Aluminum vs SS

[patenglish]

My hole shot is horrible, but my WOT is great. My present prop is a Raker 3.5 x 18. If I change to aluminum, how will it affect my RPM's on WOT? Should I increase or decrease the pitch to get a better hole shot and stay at the same WOT?

 

[DJ]

Re: Aluminum vs SS

Aluminum offers a little bit of flex, thus the pitch on an aluminum MAY be slightly higher.

 

[TilliamWe]

Re: Aluminum vs SS

You need to get trailerboats magazine's issue that has the big article on props. read it, know it, live.<br />You have not given us good info, nor enough info to even begin to help you.<br />Size of boat, engine, drive current wot rpm recommended wot rpm...

 

[rg33]

Re: Aluminum vs SS

Try posting this in the Outboards:non-repair section for quicker and larger amount of responses.

 

[Silvertip]

Re: Aluminum vs SS

Mean15 -- if your WOT rpm is correct with the current prop, you can neither increase pitch or decrease pitch and keep the same WOT rpm. Decreasing pitch raises rpm, and increasing pitch decreases it. To get a better hole shot you can try ventilating the prop. The other option is to decrease pitch, but engine rpm will increase roughly 200 RPM for each inch of pitch change. Check weight distribution in the boat. If you have everything loaded in the back, try moving some of it forward if possible. Experimenting with trim may help.

 

[Solittle]

Re: Aluminum vs SS

What is your rpms at WOT now? And where is the cavitation plate relative to the bottom of the hull?<br /><br />We need some info on your set up now before we tackle the prop as other things may come into play.

 

[patenglish]

Re: Aluminum vs SS

Sorry about the lack of information. The boat is a Champion Mean 15, 15'6", Evinrude 90 hp 90 degree. Power tilt and trim. RPM's at WOT is 5200, recommended is 4500 to 5500. My question was the difference in RPM's with an aluminum vs SS prop.

 

[patenglish]

Re: Aluminum vs SS

Originally posted by Upinsmoke:<br /> Mean15 -- if your WOT rpm is correct with the current prop, you can neither increase pitch or decrease pitch and keep the same WOT rpm. Decreasing pitch raises rpm, and increasing pitch decreases it. To get a better hole shot you can try ventilating the prop. The other option is to decrease pitch, but engine rpm will increase roughly 200 RPM for each inch of pitch change. Check weight distribution in the boat. If you have everything loaded in the back, try moving some of it forward if possible. Experimenting with trim may help.

 

[patenglish]

Re: Aluminum vs SS

How do you vent the prop. Are the rpms the same with a ss and aluminum prop?

 

[Marc J.]

Re: Aluminum vs SS

Bubbakat posted a pic under J/E repair. Go there and do a search. I don't think an aluminum prop will flex enough to affect WOT rpms on your rig. If you were running a 115 or larger it may be a factor. Maybe a 17 pitch will get you at or just over 5500 rpms. Some shops will let you try one out. My fishing boat is currently out of service due to a bent propshaft. The SS prop survived the low speed impact with very little damage. I would rather be shopping for a new prop than the situation I'm in.

 

[walleyehed]

Re: Aluminum vs SS

5200 is not "Great"...infact it is near lugging.

 

[phatmanmike]

Re: Aluminum vs SS

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