Losing Confidence

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We have always tried for perfection. Certainly that is seen in the many changes over the years... most all driven by users such as yourself providing feedback on real-life use of the product.

None of the failures we have had over the years amounted to any kind of safety or recall status. Warranty percentage has always been quite low, but we make changes to make a better product anyway. We also use the product heavily, so we want more fun and less hassle too!

What we should concentrate on first here is the rust pitting shown and the apparent initial cracking before final failure. Those may indicate other problems which may not require a material or diameter change. Perhaps a better maintenance schedule, washing, anti corrosive coatings... that sort of thing.

_________________
Matt Miller
Former - Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA
(Retired 11/7/2022)

This morning I was watching the GPS and counting pedal strokes. Counting 1/10 of a mile distances, I was averaging about 58 to 63 complete pedal strokes (Up and Down once). Of course, several factors come into play. Current, wind, and depth of stroke play a role. Also, if pedaling and paddling at the same time, to travel the same 1/10 mile required less strokes. On average though, I'm estimating about 600 pedal strokes per mile. Approximately 830 miles will have generated half a million pedal strokes. Hope that helps Hobie.

yeah, well, for all it's good points stainless Steel breaks like that sometimes. 'Can be all shiny and new then snap in two.

So what material could they use instead?

I carry spares.

I'm participating in a 42 mile race coming up this weekend (Phatwater) on the Mississippi River in Natchez, MS. Based on advice from this Hobie Forum I replaced my other mast rod today and it was a good decision. Hidden just under the rubber fin was rust in the high stress area and a crack with rust in it that went half way across the steel rod. This steel rod looked ready to snap in two which is the last thing I want to happen in a race. It lasted for 950 miles so I can't complain, especially since Hobie has made replacing the rods an easy task. I love the threaded solution. Thanks Hobie!

That threaded mast rod says china on it.

I believe stainless steel has only so many flexes till it fractures and breaks, also there's the issue of crevice corrosion.

Perhaps Hobie could suggest a number of cycles before replacement.... a replacement schedule such as 100k strokes or 10 years which ever comes first.

You can choose in between having "made in China" on the part or paying 3x the current price. (I'd like to be wrong about this.)

Cheers,
Mack

I recently bought a stainless steel food prep table. The top was covered in rust within a couple weeks. It was replaced, but the new one did the same thing. Moving to another, more expensive table, rust is no longer a problem. My guess is that there are different grades of SS, and different levels of material quality control.

It is entirely possible that Hobie got a batch of SS mast rods that were not up to spec or somehow inferior to previous batches. This sort of thing is a constant problem for companies that source parts from some areas of the Orient, where QC and material content can vary widely from batch to batch.

My guess is that the Hobie mast size and design is sound, but was and can be compromised by poor QC or non-spec material from the mast maker.

Ditto

Rnykster:
I used to race go carts in an open pro class called duels for dough. We had dual engines nitro fueled, the carts accelerated zero to 140 in about 200-300 feet. We would get at the most one to two races out of the engines before they were destroyed (usually melted pistons), or about ten minutes run time max. I'm pretty sure if we had gone back to the go cart manufacturer or the original engine maker saying we were just using the stuff normally they would have just laughed at us. I've also built several dragster engines which only lasted a two to three races before being completely destroyed. I didn't go back to GM and say your L6 engine didn't hold up, we re-designed and manufactured what we needed to make the engines perform, it wasn't GM's job to do that.
As far as your shafts go there are a couple things you might try.
option 1: It might work if you can move the high stress point away from the joint. by adding a sleeve around the shaft maybe 1/4 to 3/8 long epoxied to the shaft should help distribute some of the force away from that high stress point. If you want to eliminate the corrosion order a half dozen shafts and send them to a local plater and get them PVD coated (PVD is a diamond coating that is RC 90 hardness and should prevent any corrosion (it's what we use on plastic injection molds)).
I would always remove the shafts when not in use and install shafts from a rotating pool, serialize the shafts and log their usage so you can keep track.

Option 2: Take a stock Hobie shaft to a local tool shop (mold shop preferred, they typically know a little more about the metals) and have some custom shafts made (for racing). You can try several materials, I think the first material I would try is 420 stainless steel hardened to rc 46-48 (they all know metal very well and can advise further). This is probably twice as strong as the standard shaft, I would definatly PVD coat these shafts. I would next try M4 tool steel hardened to Rc 46-48. If you want to get really exotic try going to tungsten carbide shafts (same stuff they make carbide end mills out of).

Option 3: Go to fiberglass/carbon composite pulltrusion for the shafts this is pound for pound five to ten times stronger than the steel and doesn't fatigue like any metal does. This is what I used for my bowsprit and I can place a 3/4 dia x 3 ft piece on two bricks (one on each end) and jump up and down on the rod (250 lbs) all day long and it doesn't even begin to bend. A 300 series stainless rod would bend and eventually fatigue and break (as any metal would). Keep in mind the material they are using is mostly for marine corrosion protection, it's no where close to the strongest material available. Why would they put two $300 dollar shafts on a unit that sells for $600, I know I definately wouldn't want to pay for them since I have had no difficulty with the current design.
I've had and used heavily my mirage drives since 2007 and have yet to break a mirage shaft on any of our mirage boats. Your the only one that I know out there that's making a huge issue out of this, I'm just suggesting that you design and build what you need for your own use nobody is stopping you (as long as you don't try to sell them in a way that violates Hobies patents), thats what the rest of us do. Also keep in mind the current failure point is probably the cheapest part to replace, if you strengthen that, the next weakest point will fail, like the shaft holder, chain, or the mirage well in the boat, if it were me I would just get a good supply of replacement shafts and replace them before each race and donate the used ones to the poor (my address to follow). PS I think Tom is right they (hobie) needs to get a different metal supplier, looking at the pics, that material is crap.
Hope this helps.
Bob

Bob - I'm supplying feedback to Hobie about their product because I'm tired of my drive units breaking so often. I appreciate your feedback.

Lets see now -- Rnykster probably runs his Adventure at 60 (+?) CPM. At that cadence his boat should travel about 8 feet per cycle or 4 feet per stroke. That works out to approximately 1320 strokes per mile. His mast was on the verge of failure at 950 miles, so it had sustained about 1,254,000 flexes. His other mast failed sooner -- maybe at 850 miles or 1.122M flexes?

Bad QA? Crappy material? Here's an industry description of Hobie's mast steel:

AMETEK Specialty Metal Products: Developed by Armco, Inc (now AK Steel), 17-4 PH, combines high strength and high hardness with excellent corrosion resistance, fracture toughness and heat treatment properties.

Want more technical information?
National Specialty Alloys: 17-4 stainless steel bar, also known as UNS S17400, 17-4 PH and Grade 630.... Primarily comprised of 17% chromium, 4% nickel, 4% copper, with the balance being iron. There are also trace amounts of manganese, phosphorus, sulfur, silicon, columbium (or niobium) and tantalum. Stainless Steel 17-4 PH delivers an excellent combination of oxidation and corrosion resistance. Other characteristics include high strength, toughness, and quality mechanical properties at temperatures up to 600° F. Engineers and designers frequently choose Stainless Steel 17-4 PH due to its high strength and superior corrosion resistance when compared to many other stainless steels.

Except for heavy users with Turbofins and frequent mast benders, I seriously doubt that most owners would see a problem with these "crappy" masts in a lifetime. What is a heavy user? I would say someone regularly running their Turbos at 60 to 90 cycles (120 to 180 strokes) per minute for at least 2 hours weekly or 100 hours annually (not talking about "seat" time or leisurely cruising), with some occasional sprinting. Comparable miles depends on the individual kayak model, of course. Based on the local Hobie community, that might include maybe 1 to 2% of the Mirage Drive owners.

Rnykster, good luck in your race! Let us know the results.

Ahh, Roadrunner - you're right, most owners don't use their pedal kayaks frequently. Many people have bicycles but only a small segment of bicycle owners use them frequently for aerobic benefit. An even smaller segment use their bicycles in races. Same with pedal kayaks. Bicyclists have the option to buy better components for their bicycles that will withstand higher use and not rust like the cheap components on cheap bicycles do. If you know where to get better drive unit components for the Hobie, let me know.

If you read a previous post I added to this thread, I estimated a half million strokes to detectable threaded mast rod problems - half the flexes you indicate. I have long legs and take a deep stroke (without bottoming out.) If I kayaked using only the pedal boat, I'd have to buy two pedal drive units a year due to part failures. I'm not using the original drive unit now, but a replacement I've already bought and that is failing already.

Hobie offered the ST Turbo fins to the pubic. It is not my fault that their drive unit is not designed strong enough to hold up to the additional stresses that their ST Turbo fins apply, be it pedaling slowly or when pressure is applied to go faster, or when pressure is applied to maintain a 5+ mph speed for HOURS of sustained aerobic activity.

We're not talking about unusually high pressures applied to the drive unit in a one minute sprint (anerobic) where people max it out to all they are capable of. It is the anerobic folks that put undue stresses on the unit. I'm not a sprinter, rather, a long distance runner.

That is not an accurate statement. If it was accurate, we would see many more failures. Users like yourself are the only ones experiencing problems on a regular basis with these items. The common denominator is you, not the ST Turbo fins.

Most users have little to no problems with these fins. Once again, I'm sure Hobie will see your posts, and do as they see fit.

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Actually... no. That is US sourced material and manufacture. This is a very high grade of stainless (17-4).

Understand..."stain-less" is not "stain-free".

When you have more carbon in the material for stiffness, you can get stains. Machining tools can leave bits of carbon to rust. Another factor is the trapped moisture, debris held against the shaft by the fin.

These parts had not been passivated in the past, but we made that change, in response to this thread, to be sure that any bits of machining carbon is removed.

_________________
Matt Miller
Former - Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA
(Retired 11/7/2022)

Pointing your finger at me and saying that I am the problem is absurd.

I had ZERO fin rod failures and never saw rust on rod stress points prior to the availability of ST Turbo fins. The problems started when I bought the ST Turbo fins.