What's the right Prop?

mjobrien · #1 10-31-2016, 03:05 PM

I have a 1987 23 center console. I have just repowered with twin 2006 yamaha 150 4 strokes. They are mounted to Armstrong bracket. What would be the best prop set up?

Briguy · #2 11-01-2016, 07:01 PM

Start with Yamaha 3 blade 17's

mjobrien · #3 11-05-2016, 01:42 PM

I found 14 3/4 and 15 1/2. Top speed and fuel efficiency is more important that hole shot. should I go with the larger?

Bushwacker · #4 11-05-2016, 03:10 PM

That sounds like a pretty stern heavy rig, so I'd pay attention to min planing speed if you run offshore much. I suspect you'll need a stern lifting prop, so good offshore type 4B props (stay away from bow lifting 4B bass boat bow lifting props!) will give better hole shot, possibly better mid-range efficiency and allow you to hang on plane at lower speed, although they will cost you some WOT speed.

gofastsandman · #5 11-05-2016, 08:43 PM

Quote:

Originally Posted by Bushwacker

That sounds like a pretty stern heavy rig, so I'd pay attention to min planing speed if you run offshore much. I suspect you'll need a stern lifting prop, so good offshore type 4B props (stay away from bow lifting 4B bass boat bow lifting props!) will give better hole shot, possibly better mid-range efficiency and allow you to hang on plane at lower speed, although they will cost you some WOT speed.

Attitude and minimum plane speed.

McGillicuddy · #6 11-05-2016, 09:10 PM

Yeah 1000 lbs hanging 24 or more inches aft is substantial. You're gonna need some help. Regarding stated diameters, are they both Yammie semi-cleavers or what are they? model, diameter & pitch...
Look for easiest to turn, wide diameter, limited cup, stern lifters you can find. This might be a perfect place for powertech MQS props.

Top end and max economy may not be concurrent. I would opt for more economy and lower planing speed. at the cost of a couple of mph. at 45mph I doubt you'll notice. As Bushwacker suggested a stern lifting 4 blade a might be the ticket. Just make sure you're able to wind it up to target top rpm at full load. 14.5 x 17p probably close.

mjobrien · #7 11-10-2016, 08:03 PM

I know I increased by engine weight by 80 to 100 pounds in the change. The stern lifting props make great sense. The ones I have on now require me to keep the motors trimmed all the way down. (They are mismatched crap). Thanks for all the input.

Bushwacker · #8 11-10-2016, 11:20 PM

Good holeshot and efficiency tend to go together. I'd focus on pitch rather than diameter; most prop designs seem to increase diameter as they reduce pitch.

Moving the engines 30" or so aft on a bracket makes a boat much more sensitive to motor weight. The fact that you have to trim 'em down says the boat want's more stern lift but that also increases drag. Putting SE Sport fins on the AV plate will give you more lift, so I'd do that before screwing around with props. And make sure motor height is correct . . . AV plates should be above solid water when you're up on plane to minimize drag! When changing props, you'll want the pitch that puts your WOT rpm near the top of the recommended range with your max load for best durability. If you lug down a 2-stroke motor, they'll build up a lot of carbon and cause the rings to stick which is a long term problem, but if you lug a 4 stroke, you'll burn the exhaust valves if you run it too hard. If I had a 4-stroke motor (I/O OR OB), I'd put a vacuum gage on it and observe an intake manifold limit of 7" Hg at cruise.

GameOnSalmon · #9 11-16-2016, 11:21 PM

I have had great success on both Seacrafts and Formula 23's with the Merc Revolution 4 and Powertech OFS 4 blade and ran a Rev 4 on a 20' Scepter all with excellent Results.

Amazing Handling Can run them higher than say a mirage plus 3 blade... and IMHO the Yamaha Props seem to be the worst of them all... Diamater is not such an issue as getting Engine height and Pitch Right for Optimal Performance.

Some of us around here are as anal as you can get with the Set Up but once you dial it in... Its Money!

Robert