Propeller Performance

Thats interesting Profisher. I run my 250's at 4200 to 4400 at 30 mph. Ive fine tuned my props to get 6000 at WOT with a reasonably full load. I may still have old school thinking in the way I think running at lower rpm is better. Maybe I should bump them up a bit, It would be interesting to see how the fuel consumption differs, factoring in of coarse that Id be getting there sooner.

untitled.jpg

Fill the dam tub!
 
Thats interesting Profisher. I run my 250's at 4200 to 4400 at 30 mph. Ive fine tuned my props to get 6000 at WOT with a reasonably full load. I may still have old school thinking in the way I think running at lower rpm is better. Maybe I should bump them up a bit, It would be interesting to see how the fuel consumption differs, factoring in of coarse that Id be getting there sooner.

untitled.jpg

Fill the dam tub!
 
The Yamaha guys I talked to say as long as I didn't drop more than 300 rpm I was okay, and he also said the motors like to be worked. It's nice to know I can run it harder, but my fuel consumption goes way up.
Just curious 6000rpm would be dead empty of load, fuel, etc ? should we be checking what rpm's we get at WOT when we load up, and what be the rpms when running with a heavy load?

aug201010.jpg
 
The Yamaha guys I talked to say as long as I didn't drop more than 300 rpm I was okay, and he also said the motors like to be worked. It's nice to know I can run it harder, but my fuel consumption goes way up.
Just curious 6000rpm would be dead empty of load, fuel, etc ? should we be checking what rpm's we get at WOT when we load up, and what be the rpms when running with a heavy load?

aug201010.jpg
 
6000 rpms at your normal weight ie, full tank of fuel and loaded as you would run the boat most of the time. In other words don't lighten the boat to get 6000 rpms.
 
6000 rpms at your normal weight ie, full tank of fuel and loaded as you would run the boat most of the time. In other words don't lighten the boat to get 6000 rpms.
 
Another thing that hasn't been factored into this is water conditions. So lets say you normally cruise at 30 mph at 4400. How many days do you have to slow down because 30 mph is to uncomfortable? So lets say your down to 24-25 mph. Where are your rpms at that speed...3700-3800? Now your boat is sitting lower in the water = more drag = more work for the engine and at an rpm which puts it into a definite lugging scenario. With your set up you have less ability to go slower and not work the engine to death. Again not being argumentative, just making sure you have thought of everything that relates to getting honest engine life.
 
Another thing that hasn't been factored into this is water conditions. So lets say you normally cruise at 30 mph at 4400. How many days do you have to slow down because 30 mph is to uncomfortable? So lets say your down to 24-25 mph. Where are your rpms at that speed...3700-3800? Now your boat is sitting lower in the water = more drag = more work for the engine and at an rpm which puts it into a definite lugging scenario. With your set up you have less ability to go slower and not work the engine to death. Again not being argumentative, just making sure you have thought of everything that relates to getting honest engine life.
 
This is interesting. So, my boat, with a usual load,and sea conditions, runs at about 6000 at WOT. For the most part, under the same conditions, I like to cruise at about 4200-4300 rpm. I have a 140 Johnzuki 4 stroke.

Is it safe to say that as far as engine life goes, I should be running at a little bit higher rpm? I agree with IFL, that if this is the case, I might have to go some calculating as far as fuel consumption, considering I'll get there in a shorter amount of run time.

Thanks for the info, everyone, and I must say, it's very interesting.

FishWish
 
This is interesting. So, my boat, with a usual load,and sea conditions, runs at about 6000 at WOT. For the most part, under the same conditions, I like to cruise at about 4200-4300 rpm. I have a 140 Johnzuki 4 stroke.

Is it safe to say that as far as engine life goes, I should be running at a little bit higher rpm? I agree with IFL, that if this is the case, I might have to go some calculating as far as fuel consumption, considering I'll get there in a shorter amount of run time.

Thanks for the info, everyone, and I must say, it's very interesting.

FishWish
 
It doesn’t make any difference what speed or RPM you are cruising at. That doesn’t create lugging the engine.

The engine doesn’t know how fast you are going,water conditions, drag, or anything else... and doesn’t care. It only cares about the maximum RPM and how hard it is working (lugging). Don’t confuse the amount of drag and speed with lugging the engine. You are better off under propping a bit, than over propping. You can actually under prop the boat – just don’t run the engine exceeding the maximum RPM at WOT, unless you want to blow it up. Where over propping will diffidently create a lugging condition, as soon as you put the boat in gear and start moving at any cruising speed - at any RPM.

The boat should be propped based on your factors including, but not limited to, application, conditions, and load at WOT and the size of prop required for two identical boats can be different, based on those conditions. I prop my boats to run in the maximum loaded condition at maximum RPM at WOT. Doing it that way, you will never have a lugging condition. Just need to make sure you never exceed maximum RPM. Fuel conservation, speed, and everthing else should be secondary to engine life!

“Propeller charts are to be used only as a general reference guide. Results will differ, based on various factors including, but not limited to, application, conditions, and load. More accurate information for a particular boat/application may often be obtained from the boat manufacturer. The most effective method to select the proper propeller for a particular boat and customer (based on usage and needs) is to test various propellers directly on that boat.”

Just my two cents!
 
It doesn’t make any difference what speed or RPM you are cruising at. That doesn’t create lugging the engine.

The engine doesn’t know how fast you are going,water conditions, drag, or anything else... and doesn’t care. It only cares about the maximum RPM and how hard it is working (lugging). Don’t confuse the amount of drag and speed with lugging the engine. You are better off under propping a bit, than over propping. You can actually under prop the boat – just don’t run the engine exceeding the maximum RPM at WOT, unless you want to blow it up. Where over propping will diffidently create a lugging condition, as soon as you put the boat in gear and start moving at any cruising speed - at any RPM.

The boat should be propped based on your factors including, but not limited to, application, conditions, and load at WOT and the size of prop required for two identical boats can be different, based on those conditions. I prop my boats to run in the maximum loaded condition at maximum RPM at WOT. Doing it that way, you will never have a lugging condition. Just need to make sure you never exceed maximum RPM. Fuel conservation, speed, and everthing else should be secondary to engine life!

“Propeller charts are to be used only as a general reference guide. Results will differ, based on various factors including, but not limited to, application, conditions, and load. More accurate information for a particular boat/application may often be obtained from the boat manufacturer. The most effective method to select the proper propeller for a particular boat and customer (based on usage and needs) is to test various propellers directly on that boat.”

Just my two cents!
 
Charlie I think you know I agree with under propping slightly so that you can exceed the manufacturers rpms...just never take it up that far. My comment about not being able to go slower and avoid lugging..should have read, going into a more severe lugging condition. I agree the engine will be lugging at all rpms, but will be lugging even more at rpms where more load is added...ie, more hull in the water at plane. Using more trim tab in rough water at slower rpms but still on plane would be a prime example.
 
Charlie I think you know I agree with under propping slightly so that you can exceed the manufacturers rpms...just never take it up that far. My comment about not being able to go slower and avoid lugging..should have read, going into a more severe lugging condition. I agree the engine will be lugging at all rpms, but will be lugging even more at rpms where more load is added...ie, more hull in the water at plane. Using more trim tab in rough water at slower rpms but still on plane would be a prime example.
 
Back from hunting.
Totally right on Charlie, over proping definitely more dicey than under proping. It's to bad these outboard companies did not have more historical data with some of these variables, other than mechanics opinions, but I guess if I get 200hrs less engine life due to over proping, running to much load, running 4400rpm rather than 4600rpm, and also the west coast guys running in following seas with big swells, all the time.The outboard companies get there next sale quicker.
If I run in rougher water, trim tabs are fully engaged, which reduces my speed and I still run at 4100+
The other question is because Charlie brought it up, don't sacrifice longevity for any thing, I.E fuel savings, speed ECT. There are so many variables surrounding engine life, with hard data on some variables but none on a lot of others, water conditions,prop pitch, load in boat, service intervals,and others.All these things, if you change 1 it affects the others.
I know guys have talked about it, what would be the engine life of a 4 stroke EFI optimal condition?, which few of us fall into.
I know I'm over propped but under the conditions I run in I'm fairly positive I am causing no harm to my engine. You can hear your engine work, and you can feel it with how your engine responds with throttle input. I pretty sure I will run this motor out of hours and I keep an accurate log book so only time will tell.


aug201010.jpg
 
What make are you running?
 
Yami and Merc used to be the same powerheads on some models, thought that ended some years ago.
 
You must log in or register to reply here.

Similar threads

B
DFO SPORTVISION 2008-2012
Replies
4
Views
1K
SIR
S
Back
Top