Unintentionally bending props.

[Ian Inverarity]

Guys and Girls,

I have recently built a 90 rigger and have had a LOT of trouble bending the props. I have not run the boat very long, but on the runs I have had I have bent 4 H-50's including old and new type castings and a stainless steel one, a H-48, a 1667 and finally this weekend a 2170. The 2170's are quite thick and I was assured they would not bend. I have used the heat treatment method described for the H props on one of the H-50's and the H-48.

Some people have asked me if I thin the blades down. I do not. I only sharpen the leading edge, and the props bend through the thickest sections! :

It has been suggested to me that transom hopping may be causing this problem. While some of the props have hopped a bit, some did not and still bent. ???

The blades bend on the props over a reasonable area starting from about 1/3 of the way out from the hub. The blades are generally progressively rolled back and this can be difficult to spot until I compare it with an unbent prop. When I do the difference is dramatic tho!

I am not doing 100mph, I dont have the world's most powerful 90, thus I can only think that there is something wrong with my setup. Does anyone have any idea what may be causing these problems? I am ruining a small fortune in props here. :'(

Ian.

 

[Terry Keeley]

How are you heat treating them? If done right they'll break before they'll bend...

 

[Hammerhead]

I know that the rotors in the F-18 hornet engines are made out of berillium(SPELL?). They are heat treated with oil.

I also know that Mr. Shimizu treats his stainless props the same way.

I have tried to to sharpen one of his stainless heat treated props before, and It was a pain in the butt to file. What he does is heats up motor oil to almost boiling, then he fires the props in a kiln to 1200 degrees celsius. He then picks them up with tongs and slowly sinks them into the oil. They become black. After that he polishes them and they get the silver shiny look back. He gave me one of his test fired props that wasn't balanced before he fired it. I couldn't file it or polish it with the tools I had. If you have a beat up berillium prop laying around with no hopes, do a test temper with it. If you use a good butane blow torch, it will get the prop to 1200 degrees, no problem. That is, if you don't have a kiln. The only prop I have ever been able to bend was a V937, but they are like tin foil stock.

Hammer

 

[Slideblues]

Ian,

I have been following along with your posts on the bending props and I have scratching my head for some time now. To bend a stainless prop without it hitting something would be HARD to do, unless its something in the alloy's or molds, but you have the same problem through different brands of manufacture correct? Octura and ABC? Heat treated and not heat treated? Either your engine is a torque monster or it is something with the setup or strut. Is the bushing ok in the strut? If so the only other thing I can think is if you run at the same spot every time maybe there is a sandbar or something just under the surface? Really guessin here Dude!!! This one is for the books fer sure!!!

Not much help,

Gene ;D

 

[Ron Olson]

I saw something today on www.rcboat.com about the ABC props. It seems that they can not be heat treated. They are made of a different alloy than Prather or Octura props. Why they are bending on you has got me! I have seen thinned props fold on an outrigger hydro but yours were not thinned. The only thing that I can think of is that the props are carrying too much weight and bending. One other off-the-wall thing, could the props be hitting your starting stand before you launch the boat? I've bent some this way.

 

[Ian Inverarity]

Terry,

I heat treated some of the ABC H props using a couple of methods described by Mark Sholund who got the info from Jim Schaefer. The untreated ABC props will crack and bend. The treated props didn't crack but still bent.

I didn't heat treat the Octuras.

What heat treatment method would you recommend? ???

Hammer,

I can get my props professionally heat treated IF I know what the alloy composition is. And what hardness I should get. But many grades of stainless are not heat treatable. Also I have heard of people getting the props so hard they are brittle, and then they have blades break off! I would rather they bent than broke!

Gene,

Yes, I have bent Octura's, old (pre Jim Scheafer) ABC's and Jim's ABC props. I have bent props that other people (TwinK90) sharpened as he doesnt get the leading edge as thin. A 2170 in particular is a VERY thick prop at the trailing edge. Bent it in one run! :

I have bent props at four different places too! On 5 seperate occasions! And I have only hit a bouy once in that entire time! I have not damaged the rudder or turnfin either.

I use needle bearings and ball thrust bearings in the strut. These appear to be fine and run freely.

The engine does have pretty good torque, but I have one with a lot more in the garage! (A100).

I am guessing it is a setup problem, but I have no idea where to start. I am getting a cobalt chrome H-50 made, maybe this will solve my problems! :-

It has been suggested that I should put a 67 in the boat instead! it may yet come to that!

Nitrocrazed racing: Your home of slightly used props....

 

[[email protected]]

The bending of your props reminds me of an old Flinstone's episode when Barney asks Fred "What type of water do you have, hard or soft?' Fred tells him "wet".

You my friend have hard water. LOL

At one time guys used to drill holes at the top of the props and I was told it will prevent bending because it reliefs much of the pressure put on them. Any truth to that? I done it on my mono's and they work good for cutting the drag.

 

[Ian Inverarity]

Ron,

There seems to be some conjecture about that. Mark Sholund gave me some info that came from Jim Schaefer about how to heat treat the ABC props on an earlier thread!

The boat is pretty light for a 90, about 8.4 lbs dry. I could understand it if I had a heavy boat. :-

I designed the stand to avoid the prop hits like you describe! I have seen this a few times, and have done it to other boats lifting them off the stand (oops! :-[ ). My stand stops way short of the prop.

Rodney,

I have seen pics of props with holes in the tongue area, this is supposed to make them easier to launch. My props are bending thru the thickest part! So I dont want to be drilling holes in them! :

Nitrocrazed racing: A-90HP: more torque than props can stand.

 

[[email protected]]

NitroCrazed,

I must be doing something wrong w/my A-90's because I've yet to bend a prop. However, I'm gonna run my Jag2 set up next week for the first time. I'll let you know if I can bend it!

 

[Ian Inverarity]

Well, thanks to some setup tips from Jim Benns and some prop selection advice from a fellow club member Steve Gruber it seems I have the problem licked! I ran the boat again on the weekend and I didn't bend the prop!

I went to a lower lift prop and flattened the strut off and raised it a bit. That seems to have done the trick!

Thanks to everyone who offered advice! 8)

Ian.