Tahoe Q6 5.0mpi rpm during holeshot.

Blb2003

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Apr 20, 2019
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Bought a Q6 5.0mpi only had it out a couple times. It has a 4blade ss prop with no markings on it. Tops out at about 47mph but only 4300 rpms. When I take off hard boat seams sluggish and will only turn 2800 until I get on Plane. Is this all normal? Without knowing what the prop is and never having drove it with the original prop I need some input on the characteristics of the boat from other owners. Also a little concerned my tach is bad(jumps around intermediately) so I will be replacing it tomorrow.
 

QBhoy

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Hi
almost comparable. I have a really heavy 18ft boat with a 5.0 mpi with a cam and exhaust system (not sure the cam helps at anything other than near full throttle it is very lumpy low down)...anyway...

not long after I got the boat, I rather foolishly put a prop on it that was of far to high a pitch. Think it was a 23” or 25” laser 2 from memory. It would only get to about 4400/4500 rpm on a good day and do about 60 mph speedo speed (before I had gps). The engine really lugged and laboured and was poor to get on plane with a few onboard.
I then bought a few different props over the winter at a good price.
Long story short...even a prop of 4” lesser pitch that would hit the limiter at 5150 rpm was so much quicker too end than the prop that was of too high a pitch.
The lower pitch prop allowed the engine to get into its rpm range of 4600-5000 rpm. This is also where the engine makes its peak power. Could go on and on about it but won’t bore you haha.
Basically if all else is well with your engine...you need to go down at least 2” in prop pitch for starters.
I would maybe take a guess that your current 4 blade stainless prop will be something like a rev4 or similar. These 4 blade stainless usually have a huge diameter. This doesn’t help when the pitch it too high especially.
Hope this helps and trust me. Once you get into the rpm range...it will transform the boat.
 

Blb2003

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I sure hope you are right. I’m not very impressed at the moment. The prop is a 14.25 I did measure that but no idea on pitch. I’m taking it to get checked on Monday. Do my holeshot rpms seem low? I figured it would turn more than that wot out of the hole. I guess if I’m over propped it may not? Hope I can get the holeshot figured out. Seem to have descent power mid range but the last 1/4 of throttle doesn’t do much but make the engine louder. No rpms build and no more speed.
 

QBhoy

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I’m not sure about the hole shot to be honest. It’s maybe not something that’s too relevant or indicative I think. Lots of thing will affect that. I can’t ever really taking any notice of rpm under acceleration.
if you are at low 4000’s rpms when trimmed out well and full throttle then you defo need to drop 2” for starters.
It such a difficult thing to get totally dialled in but for certain 2” drop would be a starting point I’m certain.
I could bore you to tears with it all and my experiments with props. Can drive a man nuts. I’ve even seen a prop you think initially has too high a pitch at 90% of the rpm range...but if you have a performance hull...it will occasionally allow the boat to lift and air out...then take a considerable gain in rpm, really allowing the engine to sing at its best....but down side is it may be terrible at everything else and in most circumstances.
For a long time I chased the perfect prop...still not there but I’ve now settled for an all round performing laser 2 3 blade. It scores highly in the all round tick box department. Good hole shot...decent economy and cruising with a good top end all be it hitting the limiter if you let it.
Sorry to go on...but worth saying that the enertia I have is ridiculous for top end and cruising. I’m even after another one of a 1” pitch difference. Then I’ll be happy...I think haha.
Ok. I’ve went on enough for one post, haha. Yeahdefo get a prop 2” smaller and you’ll be amazed at the difference. Especially on that lovely engine we both have. They love to be pitched allowing the rpms over 4600 at a minimum and ideally 4800 (where I once read they make their peak power) which should see a good holeshot too.
 

Blb2003

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So here is a head scratcher. Got the prop checked today and it is a Ron Hill Sugnature 14.5x18. So I’m really confused now. On paper this prop should (being a 4blade) give me great holeshot and maybe even a little over recommended rpm? Again I am down 400-600 rpms and sluggish out of the hole. I’m not sure what to try now??
 

Blb2003

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It is actually a progressive pitch prop. Starts at about 16 and goes up to about 21 ish. Would this cause my problems?
 

TunaFish389

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Apr 26, 2018
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What is your running elevation? This is sometimes over looked when comparing like boats.
 

QBhoy

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A 4 blade will usually drop the rpm and affect too emd compared to a good 3 blade. If your drive ratio is a 1.47 I’d be tempted to try out a couple of props from the local dealer. Can’t go wrong with a laser 2 19” to start with. If your ratio is a lesser 1.61 or something then a 21”
 

Blb2003

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I’m planning on trying a 19” 3 blade. I hope I don’t lose even more hloseshot with a 3.
 

QBhoy

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I’m planning on trying a 19” 3 blade. I hope I don’t lose even more hloseshot with a 3.

Mmm. You might to be honest. Sometimes I really wish I could be there with these things. Have you any idea of the drive ratio ? Just so I can compare it to my boat ?
Mine is only 18ft (I’m guessing yours is 20ft maybe) but mine is as heavy as most 20ft boats at nearly 1400 kgs. She has a 5.0 mpi and Alpha 1.47 ratio. Also has an exhaust system and a cam, but genuinely don’t think that does much until up the top of the rpms so the lower rpm and performance should be similar I think.
With a 19” my boat is pretty average at planing. A good mono skier can get up from a deep water start but anything less than a good skier can’t (like me). It will get in the rpm range (4600-5000) no bother when trimmed down...trim up and efficiently and it will then come onto the flat running pad, air out over 60 mph and limit.
Witj a 21” it will be about as sluggish again and will fall at the low end of the rpm range but trim up and it will see mid to late 60’s gps and will occasionally but less frequently hit the limiter.
If your boat has the same gear ratio but with perhaps a larger and less performance orientated hull...perhaps even a 19” is a wee bit too much in most circumstances?
 

Blb2003

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It is a 1.47. I’m reading that a lot of people don’t like the signature props because they are all over the place with performance. Just have to hope you get one that matches what u expect for a prop with those specific numbers and people are having trouble with that. I am ordering a Hustler 14x17 4 blade. Hope it gets me where I need to be. I believe my boat came factory with a 14x19 3 blade. So going to 4 being and 18” average across the fins (progressive pitch). Wouldn’t be enough drop in pitch to go from 3-4. Especially if it’s an underperforming prop.
 

Blb2003

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On the pitch cal. I am at 4% slip. Makes sense with my rpms. Hustler website says not to drop down going from 3-4 and the prop should keep your rpms. Dies anyone have experience with Turning Point Hustler props going from 3-4? Hoping a 17 isant to much of a drop.
 

QBhoy

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On the pitch cal. I am at 4% slip. Makes sense with my rpms. Hustler website says not to drop down going from 3-4 and the prop should keep your rpms. Dies anyone have experience with Turning Point Hustler props going from 3-4? Hoping a 17 isant to much of a drop.

4% is amazing to be fair.
 

Blb2003

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Took the boat out today. With the trim tabs installed and the new 14.5x17 4 turning point prop. Not an apples to apples test as I had 5 adults and 3 kids In the boat and tons of gear. Boat planes way faster and turned 4800 at WOT. Top speed was 52 that’s a gain of over 5. I’d like to test with my normal load but I was impressed with the gains in performance today. Idk if it was the trim tabs or the prop that made the difference but I’m not changing it.
 

Scott06

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Probably the prop pitch given where your rpms are right now , seems to be ideally set up at the moment

a lot lot of folks don’t recommend 4 blades but I’ve found for 90% of how I use my boat it performs better. Only loss of top end suffers which I rarely get to use to its fullest
 
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