Propeller pitch for 1984 23 Open Fish?

[contylhil]

I'm looking for the right prop on a Seacraft 23 with 250 HP 4 stroke Yami, no bracket. I had an old SS 17 pitch (maybe from the old '93 Yami previously on the boat). Ran great, great bow lift, but WOT was 6000 rpms (max speed 40). I just tried a 19 pitch Mirage Plus to get into proper range, but poor lift, and max RPMs were 5100, max speed 39/40 with engine tilted. Should I go to a 17 pitch Mirage, or an 18, or something else? What do you all think?

[McGillicuddy]

Not sure what year your motor is but recent 4-S Yamahas are around 600lbs in that class. What are your target rpms? Logic says you need some stern lift. Have you considered a 4 blade model? PowerTech's SCE series is like Yamahas semi cleavers and they make a 4 blade version.

You might also see if you can borrow a 14.5 x 17 Black Max/Black Diamond and see if it lifts enough. If you like it, PowerTech's MQS series is its equivalent and available in stainless.

Both of these props are considered stern-lifters and easy to turn.

You might also look into Merc's 4-b Trophy Plus.

[Bigshrimpin]

You can't judge the effects of a prop when you only turn 5100rpm . . . you are over propped. The boat is going to be a dog no matter what prop you use. You need to drop down to a 17 and see where you land in the RPM range. Mirage Plus is a great prop for that hull.

[contylhil]

Thank you both. I think I am going to go with the 17 Mirage Plus. Probably can't go wrong considering I had another 17 on before and the boat ran great (albeit up to 6000 rpm). My only thought was that the 18 pitch might get me in the mid-5500s on rpm - where the rpm should be.

[BigLew]

Someone will probably crucify me, but would a 17" "Cupped" prop offer any advantage while cutting back the RPM's so he is not over reving the engine?

Only other suggestion is talking to a professional prop guy and find out his thoughts.

[eggsuckindog]

The Mirage has tons of cup and rake hence a 900 RPM difference - 2" pitch should be 400RPM normally. You also probably need to raise the engine if you go with a Mirage, it has much longer blades and can run much higher, sit them side by side and you'll see what I mean. 6000 RPM is the normal top of the RPM range on MOST 4 strokes and if so you should try and get close with a light load.

Example - my 200 ran 5700 with a 19" Merc prop - went a 19" Stlleto, similar to a Mirage, and run 5300/5400. Would actually like to trade down to a 17 frankly to get back to near the 5800 max. So if anybody has one call me.

[contylhil]

I'll let you know how they all compare when I get the 17 Mirage on later this week. The engine is a 2007 250 yami 4 stroke. With the old 17 prop (I think an original 1993 SS yami prop 17 "TL" with about a 14 in. diameter), I ran right up to 6000, engine tilted, and got great lift, great acceleration, with max speed of 40. The 17 Mirage will be a little larger diameter, and a little larger blades, so I'll be curious to see how it performs. I can always go back to the old one...