Marine Forum

Switching from 3 to 4 blade propeller

Morris

08 February 2006 10:07:00

Joined: 24 November 2005 14:54:19 | Posts: 7

I want to switch to a four blade aluminum propeller to get more stern lift and slower planning speed and just for the fun of trying something new.

My boat is a 20' I/O with a 190hp 5.0l and VP SX.
Dry weight is 2715lbs. Recommended WOT range is 4400 to 4800 rpm.

Current prop is the stock Michigan Steel aluminum 3 blade 14.25x21, Michigan Part #161004, which runs WOT at 4600 RPM with a full tank of gas and two souls aboard.

Some sources say switching to 4 blade may decrease WOT rpm 50 to 100 rpm. I understand going down in pitch will increase WOT rpm by 150 to 300 rpm. Is dropping from 21 to 19 pitch a one or two pitch drop?

I'm wondering whether I need to go down in pitch or use the same size prop. Also I have not seen a 14.25x21 4-blade, but have seen a 14x21 4-blade. Is this the same?

Any real world experience and specific size or brand recommendations would be very helpful.

Also, what's the deal with these hub kits? Are these better or worse than obtaining a prop with a built-in hub?

Re: Switching from 3 to 4 blade propeller

David

08 February 2006 10:08:17

Joined: 24 November 2005 15:06:23 | Posts: 3

If you have a local prop shop or dealer nearby, see if they will let you test a few. Most of them will allow that. As I learned the hard way, choosing a perfect prop setup is often achieved through trial and error.

Re: Switching from 3 to 4 blade propeller

SeaDog

08 February 2006 10:09:14

Joined: 14 November 2005 14:23:57 | Posts: 11

21 to 19 is a two inch drop.

i'd look at a 14.25 x 20 four blade to start with. Find a shop or dealer who will work with you, because you may need to adjust up or down as needed.

You will lose some top end, but get some mid range speed.

Re: Switching from 3 to 4 blade propeller

Morris

08 February 2006 10:11:19

Joined: 24 November 2005 14:54:19 | Posts: 7

Thanks!

Re: Switching from 3 to 4 blade propeller

DustDevil

08 February 2006 10:13:05

Joined: 17 November 2005 15:34:07 | Posts: 8

I don't think that changing from a 3 blade propeller to a 4-blade propeller is going to give you more stern lift or a slower plaining speed in knots, although you may find a slightly lower plaining speed in engine RPM.

I would try a 20" pitch. I believe even number pitches are common for 4-blade props.

Re: Switching from 3 to 4 blade propeller

Morris

08 February 2006 10:13:47

Joined: 24 November 2005 14:54:19 | Posts: 7

Thanks George. Now I'm thinking I should leave well enough alone.... Sometimes I'm irrationally compelled have to mess with things until they're broken!

Re: Switching from 3 to 4 blade propeller

John

08 February 2006 10:16:46

Joined: 24 November 2005 13:48:22 | Posts: 5

I have the 190hp 4.3 in my deck boat. I run the 4 blade 20 inch aluminum propeller when I am loading it up with more then 6 people (like 8-10) and going out for the day with coolers, food, extra clothes, etc. When it is just me and the family (4 of us) I run the 21 pitch 3 blade. I get 2-3mph more on the top end, (maybe because of the lighter running), but the 4 blade lightly loaded, although within RPM specs, seems like it is over reving at the top end of the RPM range.

I like my 4 blade propeller - it definitely gives a better jump out of the water when loaded down.

I will add that I ran a 19 pitch 3 blade for a while. I had to throttle back at speed to keep it in the RPM range on the top end, but it was a MONSTER out of the hole. Our waterways are a lot of "run for a mile" go through a channel, "run for a mile", go through a channel - as we go from lake to lake. We spend a lot of time getting on plane - and its nice to have a boat that jumps out of the water like the "go fast be louds", instead of feeling like an old man in the passing lane.

Re: Switching from 3 to 4 blade propeller

Morris

08 February 2006 10:17:41

Joined: 24 November 2005 14:54:19 | Posts: 7

Thanks,

I was thinking along the same lines - that the 4 blade prop would be good for a full load of passengers.

Seems it would give the boat a little more umph when heavily laden.

Re: Switching from 3 to 4 blade propeller

Anonymous user

27 August 2006 15:55:55

Joined: Unknown | Posts: Unknown

Check out the "Trailerboats" article on Stingray boats propfest. They tried various 3-blade stainless steel, and two 4-blade aluminum Volvo props. I have the 4.3L fuel injected V6 with 225 HP (which they used in the test). They recommeded the Volvo 4-blade 14.25"x19" prop for best all around ski/speed with load (skier drone and 300 pound boat load plus driver, etc.). I ordered one of these for my 2006 Regal 1900, and will get to try it next week. It was only $161 (including freight!) from Propellers Online web site. Trial and error, however, will ultimately be your best guide. Download the free "prop calc" spreadsheet on-line and also give it a try with your engine, gear ratio, boat weight, etc.

Re: Switching from 3 to 4 blade propeller

Anonymous user

27 August 2006 16:01:11

Joined: Unknown | Posts: Unknown

I've tried several different props for my boat and planing speed is primarily a factor of boat loading and hull design. 4-blade props will definitely get you out of the hole better and provide better mid-range acceleration, however. I pull wakeboards and wakeskates, in addition to slalom skis behind my boat. The slower speed needed for wakeskates becomes a problem in the range of 14 to 17 mph, which happens to be the minimum planing speed for my rig. I even tried a 15.25"x15" pitch prop, but it was too little pitch for mid-range and crusing speeds.

Re: Switching from 3 to 4 blade propeller

Anonymous user

12 February 2007 19:58:54

Joined: Unknown | Posts: Unknown

You may want to give Mark a call at http://www.PropMD.com

He has some sort of propeller exchange that allows you to try some different props.

He got me into a 4 blade on my 21' deck boat and WOW, what a difference. nice guy too...knows his stuff. I checked prices and he definately can't be beat.

Re: Switching from 3 to 4 blade propeller

Anonymous user

30 June 2007 00:25:19

Joined: Unknown | Posts: Unknown

I have a 2006 Regal 1900 with the 225 Hp Volvo SX outdrive. The best prop to use is the Volvo 4-blade Aluminum with a 19" pitch. The Volvo OEM props work best on this outdrive. Read the trailerboats "propfest" article for more info. -Dave

Re: Switching from 3 to 4 blade propeller

Anonymous user

25 July 2007 02:47:26

Joined: Unknown | Posts: Unknown

Hello,
Going from a 3 to a 4 blade will drop your RPM's about 100-150 RPM's, so not as much as a full inch in pitch, which will drop you down about 200 RPM per inch. So if you go from say a 19 to a 21 inch pitch, you will drop ON THE AVERAGE about 400 RPM. If you go to a four blade you can throw another 150ish RPM on top of that. You are dialed in pretty well in terms of WOT. The four will give you better hole shot, faster plane a better hold on plane, which is nice if you ski or have a loaded boat. It will even without either of those. You will also usually get better mileage and less cavitation with a 4 and typically can trim them out a little higher, but you can also expect more bow lift initially, but again, you come up on plane faster and hold it better. Typically the four will give you a sharper turn at speed before it "blows out" and you hit the cavitation spot. Where you lose on a four is top speed. More blades mean more drag in the water at top speed, but how often do you buzz around at WOT. For that couple miles per hour at the top, you should get a wider range of performance so in my opinion piss on the top end unless you have your hand all the way down all the time. If thats the case go with stainless or a three blade. I would also check out Piranha props. They have come a long way. Virtually indestructible hub and you can change pitch and wheel size in minutes. Lighter on the spin so easier on the tranny and also if you smack something the blades go, you replace and your are on your way. Stainless you have a good chance of going in the lower end and repairing that or tossing your bent to crap or broken aluminum. Also less flex so better overall performance. I had a black max on and the Piranha kicked its butt. I love stainless, cuz the shinier things look the cooler, but the Piranha will just about keep up with it and I hate 2K repair bills when you hit that submerged POS.....

Later.

Re: Switching from 3 to 4 blade propeller

Anonymous user

19 October 2011 17:30:35

Joined: Unknown | Posts: Unknown

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