Another F150 Prop Question

[PAkev]

I posted this question before and received confirming and helpful responses. However, in my search for a new aftermarket prop, I am finding it hard to find a 13 3/4 dia X 17 pitch.<br />I am finding many of the 17 pitch props to be in the 14 or 14 1/4 diameter arena. My question is how much will 1/4 to 1/2 dia. compromise my ability to turn better RPM's. I want to go with a polished SS prop.<br />_________________________________________________<br /><br /><br />Boat: 20ft Polar Center Console Bayboat (fiberglass construction)<br />Weight: Approx. 3300 lbs....rigged and loaded.<br />RPM's: 5300 WOT MPH: 42 via GPS (trimmed) <br />Prop: Steel 3 blade 13 3/4 X 19<br /><br />Upon purchasing my boat I read the owners manual which indicated the prop which came with my motor was 13 3/4 X 17. However, when I pulled the prop off for winter storage, I found out it is actually stamped 13 3/4 X 19. <br /><br />Although the boat seems to get on plane well I always fealt the boat was lacking it's true top end speed & RPM potential. Now I'm wondering if cutting back to the 17 pitch will deliver the expected performance by bringing my RPMs up into the normal operating range.

 

[Bondo]

Re: Another F150 Prop Question

Here are some of my comments on Prop Diameter,.....<br /><br />Do a Seach in the engine-I/O forums,... Or Boat Help, Not engines forum.....<br />If you'd like to see the Context of my comments..........<br />

First Off, Don't Worry About the Diameter..!!!! You have NO control over it, the prop engineers have it All Figured out for you...... dia. is determined by many factors... pitch(more pitch= less dia.), blade style(larger area vs. smaller), base metals(alu. flexes vs. SS doesn't) etc. etc. etc. <br />That said,<br />Stainless props Don't Flex anywhere Near as Much as an aluminum... so you Don't want Any More Pitch.... you're already loading the motor down to 4300rpm... that's at the bottom of the "ideal" range(4200rpm/4800rpm) of your power package....I'd think you should be starting at about 17" on a round-eared, 3 blade prop.... you May want to try a 4 or 5 blade... depends on what you need it to do...try to find a dockmate that has a prop in this range, maybe you could run seatrials with a borrowed prop... Then go buy the one that works the best on your boat...<br />Try to find a Good prop shop... they can explain this better than i can type.....<br /><br />Good Luck.....<br /><br />In All Reality,..... You have No Choice about the Diameter..... Just Forget about the Diameter Altogether..........<br /><br />You get to Choose the Pitch,+ Style of the blades,+ the # of the blades,+ the Material of the blades,.........<br />But,.......<br />The Engineer/Designer will determine the Diameter for the Application.............<br /><br />Good Luck.....<br /><br /> Don't Worry about the Diameter.... <br />You pick the Pitch......<br />The Engineers pick the Diameter.....<br />It Depends on Many things in the basic design of the props.....<br /><br />I Believe you can swing 16" on any Mercruiser prop shaft before you'll encounter any contact with the housing...... (I've measured this since 2003 when I posted this,....16" Will Clear) <br /><br />As I've said before, The Diameter is Totally Irrelevant to the end-user....<br />You Should be looking at Pitch,+ Blade design.....<br />The Dia. is determined by the engineer who designed the prop.. Low pitches Need bigger dia.s... Cleavers, Choppers, 3 blades, 4 blades, 5 blades....<br />If you walked into the biggest Prop Shop in the land,+ Wanted a prop of a given blade design,+ pitch... Then told them you wanted it in 1" smaller or larger size.... They'd Laugh you out of the parkinglot...<br /><br /><br />Prop Diameter is determined by Blade Design,+ the Engineer who did it.....<br />Pick the Pitch,+ Blade Style you need... The Diameter will be determined for you....<br /><br />quote:<br />--------------------------------------------------------------------------------<br />I assume thats 19 pitch but how do I tell the size?<br />--------------------------------------------------------------------------------<br /><br />That IS the Size.......<br /><br />Don't Worry about the Diameter.....<br />The Style of the blades will determine it anyway....<br />The Prop Engineers have that All Figured Out for you....... <br /><br /><br />Hi Moose,<br />I can't remember what your Boat is,+ I Agree with f_inscreenname about finding the proper WOT.....<br />I also Agree that a set of Smart Tabs might be the Answer to your Problem..........<br />But, I Don't see changing the Diameter of the prop a viable choice....<br />As I've stated before,<br />You Only get to choose the Pitch, <br />Material,(SSteel, Alum, Plastic)<br />And Style(Round Ear, Chopper, Cleaver, 4 blade, 5 blade, Shifting, Etc.)<br /><br />Diameter is Built into the Design by the Artist who Designed it in the 1st Place.......<br /><br />Ayuh..... What Tom says....<br />And, I'm Betting that, that 13" diameter prop is for an Outboard......<br />Smaller gear case....<br />It'll fit,.... But Ventilate......<br /><br />You get to pick the Pitch,+ Style of Blades(as well as # of blades).......<br />The Designers pick the Diameter......<br />That's Why the Pitch is part of the Part#,<br />And the Diameter Isn't........<br /><br />Good Luck...<br /><br /><br />Forget about the Diameter..............<br />You have Absolutely No Choice in the matter.......<br /><br />Diameter is determined by the Blade Design,+ Size..... <br />The People designing the prop figure it out For you............<br /><br />You decide What Pitch you need.....<br />Then,<br />You can pick the metal it's Made of........<br />You can pick the Style of Prop it is.......<br />You can pick the Number of Blades it has.......<br />You can Choose a Manufacturer......<br />But, the Diameter Really Isn't Up to You..............<br /><br />The Best thing you can do is,<br />Go to the top of this page you're reading Now,+ Click on the Big Red "Search" button,+ Type in "Prop".. (this was posted Before there was a Prop Forum,+ is in reference to the I/O forums) ............<br />It shouldn't take more than a Few Weeks to digest what you Find............... <br />

Even though My posts are directed to I/Os,.....<br />The Same holds True for Outboards,... Which with a 5300rpm redline,.. I'm Guessing you have......<br />Just Make Sure you're buying a Prop with the Right Gearcase/ Hub size...........

 

[Dhadley]

Re: Another F150 Prop Question

With outboards we pay a lot of attention to diameter. The relationship between diameter and X dimension is vital. With I'O's it still palys a part but adjusting the X dimension isn't easy so we play with diameter, among other things.<br /><br />When 4 blade props became popular folks really didnt want to change the X dimension. So manufacturers changed the diameter (smaller). In the last few years manufacturers have responded to the demand for larger diameter. Some special purpose props have a different diameter, larger or smaller. 14 1/4" has long been a standard for props in the V6 line. Some 4 stroke outboards use a very large diameter (as mauch as 16") and a very low gear ratio to help overcoms a sluggish holeshot.<br /><br />One of the benifits of a large diameter is being able to increase the X dimension to reduce drag and improve overall efficiecy. Obviously a 14 1/4" 3 blade prop should run higher than a 13 3/4" 3 blade of the same blade design.<br /><br />Anyway, with your present prop youre at abut 12% slip. Not bad but it could be better. And you could use some more rpm. A good combination.<br /><br />Try raising the motor slightly and record the difference. This will tell us how your hull and prop react to set up changes. I wouldn't buy a smaller (less pitch) prop yet if it were me. That will surely decrease overall efficiency.

 

[PAkev]

Re: Another F150 Prop Question

I have a performance bullitan from Yamaha as the same set up as mine with exception of using a 17 pitch instead of the 19 pitch which I found out to be on my motor. After having the rig for over two years, I believe it is unreasonable for me to expect the dealer to make a change (shame on me for not checking.)<br /><br />The performance bullitan shows the boat topping out at about 46MPH turning 5900 RPM's.<br /><br />I'm not necessarily after top end speed but want to realize the best performance out of my particular set up.<br /><br />Any experience and/or recommendations of performance prop options?