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cyn5351

Sorry, more Prop Questions

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Hello all,

I currently have a 2004 Chaparral 204 with a 5.0l mercruiser alpha. it has the standard  Mercury Quicksilver 14 3/4" x 21" three-blade aluminum prop.

The poor boat is a total d-o-g getting out of the hole. I ma dragging forever and a day....... Top speed is around 45, i don't remember rpm but not maxed out.

I've been researching props and there are so many different opinions which I understand. But I would like to hear from some of you who have switched out. Any feedback would be appreacited

 

I'm thinking stainless steal 4 blade 19 pitch... but going from a 14 pitch to 19? is that too crazy? I've seen comments about Hi Five & Rev 4 and I understand the reverse and top end speed issues. I'm ok with losing some mph but I would like to keep a good reverse because it seems like I don'y use reverse when in a situation I want to get out of rather quickly.

I also would like to get a good price. any suggestions on where to buy online?

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Why would you blame a prop? Positively ?  Proof ?

All other parts replaced ? Igniton  Compression test   Carb opening correct    Choke correct  Bilge full of water    Plug wires fully inserted.

Loads of parts to test / check / replace first

GPS speed & tachometer accurate ?

 

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First, confirm the engine is running correctly. Need to know the WOT RPM's you are seeing, and what your Merc's WOT RPM range is. From that you can pick a lower pitch prop. 14.25 diameter does not change, only the pitch. From my experience, I like  a 19 inch pitch with a 1.62 drive ratio. Generally, you will increase RPM's about 300 to 400 for every 2 inch drop in pitch. The difference in hole-shot will be noticeable. 

brick

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Brick is on it, is it running properly? With the little info we got I'd say drop to a 19p aluminum prop. That will get you 300 more rpm. 

I would lean towards a 4 blade aluminum 18p thou, that will also get you 300 more rpm.

Stainless not worth the doe, IMO. Aluminum 170 vs SS 450.

.

 

 

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Is the bottom clean?

Is the gas fresh?

How many hours on the engine?

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I was discussing props with the old guy at the prop repair shop while trying to get this question answered on my 180 with the 3.0L

We were talking about props when he said he used a 5 bladed prop on his stern drive because it helps with wander and bow steer when in idle zones. Has anyone ever heard of this.

Joe

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5 minutes ago, Guzzi said:

I was discussing props with the old guy at the prop repair shop while trying to get this question answered on my 180 with the 3.0L

We were talking about props when he said he used a 5 bladed prop on his stern drive because it helps with wander and bow steer when in idle zones. Has anyone ever heard of this.

Joe

More blades provide more grip and bow lift. So less likely to bow steer. But more drag, so less top speed.

brick

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2 minutes ago, brick said:

More blades provide more grip and bow lift. So less likely to bow steer. But more drag, so less top speed.

brick

Tks, Makes sense.

Joe

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The only purpose for more blades ?  The engine is so powerful that the prop is loosing traction during WOT accelerations or in turns.

My wandering stopped when I married.  OOPPSS

 

 

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I installed the www.wanderfin.com on the 186 with the 5.0L. It wiped out the wandering during off plane. Removed most of the prop side walking during docking. Removed some of the bow rise on takeoff.

PROBLEM IS IT IS     not    EFFECTIVE ON ALL HP SIZES.  I was lucky at 220 hp.     It DOES straighten the swirling flow off the prop. Makes a huge difference at faster speeds.. The power steering feels very light & easy.

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15 hours ago, Big Fun said:

Is the bottom clean?

Is the gas fresh?

How many hours on the engine?

Yes, yes and 210 hours. The problem has been there from thr start. We bought the boat last summer with 160 hrs. Had it checked by a mechanic then. He said all was well. The boat is heavy to start wkth and Problem seems to be worse with a full tank of gas so my thought was the prop is too small.

I want to say with throttle wide open its running about 3000 rims. Engine seems smooth and runs good but even at full throttle takes a good while to plane

 Once it's planed then I can back off.

 

Sorry for not providing enough info. Relatively new boat owner. I'm female and hubby says it's my boat. So I pretty much do everything and I don't know why whole lot mechanically. But I'm trying to learn.

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Don't confuse pitch with the size of the prop. Pitch is the theoretical distance the prop moves forward for every revolution. Diameter (nominal 14.25 inch for an Alpha drive) stays the same. Lower pitch is like a car in a lower gear. More pitch is like a higher gear. You have more " pull" to get out of the hole with a lower pitch. So it sounds like you need a lower pitch prop, which will improve hole-shot and increase your RPM's.

As you are new to boating, are you using the trim to adjust your boat's attitude when running? It should be fully in (down) when starting from a dead-stop. Trim up a bit as you gain speed. You will feel and hear the sweet spot. 

And welcome to boating. 

brick

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Three things can cause what you are experiencing:

 

1. Over propped- too much pitch for the power to weight ration causing cavitation (prop looses it bite in the water)

2. Over weight (not you) the boat - water trapped in bilge, too much personal stuff, 

3. Excesseive drag caused by fouled bottom or damage prop etc.

 

I have a slightly (10") smaller boat but it only has 200 hp where you have 270 hp.  I run a four blade aluminum 19 in pitch and have no problem with a hole shot, even with a load of people in the boat.  

 

I agree with brick.   Check out your engine first to make sure you are developing enough power.   Then test you speed at WOT and verity that you are reaching max RP<'s which should be around 4800 -5000.  Check you speed with GPS.. I would think that you ought to achieve 50 MPH with the right set up.

 

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