Prop or is it something else?

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MikeeH

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New to me,2004 Sea Ray 185, 4.3 Mercruiser, Alpha 1. Just took ownership this week. Boat has low hours (88), runs great. Love it so far but I'm troubled by the WOT results. Reading test reports on this model I see that with the 190 HP 4.3 turning a stock aluminum 14/23p wheel I should see 4400 RPM and about 47 MPH at WOT. I'm only getting about 4000 RPMS and 39 MPH. What could be the reason? I do have a 14/19p 3 blade stainless wheel I can put on so what changes should I expect from that?
Thanks in advance.
 
Reasons could be prop as you suggest or weight for some reason or leg angle or dinge prop or bent blade or bad gas or ethanol in gas or fuel filter or tune up but unless you will run at high speed a lot why worry? If it wee me I would run it for a while, off WOT, and see what happens.
 
Bruce,
You are correct that we can cruise at 3200/30MPH and be satisfied. I'm just wondering why the motor doesn't top out according to the specs when I have the same set up as the test vessel.
 
But are you using ethanol free gas???
 
Short answer....No. Would E85 make that big of a difference?
 
I didn't realize the difference was that big. Thanks. Regardless, do you know what going down in pitch on a prop does? I figure a better hole shot but that's just an uneducated guess.
 
If you lower the pitch you'll slow the boat down but raise the WOT RPMS (200 per inch of pitch I believe). I think you're correct that you'd get a better hole shot though. Probably not what you're after! My 2 cents is you've got the right prop. You can try some non-ethanol (that's all I run in my boat). It'll be a bit of a drive to get it but you can find it north and south of you (I drive 20 miles from my house into central PA and then truck it 50 miles to my boat as it does make a difference!). You can also buy the really good non-ethanol stuff at your local small airport but you're talking really high octane (which probably isn't an issue) and inflated prices (ethanol is good for boats but not small planes, go figure!).

Peach Bottom Marina
1798 Slate Hill Rd, Peach Bottom, PA; 717-548-2330; ethanol-free UNBRANDED 87

Easton Crown
301 N Washington St, Easton, MD; 410-822-8244; ethanol-free CROWN 90

Miller & Sons
930 Port St, Easton, MD; 410-310-3553; ethanol-free UNBRANDED 89

Here's a map of non-ethanol stations (note, some are "racing fuel" and way expensive): http://www.pure-gas.org/extensions/map.html
 
Mike, I'm no expert on this, but 23 pitch sounds awfully high. I would have a chat with a knowledgeable prop guy and see what he says.
Sounds like a nice boat you found. Hope you are enjoying it.
 
quote:
Originally posted by MikeeH

Reading test reports on this model I see that with the 190 HP 4.3 turning a stock aluminum 14/23p wheel I should see 4400 RPM and about 47 MPH at WOT. I'm only getting about 4000 RPMS and 39 MPH. What could be the reason?

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What were the test conditions in report? I bet they were perfect. Salt, fresh water, or brackish? How much fuel on board? What was the weight of the operator :-)
 
Any chance the upper gearcase was changed? All Alpha One Gen Two's have 1.62:1 gear ratio in the LOWER half of the outdrive. The UPPER gearcase sets the final drive ratio. The "V6 Ratio" is typically 1.62, meaning the Upper has equal numbers of gear teeth in the driving and driven gears, making its own ratio 1:1 which makes a "1.62 outdrive." V8's get a "taller" upper gearcase making the final drive 1.4 something. The 4-cyls get an "underdrive" upper, making their ratio about 1.8-something.

In our case (signature) Sea Ray equipped our V8 with the V6 ratio of 1.62 and that makes prop selection a little strange. The engine it came with was rated "220 at prop shaft" which is typical for OB bit unusual for IB and I/O. Ran 14x19-SS for 35-KT at 4400. New engine is rated 275 at crankshaft and ran the 14x19 into the rev limiter at 5400. Changed to 14x21-Alum and now 40-KT at 4900.

Is there someplace you can do a trial on props? My guess is 21" and that's what I thought I'd need. Was shocked the 23" would reach rated RPM AND get out of the hole like it does. With the POB we usually carry, we're at least 4500-pounds.

You already own a 14x19 so go ahead and try it. Of course make sure you aren't overloaded (like water in the inner hull) and you're running at a proper trim. If you under-rev with 23 and go over with 19, then 21 should hit your sweet spot. My personal preference is to be a little under-pitched than over.

OH, about gasoline:

We're using ValvTechT 89 ethanol-free from the marina.

AND

I hope you don't mean E-Eighty-FIVE. Regular Gas with "up to 10% Ethanol" and 87 Octane is one thing. MerC runs OK on "87." E85 a whole different animal and it destroys marine engines.
 
Manufacturers' and boat-magazine testing is almost never done with full tanks or full typical load of gear and people onboard, and engine was just tuned , props are new and hull is pristine. Most used- boats will have ahard time attaining test result figures.

I suggest you 1st complete a full tuneup , including all normally replaced ignition parts , confirm correct timing, replace all fluids and filters, clean the flame arrestor and ideally have your prop scanned to know what it's specs truly are before swapping out .That way you will be starting off on the right foot and know those items are not affecting performance. Otherwise it's a crapshoot.

But if there is no change in that 4000 rpm top rpm, it looks like your alu prop may be 2" over pitched if it is truly in excellent shape and true to it's original specs.

Note , if all prop specs remain the same except prop metal, a switch to SS from alu should provide in the neighborhood of an add'l 100 WOT RPM, and some add'l hull speed at all planing RPM due mostly to lower drag of the thinner blades.

But IMO you should be aiming for being able to attain close to the top end of the spec WOT range. This will give your prop less slip , and the boat faster time to plane, and ability to maintain much closer to a constant speed in increasing seas, both up-sea and down.

Be sure to adjust drive trim for best results ( usually way-in to attain plane, then out a ways while cruising.... but not too much ;) .) If you have adjustable trim tabs be sure to employ them only to the degree needed while on plane. They are valuable items on most motor boats.

Also keep in mind higher octane rating is definitely not an indication of "higher power" or greater energy BTU's / unit volume . it is only a rating of ability to resist damaging detonation /knock . If your engine is designed and tuned to run on 87 for instance you can lose performance if you run higher octane gasoline. My Crusader manual says just that.

If you are paying for high octane gas when your engine does not knock with lower rating gas you are just wasting your money , though use of 1 higher rating in boats could give a little octane & knock "cushion" in case of deterioration as is more rapid with gasohol blends. Valv-tect fuels are already stabilized but you can add no more than recommended amounts of stabilizer to other gas supplies when new/fresh/undeteriorated.

Fresh straight gas of any specific octane rating will have more energy and provide better performance than same rating fresh E10 , but I don't think the difference in near 10%, more like 3 1/2% difference in energy content of the mix and of economy.

Along with it's potential drawbacks, E10 keeps the system cleaner and will attch to & run small amounts of water through the system & out of the tank without harm whereas water would just build up a layer in the bottom of a tank of straight gas. E15 would be much more harmful.

1 last consideration for those thinking of running straight AVGAS with high octane numbers. Check how that compares with car pump averaged octane ratings as I believe they are not calculated in the same manner( not averaged, so not a straight comparison.)
 
It can also be the wrong outdrive.

I had that happen to me with a boat I bought new in 1976. The boat came out of the hole with a vengeance, but lacked top end speed. The dealer changed props and looked at other things before discovering the outdrive error. Seems they had put the drive for a 4 cylinder engine on my V-8 327 engined boat.

George
 
Very true about test conditions. painted bottom will slow it down and SS props do seem better. Any small prop misalignment can make a difference when looking at max performance. Even dry boats seem to absorb some water. Hot air and hot fuel can also cause a few % degradation. Test air and fuel conditions are usually 70F. Most prop shops will loan props and allow experimental changes to find what you like. I assume that you verified timing and advance. Before anything else full engine condition test needs to provide a starting place. I would start with full tune up and comp test for baseline data.

As you can see from the responses many things can be suspect. I start with the simplest first. have fun and let us know what you find.
 
quote:
Originally posted by gcolton

It can also be the wrong outdrive.
Seems they had put the drive for a 4 cylinder engine on my V-8 327 engined boat. George

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Which is what I mentioned above. At 88 hours, the original outdrive sure wouldn't've been worn out, but it still could have been replaced on a warranty issue or striking something.

This might help you determine which ratio you should have.

http://www.sterndrives.com/mercruisersterndrives.html

There may be a ratio stamped into the upper gearcase, port side, near vent plug, maybe under the decal. I don't have one here to look at.

An accredited MerC dealer can look the ratio up given Serial Number. The Engine Serial Number should work, but not if the Drive's been swapped. There are Engine, Transom Assembly, and Outdrive Serial Numbers, so your MerCruiser actually is known by three numbers.
 
quote:
Originally posted by MikeeH

Short answer....No. Would E85 make that big of a difference?

Click to expand...


If you are runnning 85% ethanol, you're begging for trouble. I know of no marine engine made to run over E10, and even that sucks.
 
OK. Lots of great input!! Thanks. Now, to answer some questions that were asked. (I did a bunch of research on the model before the purchase).The boat is a 2004 SR 185 Sport. The factory specs for the model are 4.3L, 190 HP, MCM Sterndrive. Alpha 1, Ratio 1.81:1, Prop is a 14x23 Black Max. WOT RPM 4400-4800. As best as I can tell, this boat is still set up to those mechanical specs. The boat is bottom painted.

I ran it on flat water (brackish), no wind, full fuel load (E80, not E85 like I said before), no additional gear, one person (240lbs).

So, all that in mind and all of your input he's what I'm thinking.... Certainly a tune-up is in order, although it seems to be running pretty smoothly so far. I'm also going to look into the throttle set-up; perhaps the linkage is out of adjustment due to cable stretch so the throttle isn't fully opening. I'll do all that before I swap wheels. (The SS 14X19 I have is what I took off the Wellcraft I'm selling so it has no history with this boat). I'll probably look into the throttle question this week but wait until spring for the tune up and any prop swaps.
 
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