340 Prop Size - help

[Jambrin]

I've read all of the threads on switching from 3 to 4 blade props on the 330 / 340 size cruisers. Mine is a '02 340 DA with 6.2 V-drives (year before they switched to the new-style, wider beam 340).

I'm just about convinced to make the switch, however I need to know if my current props are cupped or not. How can I tell? The parts manual lists:

17 X 19 X 1.5 R3BLC NIBRAL
17 X 19 X 1.5 L3BLC NIBRAL

So I get that R/L=Right/Left, 3B=three blade. Does the L = light cup? What does the C mean?

The Michigan Wheel folks are recommending 17x18 4 blade DQX with MEDIUM cup assuming my current props have a medium cup because I am currently hitting 5000 RPM with the stock 3 blades.

The Acme sales engineer recommended a 17x16 4 blade with .075" cup, which seems like way too much of pitch change. It seems Acme does not make a 17x18 4 blade with a 1.5" bore.

 

[CliffA]

The Michigan Wheel folks are recommending 17x18 4 blade DQX with MEDIUM cup assuming my current props have a medium cup because I am currently hitting 5000 RPM with the stock 3 blades.

the WOT engine rpm for your engine is 5,200....I you do switch props make sure you can still hit 5,200 rpm.....anything less than that and your will be 'lugging' your engine and placing too much stress on the engine....anything more than this and you will be over revving your engine...the Sea Ray engineers have done all the work and figured this out for you based on the specs of the boat.....no need to change anything....

just curious why you want to make a prop change....I have the same boat and power package as you and my boat performs well....

cliff

 

[dpmulvey]

The limiter may be your transmissions. Mine redline at 5000 RPM despite the engines redlining at 5200.

Before doing anything that expensive, I would highly recommend Dave Gerr's "Propeller Handbook". It puts a very complex process into laymans terms. I would also call a PropScan or Hale shop in your area and see what they have done for boats like yours.

It worked great for me. YMMV.

 

[Jambrin]

I suspect the RPM would be transmission limited. The SR prop chart for my boat actually lists WOT at 4800 RPM.



I'm looking to increase cruise efficiency, acceleration, and responsiveness while docking, and to decrease noise and vibration. I would like to get the bow down and plane at a lower RPM.

The MW folks are recommending 17x18 (1" less pitch) as they generally say it's needed when going from 3 to 4 blades to maintain the same WOT rpm due to the increased blade area of the 4 blade.

 

[dpmulvey]

How close to the hull is a the prop going to be? There is a formula for it.

Too close and you actually lose efficiency.

 

[Jambrin]

With 17" props there are no worries about hull clearance...the stock props are 17"

MW advised that 15% of the prop diameter is the recommended clearance between the prop and the hull. I measured 11.5" from center of shaft to the hull. An 18" prop would leave 2.5" clearance, which would be below the recommended 15% of 18" = 2.7"

SR did offer this boat with 8.1L engines swinging 18x22 props, so I guess that rule can be bent a little. Or maybe I didn't measure it quite right. I measured from the end of the shaft to the hull.

 

[dpmulvey]

With 17" props there are no worries about hull clearance...the stock props are 17"

MW advised that 15% of the prop diameter is the recommended clearance between the prop and the hull. I measured 11.5" from center of shaft to the hull. An 18" prop would leave 2.5" clearance, which would be below the recommended 15% of 18" = 2.7"

SR did offer this boat with 8.1L engines swinging 18x22 props, so I guess that rule can be bent a little. Or maybe I didn't measure it quite right. I measured from the end of the shaft to the hull.

where on the shaft did you take the measurement?

 

[CliffA]

I suspect the RPM would be transmission limited. The SR prop chart for my boat actually lists WOT at 4800 RPM.

View attachment 41511

I'm looking to increase cruise efficiency, acceleration, and responsiveness while docking, and to decrease noise and vibration. I would like to get the bow down and plane at a lower RPM.

The MW folks are recommending 17x18 (1" less pitch) as they generally say it's needed when going from 3 to 4 blades to maintain the same WOT rpm due to the increased blade area of the 4 blade.

interesting....I can hit 5,000 rpm with each engine using the stock 3 blade props....changing props will be a substantial investment of money....i hope you get enough performance improvement to justify the cost in your mind....please keep us posted on the changes you see after the prop change if you go ahead with it....I boat on an inland lake and 95% of the time we are on slow 'cocktail' cruises....but i have no problem with performance when I want to get on plane......I can cruise comfortably on plane at 25 mph (gps verified) at around 4,200 rpm...and stay on plane down to around 18 mph and 3,800 rpm....i don't know what my actual fuel burn rate is....the Admiral and I can carry-on reasonably normal conversation while cruising so no excessive noise and vibrations noticed....I do think the boat needs larger trim tabs as has been well documented by many other owners.....

good luck...

cliff

 

[srdancer340]

I had the opportunity to go from 3 blade 18x19 to a set of 18x18 DQX props.The advantage will be up and out of the hole with out the use of your tabs. The mid range speed will be about the same however you RPM for that speed will be about 200 RPM less than what you are seeing now. The disadvantage will be that you will loose about 2 mph at the top end. Around the dock 3 blade props will have better maneuverability at slow speeds than the 4 blade, the reason 4 blade props are closer with respect to each individual blade verses 3 blade props.In other word 3 blade props thrust more water in reverse. The only way that you get better mid range and docking advantage is to find a set of 3 blade props that have the same surface area as the 4 blade props that you are interested in. The company that has those props is Acme,however they are very expensive.

 

[Jambrin]

Just FYI, below are my stock 3 blade RPM vs. MPH measurements. I think these line up well with what you are seeing CliffA.

RPM MPH
1400 7
3800 21
4000 23
4200 25
4400 28
5000 32

That is measured with full fuel, full water, 2 people + gear, tabs fully deployed at all speeds.

My main complaints are it seems like the fuel efficiency at 4200 RPM is not very good, and the boat rides bow high even with full tabs. The cruise fuel efficiency seems maybe around 0.8mpg. I think it should be closer to 1mpg. I think she should plane out at 4000 RPM such that I can fully retract the tabs and hopefully pick up some speed...if I could cruise at 25mph@4000 RPM with the bow somewhat down and tabs retracted, I would be happy. With the stock props there does seem to be a lot of prop slip when accelerating to get on plane, and she feels like she is going to fall off plane if you run at anything below 3800 RPM.

I did contact Ron Jacobs at Wolverine Propeller. He seems to be very knowledgeable and is working with ACME to come up with a different recommendation for my boat. I need to re-measure the shaft to hull distances again this weekend, but right now he is thinking larger diameter (18") 3 blade with a larger blade area than the stock props. I think 18" props might be OK because SR did offer 18" props with 8.1L engines as an option on this boat, however I'm not sure if the shaft angle would be the same for the 2 different engine + prop configurations.

I'll let you know how it turns out.

 

[Jambrin]

Just a quick update...I went with 18 x 18 3 blade ACME props per Ron's suggestion. They are shipping out today and I should have them on next week. I will post updated results when I have them.

 

[Fly'n Family]

Just a quick update...I went with 18 x 18 3 blade ACME props per Ron's suggestion. They are shipping out today and I should have them on next week. I will post updated results when I have them.

FWIW.....My 370 was a dog. Didn't get out of the hole worth a hoot, took forever to get on plane etc. etc. I thought I too wanted 4 bladed props. Spoke with a couple of different prop makers including the two you've referenced. Ended up going with Acme and their computed prop suggestion (our lake is 5700' elevation) - which included keeping me with 3 bladed props. They assured me these wheels were the right answer, and backed it up with a return guarantee if not happy. Their props have literally changed my boat, and I don't think it's possible to be any happier with them. Enjoy yours.....

 

[Jimmy Buoy]

I've had Ron Jacobs / Wolverine Propellers do my prop work for the last two boats now. A true professional who really is passionate about props. He said if I were ever wanting to replace my 4 blade Hy Torques, he'd suggest the 3 bladed Acme's. Said in his experience, they will outperform my current props any day of the week. Just not there… yet.

I'm curious to see your results!

 

[dpmulvey]

Just FYI, below are my stock 3 blade RPM vs. MPH measurements. I think these line up well with what you are seeing CliffA.

RPM MPH
1400 7
3800 21
4000 23
4200 25
4400 28
5000 32

That is measured with full fuel, full water, 2 people + gear, tabs fully deployed at all speeds.

My main complaints are it seems like the fuel efficiency at 4200 RPM is not very good, and the boat rides bow high even with full tabs. The cruise fuel efficiency seems maybe around 0.8mpg. I think it should be closer to 1mpg. I think she should plane out at 4000 RPM such that I can fully retract the tabs and hopefully pick up some speed...if I could cruise at 25mph@4000 RPM with the bow somewhat down and tabs retracted, I would be happy. With the stock props there does seem to be a lot of prop slip when accelerating to get on plane, and she feels like she is going to fall off plane if you run at anything below 3800 RPM.

I did contact Ron Jacobs at Wolverine Propeller. He seems to be very knowledgeable and is working with ACME to come up with a different recommendation for my boat. I need to re-measure the shaft to hull distances again this weekend, but right now he is thinking larger diameter (18") 3 blade with a larger blade area than the stock props. I think 18" props might be OK because SR did offer 18" props with 8.1L engines as an option on this boat, however I'm not sure if the shaft angle would be the same for the 2 different engine + prop configurations.

I'll let you know how it turns out.

Something is drastically wrong here. How clean is the bottom? How dinged up are the current props, if at all? What is your tab configuration?

We have basically the same boat. Before I enlarged my tabs and had my props done I was getting 22 KNOTS at 3800 RPM and 34 knots at 5K. Since having the work done, I can cruise at 22 knots all day at 3450RPM. Top speed with a light boat and following tide is close to 38 knots with a so so bottom.

 

[CliffA]

deleted....had mph to knots conversion backwards...
cliff

 

[CliffA]

for what it is worth my boat's performance numbers closely match the numbers posted by the OP....

David, no sure why you boat seems to perform better than our boats even before the trim tab modification.....

cliff

 

[Jambrin]

Something is drastically wrong here. How clean is the bottom? How dinged up are the current props, if at all? What is your tab configuration?

We have basically the same boat. Before I enlarged my tabs and had my props done I was getting 22 KNOTS at 3800 RPM and 34 knots at 5K. Since having the work done, I can cruise at 22 knots all day at 3450RPM. Top speed with a light boat and following tide is close to 38 knots with a so so bottom.

I'm not sure why the big difference here. I got several really good looks at my props when I was down there measuring to make sure the new 18" props would fit. They appear in good shape, however I did notice the R prop had a small ding in 1 of the blades, and lo and behold I do get a little vibration from that side at cruise speeds. The bottom is very clean and in good shape. The bottom paint is only 3 years old, fresh water boat, and I spent several hours last month brushing it with the Shurhold soft bristle deck brush to remove the small layer of green stuff that had grown over the winter. The tabs are stock, which I measured a few months so I can't really remember the size...I think 18" x 12"

It seems I am getting a lot of prop slip. Not sure if you calculate it this way but here is what I came up with. 4K RPM w/2:1 transmission and 19" pitch would equal 38,000"/minute = 0.599747 miles/minute = 35.98 mph, assuming 100% efficiency. I'm measuring 23 mph per gps at 4K RPM. That would be 23/35.98 = 64% efficiency. Not very good! I don't have anything to base this on but I'm hoping the Acmes will get me around 80%, so that 23 mph would go to 27 mph using the same calculation with an 18" pitch and assuming 80% efficiency.

To be blunt, Ron says my stock props just plain suck. They are 17 x 19 L Cup HyTorq MY-T3's. I calculated the DAR on these to be 0.56 (using Michigan Wheel prop catalog/datasheet). The Acme props have a DAR of 0.7. This simply means a whole lot more blade area for the Acmes vs. the HyTorqs, and the blades will also be bigger since I'm going up in diameter. I hope it helps because the cost is definitely high!

FWIW I never felt like my boat performed very well at all. I don't think there is anything wrong with the engines as they run smooth and reach 5K RPM with no issues. It just seems like I burn a ton of gas and get nowhere very fast. I'm the 4th owner and I've only owned her for 2 years now, so no idea how it performed brand new. She only had 200 hrs on her when I got her at 11 years old, so I'm guessing she was never up on plane very much until now.

Brian

 

[Jambrin]

FWIW.....My 370 was a dog. Didn't get out of the hole worth a hoot, took forever to get on plane etc. etc. I thought I too wanted 4 bladed props. Spoke with a couple of different prop makers including the two you've referenced. Ended up going with Acme and their computed prop suggestion (our lake is 5700' elevation) - which included keeping me with 3 bladed props. They assured me these wheels were the right answer, and backed it up with a return guarantee if not happy. Their props have literally changed my boat, and I don't think it's possible to be any happier with them. Enjoy yours.....

Awesome, that is good to hear. I'm getting the same props as you, Acme PNs 1428 - 1429, 3 blade, 18 x 18, .105 cup, 1.5" bore

Brian

 

[04cobra23]

I have an early 03 340 with 8.1's and went from 3 blade to 4 blade michigan wheel DQX. MUCH smoother ride and I picked up a couple MPH at idle. I'll get some specs on RPM/MPH this week. I have 18x22 with med cup.

 

[pcarp]

Hi

I am interested in ordering the same Acme props, can you give me an idea of cost for the pair?

Thanks
Pat