Weight of SS vs Alum

[mmainelli]

Just re-powered with a VP 4.3GXi/SX drive. I'm currently on a VP 3x15x15, and want to go SS with a 3x15x17. I was astonished with the weight of the ss prop - about 14 lbs vs 71/2 lbs with aluminum. And now I recall the Yamahas and Johnson OBs and other I/Os clunking like hell with their SS props as they fowarded/reversed entering slips at the marina. Any thoughts out there on SS banging the heck out of shaft bearings, seals, etc? These SS props must have terrific angular momentum. Must the prop stop before reversing direction? Can they just "hang" on the shaft with no harm done?

 

[walleyehed]

Re: Weight of SS vs Alum

Operation is the same with either prop...The hub takes most of the shift-shock, and there isn't as much difference as one may think...<br />As for the 17SS, that will drop your WOT RPM by 500-550. Are you at max RPM now???

 

[mmainelli]

Re: Weight of SS vs Alum

Actually , I'm well over WOT with the 15P wheel that came with my repower (yard recommendation as 21' tops 4000#). WOT = 4400 - 4800, and I can easily clear 5000 with the VP.

 

[Texasmark]

Re: Weight of SS vs Alum

If you heard a rubber hub prop clunking whomever owned it needed to tighten it up. There is no clunk to a properly installed rubber hub ss prop. And don't let the weight fool you . The performance improvement, not counting the resistance to damage, of the ss far outweighs the palty 7# (one gallon of gas) increase in weight. My prop is spec'd at 55# of torque when properly installed and it is tight and quiet.<br /><br />Mark

 

[walleyehed]

Re: Weight of SS vs Alum

Well said Mark...<br />If the splines are greased and the nut is on correctly it won't knock like you are describing, as Mark said.<br />A high quality SS in 15 would put you close to 4800, maybe 4900, which is not bad...it's best to be "at" the top of the range vs. the bottom, and you need to get those R's with a normal load..is that how you got the numbers you list???

 

[mmainelli]

Re: Weight of SS vs Alum

I got the numbers when four yard staff, all excited with this new VP with Power Control Module, jumped aboard my 1976 21' Nova Wellcraft for a test run. They were reading hand-held computers checking engine performance while I was at the helm (5 people with 60 gallons of fuel). My Nova has an "offshore hull" from early Wellcraft days. I suspect with 4000# of hull, plus 5 persons plus fuel, the whole rig came in at about 5000#. At 4500 rpm, I got 38 mph. On command from the VP mechanics to push up on the throttle, she jumped to 5400 rpm with 44 mph, until they all started yelling to back off. Later I was told that readouts showed I was only at 75% of hp (225). So that's the reason I want more pitch. And I got this 3 x 15 x 17 SS OMC Viper for only $45 on ebay (seems like nobody was interested or even looking over the 6 day bid<br />period). But again, when it arrived, I couldn't believe its weight. But that seems OK, according to what everybody is saying. I'm still on warranty and don't want to mess up anything.

 

[Texasmark]

Re: Weight of SS vs Alum

Thanks Kenny. While you are handy, you did one helluva job on your prop analysis/testing. I know people will benefit from that for years to come.<br /><br />Mark

 

[walleyehed]

Re: Weight of SS vs Alum

Hope so, Mark...I'm starting to get a good load of 4-blades for another string of testing, but the 4's are not really common on my type of boat...it may be a squirrel chase...

 

[Texasmark]

Re: Weight of SS vs Alum

Hear you on that.