Late night Prop talk?

[alphaman]

What's the difference btw a 3 blade and a 4 blade prop for your out board motor. I've also seen a 5 blade prop. What prop do you have on your boat?

[bayouchub]

Google is your friend. Lol

[Nitramiii]

Way back when, I had a bass boat and I ran a 3 and then a 4 blade prop. At the time I liked the 4 because it gave me more bite in turns and eliminated chiming. But lost a little on the top in. It also stayed on plane at a lower speeds which was good for wATer sports. I'm not sure if 4 and 5 blade props are used much on bay boats. I've always had 3 on a bay boat.

[Goooh]

Originally Posted by Nitramiii

Way back when, I had a bass boat and I ran a 3 and then a 4 blade prop. At the time I liked the 4 because it gave me more bite in turns and eliminated chiming. But lost a little on the top in. It also stayed on plane at a lower speeds which was good for wATer sports. I'm not sure if 4 and 5 blade props are used much on bay boats. I've always had 3 on a bay boat.

I could be wrong, but wouldn't the hull have to be modified to tabs installed to be able to plane at lower speeds?

[keakar]

Originally Posted by alphaman

What's the difference btw a 3 blade and a 4 blade prop for your out board motor. I've also seen a 5 blade prop. What prop do you have on your boat?

I have been told that 5 blade props are used exclusively for high speed top end so its mostly bass boats and race boats that use em.

I was also told bigger heavier boats might do better with 4 blade props but the average boat doesn't need anything more then 3 blades unless there are other contributing factors requiring more stern lift.

Originally Posted by Goooh

I could be wrong, but wouldn't the hull have to be modified to tabs installed to be able to plane at lower speeds?

in most cases this is the better solution but more blades will add more stern lift from the prop so it can help you plan better at slower speeds

[bayouchub]

Different props can completely change the way a boat handles and performs. A 4 blade will plane the boat quicker, keep it on plane at slower speeds, bite better in turns but you lose top end speed. A three blade will almost always be faster and they are offered in a variety of blade shapes that can make pretty significant differences even in the same pitch and diameter. Alpha, how did you choose the prop that you have on your boat?

[CajunChristian]

Its impossible to make factual blanket statements about any prop design. For the 40/50/60 hp motors, Quicksilver makes a 4 blade Trophy Sport that is within 1-2 mph of the best 3 blade props on the market for that size unit, which is the Black Painted Yamaha Stainless Steel prop in a semi-cleaver design. The Trophy Sport will actually run as high as the Yamaha prop will, just not as fast.
Keep in mind, I only raced circles boats, none of the straight line 1/4 mile stuff, we actually had to have a boat that handled well in calm and rough water on short and long courses with 20 other boats making waves. When I raced in the 90's, we ran 4 blade props only in very rough water for the handling of the boat and only on boats that were topping over 100 mph. None of the smaller classes ran 4 blade props. We gave up a bit of speed with the 4 bladers on the faster boats to gain that handling.

Not sure about all OPC classes, but everything I witnessed, Sport C, Formula 50, SST45, SST60, SST100, SST120, SST140, Mod U, all ran 3 blade props to set their KILO speed records. Very rarely would any of them run 4 blade props. At the KILO run in 1995, NONE of the boats were running 4 blade props.
Back in the late 90's when I had my center console, I ran a 200hp EFI Mariner with a Small hub Trophy 3 blade prop on a 19' ProCraft. It was the best all around prop I could get my hands on, and I had about every make and style of prop available. Of course with a boat running in the 60+ mph range, I didn't idle much either Back then, a center console running in the 60's was the king of big lake. My how time flies and boats get faster.

Get your hands on a book titled "Everything You Need To Know About Propellers" written by the engineers at Mercury. The absolute best book written on prop technology for the layman to read. Read that short 55 page book and you will have answers to ANY propeller questions you might think of. The book explains all aspects of prop design and tells you how each aspect affects boat performance. They explain rake, angle of attack, pitch, blade area, number of blades, EVERYTHING. It is a very educational read. It is Mercury Part number 90-86144-92
I got a chance to study under some of the folks that wrote that book, they have forgotten more about propellers than most of us will ever know.
READ THE BOOK
D

[SuperDave]

4 blades carry a load better, can run at a higher X dimension, and have faster cruising speeds than a 3 blade. (Normally)

I'm running a 20p Razor 4 by Mark Croxton and I'm seeing roughly a 5-8% slip depending on speed.

I asked him about his 3 blade Razor 3 and he said I wouldn't like it for my application. Which I told him I wanted a high cruise speed.