Lets talk 4 blade vs 5 blade clevers
 

As I start looking for props for my project I have seen many 4 blades that might possibly work. Has anyone tried both on the same setup? My boat is a 98 42' big set fountain, staggered, # 4 drives with the prop shaft 1.5" above the bottom. 850hp per side. I have 1.49 ratio on the drives and I don't plan on spinning the motors to the moon. 5800-6000 max. I figured im going to be at a 33-35 pitch? I wont be buying new props so me finding that " perfect" set of props may be hard to do. So I feel that if a 4 blade may work then that opens my choices. Any first had experience? Any other opinions? Thanks

We ran 4 blades for years on boats of your vintage.
Remember we only had 5 blades for a couple years when your boat was built. There was a slow progression over to the 5 blade castings. It didn't happen over night. In 1997 we only made 5 blades up to 31 inches of pitch.
So, yes, 4 blades can work on your hull. My only concern is the 1.5" above the bottom of the boat might be a touch high. There was 1",2",and 3" spacer plates made for the #4 drives. These parts are no longer made but a 2" had a part number of 11382A3.
If you could find those and some 17.5" diameter 4 blades, you'd be in business.

Brett

What are some of the determining factors on weather a 4 or 5 blade prop will work better on a boat with no steps and a surfacing props

Deep V's often prefer 4 blades since they provide less stern lift.

Brett

Thank you , That is what I have been told now all I have to is wait till it warms up to do some testing .

Icdedppl has a 38 Flatdeck Cig with 4's and boxes. When he bought it, it had 17.5x28 five blades. Boat took forever to plane, 5000rpm burnouts and wait a long time. He added 2 inch spacers, not much help at all. Tried turning props "in", a little help, but nope, still sucked. I suggested we try a set of 4 blades. 1st set I had laying around, were some 17x29's. Boat wouldn't plane at all. Later on, he found a mint set of 17.5x27 four blades. Standard merc lab finish. Bolted them on, boat planed easily at 3k rpm in seconds. Then , removed the 2 inch spacers, boat still planed at 3k in seconds.

I went thru all of this with my boat as well. I had 3 blades that planed better than some 4 blades, and some 4 blades, that planed better than others, even with less diameter. The best set of planing props I ever had, were 16.75x27's 4 blades. I had tried 17x29, 17x28, 18x28, and a couple others. Some would not plane, some took 5000rpm and wait a long time, some 3500 and wait, etc.

Alot of these old ssm props, vary so much from prop to prop. it makes it frustrating to get dialed in. You may think because a certain 5 blade gets it on plane, that all 5 blades will, or that if you cant get on plane with a 5 blade, you'll never get on plane with a 4 blade, its really all in the prop. The #4 and #5 drives, do not have much negative trim angle, and that itself, makes it hard from a planing standpoint. First step in prop tuning, is getting on plane. If you cant get on plane, you have nothing lol.

I think 34p might be a bit steep for that setup at 5800rpm. I'd like to think with 850's, #4's, you might see speeds around 100ish. I think the 900sc #6 dry sump version of your boat, ran in the 110-115 range if I recall. My rough guess, 5800ish rpm, 1.49 drive, you might need something in the 30-32p range. BBlades might have some data on what the 900sc #6 42 ran for props. The 900sc were pretty stout engines, and the dry sump 6 is pretty darn efficient compared to a wet sump #4.

I have some 16.5x31p 26 spline four blades I am selling, if I still have them once you get the boat up and running, you are welcome to try them out to get a baseline.

[QUOTE=MILD THUNDER;4421534]

I went thru all of this with my boat as well. I had 3 blades that planed better than some 4 blades, and some 4 blades, that planed better than others, even with less diameter. The best set of planing props I ever had, were 16.75x27's 4 blades. I had tried 17x29, 17x28, 18x28, and a couple others. Some would not plane, some took 5000rpm and wait a long time, some 3500 and wait, etc.

Alot of these old ssm props, vary so much from prop to prop. it makes it frustrating to get dialed in. You may think because a certain 5 blade gets it on plane, that all 5 blades will, or that if you cant get on plane with a 5 blade, you'll never get on plane with a 4 blade, its really all in the prop. The #4 and #5 drives, do not have much negative trim angle, and that itself, makes it hard from a planing standpoint. First step in prop tuning, is getting on plane. If you cant get on plane, you have nothing lol.

Do you think the variations it the ssm props are in the manufacturing of them or fact most have been tuned up so much that they are not even close to the size they were when they were made ?

One thing that is relatively consistent is lower pitches will get you on plane easier than higher pitches no matter how many blades there are.

Brett

Thanks for the info guys. Joe I may take you up on that offer on the props thanks!