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Prop Question Need Help ASAP

C

cfth

Well-known member
While I was loading the boat at the ramp tonight after gator hunting noticed a bolt with funny looking washer on the ground. After further examination it was a sheared grade 8 unf from a prop. Turns out it was my prop. So here are the details. Boat seemed to run fine. No bad vibration etc.. Even when loading. The prop is a three blade sensenich @ 2 degrees 78" long. Motor is angle valve 0540 rebuilt by Jr. Jurnigan. The prop was installed by Jr. about 2 years ago and has not been off the boat since. The bolt sheared right where the threads start in prop adapter. It appears as though the bolt did not loosten.

So hears the question. What is the cause of this???

I am going to change the bolt out and replace all of the others. I would like to know what caused this though. Any help would be appreciated. I have a lot more gators to kill and am supposed to hunt tomorow.

I will try and post some pics tomorow.
 
i use grade 5 in the prop due to it having a little more flex, never had a problem, and remember your never seize.
 
I'm not sure you'd ever figure out why it broke,could have worked loose enough to give it movement, over thightned, bad materials, all you can do is put another one in and make sure to tighten them all even and maintain them.
 
Torque. Your prop got loose. It's not the bolts that hold that prop on there, it's the plate. You torque those bolts equally so that the plate
squeazes the prop. The friction created between the crank(or whatever drive) and that plate is what holds the prop. Without this torque your fasteners are gonna shear right off. Common fasteners grade 5 or grade 8 are not rated on a sideways shear, the strength is pull. It's easy to tell when the bolt has stretched, it will not come out straight, you'll see.
And your right to replace them in full sets.

After an initial install at some point you are supposed to re-torque( at least on a wood prop) to compensate for the compression of the prop at the hub.

It's all available here http://www.sensenichprop.com/sen_html/propguide.htm

Good luck
 
I have sheared the bolts on a terminator hub before. It was the bolts holding the inner hub plate to the prop adapter. I caught it before any catastrophic failure occured. It was enough to convince me to periodically remove the blades check torque periodically. I now run a 78" 3 blade Senseniche so any more info would be appreciated.
 
Just stuck two pics in my gallery if someone could post them for me. If you will notice the bolts have a little rust on one side. Indicating to me they were starting to shear for a while and must have finally broke loose last night. Does any one know if the double lock washers can be store bought or are they sensinich only items. I will also call sensinich tomorow and see what they say. Thanks for the input.

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CFTH,Harmonics are the problem.Especially if your engine doesn't have counterweights.Wood props and warp drives are solid and would absorb the harmonics.The hollow carbon fiber props don't. I have broke 4 bolts out of 6 on the newer 6 bolt hub. I have a friend with a 300 upstack who broke all 3 on a 3 bolt hub. He was thrown from and hit by his own boat.JC Stanley can get an FAA APPROVED DAMPENER that will bolt directly to your lycoming ring gear. Don at sensenich is aware of this problem.I now run one of these dampeners on my 0550 and it seems to have cured the problem.My friend with the 300 upstack has one also.They cost about $ 450.00. there is a picture of my engine in my gallery and you can see what the dampener looks like. I don't know how to move the picture to this thread. It is the second photo on page 16.You could probably get the washers from diamondback. Sensenich can switch you to the newer 6 bolt hub.
 
cfth,call Don at Senenich he will swap hubs to a six bolt for you propably at no cost,as long as you bring him the broken parts.Worst case it would be a $150 exchange.
 
When was the last time you torqued checked your bolt's. Also the 6 bolt is the only way to fly it's a much better (safer) way to hold your prop hub together.
 
UTOOH, do we have a problem with another brand prop?
Could this be our nemesis to the question we have all been asking?

Did those guys who blew props up have the proper flex plate on their motors?

Were their harmonics off?

The jury is still out IMO?
 
I think we have identified the culprit.......Mr harmonics, or could it be Mr Rain getting in those blades on boats stored outside?
 
Or, could it be the need for internal harmonics dampeners - like those used on Merc. and Yamaha props - or on torsion axle trailers?

But wait....the Great Satan was already declared to be WW / PS.....and at a terrible cost to folks who have stood long and lonely to benefit each and every one of us.

I am guilty of sometimes rushing to judgement and declaring a certain thing to be at fault and doing that before all the facts are discovered and evaluated.

This is a time of terrific change in the airboat industry as large ride boats, greatly increased weights, more HP & torque, radical cupped prop design and deep gear reduction becomes the norm - rather than the traditional small personal DD airboats that have been our tradition. We're likely to open several unexpected sources of unexpected events before this period of evolution stabilizes.
 
I am not getting into the PW/WW argument but I will say this. Just hung up with Don. My new hub will be here on Wed. No questions asked no issues just sending it out to make sure I can stay on the water killing lizards. This is why I personally bought a Sensenich Prop. I had always heard they had great customer service and now they proved it. Thanks to Don. And by the way he apparently reads SA.
 
I don't think the brand has any thing to do with it. The fact that they are hollow seems to be the culprit. It seems to be not that much a problem at low rpms, or detached from engine( geardeive). About 200 hrs has been all I could expect on working boat reguardless of brand and you better check for broken or loose bolts daily.

Grant
 
The 6 bolt hub will definitely help but will not stop bolts from breaking. There is nothing wrong with the prop or hub. You can not run an automotive engine without a harmonic balancer/dampener. The dampener i use deadens harmonics before they reach the prop.They use these on alot of the aerobatic planes. I do not have the counterweights in my engine. If i did i probably would not need the dampener. Alot of engine builders who have built aircraft engines for airboats usually don't put counterweights back in. Don at sensenich was also very helpful when i had problems with bolts breaking. He swapped hubs at no charge and even let me try the Q SERIES blades at no extra cost. My next aircraft engine will definitely have the crankshaft counterweights put back in. I also replace hub bolts every 50 hrs.
 
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