Propeller pitch for 1984 23 Open Fish?

contylhil · #1 06-06-2010, 09:57 PM

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 · #2 06-06-2010, 10:30 PM

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 · #3 06-07-2010, 08:43 AM

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 · #4 06-07-2010, 07:13 PM

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 · #5 06-07-2010, 09:11 PM

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 · #6 06-07-2010, 10:08 PM

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 · #7 06-12-2010, 08:51 AM

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...

McGillicuddy · #8 06-13-2010, 03:56 AM

I suspect you'll be pleased with the over all lift of the Mirage + if you got into the right pitch. Not sure what you mean by "engine tilted." Hopefully you get more lift on the stern bringing the bow down rather than the bow lift your TL gave you... Look forward to reading your results.

contylhil · #9 08-05-2010, 10:56 PM

OK, sorry about the long delay in responding. Kids, summer camp, etc. Here are my conclusions after comparing the 17 pitch Mirage Plus, and the old original SS 17 pitch on the 250 4 stroke Yami: the Mirage Plus stinks on my 1984 23 cc. It drives the boat into the water, not matter how I tilt the engine. The Mirage is fine in flat water (although it still rides low, on all 3 chines). On the plus side it gives me the same top end speed of 40 mph. However, in heavy seas it simply plows into the waves, with no lift, poor stability, and soaks everyone, constantly. I am going back to the 15-20 year old SS 17 pitch prop. That old prop gives great lift, and eats up heavy seas, riding high. Frankly, I don't know what I was thinking going to the Mirage. I ride on all 3 chines, or at least 2, at all times with the Mirage. Perhaps this has to do with the fact that the engine is not on a bracket, and is mounted direct, but no matter. The old prop rules, and the Mirage Plus is a no-go. I pop up on 1 chine in less than 5-7 seconds with the old prop.

McGillicuddy · #10 08-06-2010, 01:01 AM

Sorry that prop ain't workin' right.
Seems another Seacraft owner had a running angle issue and one of the points made was relative to the amount of negative trim on the Yammie engine mounts. Apparently a mount design adapted to overcompensate for the weight of their four strokes.

Could such a trim angle be working in conjunction with that prop to be causing your bow stuffing?

It might be helpful to post some side shots of the motor all the way down.

Do you have trim tabs?

Love to see pics of your old prop, too.

Why not pitch down in similar geometry. Old school yammi props are still being made.