Sacrificial Aluminum Prop

[jimmbo]

Deleted

 

[jimmbo]

As I said, At speeds over a 100mph, the Flex would be approx 1/100". Water will move long before a Blade will Flex. But as I said many have fallen for that, basic Lie, and rushed out for a SS. SS Props are more Efficient because of thinner Blades, and the higher strength of SS will permit different blade Shapes

 

[bruceb58]

Water will move long before a Blade will Flex.

You don't think an aluminum prop will hold its flex...let's say under acceleration? You aren't an engineer are you?

And where do you get this 1/100" BS? The flex of a prop depends on blade thickness, blade pitch, prop diameter, HP and torque of the engine turning it among other things.

 

[jimmbo]

You don't think an aluminum prop will hold its flex...let's say under acceleration? You aren't an engineer are you?

And where do you get this 1/100" BS? The flex of a prop depends on blade thickness, blade pitch, prop diameter, HP and torque of the engine turning it among other things.

The Flex is probably even Less than 1/100",
Where do you get your BS? Advertising/Marketing/Social Media?

 

[bruceb58]

The Flex is probably even Less than 1/100",
Where do you get your BS? Advertising/Marketing/Social Media?

LOL...I was expecting a BS answer from you like that!

 

[KJM]

40mph Speed Limit for a Prop? That is a New One
Reading the Chart, shows approx what Top Speed would be if the Engine was at top rpm, and that was taken into account for the Load
If you use a Prop that is too low in pitch for the Load, the Top Speed you will get will be higher simply because the Engine is Over Revving.
BTW the "Flex" of an Aluminum Prop is in the Range of less than 1/100" Go grab a blade and try to get it to Flex. It is not going to happen as the Water is trying to push will certainly be yielding to the Blade. That bit of Fear Mongering has sold Millions of SS Props though.

I've always thought the same thing.....I can't see how a prop blade can flex enough to make a noticeable difference. Wouldn't metal fatigue eventually cause the blade to just crack off if that were the case?

 

[KJM]

Sorry to burst your uneducated bubble but aluminum props do flex. Even stainless steel props flex but not as much as aluminum.

You aren't going to get them to flex with your hand! That was just hilarious!

Stainless steel props can be made less thick to provide the same amount of strength. Since they are less thick, they have less drag. That is the main advantage of stainless steel props. Do i have a stainless prop on my pontoon boat with a 90HP motor...that would be a NO since there is no advantage on a boat like that. On my 26' Cobalt with a 350HP dual prop drive...yes....it matters.

I am going to take a guess but you probably have a boat motor combination that would not benefit from a stainless steel prop.

Not arguing, just curious, and I'll be the first to admit that I know very little about different props, but would the drag from a slightly thicker blade really make a noticeable difference?

 

[KJM]

Got a smokin' deal on a reconditioned set of D5 (Aluminum) duoprops for my VP 5.7GXi/1:1.95 firmly attached to my 6500lb cruiser. Current prop is F3 (Stainless). I have no issues with the performance of the F3 - snappy to get on plane, tops out at 40+ mph and cruises comfortably at 20-25 @ 3000RPM . I bought the D5 as a "sacrificial spare" only to be used when I venture to remote and rock infested Isle Royale. When I head toward the island, I'll switch to the aluminum and stow the stainless as my 'get home' prop ... just in case I hit that special rock that dings the aluminum D5 - hopefully sparing any engine/drive damage. I realize that the D5 is probably too much prop for my boat but all I really need is an efficient cruise speed (20-25 is plenty fast - the D5 has a 35 mph speed limit) to get back and forth over the 22 miles of open water. While at the island cruising will be slow to wakeless.

Any thoughts or concerns operating "too big of prop" if I limit the 320 HP 5.7 GXi to 60-75% and keep the speed below the prop speed limit? What could go wrong?

I've always wondered, how exactly do you change out a prop when on the water, or do you beach the boat to do that?

 

[bruceb58]

Not arguing, just curious, and I'll be the first to admit that I know very little about different props, but would the drag from a slightly thicker blade really make a noticeable difference?

I had one boat where we switched to a stainless from an aluminum prop. For identical altitudes, we had to go with 1" less pitch on the stainless to account for blade flex(pitch reduction). We actually tried the identical pitch first but no longer reached the WOT RPMs that we got with the aluminum prop. All caused by pitch reduction on the aluminum.

 

[bruceb58]

I've always thought the same thing.....I can't see how a prop blade can flex enough to make a noticeable difference. Wouldn't metal fatigue eventually cause the blade to just crack off if that were the case?

Depends if you started to get into the "yield" portion of the aluminum.

Aluminum props can actually crack like you suggest and there are many cases of props losing blades because of it. You won't see it on a 90HP outboard like my pontoon has but you might see it on a 300HP outboard. It's one of the reasons why you never see aluminum props anymore on high horsepower outboards.

On my 350HP Bravo3, you can't even get aluminum props for it

 

[KJM]

Depends if you started to get into the "yield" portion of the aluminum.

Aluminum props can actually crack like you suggest and there are many cases of props losing blades because of it. You won't see it on a 90HP outboard like my pontoon has but you might see it on a 300HP outboard. It's one of the reasons why you never see aluminum props anymore on high horsepower outboards.

On my 350HP Bravo3, you can't even get aluminum props for it

Interesting. I did a bit of research and it does indeed appear that big motors at high speeds do cause noticeable flex/ pitch problems. Also ss props can be more easily made into more cupped blades. You learn something new every day! Won't be a problem for me with my 90hp. My wife won't let me go more then half throttle even with that........