Confusing prop situation, can ya help?

[reddogg]

ok, the engine is an 82 Evinrude 150 ( E150TRXCNM), I, have rebuilt the carbs, rebuilt fuel pumps ( dual pulse type set up), new fuel hose, new bulb, new fuel/water sepperator, new spark plugs. Basically the engine is in wonderful condition, start easy, idles great and runs great throught the entire rpm band. Here is my question. I have 2 props for it. one is a stainless 15 x 15, it runs at 5000rpm @ 35mph at wot. The second is an aluminum solas prop I bought from I-Boats, it is a 15 1/ 4 x 13 and runs at 4600 rpm@32mph wot. Why is the 15 pitch prop giving me more rpm's than the 13 prop? I thought i would gain approx 200 rpm and a few mph with the 13 pitch prop? Anyone have an answer for this one? For now I'm just going to keep the solas prop as a spare, but the whole situation kinda defies logic.

Red

 

[QC]

Re: Confusing prop situation, can ya help?

One is marked wrong? The Stainless has been reworked down to a 13 or less. The Solas is a POS. You're running the Solas in another dimension. Your tach works backwards. That's my first crack at it . . .

 

[reddogg]

Re: Confusing prop situation, can ya help?

Lol, i can almost believe you, but you see what I mean, it kinda defies the "prop logic" as I know it. Anyone else?

Red

 

[reddogg]

Re: Confusing prop situation, can ya help?

Bump, I'd really love to hear about this from one of the experts

Red

 

[QC]

Re: Confusing prop situation, can ya help?

What am I chopped liver? I was almost serious. Numbers suck. Something ain't right . . .

 

[reddogg]

Re: Confusing prop situation, can ya help?

Lol, didn't mean anything by that QC, I thought you were just goofin around, no crap intended It just that by all I know about props I should have gained rpm instead of lost them and I, for the life of me< can't figure it out. What I said about the engine was true, no bs there. All that was done and a link and sync as well. The engine runs as close to perfect as a motor that old can. The only thing that I can think of is like you said, solas props are crap, but evan than I would have expected diff results than what I got.

Red

 

[NHGuy]

Re: Confusing prop situation, can ya help?

Stainless blades are thinner. Maybe the SS has been reworked to less pitch than it's mark. That stinks that the aluminum 13 pitch works the motor harder and goes slower.
I really like Michigan Wheel Aluminum props. Never ran a Solas.

 

[steelespike]

Re: Confusing prop situation, can ya help?

When going from ss to al. or al. to ss throw out the logic. Usually the ss prop will have less drag and also have better slip numbers. The ss will likely affect the hull more than the al when trimming.Also when changing brands it removes you even farther from the norm.
Though it is somewhat of a comprimise you could have the ss repitched or have a little of the cup rtemoved ,if any.What size/type boat are you running?

 

[QC]

Re: Confusing prop situation, can ya help?

Lol, didn't mean anything by that QC, I thought you were just goofin around

I was. All good

 

[reddogg]

Re: Confusing prop situation, can ya help?

Hmmm, I didn't know that going from ss to alum was like that. That really gives me food for thought. Is there a thread or web page somewhere that talks about this in deapth, I'd really like to know the "why" of it for my personal info. Thx for for your help.

Red

 

[Tig]

Re: Confusing prop situation, can ya help?

Is the SS at all damaged, or is it not cupped?
I recently changed aluminum props. From 13p 3 blade at 6300 rpm to 12p 4 blade Solas at 5600 rpm.
As mentioned, the result of big changes are hard to predict. I did a bit of research into the math behind props. It's more than I have time to digest. A well stocked prop shop with an exchange program seems like the expedient route.

 

[reddogg]

Re: Confusing prop situation, can ya help?

The stainless prop was a 17 that was worked down to a 15 with no cup. How would that make such a diff compared to a brandnew 13? Also, if I had the 13 aluminum prop worked to say a 10 would that up my rpm's in comparison to the ss 15?

Red

 

[Tig]

Re: Confusing prop situation, can ya help?

If you were to record your rpm vs gps speed, you will see how much more efficient the new prop is. I'm not certain if an aluminum prop can be reworked to lower pitch, but if it can rpm will go up and I would speculate that efficiency will decrease since there is so much more to prop design than just pitch.
Check out the sticky at the top of the prop forum. Post the data requested and the prop experts will be able to advise you.