4 blade prop, 5 blade prop? Or stay with 3 blade prop?

Cableguy Greg

Alswagg said:

The newer 4/3 prop sets for B3 are quicker to plane and give better docking experience. I tested on several models from heavy cruisers to 24' runabouts.  All experienced less prop slippage usually around 8 to 9% verses 10 to 12% with a 3/3.   Drop one inch in pitch ie 22 3/3. 21 4/3.  

Since I have 22's, I would have to replace both at 21's, correct?

Glassguy54

I have a 246 Captiva, 350 MAG MPI Mercruiser/ Bravo III duo-prop 24 pitch, 3 blade. Would I benefit from the 4/3 combo as far as hole shot, economy, lower planing speed, etc. etc.? I don't know the gear ratio of my out drive as the sticker has worn away. How can one determine gear ratio?

Handymans342

I talked to a great technician at Prop Tech and he was great. I will post the info

JoeStang

My 276 has the 4x3 Bravo 3 and it's exceeded my expectations for planing speed and fuel mileage. Top speed mid 40s and cruises at 3600rpm around 28mph-30mph. If I broke the current props I might try the Hill marine 4x4 for a little better planing and go down a pitch for a bit better cruising speed. 

Handymans342

Joe, what speed can you maintain plane at? Before and after?

Handymans342

I think I will be going to a 4 blade prop. I have 19 by 23 pitch so I will go to a 19 by 21 pitch.

Michael T

Steve, I've tried lots of 4  and 5 bladed props on Bravo 1s. More blades more lift, more bite, lower rpms needed to stay on plane BUT lower top end (mph). Some five blades can make a boat squirrely at higher rpms. Precision Propeller of Indiana used to make amazing props in off sizes and could custom blue print and modify anything. If they are still in business they would be a great source of info.

Handymans342

Since my boat tops out at 28 MPH it drops out of plane at 25 MPH like all the other 342s. Now if I could keep it on plane at 22 - 25 MPH WOW I could get 5 MPG

minnesota

If I drop 2 inches pitch, would my gas mileage get worse during my cruise mostly at 3500rpm?

Michael T

If your blade diameter stays the same and you drop pitch your propeller will spin faster (higher rpm) which will place you higher or maybe even outside your top of your rpm band - so watch that one. Short answer  - your engine will have to spin faster to equal the same speed of your older prop IF it was propped correctly, therefore, yes,  more gas usage. For example, if you had to stay on plane at 25 mpg and were turning 3200 rpm to do that you would need to turn approx. 3600 rpm if you dropped 2" pitch so, again,  yes you'd burn more gas. Faster hole shot and acceleration probably. On many propellers 1" pitch = 200 rpm change. This becomes more complex when calculating slippage and gas use with duo-prop sets and duo-prop sets with different diameter and/or blade numbers (3 or 4). Help at all?

Handymans342

No help. What if I drop 1 pitch?

Michael T

down 1" pitch - I'd say down 100 rpm -  PER blade - if the diameter and rake stay the same. I'll see if I can find the number for Precision Propeller of Indiana - IF they are still in business & post it if they are. Those guys would change the rake, diameter and/or pitch on SS blades - which is one heck of a task. Best of all they were real neat guys who could tell you exactly what you needed if you could give them the weight of your boat with its make and model, your engine info and your drive gear ratio.

Michael T

ERROR - sorry Steve and colleagues! I misspoke - the propeller shop I have such huge respect for is Precision  Propeller Indiana Inc.  (at least I got that right LOL). Their phone number is 1-317-545-9080.

jme097

Guys - Read through this whole thread. A lot of great info and perspectives. I took a picture of my prop under water and the info on it with my gopro. Is the "20P" mean the pitch is 20? Would I go to a 19 if I wanted to go to a 4x3 or a 4x4 set up?

MarkB

Yes, that is a 20 pitch prop.

jme097

Just wondering if its worth waiting until next season and just swap both of them to a 4 blade rather than just doing one. Would I go to a 19P?

Michael T

jme097, just read your last two posts on this thread. You don't seem to mention why you want to swap your props. Are they not putting you into the correct wot range due to a change in equipment on your boat or a change in the altitude relative to sea level that you are now boating at?  Why the change now?  I assume you are off warranty and not worried that a prop change will negate warranty.

Handymans342

MT the Prop Shop you recommended is no good. they only do Yamaha now. 

jme097

Just looking for what everyone else is...faster planning, lower RPM's, etc. The boat is a 2007 so I doubt any warranty is still valid. 

Handymans342

JME, have you called any Prop shops yet to discuss your setup?

jme097

No not yet. Will definitely consult a professional before forking over $500+. I have seen several references on here about who to call. Any recommendations on who to consult that has good knowledge for Merc?

Handymans342

JME, I had sought out Als advice but he didnt respond. 
Has anyone ever had their props repitched?????

Michael T

Steve, I didn't know that was the advice you were looking for. I had a 23" SS prop re-pitched. It was done by a highly recommended shop. It was a disaster. Eventually I had to reduce the diameter to get it to work. I know others on here have had a good experience but based on my experience and those of a few friends, I would try to sell a prop I didn't like and buy a used one to replace it. I know of friends who have had aluminum props re-pitched with great success but I and two friends with SS props had bad experiences.

Black_Diamond

Repitching would cost more than new I bet. I just had all 4 B3 props tuned and balanced and it was $800. 

You could always PM Al.    j/k

Michael T

@LaRea I too have had SS props blueprinted with great success. I did end-up paying more for an unsuccessful re-pitching of my SS prop than it cost - then I had to have the diameter changed for another $200. Disaster! As well, how the prop was constructed plays a big part. Was it cast in one piece or were the blades welded on to the hub body?

Handymans342

I was told by my Marina tech that Merc props are the best but they dont make what I need any more. They dont even make what I have. So we will try to repitch my blades. The only other alternative is to go to a 4 blade prop. 

Michael T

Steve, you have Bllls? Are there any used for sale in your pitch range?

Handymans342

No, I have B2s. I need to get 300 more RPMS out of my motors. 

Michael T

A lot of Blls were aluminum props. Yours are SS?

Black_Diamond

There ya go. 1" of pitch will get you 200 rpm change.