23CC Evinrude 225 WOT..
 

'86 23CC with a 2005 Evinrude 225. No name, no number prop. So I don't have a clue on pitch and size. No trim tabs (well currently not working)

WOT is currently 5000rpm and 33-34 knots based on boat mounted GPS. Planes out at 3800-4000rpm. Engine is capable of 6200rpm. New throttle cables so next time I'm down at the boat I'm going to pull the cover off the engine and make sure I'm getting full opening on the TB.

I'd like to be able to get redline if I wanted to (for whatever reason there would be for that) but don't "need" to. 40+ knots at a decent RPM would be nice to make the tower run on a calm day that much shorter but again; that's a want not a need.

Should I start messing with prop sizes or leave well enough alone?

it's all about load


that motor should be able to run it's max RPM,with the boat loaded in the condition it's normally ran - read that as,if you're running your boat with 4 people,full fuel and 600lbs of gear - duplicate weight conditons

take the boat out and run it on the pin - wide open throttle...record the max rpm you see

check the height of the motor - antiventilation plates out of the water ?

check that the throttle is opening fully...

a motor that's under the rated rpm is overloaded - people often think it's ok,because they never run it hard - that's incorrect,overloaded is overloaded...


every inch of pitch will give approx. 150RPM - problem with that is,when the hull begins to get some air under it,rpm's will climb...read that as,if you're 1,200 rpm down,you won't need to drop 6" in pitch - 2" in pitch is a big difference

a motor being able to reach it's max rpm,is more fuel efficient and it will last longer - overloading the motor,it greatly reduces the durability of ANY motor...

Is that an E-TEC or Ficht motor? A 2005 would be a BRP motor, probably an early E-TEC, and if so you are seriously over-propped! Pelican is right, it's hard on the motor if you're running a prop with too much pitch!

In addition to the commonly published very wide "Recommended Operating Range" like 5000-6000 rpm, BRP has published the OPTIMUM WOT Operating Range for most of the E-TEC's. Haven't been able to find a chart for a 2005, but optimum is probably similar to the 2007 models, which is 5500-5600 with the max load you normally carry. Even if it's a Ficht motor, I suspect optimum RPM would be similar. This assumes motor height is correct, with AV plate running above solid water when on plane, AND your RPM measurement is accurate! (Analog tachs are notoriously inaccurate - a digital I-Command gauge or an NMEA 2000 compatible chartplotter that gets the rpm signal from the EMM is preferred.)

A good prop shop could probably identify or at least measure your current prop and tell you what pitch it is. IF your height and RPM data are correct, having that information on your current prop will eliminate much guesswork in selecting the correct prop!

15x15 sst2 prop. 6100 WOT going 40 mph. 4200 rpm cruise going 30 mph

You need to make some changes

Thanks for the responses guys.

Little more info, it is a late Ficht motor. The test was done without a loadout and 3/4 tank of fuel. Original tank as far as I know. Only me onboard. Flat sea state.

Tach is new and compatable to the Evinrude tach signal. It is however an analog gauge. So grain of salt... GPS unit, older... Can/Do you calibrate those?

So step one- I'm going to ensure the TB is fully opening. Figured the mechanic would have done that so I didn't check before I took her out... Assumptions and all that.

Step two- Check where the AV plate is height wise. Draw a straight line from the bottom of the hull? AV plate 1" above that line?

If those two check out, take current prop to a prop shop and get it measured.

Sounds like a good plan! If you're testing with a relatively light load, you'll want to target the upper end of the optimum rpm range, like 5600-5700, so that you'll still be ok when fully loaded. When prop testing, besides a full fuel tank, I typically fill the live well and fill a couple of 60-70 qt coolers with sea water to simulate a heavy cruising load.

Years ago I had a new OMC tach that read high by about 300 rpm that led me to pick the wrong prop, so just because it's new doesn't mean it's accurate! Dealer checked the tach and replaced it under warranty. Not 100% sure, but I think the Ficht is similar to an E-TEC in that a dealer or you should be able to plug a laptop with the diagnostic software into the EMM and read rpm and a bunch of other stuff, so yes a dealer should be able to tell you if the tach is accurate.

On the AV plate, I think I'd start with AV plate about 1.5" above keel, measured with motor trimmed so plate is parallel to bottom. I like to get it too high to where prop ventilates on a sudden hard turn and then drop it down a hole. How high you can run it depends a lot on the prop. A good highly cupped SS prop can typically run much higher than a cheap aluminum prop w/o much cup. BTW if the prop you have is aluminum, a good shop can repitch it to get you close to optimum before you spend big $ for a SS prop.

JJ - Where's the 17P mirage plus data???

Doh! Waiting for you to record it ;)

Ran down to dry storage today. Didn't have time to get the boat taken down but it is on the bottom rack so I ran inside and looked at the prop again. Turns out there are numbers on the hub. What I have found is it's a Stiletto Advantage II 14 1/4" X 17P stainless steel.

Also a quick measurement of the AV plate puts it around 1 1/2"- 2" above the keel. I have no more holes to go down but I can go up with the motor.

The TB opening properly is still a variable...

So got a chance to go down to the boat yesterday and check the TB opening. They are adjusted properly and opening fully.

Seems it is time to start playing with props. If I decided to go the cheap aluminum route to find the right prop, will a Stainless prop react the same when I find a pitch and diameter that works for me?

I'm going to start with a 15 X 15 as thehermit stated and go from there.