New to me boat -- prop seems odd

[hcooperrn]

After doing some research about props, it seems the choice the previous owner made might be a little strange. He did say he picked it for watersports, but I'm wondering if I can get a better all around prop. It seems like a lot of people with my size boat/engine have something in the 19-21 pitch. I will mostly be doing watersports, but want to be able to cruise on a big lake like Powell as well -- maybe I need two?

I made a rookie mistake this morning as well -- I hit some rocks near the dock I didn't see, and it did ding up my current prop, so I need to replace before this weekend anyway. I know I would get better performance from stainless, but for now, I want to go with aluminum.

1) Performance issue you are trying to correct.
Good enough holeshot for slalom skiing, wakeboarding, and tubing, but still be able to cruise comfortably at 3/4 throttle

2) Current prop manufacturer, model, aluminum or stainless and as a minimum.
Mercury Mirage Plus Stainless Steel

3) Current prop diameter and pitch (required).
15 3/4" x 15 Pitch 48-19838

4) Wide open throttle RPM and speed with an average load (very helpful)
Only gets to about 4200-4300 and 36mph

5) Engine/drive make, model, year, and HP
2001 Reinell 190, 19 foot, 2450 lbs
Volvo Penta 5.0GL, 200hp, SX-M Outdrive

These boards are incredible, thanks in advance for the help!!

 

[hcooperrn]

Re: New to me boat -- prop seems odd

Forgot to mention, I did put on a hydrofoil to help smooth out the ride, it did seem to make it plane easier and ride through chop smoother.

I just tried a spare prop I had laying around off of an alpha one. If I use the hub from the VP drive, it seems to fit together right.

It is a 14.5 inch x 18 pitch 4 blade aluminum. What kind of difference am I looking at if I try that one?

Thanks for helping me out!

 

[steelespike]

Re: New to me boat -- prop seems odd

Yes you would normally run more prop 19-21 at least. and likely speeds approaching 50.At this point the 18 wouldfurther reduce your rpm.
Some things to check::
Is the bottom clean and smooth?
Throttle opening all the way.
Engine timed and advancing as it should.
Is a plug wire off or shorted?
Do a compression check;note plug locations and condition.

 

[hcooperrn]

Re: New to me boat -- prop seems odd

Thanks for the response!

Bottom is clean and smooth, no hooking or cupping that I can see,

Throttle opens fully, carb passages look clean, though I haven't rebuilt the carb. It does have crisp throttle response off of idle,

New MR43LTS plugs, gapped to .035 per manual, timing 8* BTDS because it has a tank of 85 octane (I live in Denver, boat at 5400' altitude)

New 8mm wires, new Accel Super Stock Coil

Compression -- 7 of 8 at 150, cylinder number 4 at 120 -- within 70% range

Engine temp running 160, light load of 1-2 passengers, fresh oil not overfilled, factory gear ratio in outdrive.

I will recheck the throttle opening again, and I have not checked fuel pressure -- it starts up at the first bump of the key and has good throttle response, so I assumed good.

I honestly thought the diameter of the prop was giving me the lower rpm's.

I will take the boat out again in the morning with the backup prop and post the results to see if they're different.

Thanks again, and please let me know if you have any other ideas -- 50mph is way too fast for our small suburb lakes, but would be nice at Powell....

 

[BoomerSooner]

Re: New to me boat -- prop seems odd

A 15 pitch prop spinning only 4200 RPM's? That doesn't seem right for a 5.0. I can understand the 36 MPH with it, but seems low on the RPM's. I'd definately check to make sure she's running on all cylinders, no pun intended. As mentioned before, compression, plugs, wires, etc. When you are sure she's running 100%, then worry about the prop.

 

[steelespike]

Re: New to me boat -- prop seems odd

5400 ft would sap some power.I'm pretty sure 5000 ft would require a re jet(smaller) to be right.And a pitch reduction would be normal though 15" seems extreme If jetted right.

 

[hcooperrn]

Re: New to me boat -- prop seems odd

I tried out my back up prop today, and I'm still scratching my head. The engine is running right, running on all cylinders, starts smooth, accelerates smooth, good throttle response.

I went from a 15 3/4" x 15p 3-blade SS to a 14.5" x 18p 4-blade aluminum, and my speed and RPM's didn't really change?

I ran 36.5mph GPS, and 4200 RPM max at WOT. I've checked the tach against a multimeter tach, and it's accurate.

The boat does plane easier and "seems" to hold the plane at a slightly slower speed. I'm sure it will be fine for playing the rest of this summer.

I can see the altitude being part of the problem -- I'll look into playing with the jets. But even if I get the rest of the 4800rpm, that isn't going to get me to 50mph with this 18p prop, is it? I'm just worried if I am maxing my horsepower and rpm at altitude with an 18p, going to a 19-21 really isn't going to do much, is it?

Thanks again for the help!

 

[steelespike]

Re: New to me boat -- prop seems odd

It will very likely require both a prop reduction and a jet reduction and your performance will still likely suffer.
When you change number of blades,pitch,and material all bets are off as far as any rule of thumb numbers.The 4 blade did improve your hole shot as it should and you may notice it is smoother and handle better at the dock.
There may be a formula or % of power loss for 5,000ft. somewhere based on properly jetted motors. You have too much fuel at present sort of flooding it.
No you won't see 50 at 5,000ft.Just be thankful your not dealing with a 3.0.
Power loss with a properly jetted motor is 3% per 1000ft. so at 5400 your at about
15-17% about 140hp like driving a 3.0.