4 blade to 5 blade & pitch drop?

250Gimp

250Gimp

Petty Officer 2nd Class
Joined
Jul 13, 2007
Messages
145
Hi all

I am hoping you can help me make some decisions about prop choice.

Current specs:

2006 Maxum 1800 SR3
Mercruiser 4.3l MPI, 220hp
Alpha 1 Gen II, 1:81 gear ratio
Mercury Bravo 1 prop, 48-831912 24P, 4 blade stainless (I don't know what all the numbers mean except the 24 pitch)
Max RPM = 4450 rpm @ 52 mph (on boat speedo)

The problem is it is slow out of the hole when pulling up a slalom skier, and the skier gets dragged a bit before coming out. I also have a lot of bow rise, even when not towing someone.

I have smart tabs, but have not installed them yet.

I have done some diggin on the net, and it sounds like going to a 5 blade lower pitch prop may help.

I saw a recomendation for a High 5, 21p for my boat/engine combo.

My question is, does this make sense for what I am trying to obtain? I don't mind loosing a few mph if the hole shot is improved a fair bit.

I have found a 23p High 5 used in my area, and am wondering if that will give me enough oomph just dropping 1" in pitch?

Thanks a lot for the help!
 
90stingray

90stingray

Lieutenant Junior Grade
Joined
Oct 26, 2010
Messages
1,162
Re: 4 blade to 5 blade & pitch drop?

I would install the trim tabs before deciding on a prop. But the 24p does seem a little tall for that boat. The 21 would do you well but you may over rev on the topend.
 
250Gimp

250Gimp

Petty Officer 2nd Class
Joined
Jul 13, 2007
Messages
145
Re: 4 blade to 5 blade & pitch drop?

Thanks for the info 90stingray!

I have the tabs on.... Now to wait for the weekend to try them out!

Anyone else have any thoughts?

I have been in touch with someone with my same boat, but the carb 4.3, and he uses a 21p without any over rev problems.

Is the 220hp MPI going to be much difference from the carb version?

Thanks
 
Tail_Gunner

Tail_Gunner

Admiral
Joined
Jan 13, 2006
Messages
6,237
Re: 4 blade to 5 blade & pitch drop?

250Gimp said:
Hi all

I am hoping you can help me make some decisions about prop choice.

Current specs:

2006 Maxum 1800 SR3
Mercruiser 4.3l MPI, 220hp
Alpha 1 Gen II, 1:81 gear ratio
Mercury Bravo 1 prop, 48-831912 24P, 4 blade stainless (I don't know what all the numbers mean except the 24 pitch)
Max RPM = 4450 rpm @ 52 mph (on boat speedo)

The problem is it is slow out of the hole when pulling up a slalom skier, and the skier gets dragged a bit before coming out. I also have a lot of bow rise, even when not towing someone.

I have smart tabs, but have not installed them yet.

I have done some diggin on the net, and it sounds like going to a 5 blade lower pitch prop may help.

I saw a recomendation for a High 5, 21p for my boat/engine combo.

My question is, does this make sense for what I am trying to obtain? I don't mind loosing a few mph if the hole shot is improved a fair bit.

I have found a 23p High 5 used in my area, and am wondering if that will give me enough oomph just dropping 1" in pitch?

Thanks a lot for the help!
Click to expand...


Your over propped....That 4500 is that with a empty boat or with people on board?
 
250Gimp

250Gimp

Petty Officer 2nd Class
Joined
Jul 13, 2007
Messages
145
Re: 4 blade to 5 blade & pitch drop?

Hey Tail Gunner

I know I am over propped. That rpm is with a lightish load, but 3/4 tank of fuel.

I am curious if I dropping to a 21p High 5 will make me way over rev, or if I will be at ~4800rpm, where I want to be for skiing.

Thanks
 
Tail_Gunner

Tail_Gunner

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Joined
Jan 13, 2006
Messages
6,237
Re: 4 blade to 5 blade & pitch drop?

I havnt played with a high five so dunno..Sorry but a 21p Solas titan should allow you to pull arms right out of there sockets.....Thats really the way to go...Your really running a 24p 4 blade ss at 4500 rpm and its a bravo???
 
J

jkust

Rear Admiral
Joined
Aug 2, 2008
Messages
4,942
Re: 4 blade to 5 blade & pitch drop?

Also, pretty sure the 4.3 mpi doesn't have the 1:81 ratio. The 1.81 is for the Carb version. The MPI actually does make a respectable difference over the carb 4.3.
 
250Gimp

250Gimp

Petty Officer 2nd Class
Joined
Jul 13, 2007
Messages
145
Re: 4 blade to 5 blade & pitch drop?

Hey Tail Gunner.

Alpha 1 gen 2 drive, and the boat came to me with a Bravo 1 4 blade prop on it, exactly as noted in my original post. Acording to the original owner, the 4 blade was recomended and installed by the dealer that sold the boat to him. Once on plane she goes pretty good, but only pulling about 4500 rpm @ 52mph on the speedo.

jkust, the drive is stamped 1:81 for the ratio. What ratio were you thinking it would be? I don't imagine the difference between the carb & MPI would be enough to jstify a different drive ratio, more likely just a pitch change.
 
J

jkust

Rear Admiral
Joined
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Messages
4,942
Re: 4 blade to 5 blade & pitch drop?

250Gimp;3310233 jkust said:
I've never seen a 4.3 mpi with anything but the 1.62 ratio. This is the first I've even heard of a 1.81 on that engine. Just searching a bit I see where the 1:81 is listed as the high altitude option for the MPI 4.3 for what it is worth.
Click to expand...
 
Tail_Gunner

Tail_Gunner

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Joined
Jan 13, 2006
Messages
6,237
Re: 4 blade to 5 blade & pitch drop?

All your numbers seem to make sense...If it were my boat a Stilletto baypro 2 in a 22p would be the answer
 
250Gimp

250Gimp

Petty Officer 2nd Class
Joined
Jul 13, 2007
Messages
145
Re: 4 blade to 5 blade & pitch drop?

Hey Gunner....why the Stilletto vs. the high 5?

jkust, this is my first IO, so I don't have experience with other drives.

Thanks
 
Tail_Gunner

Tail_Gunner

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Joined
Jan 13, 2006
Messages
6,237
Re: 4 blade to 5 blade & pitch drop?

Money and benefit as well performance...The Baypro just does a better job in all aspects..And thats a opinion
 
250Gimp

250Gimp

Petty Officer 2nd Class
Joined
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Messages
145
Re: 4 blade to 5 blade & pitch drop?

Thanks Gunner

I'll look into the Baypro.

Cheers
 
SparkieBoat

SparkieBoat

Captain
Joined
Aug 17, 2009
Messages
3,643
Re: 4 blade to 5 blade & pitch drop?

trim tabs should solve your problem..but dropping 1-2 pitchs will keep you RPMs ok at WOT and boost your hole shot. you will most likely lose 2 or 3 MPH
 
S

sschefer

Rear Admiral
Joined
Nov 13, 2008
Messages
4,530
Re: 4 blade to 5 blade & pitch drop?

Tail_Gunner said:
All your numbers seem to make sense...If it were my boat a Stilletto baypro 2 in a 22p would be the answer
Click to expand...
Sounds like the right choice to me also. Plenty of stern lift with the Bay Pro.
 
250Gimp

250Gimp

Petty Officer 2nd Class
Joined
Jul 13, 2007
Messages
145
Re: 4 blade to 5 blade & pitch drop?

Thanks Sparkie & sscheffer!

I think I will keep looking for a used 21 or 22p high five.

If I can test a 4 blade in that range I will, but my main thing I am after is towing, so I think teh High 5 will give me the best bite!

Cheers
 
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