Under proped with light load

[Mcfltfyter]

2007 Tahoe Q7I 20'
5.0mpi alpha one
48 832828a45 17p (aluminum 15x17)

With 2 bodies on board and pretty light on gear it does 48mph GPS @ 5500 (verified tach at idle and 2k)

Does this sound ok for 6 people and tubing and such? I need to have this prop repaired and wanting to try a different prop and also to have a spare. Obviously I have little experience, and wasn't planning to need a prop repair this soon, but let's not talk about that. Any thoughts on what I should try, or what roll this 17" fills?

 

[QBhoy]

No way that’s right or verified as right. That engine won’t physically let you rev to more than around 5100-5150, then the limiter kicks in. 100%.
Hope that helps. Maybe have another look at the tachometer or verify it with the vessel view mobile device. Great wee thing for propping your mpi.

 

[Mcfltfyter]

The slip at 5100 looks better after some more digging. Thank you for the vessel view recommendation, I just assumed the mpi was too old for that. I found a prop shop an hour from my work, so I will let them recommend a prop since it is returnable.

 

[QBhoy]

The slip at 5100 looks better after some more digging. Thank you for the vessel view recommendation, I just assumed the mpi was too old for that. I found a prop shop an hour from my work, so I will let them recommend a prop since it is returnable.

Good luck. If it’s beeping on dash wot..you’ll be on the limiter at around 5100/5150ish. Good idea to get the VVM. Tells you exactly where you’re at.

 

[Mcfltfyter]

I ordered the vessel view and a 17p spitfire. I'll see where I'm at with the spitfire and maybe order a few more cheap props to play with, then if I decide to try something expensive I'll make the trip to the prop shop.

 

[Scott06]

I ordered the vessel view and a 17p spitfire. I'll see where I'm at with the spitfire and maybe order a few more cheap props to play with, then if I decide to try something expensive I'll make the trip to the prop shop.

Ive had good luck with Michigan Vortex 4 blade props. They are relatively inexpensive. Used to run a 16" for skiing and 18" for general use and tubing. I would think an 18" would do pretty good with that boat and engine. 48 mph is about what I would expect with that combo, actually surprised with a 17" it goes that fast.

If you find that you like 4 blades for how you use your boat and you want to spend for stainless, look at the Revolution 4. Its epxensive but works very well.

 

[Mcfltfyter]

The prop shop was a bust. Up to $100 to repair 3 blade aluminum, and they can't straighten stainless. What's the point? No wonder they build trailers and other random stuff.

 

[achris]

.. and they can't straighten stainless.

Stainless props are the easiest to repair, and straightening them is a 'stock in trade' part of a prop shop business. If they can't (more like 'won't' as they want you to buy a new one), find another prop shop.

Chris.....

 

[achris]

or what roll this 17" fills?

Prop terminology.
Diameter (obvious)
Pitch. Less obvious, until you understand it. Pitch is the number of inches forward the prop would move in one revolution without any slip (like a screw turning through wood).
If you get a prop with more pitch, it will want to move further forward in a single revolution, so impose a greater load on the engine. Just like a higher gear in a car gearbox.
The way the 'correct' prop is selected is by RPM at WOT (I think you know that already), but each inch of pitch is worth about 200rpm. More pitch, less rpm at WOT. And as propellers usually come in 2" increments, each prop change (up or down) will move the WOT rpm up or down about 400rpm.

When propping a boat/engine I like to aim for right at the very top of the range, so if the recommended is 4400-4800, I'm aiming at 4700-4900 with a normal load. The reason I like the lower pitch is because we rarely operate at WOT, and having the lower pitch reduces the load on the engine and drive at all revs, not just the top (again, same as driving a car a gear lower, you're not lugging the engine)...

Chris.......

(And no, it's not going to use more fuel, but it will be nicer to drive, and have better throttle response)

 

[Mcfltfyter]

I was questioning the actual usage of the 17p prop. Sure, it over revs with a really light load, but I'd guess I'd need to drop some more pitch if I added 7 people with gear and a 3 person tube.

I did test the vessel view last night, and it seems to be working, so that should be helpful.