[Chris]

Went out on a friend's boat tonight. He has a 28' tritoon with a 40hp Koehler and 60" prop. We slowed down to make sure we weren't going to hit a bridge that we were going under and when we went to take off again, the shaft on the fan stand broke and it went in the lake.

We were pretty fortunate that it didn't fall in the boat because one of the guys little girl was sitting close to it. And it was close to a bridge so that helped get it back on the boat. Oh, and we had 6 grown men there to get it recovered.

Anyhow, I'm in the process of building a fan for my boat, how can I avoid the potential of this happening to mine?

 

[Chris]

Some pictures

 

[Chris]

One more..

 

[Dolium Piscium]

Glad 2 hear that no one got hurt. I don't think i have heard of that happening B4? There have been plenty of stories of fan blades coming apart on here though. Maybe consider building a "Globe" fan if your concerned with that type of safety issue. Something like "Beaver" had. Roughfish Assassins has a great example of this with their new boat. Good luck with your build.

 

[eshaw]

It looks like a metal fatigue failure. I suggest that anytime a person builds that they over build. You want to use metal for the shaft that is tough, not hard. Metal in the 4XXX series of steel is what I'd use for something that is unsupported on one end. This type of material is used in axle shafts and heavy truck transmission shafts as a couple of examples. Another thing I'd look at very carefully would be to get the weight centered on the shaft so as to limit side loading.

 

[Phillips_211]

Just like carp coffin said, build a globe fan, the globe fans have 2 points of rotation rather than just one. Fullbore just built one, im sure you can find his build pretty easily on here.

 

[Chris]

I'll look into globe fans. Mine won't be quite as heavy or strong as his though. Mine will also be 60" but only a 22hp and reduction.

 

[Chris]

It looks like a metal fatigue failure. I suggest that anytime a person builds that they over build. You want to use metal for the shaft that is tough, not hard. Metal in the 4XXX series of steel is what I'd use for something that is unsupported on one end. This type of material is used in axle shafts and heavy truck transmission shafts as a couple of examples. Another thing I'd look at very carefully would be to get the weight centered on the shaft so as to limit side loading.

I also thought about the fact that it broke like that from possibly being hardened.

Another thing to note, is they had gussets on the shaft buy it probably had 2-3 inches of bare shaft between the bottom of the gusset and the flange bearing. Allowing it to flex a little more than I would like. Also, they had pins to keep lock the fan sideways for trailering. No straps so it shook a lot when hitting bumps in the road. I bet that played a roll in it for sure.

 

[Magnolia Outdoors Guy]

That SUCKS big time! I hate that happened to your bud!

After spending several years planning, tons of money, and the last 5 months working on mine I've had a reoccurring dread of that happening. Even had a nightmare one night about it. I keep checking nuts & bolts along with the 8 motor mounts that isolates the motor mount plate from the turntable. From all accounts I overbuilt but it still doesn't ease my worry.

 

[Chris]

Here are some pictures of where the shaft broke on the fan side.

 

[Night-prowler]

Here are some pictures of where the shaft broke on the fan side.

Looks like the welding on the shaft hardend the the steel and thats why she snaped. We use cold rolled steel for all our shafts at work for huge pressure chamber lid pins that weigh 5ton. Only catch you cannot weld on them.

 

[Night-prowler]

Your shaft ends can be welded with stop plates if needed but for any vertical support look into dodge bearing and lock collars. Anytime you weld on shafts like that it becomes brittle and in the drink ya go.

 

[Chris]

Your shaft ends can be welded with stop plates if needed but for any vertical support look into dodge bearing and lock collars. Anytime you weld on shafts like that it becomes brittle and in the drink ya go.

I'll look into that. Thanks.

 

[Magnolia Outdoors Guy]

If I'm looking at it right and understanding what I believe I'm seeing, I'm thinking the two roller contact for weight bearing parallel to the propeller & shroud rather than 4 rollers providing weight bearing and contact both parallel and perpendicular to the fan & shroud allowed the shaft enough wobble in that single direction to eventually fatigue the shaft between the bearing and the motor mount. The most fatigue would have occurred exactly where it failed. I hate that it tore the fella's engine cowl.

 

[jimmypate]

How do you go about selling a boat on this site...I just registered but dont see where you can sell a boat

 

[BlackBeard]

Post it in the classified section

 

[Shooter007]

Good introduction "Jimmyplate".... shoot us your address so we can send you some glasses... LOL

Chris, I'd go the globe fan route as well, safer and more secure, not to mention typically a bit lower, not sure what you have for storage but coming from experience if you want to store your rig indoors your going to have to think about height in most situations.

 

[Chris]

If I'm looking at it right and understanding what I believe I'm seeing, I'm thinking the two roller contact for weight bearing parallel to the propeller & shroud rather than 4 rollers providing weight bearing and contact both parallel and perpendicular to the fan & shroud allowed the shaft enough wobble in that single direction to eventually fatigue the shaft between the bearing and the motor mount. The most fatigue would have occurred exactly where it failed. I hate that it tore the fella's engine cowl.

You're seeing it perfectly. Poor design without a doubt.

 

[Chris]

Good introduction "Jimmyplate".... shoot us your address so we can send you some glasses... LOL

Chris, I'd go the globe fan route as well, safer and more secure, not to mention typically a bit lower, not sure what you have for storage but coming from experience if you want to store your rig indoors your going to have to think about height in most situations.

Outdoor storage. But height is definitely a concern.