Hub bolt shear and prop damage - pictures attached

Airboats with smaller powerplants.
RC
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Hub bolt shear and prop damage - pictures attached

Postby RC » Fri Jul 10, 2015 10:29 am

Hello everyone,
I have put together a mini airboat a few years back. It is a 13hp Harbor Freight motor with a 36" wooden prop. I have had good results with this set up. It only has 20-30 hours run time. I use it primarily in a swamp for duck hunting and work in the area. I was out last weekend and had a bad experience. I was on my way back to the launch when I heard a loud noise, such as a 22 gun shot. Then a second shot in less than 5 seconds. I shut it down asap. Upon inspection, I found that the hub bolts look as if they had backed out, as if loose. I then found some prop damage. I then found that not only two of the hub bolts had broken, but all 4 had broken! Evidently, two had broken previously when someone else was running it and did not know that it had happened. The two that broke while was running it, had hit the prop damaging the prop. Needless to say, we had to pole and paddle back in. Luckily, it was only about a quarter mile to the ramp. I did find a few other instances in the forum where this had happened, although I don't understand why this happened. I admit that I had not checked the hub boats in a while, and cant say if they were indeed still at the correct torque. I do know that I had used self locking nuts and blue locktite when I installed the prop. The motor had always been kept inside my shop until this year. It has been used more this year so we have left it outside, uncovered. A few details on the arrangement are: the bolts where grade 8, 5/16" yellow plated head stamped 01RL. This is approved astm bolt, although it is foreign made. This strangest part that I dont understand, is that the bolts broke on the back side of the hub, not at the obvious shear point, such as the shear line of between the hub and prop. Each bolt broke in exactly the same place, immediately beneath the nut! This seems to me to be a very strange location for bolt failure. Each bolt was still extending into the hub. The prop and hub was still in perfect rotational alignment. If anyone can help me understand why that this has happened, I would be very grateful. Also due to extent of the damage, I am not planning to run the prop until I hear from you guys on what you have to say about the prop damage. I do not have any experience with such things and am relying on your advise on what to do with the prop. Please let me know what you think about continuing to using the prop as it is. The damage occurred on the leading edge at the tip of the blade. The damage is a 2" long. Before I go, I would like to say a "Thank You" to those that take part in this site. I could not have built the set up with out you all's input.
Last edited by RC on Sat Jul 18, 2015 2:31 pm, edited 1 time in total.
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RC

blow boat
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Re: Hub bolt shear and prop damage - advise please

Postby blow boat » Fri Jul 10, 2015 11:00 am

I would say bolts are a low quality,but
In saying that not seeing it's hard to say.
If set up was running good and smooth?
However if this has happened before
I would check and go threw everything,
And if prop has leading edge damage
To be safe would send in for repair if it were
Just a gouge in wood could epoxy to fill in.
If all checks out ok buy hi quality bolts#8
Like dorman or such made in USA , assemble
And monitor it and I mean a lot every time
You use and them some and keep it covered
And don't let prop get wet and remember
Safety first....!!!!!!

happy harold
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Re: Hub bolt shear and prop damage - advise please

Postby happy harold » Sat Jul 11, 2015 8:02 am

the making of bolts is a just short of a miracle. if you can find a video of the procedure, you will begin understand how this happened. blow boat is giving you the straight dope--go USA, and since the standards are higher--they will cost more.

RC
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Re: Hub bolt shear and prop damage - advise please

Postby RC » Tue Jul 14, 2015 6:48 pm

Thanks for the info. I have tried to post a photo, but am unable to. I can load the photo, but when it loads the main screen just turns white and i can never see to submit the photo. It just stalls out. I did post the photo in the members gallery, labeled as RC. What do you all think of this damage? Is the prop usable?
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RC

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rick
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Re: Hub bolt shear and prop damage - advise please

Postby rick » Tue Jul 14, 2015 6:57 pm

RC, if you can email the pics to me, I'll get them posted: webmaster@southernairboat.com

Rick

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Re: Hub bolt shear and prop damage - advise please

Postby blow boat » Tue Jul 14, 2015 8:05 pm

Yup, prop needs to be repaired for sure!

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Re: Hub bolt shear and prop damage - advise please

Postby rick » Tue Jul 14, 2015 10:41 pm

Sorry for the delay...here's those pics:

Image

Image

Rick

RC
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Re: Hub bolt shear and prop damage - pictures attached

Postby RC » Sat Jul 18, 2015 2:52 pm

Well, I have taken you all's advise and have began the repair process. I am using West Systems two part epoxy with some thickener. This is a very high quality product that I have use to before. What do you all think of putting a layer of fiberglass over the repair. I would then varnish over this. It would be very smooth and clear when completed. The glass would be very durable and help ensure that the repair does not come apart. The one thing that I am concerned with is the balance of the prop. Any tips on balancing the prop after repairs are complete?

Another thing that I want to bring up again is the broken bolts. I have had a couple of engineering friends to examine the broken bolts. Each said the same thing. The bolts broke because of stretch. This is most evident under a magnifying glass. The last remaining threads are stretched. We have determined that the wood has expanded to the point that it broke the bolts. When the first bolt broke it instantly transferred the entire compression load to the remaining bolts that instantly broke again from overload. Which leads back to what everyone has said, check the torque often! In this case I should have backed the nuts off a turn and re-torqued. I will put up some pictures of the repair soon.
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RC

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Re: Hub bolt shear and prop damage - pictures attached

Postby Scarecrow » Sat Jul 18, 2015 5:16 pm

I would send that prop back to the manufacturer or get a new one, for your safety and those around you. :thumbleft: :rebel:

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mojoe
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Re: Hub bolt shear and prop damage - pictures attached

Postby mojoe » Sun Jul 19, 2015 4:32 pm

RC please fill in your location in your info. I want to be sure I am nowhere near that prop when you are running it. It's gonna turn into splintering projectiles!
Airboating is like marriage: There are unlimited ways a person can be right, and somehow still be wrong at the same time!!

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Re: Hub bolt shear and prop damage - pictures attached

Postby blow boat » Sun Jul 19, 2015 5:40 pm

Brother its your deal, but that prop needs
To be sent in for repair !! Your repair will
Make that side of prop heavier and when
You spin it up = out of balance= not safe
If you've never seen a prop come apart
You should try and keep it that way cuz I
Have seen it sling tips off go threw hull
And sink and I'm sure people will chime
In also it is worth the money trust me

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Deano
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Re: Hub bolt shear and prop damage - pictures attached

Postby Deano » Sun Jul 19, 2015 6:10 pm

I would be willing to bet that the manufacture would not even offer to repair those remains.
The best way to salvage what you have left there, is to make a clock out of it.

If you do anything else, be sure nobody is anywhere around the first time you spin it up.
And if you can borrow a suit of armor, making that attempt would be a good reason to do so.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

SWAMPHUNTER45
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Re: Hub bolt shear and prop damage - pictures attached

Postby SWAMPHUNTER45 » Sun Jul 19, 2015 7:00 pm

HIGHLY LIKELY ANY SUCH DIY REPAIR WILL CAUSE INJURY or DEATH


CHECKLIST: Post repair operation

1) Life Insurance paid

2) Organ donor card in wallet

3) Say heartfelt goodbye to family and friends

4) Leave copy of current will on kitchen table

happy harold
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Re: Hub bolt shear and prop damage - pictures attached

Postby happy harold » Mon Jul 20, 2015 7:43 am

wooden props are not to be tightened over 35 to 40 pounds. check your hub. you may find cracks of over tightening. if so, junk your prop or make a clock out of it. jmo

RC
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Re: Hub bolt shear and prop damage - pictures attached

Postby RC » Sat Jul 25, 2015 5:44 pm

OK, I get the picture. Everyone set at ease; a new prop has been ordered. Thanks to everyone for your advice. I know this comes from valuable experience, and that is want i want! The old one will just be hanging around the shop, no more rides for it.
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RC

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Deano
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Re: Hub bolt shear and prop damage - pictures attached

Postby Deano » Sat Jul 25, 2015 6:18 pm

Good call. . . Great Decision. . . . Even better post.

If you ever see or even hear one come from together, :shock:
you will post the same as we did when you next see the opportunity. :)

It would make a good shop clock.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

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pipedog
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Re: Hub bolt shear and prop damage - pictures attached

Postby pipedog » Sat Jul 25, 2015 9:24 pm

Image
Palm Beach open hull 13'9" with 6.0 F.I. LS - Ox Box and a 3bld "R"

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Deano
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Re: Hub bolt shear and prop damage - pictures attached

Postby Deano » Sun Jul 26, 2015 8:32 am

Gotta say, you're fire pit is surely substantial enough. :thumbleft: I like it.

If somebody is going to try and steal that, they better eat a BIG breakfast. :D
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

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Re: Hub bolt shear and prop damage - pictures attached

Postby pipedog » Sun Jul 26, 2015 9:17 am

Thanks Deano :salute: I had my share of wood props, nothing wrong with them as long as there in good condition.
Palm Beach open hull 13'9" with 6.0 F.I. LS - Ox Box and a 3bld "R"


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