Help with Prop-- Top speed RPM won't increase even after pitched

[danf1000]

1) Performance issue you are trying to correct.

Run it up to top end on the original 14 in, 21 pitch prop and it does 33 mph on gps, 3800 RPM.

swap prop for a 4 blade 18 pitch, and it does 32 mph on gps, 3900 RPM


2) Current prop manufacturer, model, aluminum or stainless and as a minimum.

21P- Volvo, 18P- Michigan Wheel Vortex

3) Current prop diameter and pitch (required).

above

4) Wide open throttle RPM and speed with an average load (very helpful)

above

5) Engine/drive make, model, year, and HP

2008 volvo penta 3.0 135 brand new

6) Boat make model, year, length and weight

2008 Glastron 175, around 2100lbs? bought brand new couple of months ago as a boat that had been setting around for too long...

not really worried about the top end, just wondering if there is some horsepower left on the table. With 18 pitch 4-blade, the boat planes effortlessly and at around 3 mph less than the 21p.

is the engine set up rich right off the floor for safety?

 

[danf1000]

Re: Help with Prop-- Top speed RPM won't increase even after pitched

More info:

1. Year, make and model of boat: 2008 Glastron 175

2. Length, width and base weight of boat: 17 foot, around 2100 lbs?

3. Number of people and gallons of gas normally on boat: 2 people

4. What do you use the boat for: Watersports - wake and knee board

5. Is it a Deep Vee and if so how many degrees of deadrise: Yes a deep vee

6. Year, make. manufacturer and model of motor: 2008 3.0 Penta

7. HP and gear ratio of motor IMPORTANT: 135 HP

8. Manufacturer?s recommended Wide Open Throttle (WOT) range: 4400 - 4800 rpm

10. Is it a bass boat or does it have a pad bottom: No

11. Does it have a hydrafoil, dolefin or trim tabs: No

12. Make, model, diameter, pitch, number of blades and whether SS or aluminum prop

Prop #1: Volvo 21P 3 blade Al- 2 people, 10 gals gas, WOT - 3800, GPS - 32mph

Prop #2: Michigan Vortex 4 blade Al- 2 people, 10 gals gas, WOT 3900, GPS 32mph

14. Are you at sea level or a higher elevation, give us the elevation in feet: Sea level

15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM: not checked

16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop: Swapped to get more top end--didn't get it

17. Does the prop show any damage that you can see: No

18. What problems are you trying to cure?: Get some more top end

 

[steelespike]

Re: Help with Prop-- Top speed RPM won't increase even after pitched

That is a real load NADA says 2300 lbs.
A 4 blade isn't the usual choice for more top end.It should improve low end performance.
Even so original prop I think it should do better than 33 at 3800.
If the 21 is the proper factory prop I would think 4600 and close to 40 would be possible.
Might be a little sluggish out of the hole and not do too well as you add load.
Is it a deep V?Is it broken in? Problem could be as simple as throttle cable adjustment.
Don't assume eferything is right because its new.

 

[danf1000]

Re: Help with Prop-- Top speed RPM won't increase even after pitched

Looks like I got more RPm from the pitch change, but might have eaten some of that up with the 4-blade...netting little change in top end?

ok, then looks like I do have a power issue. Any suggestions other than the ones listed already?

Weight is 2280 lbs.

 

[fossill]

Re: Help with Prop-- Top speed RPM won't increase even after pitched

2008 should be under warranty still. I'd let the dealer sort that one out. Sounds like it wasn't pre-delivered properly if they let it out the door with that kind of performance isssue.

 

[180shabah]

Re: Help with Prop-- Top speed RPM won't increase even after pitched

You really should be getting more out of it. 46-4800 at close to 40mph woud be normal.

You need to look at FULL/COMPLETE tune up, not just new plugs. Have you compression checked the engine?

 

[steelespike]

Re: Help with Prop-- Top speed RPM won't increase even after pitched

After sitting 2 years it could be a gunked up carb/fuel system,stuck timing advance,
a sticky valve,If overall performance seems sluggish could be a plug wire off.