old antique pinch is all that was used in the day (I use 2)
Failed me once in 11 1/2 years (I can live with that...)
And yes again, a tapered coupling connection would be better, but there isn't much space and the redesign never gets much thought until there's an incident... (I haven't run across any standard specs to go from)
Driving? Not poor navigation or bad location?

whoosh
What's 2205 like?
Will it bend? How much before it breaks?
I want something that will bend, just not too easily...

mark775
Good for you...
I'd have to agree on that tapered coupling... I installed one on my father-in law's CC Barrelback, but he has an extra foot behind the engine to play with. The coupling we got from the prop shop takes 3" to remove (I've only got 2.375"?)
Pinch screw are those pointed set screws with the safety wire hole in them...
I always thought these set screws and the brass key I use would be the first to fail, but I've only ever had one complete failure...
And the reason for the bad "milled" in keyway's - my lack of tools... (I made the shafts myself...)
Would it be okay if the prop has a keyway, the shaft does not, and no key used at all? should a bastered key be made to fill the void?

Yellowjacket
Thanks for your thoughts, very helpful...
The tapered end break was caused by a high speed rock! Nothing will probably stop this except maybe to drill a hole in the rock and use some dynamite?
The other shaft break was fatigue from my antiquated setup?
Might it be better to bend than break? This is my thinking...
As for shaft material verse price... Is the aqua-whatever worth the extra $125 over the stainless when there's a possibility of loosing a prop... This is what I'm trying to determine for myself... (and to find out if others are using different solutions)

Frosty
Can't ever seem to get enough in... ever!
The vibrations must be bad... In a wooden boat? Have you ever ridden in one?
The wood flexes quite a bit... fore to aft measurements change around an inch from winter storage to summer use...
Rides in my buddies mastercraft are much rougher and feel totally different...
You can change the size of the cutlass... Really?

Yellowjacket
Don't worry about Frosty... Every post I read where he comes up, it's the same old... (you should, I have done, etc)
Do you know where I can find some specs on shaft tapers for couplings?
When I first got the boat, someone had repowered it with a 350 v8 and was using a different strut with 1 1/2" cutlass... (broke, cracked, destroyed lots of the frame...)

Frosty
Your experience must have been very sheltered. Or your ego just can't see past the tip of your own nose?
I have got to enjoy my boat everyday except 3 this year... (since it's been in the water May 30)
Twice due to rain and once to take my damaged props to the repair shop. (they're always happy to see me and my $$$)
So easy to fix... Can pull the boat; change the prop, shaft, and coupling in a couple of hours; and be back in the water to enjoy a nice ride with my wife and dogs before going to work...

Thanks everybody, you've given my lot to think about...
Type of metal for coupling?
SAE coupling specs?
What shaft material should I use?

All is good in life, when your boating... :D

[baeckmo]

Here we go again...
As I said, there probably aren't any real simple solutions here since stiffening one part will just transfer the loads somewhere else and push the failure upstream to the next weakest link. Unless he can keep from hitting big chunks of wood at speed, he is likely going to have some damage, the only question is where that is going to occur, and how much collatteral damage is going to happen along with it.

Exactly, and this is why I proposed a highly flexible coupling in the other thread. The fact that this is a wooden boat, which does a lot of flexing, makes this even more important. And I hope that you do the final shaft line-up with the boat in the water??!

As for tapering the coupling end of shaft; forget it! Use one of the excellent clamping couplings instead (Even if you don't go the rubber coupling route)! For the shaft speed here, use the type with conical compression rings, not the slotted variety. Some of the materials available for shafts have been sensitive to "slot corrosion"; so give the coupling/shaft end a spray with thin corrosion protector ("Tectyl" or similar), giving a waxlike surface when dry.

[Sindel]

baeckmo
Exactly why I started the discussion...
Worried about breaking a shaft or something worst...
Cost-wise I'm thinking about going back to my homemade ss shafts...
But maybe there's something else to use, hence the questions...
As for the clamping couplings, how do they come apart?
Who makes them?
Tectyl? Never heard of this... (I'll have to google it...)
What kind of flexible couplings are available?

[apex1]

Go "Vetus.com", you´ll find most of the stuff you need, proper descriptions and fair pricing.
And do´nt be bothered when others tell you, you could have done better. These are the folks having usually less hours on their mains, than we on our wiper motor.
Stay with your bronce props, they bend, dent before they break and can be hammered back as often as you like to hit the rocks. The duplex steel shafts are pretty strong, but not too strong (to kill the gear instead), as I mentioned one page back, do´nt make the gear the weakest point. The Bullflex coupling is a nice thing but not cheap. When you cannot manage to align your system perfectly you might need it unfortunately. And make the final alignment on the floating vessel! As Baeckmo said, you have a flexible boat (all boats are), so a "dry" alignment is just a first, broad one. And listen to Baeckmo´s advice, he knows what he´s talking! (yes some others too, but I cannot comment on their expertise)
Tectyl 506 EH is what you are looking for.

Regards
Richard

[CDK]

Sindel, I you have no problems making your own prop shafts, making a clamping coupling should be a piece of cake. Mine were made from high carbon steel with 2 Allan screw on each side. The insert does the conversion from a 1" shaft to SAE splines for a universal joint. That piece was made from a tungsten/steel alloy.
http://www.boatdesign.net/forums/attachments/surface-drives/18665d1202409076-diy-tunnel-drive-spline-adapter.jpg

[Yellowjacket]

Baeckmo is right in that it is probably easier to use a more modern coupling but I am thinking that Sindel wants to keep the design close enough to what is original that he can show the boat and not install a different shaft every time he goes to a show. If that is his desire then he can make a mild steel coupling with the outside dimensions and flange that is the same as his current coupling and cut the inside to an SAE # 1 coupling, and drill and tap the outside with four faux set screws and he will have a centered modern coupling that looks like his original. A bit of work, but if he has access to a lathe and a mill it isn't going to take more than a day to make it.

Here is a link to Gerr's Propeller handbook table that has the dimensions of SAE prop shaft couplings (look at tables 1 and 4) which go down to a 3/4" shaft diameters and will work fine for what he wants to do. If the link doesn't work just google "SAE shaft couplings" and this popped up as one of the first hits.

http://books.google.com/books?id=8w09O4hooWUC&pg=PA130&lpg=PA130&dq=sae+shaft+couplings&source=bl&ots=AdmEXdrDHW&sig=nCLbvvqhG3haJ_hb0Hpxg4aERcE&hl=en&ei=2F2JSsmAOpK2Nq2xxfsO&sa=X&oi=book_result&ct=result&resnum=1#

I am also in agreement with Baeckmo in that boats are flexible and that some type of coupling with a high degree of misalignment (radial and angular, but in particular radial) are good practice. You are going to have to take it out for showing, but it will likely save you a lot of headaches in the long run to have it in there on a daily basis.

[mark775]

"As for tapering the coupling end of shaft; forget it! ...use the type with conical compression rings" - Could you please post a pic? A tapered coupling is the easiest way to perfect alignment, every time, that I know. Enlighten me - you are very confident!
Not using a key? Drag boats with thousands of horsepower don't use keys. The Morse taper of your drill press handles much more torque than your propshaft. It's not a Morse taper but something else - 1/16" per inch, maybe? I don't know. Make sure to lap the prop to the shaft. The worst that can happen is that your prop spin if nuts not torqued enough, right? It might even save you a tranny if you mine rocks again.
These "pinch bolts" have no place anywhere near this application, IMO.
Alignment in or out of the water - I have my own way of doing things here and what these guys are saying is customary and accepted. I feel, align out of the water and check in the water and note the difference but do align to the Nth degree.

[Sindel]

apex1
Wow, what they make for boats these days... Thanks for the site.
I'd like to stay with the Bronze prop, but what if I loose it? (I'd like a spare...)
Rocks have been located (for this year), I just can't believe how much the ice flow in the spring can move some of those monster boulders.
But hammering the prop back to shape? I would hope the prop repair shop would do it differently...
Might just have to give that duplex ss a try when I redesign my coupling... Really am amazed by that bullflex, its design is inspiring... Perhaps I could design a coupling with build-in flexibility? (space is limited...)
Alignment is done before the boat goes into the water, then again while it's in the water - daily for the next 3 days... And yes it moves, seems to be about the same each year... I usually have to lower the front of the engine on day 2, but in the fall when the weather gets cooler, it usually need to go back up a little...
Is that Tectyl 506 EH available in small quantities, perhaps under a different name? Are any of those aerosols they make any good for my needs?

CDK
I've been meaning to redesign that coupling for years; just didn't have a clue as where to start. Most of the "old" boat people I talk to think it's ridiculous to want to change anything for the better on these wooden boats (ie They all run points? Lots of 6 volters? Most only see the water for shows?) Why have a boat, I always ask myself?
I don't have room for a universal or anything, but that coupling of yours is so simple, it really take away my fear to design and build something better for my boat... Thanks for the photo...

Yellowjacket
Did you get wet today? It hammered down rain this afternoon here, stopped for a bit after dinner (for me to take a boat ride :D ), now it's raining cats and dogs again...
Your right on with my desire to keep things looking original. Would mild steel be strong enough? My taper could only be about 1 1/2" or so... (I'll have to check out the link/specs you gave me...)
I do have access to "big enough" leftover stubs of mild steel, various high carbon steels, even tungsten/steel alloy. (I make my current coupling from tungsten - probably overkill is't it?)
And the flexible coupling... Ever see anything that's not so ugly?
I only take the boat (for showing) to 2 or 3 shows a year, so taking out something like my drivesaver isn't really that much of a hassle. Something with pins, a bunch of retaining rings, and 3 specialty tools tools might become a bit much, but something one piece would be easy enough... However, I'm not sure that my drivesaver does a good enough job, any thought or suggestions on this?

mark775
I'm not sure about this conical compression rings type coupling either...
I definitely see and more importantly understand (in my mind) how the taper would work to center the shaft and believe this to be the way to go... Thanks.
Not using a key? I'm still not convinced... I would feel the need to pull the boat out of the water often to recheck the nut for tightness (especially without a cotterpin and me hitting logs...)
With a drill press, you're always exerting more force to the taper making it tighter, and the drag boats don't stay in the water for months without checking things, do they?
If I were to go without a key, I think I would feel safer with a cotterpin, but then torquing becomes an issue...
Arg... Not sure here... Affects would be minimal... (loose a little cotterpin drag, but oh, I got a big fat rudder) I'm not sure I see any benefits with this other than not needing to cut my own brass keys or buying a cotterpins?
The idea of the prop spinning on a hit is okay, but if the prop somehow got loose when I'm out in the middle of Lake Erie and there a storm rolling in... :confused: Then what?

[mark775]

I grew up with the drag boats on Spanaway Lake and Thunder Boats on Lake Washington - Never could resist sneaking peeks at what's underneith/inside when I could.
The advantage to no key is probably moot here if the prop is installed properly. Big horsepower will find weaknesses like keyways and you don't have big horsepower. I'll tell you what, I've never done this on a boat where it is critical to keep going but I will. I will put a new prop on my passenger boat and there will be no keyway ( I intended to do this anyway as I am marginal with something like 1,100 ft.lbs of torque through a 2" shaft and want to dispense with the keyway). I'll let you know in one year if it worked! The important thing is to lap the prop to the shaft well and torque and jam nut. Lapping is critical with or without a key and nobody does it anymore!
I certainly don't intend to offend here by questioning your abilities but just to make sure: Install prop on shaft without key. Torque nut on lubricated threads and prop face. Make a Sharpie line at the highest point of the prop. Remove prop. Place key. Repeat install and if the prop did not go as far up the shaft as it did the first time, you are riding on the key with no chance of fit.
The cotter pin might keep a prop from falling off, I 'spose but if the prop is that loose...I just always have seen them to be ugly, hurt, catch fishing line and unnecessary. Try jam nutting in Rectorseal or 5200 as a lubricant.

[Yellowjacket]

Sindel,

No, it blew over us, we have't seen rain in two weeks. Every time it looks like it wants to rain, it just passes us by....

Mild steel will work fine here, there isn't much stress in it and the original coupling was probably mild steel. You can get the same "patina" pretty quickly in mild steel...

The SAE couplings have a keyway in them. I would look at the amount of taper length that you have available, and if it is more than the SAE spec then maybe you won't need the key. If it is less you should put it in for sure. Mark 775 is right in that there isn't a lot of torque here, but if it slips it is going to make a mess of things. I'd probably just put a key in it and walk away. Also make sure you find a low height locking nut for the end of the shaft. Our dyno came with an SAE coupling and it had a slotted end low height lock nut that fit really nicely in the recess of the coupling. McMaster-Carr has them, they are called Flexloc style expanding lock nuts. They are better than Nyloc nuts and come in stainless steel.

[mark775]

Thanks a lot, Yellowjacket - I just killed hours on the McMaster sight!

[Frosty]

This is an interesting thread. A guy who is well capable of fixing his problems asks questions that he knows the answer to.

He gets people dancing to his tune as he gets everyone to talk about his beloved boat. When some one gives him a good answer he comes up with, Oh My brother in law has the propeller, or I don't want to move a way from original (crap 50 year old engineering), or I don't have the money,--he just wants to talk about his boat some more.

His boat is original he says then posts pictures of a fibre glassed bottom!!!!

Whats next --? lets discuss the flag pole position.

Im going to thank you Sindel for helping me to see the light. I wonder how many other threads absorb time by members trying their best to hep and get kicked in the teeth.

Ive learned a lot from you.

[Sindel]

mark775
It's not that I don't think "no key" won't work...
I like the thought of the redundant features (key and cotterpin) since I'm lazy and forgetful...
And, I don't see the need (105 hp)
As for spinning on the shaft, probably not a good thing...
But I'd still be interested in how it works out for you.
Wish I had someone to explain that key interference thing to me years ago. I had the hardest time fitting the key when I purchased my first aqualloy shaft. It had rounded edges in the keyway all the ones I made had a square "milled" bottom... I did exactly what you suggested after having already tried to tighten the thing 2 or 3 times unsuccessfully.

Yellowjacket
Still no rain?
We got hit again today... Got over 5" these past few days and the river shot up 4 feet.
Thanks for the confirmation; I'll have to keep my eyes open for a chunk of mild steel for a new coupling... The original that I got with my engine was actually cast, but almost every other I've seen has been steel. I'm sure using it will add the patina quick enough.
The SAE couplings look easy enough to make and I should have room. I guess the biggest thing will be room to get to the nut? Nuts at McMaster, great! Thanks...

mark775
Thanks for looking out and sorry about your time. Searching that McMaster site can be maddening...

Frosty
Yes, capable, but needing the direction of others... (I thought this was a "discussion" forum)
There isn't much room to dance and you'll have to bring a radio if you want tunes...
Sorry you don't approve that I married into a family with 7 chris crafts and 3 lynmans.
Money's not the issue, it's paying more for something when less will do better. (at least in my situation)
Trying to maintain the boats original appearance doesn't always mean like the factory did it. The factory only put 2 or 3 coats of varnish on the boat, never considered bookmatched planks, etc.
The west system bottom was a bad idea (I feel now), but my father-in-law said it would be my best solution since this was my very first boat ever. There are 2 other boats in the family with west bottoms... The latest boats we've restored have been given 5200 bottoms.
Is there something wrong with the position of my flag? I've seen several other Rivieras with their flags mounted in the same place?
What would indubitably help here would be if you could enlighten us about their proper placement...

[portacruise]

Here's some thinking out of the box type stuff that has been used for shafts in much LOWER power applications. Don't know if it can be scaled up to your power levels. Spring steel ie. piano or music wire used by Rick Willoughby in human power applications, 10mm up to 0.5 hp. I have use fiberglass shafts up to about 100 watts. Both are mostly indestructible because they give and realign upon severe impacts. Spiral wound or braided carbon fiber is much stronger than fiberglass and might take the impacts. Bushings are glued to the shaft and then ball bearings to mate with the bushings. FWIW.

Porta

baeckmo
Exactly why I started the discussion...
Worried about breaking a shaft or something worst...
Cost-wise I'm thinking about going back to my homemade ss shafts...
But maybe there's something else to use, hence the questions...
As for the clamping couplings, how do they come apart?
Who makes them?
Tectyl? Never heard of this... (I'll have to google it...)
What kind of flexible couplings are available?

[baeckmo]

Must say I share Frosty's opinion on your coupling design; set screws plus key are crap engineering, and they were so a hundred years ago as well! At that time, good engineering had been a tapered end with double nuts. Today, the prefabricated clamping units do the same thing easier and better. Attached you will find three varieties used here; I am sure you will find those all over the globe. I don't remember having milled a key recess for many years now! Shaft keys are only acceptable if components have to sit at a specific angle on the shaft!

The tabular texts should be selfexplaining, suffice to say that "daNm" is torque in Nm/10, ie ~kpm. The first page shows the necessary outer hubdia for various hub materials.

Now to the shaft material. With the engine power, rpm's and shaft dia given, only the Duplex steel 1.4462 as mentioned by Apex1, has the strength required for full power! All the others will fail due to either overload or fatigue. In addition, the bronze shaft has only half the modulus of elasticity, compared to steel. As the shaft length is close to the allowed limit for one bearing, the soft material will thus deflect under rotating load, causing premature failure due to the combined effects of torque+radial deflection+compression.

In order to save your props when shoveling rocks, use a short brass key as a torque limiter. Fit propeller to taper, use a closed hub-nut plus shims to press the prop ~1 mm onto the taper (with hub-nut bottoming on shaft end).

[Yellowjacket]

Sorry Beckmo, but I disagree that the stress is that high in the shaft, or that he needs a material such as a duplex steel to work if he has the right coupling and prop.

At 105 hp and with the engine running at 3200 rpm, the shaft shear stress is 10.5 ksi in a 1 inch shaft. Even the 316 stainless can handle that assuming a 42ksi yield strength and a .577 shear factor (max stress to prevent yield is going to be 24 ksi). You need to avoid any big stress concentrations, which is why the a tapered coupling is a good idea, and I probably would like a margin for any stress concentration, but a 2.3 factor of safety is likely ok. It isn't a huge safety factor, and could have a lot to do with why the shaft failed in under the pinch screws, but for a proper tapered coupling it will work fine for a long long time.

Looking at the bending stress in the shaft at the prop end, and taking your numbers for thrust at 232 kg of force fwd and 91 aft, and converting that into a moment of 323 kg f (712 lb force) at a 5 inch radius (avg 10 inch dia of action on a 12 inch prop dia) I get a total moment on the shaft due to prop thrust being uneven is about 1615 inch pounds. This results in a stress of about 16.5 ksi in bending, or about 1/3 of the yield strength of 316. I don't have a modified Goodman diagram for 316, but without a significant stress riser the shaft isn't going to break as a result of high cylce fatigue with that load in it.

I agree that the margins aren't huge, and I'd like them to be bigger, but it isn't going to twist right off in short order either. The fact that he has successfully run the 316 shaft for a good long while, even with the nasty prop offset loads indicates that the system will work if he doesn't solve his prop issues. If he does fix the prop, the shaft cyclic bending stress only goes down and things even look better.

[baeckmo]

Yes, you are correct there, as long as you check on the "intact" part of the shaft! Admitting a slight "constructive laziness", and a bias towards design for commercial duty, I used the shaft supplier's charts for dimensioning, and came out with my conclusion. This is based on the critical area at the propeller end, where area reduction due to taper and due to key notch combine to a high, asymmetrical stress concentration. Please note that I wrote "....strength for full power...".

Note that the "force" figures from the other thread are for the infinitesimal area strip dA at 0.7*r. You have to integrate this product over the whole blade area in order to use it in another context! The total propeller thrust is something like 3500 N, still with the asymmetric pressure distribution indicated by the ratio given in the "rake" thread. This increases the shaft stress considerably. Also note that the force asymmetry plus the blade pulsations result in a pulsating load on the shaft.

Another factor is the shaft length/dia ratio. With a fixed coupling, the minimum length between supports should be 40d, ie 1000 mm (dNV). This shaft is 832 mm, and should thus have a flexible coupling. There are also limits for maximum length between supports (Lloyds give a max length of about 600 mm for a 25 mm shaft whirling at 3200 rpm!). Unless this rotating mass is carefully enclosed; safety first!

[Yellowjacket]

I wouldn't worry too much about shaft length. The overall length is about 32.75 inches, the length between supports isn't any higher than 28 inches, which gives you a first mode critical speed of over 6,000 rpm. In addition there is some centrifugal stiffening from the prop, so you aren't going to see a shaft whip problem until you are probably over 7,000 rpm in the real world. Even if the shaft length between supports was 32.5 inches the first mode would be at 4500 rpm, which is a 45% margin on critical speed, which is plenty.

The shaft bending stress then is a good bit higher, which may indeed be the limiting factor..

[mark775]

"~1 mm onto the taper" - One mm from where? I like these couplings. I used these on yachts - http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=12_1_1

[baeckmo]

Yellowjacket, I'm buying your engineering arguments on shaft length hands down. What I was trying to say was that when you give advice to a client, there are two important additional issues:

A) There may be mandatory design rules covering the subject.
B) Supplyers limitations for their equipment.

If your design, or advice, does not adhere to the possible limitations from those sources, any faults occurring to, or as a result of, the equipment (or, in fact, connected equipment as well) is YOUR responsibility, no matter how careless your client has been! You are the one who has to prove that your design is ok if you don't have a written acceptance either from A and/or B.

A "non-responsibility" chart from your client will not save your ass, neither legally nor in terms of professional reputation.

[Ad Hoc]

"...A "non-responsibility" chart from your client will not save your ass, neither legally nor in terms of professional reputation..."

Yup, that about sums it up. Since we don't know each other from a bar of soap, nor if all the information given is correct, or being done as suggested. So, least we can do is, well, summed up by A) and B). Fully concur.

[Yellowjacket]

Beckmo and Ad Hock

Points well taken....