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Author Topic:   99 Outrage RPM
prxmid posted 07-17-2002 03:00 PM ET (US)   Profile for prxmid   Send Email to prxmid  
I know that there are a lot of prop threads but I am having trouble finding what I need.
I have a 99 Outrage 18 with a 150 Merc DFI.
WOT with one person barely hits 5000 RPM. I think I'm overpropped. There is a 17 P on there now. That's the extent of my knowledge.

The Whaler mechanic said it should be a 15. I can buy a new one for $480 or have it machined to 15P for about a hundred. Whaler hasn't gotten back yet with what they recommend. Any suggestions? And what better performance can I expect with the right prop?

JBCornwell posted 07-17-2002 04:02 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
I know that boat is very heavy compared to the Classic 18, But I didn't think it was that heavy.

I guess the deeper Vee makes a difference.

I agree that you are overpropped, and I would give the 15" a try, but only as a demo. If it does really reach 5500 and you are happy with the performance, go with it.

Red sky at night. . .
JB :)

prxmid posted 07-17-2002 05:09 PM ET (US)     Profile for prxmid  Send Email to prxmid     
I just took it out. One person WOT, barely 5100 RPM and 36.3mph.
lhg posted 07-17-2002 05:19 PM ET (US)     Profile for lhg    
A 15" Merc Mirage prop should do the trick for you. I think (in Ft Myers FL) ships them for $390 each.
John from Madison CT posted 07-17-2002 05:28 PM ET (US)     Profile for John from Madison CT  Send Email to John from Madison CT     
I find it odd that an 18' Whaler with a 150hp motor would need a 15" prop to get to the proper RPM's.

Something is not right IMO.

15" props are typically used in underpowered boats.

John from Madison, CT

bsmotril posted 07-17-2002 10:40 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
I agree with John, something is not right with the motor's powr output. On an 18' boat in that weight range with a 150hp engine, I would look for a prop in the 18-21" range for max RPM. Especially with an Opti which has gobs of torque and dyno's at the high end of the +- 10% range allowed for rating horsepower. Is the engine still in it's initial break in mode? That might account for the reduced power. The CPU sets this mode automatically, or you can force it into that mode by turning on the ignition and pumping the throttle 4 times in the first 15 seconds. If you do, you will have the engine running with extra oil for another 8 hours of runtime. You might also try raising the mounting up a hole or two as the motor might be set too deep.
prxmid posted 07-18-2002 08:12 AM ET (US)     Profile for prxmid  Send Email to prxmid     
Ergo my confusion, mechanic says 15P, knowledgeable owners say higher. Boat is a 99 that I've had for a year. Has performed this way since I got it. It does everything I need, I just don't feel I'm getting the performance I should. If it isn't the prop, what might be wrong with the engine that I could check?. It sounds like it's running fine.
aubv posted 07-18-2002 08:57 AM ET (US)     Profile for aubv  Send Email to aubv     

This might help you.


VMG posted 07-18-2002 01:49 PM ET (US)     Profile for VMG  Send Email to VMG     
Maybe the motor is mounted too low, as in too much lower unit in the water.
VMG posted 07-18-2002 02:32 PM ET (US)     Profile for VMG  Send Email to VMG     
To clarify, if your boat/motor is only producing 36 mph at 5100 rpm that means the prop is grossly inefficient -- a slip value in the 18% ballpark. The question is why...

Too much lower unit in the water (engine mounted too low) can be a factor since that would increase drag. However, its hard to imagine that the engine is so radically low that you're producing that much slip. (Normal slip values at top end are considerably lower -- reference the prop calculator section).

Also, confirm for us that whatever device you're using to reference speed is displaying mph (statute miles per hour) and not knots (nautical miles per hour). If that 36.3 is actually knots instead of mph, then your boat speed is in the speed range nominally expected for a prop running at that rpm (36.3kts x 1.15 = 41.74 mph).

prxmid posted 07-18-2002 04:06 PM ET (US)     Profile for prxmid  Send Email to prxmid     
OK sorry 36.3 was from my Garmin GPS, which, pardon my ignorance I assume is in knots
prxmid posted 07-18-2002 04:16 PM ET (US)     Profile for prxmid  Send Email to prxmid     
I think I've ruled out lower unit mounted too low. At least thats what the inteligentsia around here feel from visual inspection.
Bigshot posted 07-18-2002 04:57 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
How trimmed out are you. I agree only a 21' with a 150 should run a 15" I would initially say a 19" on that package. The classic would probably run a 21". Make sure the Garmin is reading in MPH or knots. Before you freak, try trimming the balls out of it until you are shooting a roostertail or it starts blowing out, then tell us how many RPM's. If I tuck mine to straight I will lose about 5mph and 400rpm's.
VMG posted 07-18-2002 06:56 PM ET (US)     Profile for VMG  Send Email to VMG     
Prx -- I don't have any experience w/ Garmin units but most GPS systems have display options that allow selection of either mph or kts. Your owners manual should outline it for ya, as well as what the default selction might be.

If you're in the Severn River or Ches Bay you'll also have to factor in a wag for tide and river currents given your direction of travel. Depending where you're at, time of day, etc I've seen up to 3 mph difference.

bsmotril posted 07-18-2002 09:51 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
If there is a tide running, do two speed runs in opposite directions and take the average makx speed. I would also inspect the throttle linkage/cable to be sure that you are getting true wide open throttle when your control lever is full forward.
John from Madison CT posted 07-19-2002 07:22 AM ET (US)     Profile for John from Madison CT  Send Email to John from Madison CT     
FWIW, my Garmin GPS came out of the box reading in Knots, not MPH.

Yes, it (units) can be changed.

John from Madison, CT

jacko posted 07-19-2002 08:52 AM ET (US)     Profile for jacko  Send Email to jacko     
I agree with Bigshot and try trimming it out. When I first bought my Outrage 18 I was running around at 4600rpm max. With a bit of feathering she will now run at 50 mph at 5000rpm.
Just for a comparison, I probably have a similar weighted boat and a 175 Yamaha with, I think, a 19" prop (standard). It does seem very strange that you require a 15".
BillD posted 07-19-2002 09:07 AM ET (US)     Profile for BillD  Send Email to BillD     

I have the same boat motor and Probably prob. Mine is a Mirage Plus 15 1/2 Diameter 17p. I am also not completely happy with the set up. With 1 person the boat gets up to about 5100 RPM and 44 mph (according to the paddle wheel on my Fish Finder, I know not the most accurate, but the numbers are bigger than my gps speed read out and I am trying to drive).

My problem is when I put more people on. The boat sort of slugs until the RPMs wind up. I recently purchased a new Prop. Still a 17p but I went down in diameter to 14 1/2 inches. I bought an aluminum prop from I ended up calling them and going over what I was looking to improve, Hole shot, time to wind up RPM, heavy load performance. They were very helpful. With the smaller diameter and aluminum prop I will be giving up some top end speed, but I do not use the top end much so it will not bother me. The prop including shipping and a washer that I needed was $130. I can exchange it for another prop after I test it for a $15 fee which seems fair.

For the record the 18' 1999 -2000 Outrage has a dry weight of approx. 2500 pounds, the engine is about 450 and it holds 90 gallons of gas. With a full tank it weighs about 3500 lbs., which is a lot for 18'. The person I spoke with at Propco also initially thought that a 17p was too small for an 18' boat, but once I gave him all the specs he agreed that was the proper range for the prop. If the prop I bought does not do it for me he was going to recommend a 4 blade 22p with a smaller diameter.

I am fishing Sat, hauling the boat (it is on a mooring) at night and changing the prop. I'll be running the new prop Sunday, and post the results Sun night / Mon morning if you like.

Propco was suggested to me by "Chaps" see thread

BillD posted 07-19-2002 09:08 AM ET (US)     Profile for BillD  Send Email to BillD     
I forgot to mention that the RPM range on the 150 Optimax is 5000 - 5600
Bigshot posted 07-19-2002 10:14 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
good point a 15+" is too big diameter, get one in the 14's.
VMG posted 07-19-2002 10:29 AM ET (US)     Profile for VMG  Send Email to VMG     
Agree w/ the others on the diameter issue.

So...before you spend $$ on a new prop --

-check the mounting height of the engine (ask Bill D what hole his is mounted at)
-make sure its trimmed properly
-verify the unit of measure for your speed readout
-get plenty of informed opinions on the problem from people who have no vested interest in making $$ off of you with a solution

Good luck with it.

prxmid posted 07-19-2002 06:55 PM ET (US)     Profile for prxmid  Send Email to prxmid     
First, Thanks, I did check and the Garmin is reading knots so +/- 41mph @ 5100 rpm

I did the run in the Severn twice going in each direction...same results.

I know I have a 17P, sorry I don't know the diameter (the Whaler mechanic told me not bother finding it)

The fact that BillD has the same boat and motor and is achieving the sames results says maybe that's what it is.

For VMG....yes 36.3 was knots, the motor is mounted in the middle hole of 5.

Bill...I am very interested to hear of your results with the new prop.

Glad I got on this thread..I was all set to go to the 15 which sounds like a mistake


BillD posted 07-22-2002 07:57 AM ET (US)     Profile for BillD  Send Email to BillD     
Unfortunatly I did not get to haul the boat and switch the prop. Something came up which shortened the weekend. Also do to a number of other commitments I will also not be able to get back to the boat for about 3 weeks. So I have no reports on the new prop.

I did however get to do some more test runs and the results were consistant with yours. I do think that the smaller diameter will make a difference.

jimh posted 07-22-2002 08:28 AM ET (US)     Profile for jimh  Send Email to jimh     
From the prop calc:

Speed=36.3 Kn

This gives a Slip of only 5%, which is excellent prop performance.

prxmid posted 07-22-2002 01:52 PM ET (US)     Profile for prxmid  Send Email to prxmid     

Is the inference that this is good performance and due to the weight, Deep V etc that that is what should be expected.

I raised the issue because I was told that I should expect close to 6000 RPM, and if it is only 5000 it would affect the RPM I normally cruise at

Hoss posted 07-23-2002 05:37 PM ET (US)     Profile for Hoss  Send Email to Hoss     
I had much better speed and overall preformance on my 96' 17 Outrage 150 H.P. when I switched to the Mercury Offshore 4 blade prop. Might Be worth a try.
jimh posted 07-23-2002 08:27 PM ET (US)     Profile for jimh  Send Email to jimh     
I am assuming your "150 Merc DFI" is an Optimax. The redline for that engine is 5600 RPM, not 6000.

Right now you are propped for a WOT of 5100. If you move down to a 15-inch prop, which is really a small prop for a 150-HP engine, you'd get 35 Kn at 5600 RPM, a slight drop in top speed.

Does your boat have any of the following:

--bottom paint?
--Tee Top?
--Radar Arch?

What condition is the prop in? Any dings or nicks in the blades?

Remember, we are talking in Knots, so 36 Kn is really 41 MPH, a respectable speed.

I'd try to borrow a 15-inch or 16-inch pitch prop and try it just to see where the WOT lands. If it still won't go above 5100 then there is something holding your engine back.

prxmid posted 07-24-2002 01:17 PM ET (US)     Profile for prxmid  Send Email to prxmid     

Yes the 150 is an Optimax, the prop is a Mirage SS, 17P in good condition, no dings

I have bottom paint as I keep it in a slip all season. The bottom is cleaned as well as it can be, being in the water.

No T Top,however a bimini, no radar arch.

It sound like I'm not too far off performance wise, for the expense and trouble there doesn't seem to be a great return

BillD posted 08-18-2002 10:35 PM ET (US)     Profile for BillD  Send Email to BillD     

I finaly switched out my prop this weekend and am very happy with the performance.

I went from the same prop you have to a 17P 14.5 inch diam. aluminum prop.

I get essentially the same top end speed (low 40s) with a better hole shot, time to plane, and no slugging as the rpms wind up. Basically it seams that the smaller diameter makes the prop easier to turn and allows the engine to spool up faster.

The reason I wanted to change props was that it felt like the engine was straining to get wound up.

Swellmonster posted 08-21-2002 12:44 PM ET (US)     Profile for Swellmonster  Send Email to Swellmonster     
Aluminum flex = less load.

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