Author Topic: Prop question  (Read 672 times)

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Offline pyro225

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Prop question
« on: September 07, 2017, 11:35:21 AM »
Ok this is a little bit naughty as this isn't for my glastron it's for my regal but hoping you will let it slide and help me ;-) - so it's an 18ft bowrider with a 120 mercruiser diesel.

It came with a 14.25x21p prop and the alpha 1.

Problem:
 
3ppl plus gear or 4ppl no gear get to speed and on the plane no problem although it is a slow process takes me about 30 seconds to get up .

Now if I'm doing a big trip with gear and 6 ppl she just shoves the bow in the air and goes about 12mph flat out.

I bought a vengeance prop 13.75 x21p and still the same problem but it makes just below planing speed flat out now 15mph.

I am not interested in losing a couple of mph top end I just want to be able to cruise on plane.. FYI mechanically she's sound....

I also bought a 19p laser II but think she will over rev...

So now after some serious research I'm thinking of trading all 3 props for a high five but wondered if anyone has any experience with these and if there's a chance it will cure me? Also pitch wise do I stick at 21 or drop?

Thanks!!!


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Offline Plugcheck

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Re: Prop question
« Reply #1 on: September 07, 2017, 11:47:25 AM »
      Certainly I'm  no expert on props, but just to clarify, its a Mercruiser 120hp DIESEL engine?   I would suggest a prop with more stern lift.
Michael
1979 CVZ-18 388 CI Vortec Mouse
1980 CVX-16SS 140 Mercruiser
1979 CVX-16 Johnson 175
2002 Bennington 2275CC 90 Mercury
1985 Intimidator project, gps 85 mph (on trailer)
1989 Lowe 200 Redneck fishin Toon

Offline Diamond Chad

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Re: Prop question
« Reply #2 on: September 07, 2017, 12:22:33 PM »
If it cannot push the boat up on to plane with the 21p at that weight, try the 19p.  That is not such a big step that over rev should be a problem.  If you were saying that you were going to try a 13p, then yes, maybe. 
« Last Edit: September 07, 2017, 01:02:53 PM by Diamond Chad »
87 CVX18 5.7
88 CVX16 115 Merc
57 Dunphy Imperial Musky - 57 Golden Javelin
01 Malibu Sunsetter 21 LSV 340 EFI

Offline pyro225

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Re: Prop question
« Reply #3 on: September 07, 2017, 12:25:42 PM »
It's is indeed a strange combo - take a look at the comparison for reference http://www.popularmechanics.com/adventure/outdoors/a207/1277216/




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Offline pyro225

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Re: Prop question
« Reply #4 on: September 07, 2017, 12:26:35 PM »
Ok diamond chad - would the high five bring much more to the table? If so which pitch?


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Offline dorelse

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Re: Prop question
« Reply #5 on: September 07, 2017, 01:07:49 PM »
Ok diamond chad - would the high five bring much more to the table? If so which pitch?


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None of us have Diesel's...so you're going to have to figure it out, or ask the European guys.
1981 Metric C-512 "Barfly"

Offline pyro225

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Re: Prop question
« Reply #6 on: September 07, 2017, 01:08:58 PM »
fair point - as it has more torque and only a little less power than the 3.0 gas - if we were talking about that would it make any difference ?


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Offline Diamond Chad

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Re: Prop question
« Reply #7 on: September 07, 2017, 01:12:18 PM »
I think a high 5 slips less, and drags more (uses more energy to turn).  I have heard that you drop a step (2 ") in pitch when you go to a 5 blade.  I do not have first hand knowledge.  But if your 21" 3 blade was not spinning out or losing grip while trying to push it onto plane at 12 mph with the nose up, the 19 probably will not either so grip is not the problem, its pitch.
87 CVX18 5.7
88 CVX16 115 Merc
57 Dunphy Imperial Musky - 57 Golden Javelin
01 Malibu Sunsetter 21 LSV 340 EFI

Offline fireman24mn

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Re: Prop question
« Reply #8 on: September 07, 2017, 01:22:22 PM »
I would try something in a 4 blade 20p.
I think this has become an addiction.


1977 CV-23 I/O Being restored
1976 CV-23 Jet
1985 Pearson MotorYacht 43ft

Offline pyro225

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Re: Prop question
« Reply #9 on: September 07, 2017, 04:23:10 PM »
Ok maybe I will try the laser - do i need to cover the vent holes on these boats ?


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Offline Diamond Chad

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Re: Prop question
« Reply #10 on: September 07, 2017, 04:52:02 PM »
Since you already own it, it won't cost you anything to try.  Vent holes help 2 stokes get needed rpm.  I think you plug them on an I/O.
« Last Edit: September 08, 2017, 07:43:18 AM by Diamond Chad »
87 CVX18 5.7
88 CVX16 115 Merc
57 Dunphy Imperial Musky - 57 Golden Javelin
01 Malibu Sunsetter 21 LSV 340 EFI

Offline Hyperacme

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Re: Prop question
« Reply #11 on: September 08, 2017, 09:26:02 AM »
Mercury PVS plugs ...
https://www.youtube.com/watch?v=UvYz9iyfyYE

You can play with this ...
https://www.mercurymarine.com/en/us/propellers/selector/#/step-one

There are so many variable with your boat / motor / weight / loads / weather / water conditions / etc. that the only way to know is testing some props. Even if you find one that works well for a light load, you might need another for heavy loads.
I have a Laser II 22P for speed and keep a spare Aluminum 19P to pull a tube / skier.

" I also bought a 19p laser II but think she will over rev... "

Try it ! 
You'll never know until you do.


 
Gregg
'76 CV16

Offline pyro225

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Re: Prop question
« Reply #12 on: September 11, 2017, 01:58:25 PM »
Ha thanks guys - sorry I know it sounds like I like the sound of my own voice on this but my local dealer rang (I left my number a while ago) and said he has brand new 4 blade alu props clearance event for 50 - if I were to try one they have a 20 or 18 pitch which would be safer to buy if mine was 21 stock? The diameter is slightly less than stock sat well stock 14.25 these are 13.75


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Offline Plugcheck

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Re: Prop question
« Reply #13 on: September 11, 2017, 02:04:42 PM »
    New aluminum props for 50 quid?   I'd jump on that, smaller diameter than your 21p, I'd give the 19 a go.   Easy to get your money back at that price if it doesn't work out.
Michael
1979 CVZ-18 388 CI Vortec Mouse
1980 CVX-16SS 140 Mercruiser
1979 CVX-16 Johnson 175
2002 Bennington 2275CC 90 Mercury
1985 Intimidator project, gps 85 mph (on trailer)
1989 Lowe 200 Redneck fishin Toon

Offline pyro225

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Re: Prop question
« Reply #14 on: September 11, 2017, 02:06:14 PM »
Yep brand new but they are even sizes (which is odd ) maybe why they are cheap only have 20p or 18p which is either side of ideal what do you reckon would be best overall? 18 for less strain and easier plane?


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Offline Plugcheck

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Re: Prop question
« Reply #15 on: September 11, 2017, 02:23:52 PM »
      Well, I'm not an expert, but most every boat has a target WOT(Wide open Throttle) RPM range printed on it, or it can be found somewhere in literature on the product.  Just a guess, maybe 3000 RPM for that Diesel?   Propping down in diameter without changing pitch will change the engine RPM's, how far are they off.   If only a few hundred then the 20 would be a good start, but if 600 rpms or more then I'd opt for the 18.     Someone correct me, but I seem to remember about 200-300 rpms per inch of pitch?  Considering the diameter remains the same.
Michael
1979 CVZ-18 388 CI Vortec Mouse
1980 CVX-16SS 140 Mercruiser
1979 CVX-16 Johnson 175
2002 Bennington 2275CC 90 Mercury
1985 Intimidator project, gps 85 mph (on trailer)
1989 Lowe 200 Redneck fishin Toon

Offline pyro225

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Re: Prop question
« Reply #16 on: September 11, 2017, 03:10:21 PM »
Not to sound like a massive loser but it's a performance turbo diesel :-) 120bhp 1.7 and 4400-4600rpm not far from the 3.0 loaded it's about 500 rpm off unloaded it hits full chat within 30 seconds of wot


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Offline Plugcheck

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Re: Prop question
« Reply #17 on: September 11, 2017, 03:30:04 PM »
    Specs call for a 14.5 diameter in 19 pitch.   Try the 13.75 in a 20p, hard to go wrong for the price.     I still would try the Laser first with the PVS holes covered first and get an idea where your RPM's are.
Michael
1979 CVZ-18 388 CI Vortec Mouse
1980 CVX-16SS 140 Mercruiser
1979 CVX-16 Johnson 175
2002 Bennington 2275CC 90 Mercury
1985 Intimidator project, gps 85 mph (on trailer)
1989 Lowe 200 Redneck fishin Toon

Offline pyro225

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Re: Prop question
« Reply #18 on: September 12, 2017, 08:01:56 AM »
Hmm I rang back and I think I misunderstood its one of these not alu - any experience? http://comprop.com


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Offline dorelse

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Re: Prop question
« Reply #19 on: September 12, 2017, 09:39:58 AM »
Hmm I rang back and I think I misunderstood its one of these not alu - any experience? http://comprop.com


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Yep, that's a composite (Plastic) prop.  I have a couple Piranha props, also composite, and a Gil Six Gun prop as well.

I like the Piranha because they help protect the outdrive by their ability to flex and absorb any hits, while breaking more easily if I hit something serious.  Blades are $19 each to replace and slide into the hub.  I have a 4 blade & 3 blade hub, and run a 23p 3 blade, or a 21p 4 blade.

My Gil Six Gun has 6 smaller blades and I run a 21p on it as well.  I think that prop was $79 and also has individually replaceable blades, though they're out of business now, so blades are hard to find.  My Metric likes this prop a lot more than my CVZ did.

Comprops are essentially molded props that, like it says, are temporary spares to get you home.  I've used the Piranha as my primary prop for years now and have been really happy.  I think I lose about 1-2 mph on the top end over a SS but am on par with a Aluminum prop.

I like them b/c I don't have a lot money in props...and if they break...$19...no big deal.
1981 Metric C-512 "Barfly"