Seeking prop perfection

[jklnhyde]

I have a 1986 Sea Ray Seville 19 cuddy with a OMC 3.0L/Cobra that is in top shape and served me well this season. I did have a concern with the prop, though. First let me assure you the engine is fully tuned. It has a Pertonix coil and ignition, MagStar plug wires and new fuel filters among a ton of other normal maintenance work I've done. Here's the deal:

At WOT (roughly trimmed, on glass-smooth water, just me and 1/2 tank of fuel), the boat climbs steadily to 32MPH @ 3800RPM. With a bit more finessing the trim, it moves to 33MPH @ 4000RPM.
I'm satisfied with the time it takes to plane; I'm no speed racer, and I normally cruise at 3200-3500RPM (25-27MPH or so), but here's the catch-
I know the OMC 3.0L should rev to 4400-4600RPM, but my throttle is maxed at the control and the carb linkage cannot go any further. The engine sounds rougher than I think it should, but has worked fine this way. The prop is a Vortex MI aluminum, 13.25x17.

Would switching to a different prop (SS/4-blade/different/pitch/etc) do anything to move me closer to the WOT RPM or give me a quicker holeshot? Would switching give me one or the other, but not both?
Do I have a good combination already and should be happy?

 

[Randybeall]

Re: Seeking prop perfection

Well, except for what you said about seeming rough, I would suggest the Hustler Turning Point 13 3/4 x 15. That would bring the rpm up to where you were not lugging the engine, and they have had very favorable reports by some experienced people. However, any question of how good the engine is running throws up a red flag. Missfire under load is a huge waste of energy and the prop load is always the same. That means that without any missfire the 17 inch prop might be 'perfection'. Compression test? Carb cleaning? Spark test? Something is not quite right and being a mechanic I have learned to suspect even new parts when it does not run right. Fix that first and then evaulate whether you need a different prop. Happy Boating.

 

[steelespike]

Re: Seeking prop perfection

It sure seems to me that with the 17 you should be a lot closer to your max rated rpm.I found a 86 140 hp Seville cuddy 18ft.Couldn't find a 19 .Found a 19 in 87 at 165 hp. all were about 2,000 lbs.Your down bout 600 rpm that would put you at 14" to get 4,600. darn low number as is 15 Any chance you might have gotten the polarity reversed on the new coil?

 

[jklnhyde]

Re: Seeking prop perfection

Well, what I meant by 'rough', is just the sound, not physically running rough. These 4 cylinders are no smooth runners at higher RPM's, so I'm just referring to the fact that I wouldn't run it at 4000 or higher more that a few seconds because it just sounds rougher than I like.
It has a smooth idle at 650RPM and throttle response is amazing at any speed. Believe me, it's tuned to the best of my ability.

 

[steelespike]

Re: Seeking prop perfection

Well in my opinion your missing 600 rpm.Prop is darn close to what you need ?
Perhaps the Sea Ray has an exceptionally deep V??
You might check the tach perhaps borrow a shop tach see how it compares to yours.In my opinion boat should be close to 40 mph. A stainless prop should improve your performance.A 4 blade would improve low end performance but probably lower max rpm.

 

[Cruiserman]

Re: Seeking prop perfection

sounds like the power to me. The prop is factory spec Searay. Stainless is too heavy. 4 blade is unnecessary. Ignition is probably breaking down or fuel is impeded somehow. Of course this assumes that your prop shaft and outdrive in general is spinning true.. and that encompasses a lot of components. The 19 cuddy is a lot of boat for a 4 cylinder.

 

[steelespike]

Re: Seeking prop perfection

sounds like the power to me. The prop is factory spec Searay. Stainless is too heavy. 4 blade is unnecessary. Ignition is probably breaking down or fuel is impeded somehow. Of course this assumes that your prop shaft and outdrive in general is spinning true.. and that encompasses a lot of components. The 19 cuddy is a lot of boat for a 4 cylinder.

Stainless weight is a non issue.only the slightest difference when shifting.
And doesn't affect general operation.The Hustler props deliver near stainless performance at aluminum prices.

 

[jklnhyde]

Re: Seeking prop perfection

I agree that there is a 600RPM deficit. I had a 19ft Raven BR that had the same engine (Mercruiser) and she got up to 4600RPM like nothing. I had that 3.0L tuned just like I have this one tuned, and that's why I'm asking. The Sea Ray does have a tall/deep V-profile and she's quite big for a 19 footer, though, and the she does have crappy/flaky bottom paint...

On my Raven I had switched the prop to a Hustler, so maybe a prop change could do it for me on the SR. I wish I had the specs saved. I'll check my tach accuracy and timing at WOT to see if the ignition is acting up, but I seriously doubt it. I would suspect the fuel pump if anything, since it's 22 years old...

 

[steelespike]

Re: Seeking prop perfection

I agree that there is a 600RPM deficit. I had a 19ft Raven BR that had the same engine (Mercruiser) and she got up to 4600RPM like nothing. I had that 3.0L tuned just like I have this one tuned, and that's why I'm asking. The Sea Ray does have a tall/deep V-profile and she's quite big for a 19 footer, though, and the she does have crappy/flaky bottom paint...

On my Raven I had switched the prop to a Hustler, so maybe a prop change could do it for me on the SR. I wish I had the specs saved. I'll check my tach accuracy and timing at WOT to see if the ignition is acting up, but I seriously doubt it. I would suspect the fuel pump if anything, since it's 22 years old...

22 years old;hows the compression?