4 Blade Alum B Worth the Performance on 4.3l ?

[tahoejag]

Currently running Mich Wheel 14 1/4 x 21p 3 blade alum. At WOT 48-4900 rpm on gauge, 43 mph (gps). moderately loaded (aprx 700lbs). SX smart tabs installed 60 lb. Recommended max rpm for 4.3l 190 hp is4400 to 4800. By reading these #'s sounds about the ideal set-up..however I am getting aprx 18% prop slip.

I have read thru other posts/threads that I may not even have the hp to go to a 4 blade prop in which I am looking to do.

As everyone recommends....drop 1 to 2" pitch when doing this. I feel that would give me better mid-range cruising and a bit more bite out of hole and LESS prop slip? 14 x 20p 4 blade alum - would it be a noticeable diff or should I drop to a 14 x 19p? I am losing 1/2 dia but gaining one blade. Would such a pitch change put my rpm's in the red? The props in mind are the merc alpha 4; quicksilver black diamond 4 or heard alot about hustler turning point legacy.....what's everyone's opinion....and/or prop suggestions. Thanks!

20.5 ft runabout
4.3l carb 190 hp
alpha I gen II 1:81 ratio

 

[Bifflefan]

Re: 4 Blade Alum B Worth the Performance on 4.3l ?

As a "rule of thumb" drop 1" p when switching from 3 to 4 blades.
I have both and use for different things. The 4 is used most of the time, as I believe it gives better hole shot, mid, and low speed handling. In fact, I don't think I put the 3 blade on at all this year.
I have the Black Diamond 4 blade and love it. It also corrected a proposing issue I had with a 3 blade.
Most (not all) 4 blades come in even p's so its an easy switch.

Remember, there is no law that says you have to run the throttle to the firewall. You can pull it back when running light to keep the RPM's in range.

 

[fishrdan]

Re: 4 Blade Alum B Worth the Performance on 4.3l ?

I have read thru other posts/threads that I may not even have the hp to go to a 4 blade prop in which I am looking to do.

It doesn't matter about HP, I'm running an Alpha4 on a Mercruiser 140HP and it made my boat, a totally different boat. It's all about selecting the "right" prop for "your" boat.

Are you trying to solve anything going to the 4 blade, besides high slip, slow holeshot, doing watersports, top end speed, etc.? How good of condition is the old MW prop, dinged, bent, chunked up??

I wouldn't worry about the 4800-4900WOT RPM as you are just slightly over. Keep the RPM's down to a sane level while cruising around and you'll be fine. Let someone inexperienced drive your boat around and have them hammer the engine to 5K for hours on end, that might cause an issue....

I'm thinking, either the same pitch 4 blade or a higher pitch 3 blade.

 

[tahoejag]

Re: 4 Blade Alum B Worth the Performance on 4.3l ?

It doesn't matter about HP, I'm running an Alpha4 on a Mercruiser 140HP and it made my boat, a totally different boat. It's all about selecting the "right" prop for "your" boat.

Are you trying to solve anything going to the 4 blade, besides high slip, slow holeshot, doing watersports, top end speed, etc.? How good of condition is the old MW prop, dinged, bent, chunked up??

Fishrdan - what made it a "totally diff boat"? Am trying to achieve better mid range cruising. Holeshot is good, I seldom pull a tuber which pulls ok and top end is not important, I get 43/44 mph on gps. I contend with a 8+ mph current often and can feel the boat bog/slow down when going thru the stronger current. Also my cruising rpm is 2800 and falls off plane often. Noticed this year it was up to 3000 (maybe tune-up is in order). My prop looks good (no dings or knicks) the only thing, is ran sand a few times (may be wore down)....feels like the cups are flattened out??? It is a vented prop. I have smart tabs on it as well. The boat is a deep V - runabout 20.5 ft. Just seems that the boat is capable of better...JMO

 

[Rentaltux]

Re: 4 Blade Alum B Worth the Performance on 4.3l ?

I run a 4 blade 21p Hustler and run about 46mph gps at 4400. I have squeaked out 48 in perfect conditions. I generally have 2 adults and 2 small children. Holeshot is good but I have nothing to compare to as this is the only prop I have run. I want to try a 3 blade 21p Hustler to compare..

R

 

[tahoejag]

Re: 4 Blade Alum B Worth the Performance on 4.3l ?

Rentaltux.....I noticed in your signature block...we have same vessel. Curious what your drive ratio is. I have the 1:81. How is that boat for you...any slow/no wake speed wandering?

 

[tahoejag]

Re: 4 Blade Alum B Worth the Performance on 4.3l ?

Updated Post: Installed a 14x20x4 MW Vortex Alum on a 21 ft runabout (purchased prop on Iboat thru a price match for $85). Went on Merc's propeller guide site which recommended this size prop in a 4 blade for my needs. It was an improvement in all areas from a used 14.25 x 3 blade alum which I honestly did not know the actual pitch size (a guesstimate measuring put it at a 19/21p).

RESULTS with the 4 blade....I run at 47/49 mph (gps) at 4800 wot (which is pretty close to the old prop numbers). Average to heavy load (3600lbs total). Awesome hole shot and smooth mid-range cruising speed, min cruising plane speed 15/16 mph at 2800 rpm (before was 19 mph at 3k). Does not blow out in turns (old prop did)...I mean real tite turns! Took all wandering out on no-wake speed totally (I had installed smart tabs previously to correct this issue). Big improvement on docking control. If I would have known the large improvement this 4 blade made I would have went with it a long time ago!

 

[steelespike]

Re: 4 Blade Alum B Worth the Performance on 4.3l ?

I'm a little late for this thread but your results are pretty much exactly what is expected.
You might want to ease off your tabs and see if you can get back to your old speed.I would think you don't need them for hole shot anymore.

 

[tahoejag]

Re: 4 Blade Alum B Worth the Performance on 4.3l ?

steelspike, have been playing around with the tab settings a bit and it does seem to call or run on a lighter setting better rather than a stronger one. just looking for that "happy medium" now because load/weight is always changing and tabs are manual adjustment rather than on-the-fly (elec or hydraulic tabs).

 

[fishrdan]

Re: 4 Blade Alum B Worth the Performance on 4.3l ?

Fishrdan - what made it a "totally diff boat"?

Sorry, didn't see your question until now...

But I think you found out what I was talking about, "making it a totally different boat"