4-blade vs. 3-blade / Pros & Cons

4-blade vs. 3-blade / Pros & Cons

Joined: October 17th, 2008, 6:09 am

January 27th, 2009, 5:47 am #1

Greetings all.

I'm wondering what advantages I would realize if I change from the 3 blade original props on my 31' Express w/327Q's to 4 blade props. My planned use for the boat would be slow putting around, cruising on plane, and very seldom I'll crack the throttles forward to the stops.

It seems like I could get a faster plane, and better mid-range throttle response. I would hope to get better economy at cruise, and better slow speed handling (docking).

Also:

Brass? Bronze? Nibral? Stainless? With my speedboats, I was always told stainless props performed better than aluminium props as they don't flex / bend.

All input / advice is appreciated.

Thanks in advance.

Kevin Bray
'06 CC Launch 22
'69 31' Commander Express
Quote
Like
Share

Joined: December 21st, 2006, 1:10 am

January 27th, 2009, 1:10 pm #2

ALL inboard props are either bronze or nibral. A 4 blade MAY help a little, but the cost of replacing those expensive props will probably never be recouped. The first step is to determine how your existing props perform.

You will gain more benefit for the money by making sure your engines are in top notch condition and dialed in properly..carbs are calibrated properly, and distributors are advancing correctly.
Quote
Like
Share

Bill Millar
Bill Millar

January 27th, 2009, 1:47 pm #3

Greetings all.

I'm wondering what advantages I would realize if I change from the 3 blade original props on my 31' Express w/327Q's to 4 blade props. My planned use for the boat would be slow putting around, cruising on plane, and very seldom I'll crack the throttles forward to the stops.

It seems like I could get a faster plane, and better mid-range throttle response. I would hope to get better economy at cruise, and better slow speed handling (docking).

Also:

Brass? Bronze? Nibral? Stainless? With my speedboats, I was always told stainless props performed better than aluminium props as they don't flex / bend.

All input / advice is appreciated.

Thanks in advance.

Kevin Bray
'06 CC Launch 22
'69 31' Commander Express
Kevin, I swapped out a pair of Michigan Dyna jet 3 blade for a pair of Michigan DQX 4 blade wheels. The first thing I noticed was the change of harmonics. The boat ran so much quieter, and smoother at speed. I did not loose any top end, and I gained a little mid range efficiency. These nibral wheels are not cheep. I keep all my wheels tuned to the highest standard, so the most noticeble difference for me between a tuned 3 blade to a tuned 4 blade was the lower harmonic noise level with the 4 blade wheels. I am running 22 X 24 nibral 4 blade DQX tuned by Acutec propeller of North Hampton N. H. The boat is a 1977 30 Hunt Sportsman, set up for off shore fishing, with a pair of 300 Cummins diesels. I run the boat off shore 20 to 60 miles so the lower noise is worth the cost for me.
Quote
Share

Joined: October 17th, 2008, 6:09 am

January 27th, 2009, 2:29 pm #4

Bill,

Hmmm. I hadn't really given thought to noise / vibration advantages. Interesting. Less noise / vibrations in my mind equates to less wear to the entire drive train, or for that matter, the entire boat.

From what I've researched about the 31' Express, it seems that a properly tuned boat will cruise around ~ 20mph (+/-) and I'm looking to maximize my fuel economy.

The cost of fuel this past summer just about put me off buying this boat. While crude oil has come way down from the summer prices, it will surely head back up again. A previous post makes a good point regarding the recouping of the cost for new props, but in the long run, (long run meaning years of use) with expensive gasoline, improving economy, even slightly, is a goal I hope to achieve.
Quote
Like
Share

Paul
Paul

January 27th, 2009, 7:02 pm #5

Hi Kevin, Welcome Aboard!

I made the switch from 3 to 4 blade on my 38 Express, and unfortunately I didn't do my homework very well. I went from a 23 x 25 3-blade to a 23 x 24 4-blade, when I should have gone to a 23 x 23 4-blade. As a result I'm overpropped, and I plan on having them repitched next time the boat is out.








The photos above show the props when installed, and they sure look good! They actually perform well, but they will need to go back for a repitch someday in the near future.



(ABOVE): TRADITION at speed, Cumberland River, November 29, 2008, photo by Reece Ewton, aboard FANDANGO.

What I noticed, however, is the boat will get onto a plane at lower rpm, probably a function of overpropping more than the number of blades. This is really a non issue, however, as nobody in their right mind is doing "hole shots" in a cruiser, waaaaaaaaaay too much stress on the equipment. I use my boat for moderate cruising and many times we're down in the 1200 to 1500 rpm range for cocktail cruising. At 2900 RPM the 427 is developing max torque so they really don't mind all that much, but I am not able to get the RPM up to the rated 4000, again another signal I'm overpropped. The rule is to drop two inches of pitch if you go from 3 to 4, and even then, better check with your prop manufacturer about your particular boat and prop style. And yes, they ARE expensive. Top end "normally" will suffer from a good 3-blade to moving to a 4-blade, simply because there is more prop surface and therefore more friction to rob power. There are other factors, but seldom if ever do you see higher speeds with more blades. Thats why most all the racing hydros use a two blade.

I think they run smoother and they pull better at docking speeds. That's not to say you can't dock like a pro with 3-blades!

Regards,

Paul
forum moderator

TRADITION
FXA-38-3004-R
1966 38 Express
Original big dog power


Quote
Share

Greg42sf
Greg42sf

January 27th, 2009, 11:25 pm #6

Greetings all.

I'm wondering what advantages I would realize if I change from the 3 blade original props on my 31' Express w/327Q's to 4 blade props. My planned use for the boat would be slow putting around, cruising on plane, and very seldom I'll crack the throttles forward to the stops.

It seems like I could get a faster plane, and better mid-range throttle response. I would hope to get better economy at cruise, and better slow speed handling (docking).

Also:

Brass? Bronze? Nibral? Stainless? With my speedboats, I was always told stainless props performed better than aluminium props as they don't flex / bend.

All input / advice is appreciated.

Thanks in advance.

Kevin Bray
'06 CC Launch 22
'69 31' Commander Express
I would take your existing props to a prop shop that has computer diognostics. It is normally more expensive but they can make sure that the props are perfect in pitch, flare, and blade matching. I recentyl sent mine out and they confidently boast that i will gain 2 nots in speed and fuel efficenty. 4 blade props from what I know ( i have them) they run smoother, but i have not been able to notice any difference in efficency at the pump or in performance.
Quote
Share

Joined: October 17th, 2008, 6:09 am

January 28th, 2009, 3:40 am #7

Hi Kevin, Welcome Aboard!

I made the switch from 3 to 4 blade on my 38 Express, and unfortunately I didn't do my homework very well. I went from a 23 x 25 3-blade to a 23 x 24 4-blade, when I should have gone to a 23 x 23 4-blade. As a result I'm overpropped, and I plan on having them repitched next time the boat is out.








The photos above show the props when installed, and they sure look good! They actually perform well, but they will need to go back for a repitch someday in the near future.



(ABOVE): TRADITION at speed, Cumberland River, November 29, 2008, photo by Reece Ewton, aboard FANDANGO.

What I noticed, however, is the boat will get onto a plane at lower rpm, probably a function of overpropping more than the number of blades. This is really a non issue, however, as nobody in their right mind is doing "hole shots" in a cruiser, waaaaaaaaaay too much stress on the equipment. I use my boat for moderate cruising and many times we're down in the 1200 to 1500 rpm range for cocktail cruising. At 2900 RPM the 427 is developing max torque so they really don't mind all that much, but I am not able to get the RPM up to the rated 4000, again another signal I'm overpropped. The rule is to drop two inches of pitch if you go from 3 to 4, and even then, better check with your prop manufacturer about your particular boat and prop style. And yes, they ARE expensive. Top end "normally" will suffer from a good 3-blade to moving to a 4-blade, simply because there is more prop surface and therefore more friction to rob power. There are other factors, but seldom if ever do you see higher speeds with more blades. Thats why most all the racing hydros use a two blade.

I think they run smoother and they pull better at docking speeds. That's not to say you can't dock like a pro with 3-blades!

Regards,

Paul
forum moderator

TRADITION
FXA-38-3004-R
1966 38 Express
Original big dog power

Thanks Paul. FWIW, what I mean by hole-shot is powering up and getting on plane in a reasonable, but shortest (efficient) amount of time. I've got a speedy runabout for going fast in a hurry if need be.

I frankly don't have any idea how good or bad the bottom gear is on this boat. I've talked to the previous owner, but he's pretty chill-axed and cocktail cruising at ~1400 is mostly all he ever did. I've also talked to the mechanic he's had working on the boat the past 5 years, as well as the yacht service outfit that lifted the boat and did the bottom job. All say the old boat is real solid, etc. We'll see.

I like the idea of running smoother, especially on older equipment like this. I imagine that when it's time for it's next bottom job, I'll go through the expense of making sure all of the shafts / props / bearings / etc. are dress-right-dress and in proper condition.

Kevin Bray
'06 CC Launch 22
'69 31' Commander Express
Quote
Like
Share

Reece
Reece

January 28th, 2009, 4:28 am #8

Kevin, I swapped out a pair of Michigan Dyna jet 3 blade for a pair of Michigan DQX 4 blade wheels. The first thing I noticed was the change of harmonics. The boat ran so much quieter, and smoother at speed. I did not loose any top end, and I gained a little mid range efficiency. These nibral wheels are not cheep. I keep all my wheels tuned to the highest standard, so the most noticeble difference for me between a tuned 3 blade to a tuned 4 blade was the lower harmonic noise level with the 4 blade wheels. I am running 22 X 24 nibral 4 blade DQX tuned by Acutec propeller of North Hampton N. H. The boat is a 1977 30 Hunt Sportsman, set up for off shore fishing, with a pair of 300 Cummins diesels. I run the boat off shore 20 to 60 miles so the lower noise is worth the cost for me.
I called a Michigan Wheel deasler asnd they told me i needed a 22x25 blade for the 36 SF. They said that going to 4 blade would give better mid throttle performance while giving up some top end.


i currently have 22x26 bronze 3 blades, so it seems like you go down a pitch for the 4 blade. This is what the dealer told me.


RE
Quote
Share

Reece
Reece

January 28th, 2009, 4:30 am #9

I would take your existing props to a prop shop that has computer diognostics. It is normally more expensive but they can make sure that the props are perfect in pitch, flare, and blade matching. I recentyl sent mine out and they confidently boast that i will gain 2 nots in speed and fuel efficenty. 4 blade props from what I know ( i have them) they run smoother, but i have not been able to notice any difference in efficency at the pump or in performance.
I just had my 22x26s tuned and it made a BIG difference. I had a blade out of whack and now its perfect. It weas ~800 including shiooing. A lot less than $3400 for new nibrals.

Quote
Share

Paul
Paul

January 28th, 2009, 6:39 am #10

Curious where this was done, I have two pair needing attention. I need to start with the old 3 blades, will probably run those most of 2009.

Also need to do an alignment on the starboard side. More fun in the bilge. They don't fix themselves! Then Im still looking for the perfect prop for that Gallatin Marina breakfast boat too!

Regards,

Paul
Quote
Share