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Author Topic:   Safety: SS prop vs Alum
wetdogsoup posted 02-05-2004 10:19 AM ET (US)   Profile for wetdogsoup   Send Email to wetdogsoup  
Getting ready to re-prop a '99 Merc 60/2 on a dauntless 15. Run mainly in the ICW off NC.

Was advised by local shop to just buy alum and replace prop every couple of years, thereby protecting engine shaft from damage when prop hits submerged flotsam.

Would rather have SS from performance standpoint - does delrin (plastic) shaft insert do its job and protect shaft from damage when running SS prop?


Bigshot posted 02-05-2004 12:22 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I NEVER run Aluminum and I have NEVER ruined a lower unit by hitting stuff. Unless you are a chronic dredger, go with SS.
lhg posted 02-05-2004 01:09 PM ET (US)     Profile for lhg    
My general theory on props, from experience and reading Mercury's extensive literature on the subject, is that if your boat will do over 30, you're going to get better performance, holding and economy with an SS prop. This idea that an aluminum prop will save a gearcase while an SS prop will wreck it, is crazy considering the way props are designed to shear today. Actually in the event of damage, an SS prop is much more likely to get you home.

If your boat will run over 40, then a higher rake, bow lifting performance SS prop, at an elevated transom height, will be highly beneficial. Running at 50 mph with a conventional SS prop, one of these props can increase your top speed by 5 mph!

wetdogsoup posted 02-05-2004 05:12 PM ET (US)     Profile for wetdogsoup  Send Email to wetdogsoup     
Would a Merc trophy sport, stilletto, and Mich wheel rapture all be considered 'performance' props?

And would a Merc vengeance be a conventional SS?

thanks don

lhg posted 02-05-2004 06:10 PM ET (US)     Profile for lhg    
Correct, Don. I would think the 4 bladed Trophy Sport would be the best of the three, and probably the most expensive. I hear they're pretty hot performers.
Lars Simonsen posted 02-05-2004 07:48 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
I purchased a three blade Stilletto from, and am very satisfied. It's a very inexpensive prop (compared to everything else I saw). It provides a lot of stern lift, and made a very noticeable difference in how my boat performed.


Dick posted 02-06-2004 08:59 PM ET (US)     Profile for Dick  Send Email to Dick     
I installed a Merc ss 4 blade Trophy Sport on the Merc 50 4 stroke on my Montauk and was very happy with the performance.

A ss merc prop will do no more damage to the prop shaft than an aluminum prop due to the break away hub system installed in both. Both the ss and aluminum props use the same hub system and it will break long before shaft damage can happen.

If you use an off brand ss prop, other than Merc, anything can happen.


dfmcintyre posted 02-06-2004 09:39 PM ET (US)     Profile for dfmcintyre  Send Email to dfmcintyre     
Don -

I figured that another member would have jumped in and related his story, but suffice it to say that in regard to Evinrude hubs and ss vs aluminum there was (at least once, or was it twice?.....) or is a risk difference.

My close friend grounded on a rock bottom and bent not only the ss prop but the shaft. And he's positive that an aluminum prop would have snapped off, but the ss prop bent and transfered some of the shock.

Ignoring the upper end speed data, you must decide what you _may_ have a chance in gounding on, based on your usual cruising area.

Best - Don

jimh posted 02-06-2004 09:56 PM ET (US)     Profile for jimh  Send Email to jimh     
In a really hard grounding on a rock, you are going to hit first with your aluminum skeg before your propeller--either steel, aluminum, or composite plastic--makes contact. You will be in for some major damage to the lower unit no matter what.

There is probably some situation in which having a steel propeller might cause you to receive more damage to the the gear train than you would if you had a plastic or aluminum propeller, but it is hard to say if this is the most likely situation.

I think it is more common to hit something in the water like wood, sand or gravel bottom, mud, shells, or thick marine growth. In this kind of contact, you are probably better off with a steel propeller. The greater strength of the steel propeller will endure the contact with a object (other than pure hard rock) and probably come away with little damage. My experience with aluminum propellers is practically any contact means damage.

If you do your boating in an area like the North Channel of Lake Huron, where the bottom is mainly granite rock and radical depth changes are common, you may be better off with an aluminum propeller and its ablative qualities.

If you boat in an area with a lot of timber in the water, a steel propeller may be the way to go. You can chop up a lot of drift wood with a good steel propeller--wood that might have ruined an aluminum prop.

There is a rather concise summary of the differences between steel, aluminum, and plastic propellers in an article I wrote for the Reference section:

wetdogsoup posted 02-06-2004 11:08 PM ET (US)     Profile for wetdogsoup  Send Email to wetdogsoup     
Then stainless it is!

On the Carolina coast we're seeing mainly sandy bottom with the occasional rock. Almost more of a concern is the floating wood (no doubt a piece of pier liberated by the last storm - seeing Jim Cantore show up in your coastal community during hurricane season has lost it's star appeal!)

The Trophy Sport looks sweet, as it should at $290.
Anyone know the difference between the Turbo or Stiletto props? (both $210) Both made by Precision Propeller.

Thanks, don

WSTEFFENS posted 02-08-2004 11:17 AM ET (US)     Profile for WSTEFFENS  Send Email to WSTEFFENS     

To follow up on dfmcintyre's post. I am the guy. In the north channel of lake Huron I did serious dammage to my twin 150's. I was east of Turnbull Island and when climbing out from idle to plane hit a large rock. I broke 2 skegs and bent two SS props and bent the port engine drive shaft .38 in out (TIR total indicated runnout.) Total cost $4k. With an earlier boat equiiped with 115 V4 engines I struck an underwater pile (wood) at speed and just seriously bent the aluminum prop. Changed it and went on with the trip.

Supriseingly, the SS props were not that severly dammaged compaired to the other components. From my experience carrying a spare is a waste of time. I ran 50 miles across the channel and to home on dammaged components. If I had to do it over and they were available in counter rotation models, I would be using aluminum.

As a side light, yes there are companies that can repair broken skegs and lower units very well. The ones on my 150 Erudes look just as as good as the day they were made in 1991.



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