Prop Sizes?

[barkleydave]

Lower pitch = Higher Engine RPMs. = more power out of hole and less top end speed
Higher Pitch= More load on engine= lower max RPMs. Less power out of the hole...Higher top end (primarily in the lower planning speeds)

If you spend more time under planning speeds a higher pitch will increase your low end speed plus better fuel economy.

Folks that spend a lot of time trolling for fish often will prop down so they have a lower idle speed.


safe boating,

dave

[ericinga]

I have a cupped 14x10 on our 28. It drops WOT RPM from 4200 down to 3500. The engines works harder and burns more fuel throughout the power range.

One option is to remove the current prop, take it to a prop repair shop and have it "bent" to remove a degree. You can send it to Michigan Wheel and have it done too. The second option is to buy a new prop.

Eric

[yooper]

I just happened to print out the prop sizes from the marinette.com web site because I damaged my props. The 28" with single 318 225HP with 1:1 tranny is 14" x 9", 3 blade, cupped. With 1.52:1 tranny is 16" x 15", 3 blade, cupped.

What happened to the marinette.com site? I can scan the two pages of prop sizes - then what?. What about the rest of the performance stuff on that site?

[yooper]

I scanned the prop sizes document and got two Jpg files totaling 574 Mg. I don't know how to post them on the forum. Any Aministrator send me a private message with an Email so I can send them on an attachment. Then you figure out how to post them.

Owner without a prop. I made an earlier post with prop sizes for your 28 single. I got cheap used props for my first Marinette from EBAY a couple of years ago. Singles were available for about $75 because some twin engine boaters only wrecked oneside. Used props for 1" propshafts are very rare. I fitted a prop with a tapered 1 1/4" bore using a nylon sleeve to take it down to fit a 1" shaft. I first tried a brass sleeve but it twisted right off. I think the key might have been loose.

[collins69s]

Rockxx a simple rule of thumb is one inch of pitch or diameter = 100 rpm. Add an inch, lower rpmx100. Decrease an inch increase rpmx100.
And I can't remember the other one.. I think more pitch = quicker to get on plane or "out of the hole". Think about the fact that in a perfect world one more inch of pitch should move the boat one more inch forward faster per prop revolution.. You have to check if your engine is reaching WOT.. There is so so much that goes into this. Call Ron Jacobs at Wolverine Prop in Michigan. I'm sure he's propped dozens of Ms like yours. He's very helpful.

[Rockxx]

Looks like I'm going to finally launch next week and can run the boat enough to figure out what To expect. Tach isn't working so I can't tell what rpm I'm turning at wot. I do know that from about half throttle to wot there's very little increase in speed. The boat has 11 x 42 trim tabs so surely I can get on plane with either prop.

[bcassedy]

Balthaus,
Running thru the forum found your notation that you may some info very useful to members - prop sizes / gph-rpm-mph. Were you ever able to find it?

Bill

[Rockxx]

I have a 1972 28' Express, single 318 and am fortunate to have the original delivery sheet from the factory which shows it delivered with a 14/10. This is what I'm running now and when I finally got the boat on my home water last summer ran it up to 27 mph, according to the GPS. Tach wasn't working so I have no idea as to rpm. Once I felt it was topped out I brought the rpm down as didn't want to abuse my 50 year old baby. I'm not sure what a 14/9 would do but believe the 14/9 works fine.
Glad to see all you guys coming out of hibernation. Come on spring..
Regards to all,
Rockxx

[Leviathon]

Marinette page says 14 x 9. I have used 14x9, 14x10, 14x11, and 15x10. and did not notice any significant difference. Look on Ebay - there is always tons of them. 1" shaft.