Recommendation for 50 HP 4 cycle Out Board Motor

[dive4it]

I have the Evinrude 50hp 4 stroke fuel injected on my and so far love it. Quiet as can be and barely sips the fuel. At 4000 rpm, I do a solid 20.5 mph. That's with a brand new 4 blade 10 pitch....wish I would have gone with the 4 blade 8 pitch as 4500 rpm is all I can get out of it.

I would reprop that puppy before you do some engine damage. I don't know for fact what the WOT range is supposed to be, but this web site says it should be 5900-6500 rpm. 4k rpm is way under, and not good for the engine, as it's essentially lugging.

http://www.marineengine.com/parts/prop/wot_prop.html

A more authoritative source would be better, of course. Something like the user's manual, or a shop manual. But 4k sounds awfully slow by any measure.

I very much agree. When I purchased the boat, it came with a 11 3/8 X 14 pitch prop. It was pretty damaged and chewn up so I knew that I would not get a good RPM reading from it. I called my local marine supply shop and he "did some research" for my boat size and engine....recommending a 13 pitch three blade....needless to say I wasn't very confident with his choice but had him order it anyway. After three weeks of waiting for it to come in, I got impatient and bought one off an internet marine suply place....4 blade 10 pitch. This is what I installed thinking that it would give more low end pull and since they are not race boats, I didn't really get concerned about the additional drag. Now that I've tested it and see the RPM, I wish I would have gone with the 8 pitch with should get me closer to 5500 RPM. It doesn't apear that anyone on this forum has the same motor combo that I do so it's sort of hit and miss for me.

JT

[Seapup]

It doesn't apear that anyone on this forum has the same motor combo that I do so it's sort of hit and miss for me.

JT, I am 99% sure your evinrude is a rebadged suzuki DF50. Evinrude/Johnson sold the suzukis for a few years under their name during their crossover years.

[dive4it]

It doesn't apear that anyone on this forum has the same motor combo that I do so it's sort of hit and miss for me.

JT, I am 99% sure your evinrude is a rebadged suzuki DF50. Evinrude/Johnson sold the suzukis for a few years under their name during their crossover years.

That is very correct. It is a Suzuki powerhead unit with an Evinrude name. I ordered some spare stuff for it the other day at the Evinrude dealer and they confirmed that it is indeed a Suzuki made unit for Evinrude.

JT

[Tomfoolery]

My Honda BF50 has the same prop speed at max engine speed (2.08:1, 6000 rpm engine, 2885 rpm prop) as your Evinrude (2.27:1, 6500 rpm engine, 2863 rpm prop). Most folks with the same Honda, sailing the , use an 11.75" dia. x 10" pitch three-blade OEM prop, or a 11.8" dia. x 9" pitch 4-blade Solas. I would imagine yours, being the same boat and having the same prop speed at max engine speed, would use something similar, though there can be small differences in props (like cupping).

I have a new 4-blade Solas, but I can't report on the performance since the boat isn't in the water yet.

[dive4it]

My Honda BF50 has the same prop speed at max engine speed (2.08:1, 6000 rpm engine, 2885 rpm prop) as your Evinrude (2.27:1, 6500 rpm engine, 2863 rpm prop). Most folks with the same Honda, sailing the , use an 11.75" dia. x 10" pitch three-blade OEM prop, or a 11.8" dia. x 9" pitch 4-blade Solas. I would imagine yours, being the same boat and having the same prop speed at max engine speed, would use something similar, though there can be small differences in props (like cupping).

I have a new 4-blade Solas, but I can't report on the performance since the boat isn't in the water yet.

That's intersting news, I decided on the ten pitch because of what I read on this forum on the Hondas. I do realize that you guys have larger diameter props and that has a lot of effect on it. There is a 9 and an 8 pitch available in the same blade that I purchased so I'll probably go with an 8. I just called the supplier and they don't take returns after they've been installed (understandable). No problem, I'll have plenty of spares now with the 3 and the 4 blade. They're not optimum but it'll sure get me back to the ramp if needed.

JT

[dive4it]

your either reading this speed off of a pitot tube type speedo or your running a 90hp motor with 50 decals on your doing 20knts , as it's physically impossible for 50hp to push your boat 20.5mph.

It might partly be because of the fact that it's not a blue hull?

[Tomfoolery]

I do realize that you guys have larger diameter props and that has a lot of effect on it. There is a 9 and an 8 pitch available in the same blade that I purchased so I'll probably go with an 8.

I believe your prop(s) are the same diameter as the Hondas. That's why I compared prop speed to prop speed. That's not a sure thing, of course, but I would expect similar performance on the same boat, under the same conditions (no ballast, mast up, three people on board), with the same size prop with the same pitch turning at the same speed. If you're not, it might be worth it to look into the engine a bit. You're a long way off of max engine speed.

I just called the supplier and they don't take returns after they've been installed (understandable). No problem, I'll have plenty of spares now with the 3 and the 4 blade. They're not optimum but it'll sure get me back to the ramp if needed.

You might want to put one of them up for sale here. If it's brand new, you should be able to get at least half your money back. ebay is another option.

[dive4it]

I do realize that you guys have larger diameter props and that has a lot of effect on it. There is a 9 and an 8 pitch available in the same blade that I purchased so I'll probably go with an 8.

I believe your prop(s) are the same diameter as the Hondas. That's why I compared prop speed to prop speed. That's not a sure thing, of course, but I would expect similar performance on the same boat, under the same conditions (no ballast, mast up, three people on board), with the same size prop with the same pitch turning at the same speed. If you're not, it might be worth it to look into the engine a bit. You're a long way off of max engine speed.

I think by the speed that it's producing, the engine is running strong as an ox. I'm a little hesitant to change a thing since I'm getting a true 20 mph out of her. I checked again and it's giving me closer to 4600 rpm at WOT....like I said, the last 1/4 throttle didn't gain any more RPM so I know it's lugging. I'm under the understanding that for each pitch you get aprox 300 rpm increase and the difference between a 3 and 4 blade of same rating is aprox 1 1/2 pitch difference with same pitch marking. Having said all of this, the tach on it is a nissan/tahatsu (probably from the origional motor). I might install a tinytach temporarily to see if it's completely accurate.

JT

[Tomfoolery]

Yeah, the tack could be off, the properties of the prop may not be the same - a lot of variables. Looks like you're on the right track, though. I wish my with its BF50 went that fast. I've maxed it out at 16 mph with no ballast, 3 men, and the mast up. Mine has bottom paint, and a fair bit of slime at the time I measured it with a gps. For what that's worth.

[DaveB]

Last weekend I put on a new Solas 11.8 x 9 four blade. It made a singing winding noise between 1900 rpms and 2600 rpms. My boat has 3 batteries, 3 anchors, 65 quart Refig./Freezer, 18 gals water, 12 gal. fuel, 425lbs persons and a lot of other gear. No bottom paint. Top end was 16.4 mph @5800 rpms.1ft. waves,no current.
My other Prop was a 11.8 x 11 pitch 4 blade, full throttle got 14.5 mph @4800 rpms. Reason I put on the 11 pitch is to cruise at 6mph @2400 rpms. New prop. takes 2700 rpms to do 6 mph.
95% of time I do 6mph but with new prop. at 7.2 mph at 3100 rpms the motor sounds good and not loud.
I haven't done a fuel test yet but the engine doesn't work as hard with the 9 pitch.
The higher rpms means more HP ,why I got almost 2 mph faster. The winding noise I will live with as I will be doing 2800-3100 rpms cruiseing were there is no singing or 1800 rpms were I still move 4.8 mph.
Dave

My Honda BF50 has the same prop speed at max engine speed (2.08:1, 6000 rpm engine, 2885 rpm prop) as your Evinrude (2.27:1, 6500 rpm engine, 2863 rpm prop). Most folks with the same Honda, sailing the , use an 11.75" dia. x 10" pitch three-blade OEM prop, or a 11.8" dia. x 9" pitch 4-blade Solas. I would imagine yours, being the same boat and having the same prop speed at max engine speed, would use something similar, though there can be small differences in props (like cupping).

I have a new 4-blade Solas, but I can't report on the performance since the boat isn't in the water yet.

That's intersting news, I decided on the ten pitch because of what I read on this forum on the Hondas. I do realize that you guys have larger diameter props and that has a lot of effect on it. There is a 9 and an 8 pitch available in the same blade that I purchased so I'll probably go with an 8. I just called the supplier and they don't take returns after they've been installed (understandable). No problem, I'll have plenty of spares now with the 3 and the 4 blade. They're not optimum but it'll sure get me back to the ramp if needed.

JT

[rwmiller56]

Last weekend I put on a new Solas 11.8 x 9 four blade. It made a singing winding noise between 1900 rpms and 2600 rpms. My boat has 3 batteries, 3 anchors, 65 quart Refig./Freezer, 18 gals water, 12 gal. fuel, 425lbs persons and a lot of other gear. No bottom paint. Top end was 16.4 mph @5800 rpms.1ft. waves,no current.
My other Prop was a 11.8 x 11 pitch 4 blade, full throttle got 14.5 mph @4800 rpms. Reason I put on the 11 pitch is to cruise at 6mph @2400 rpms. New prop. takes 2700 rpms to do 6 mph.
95% of time I do 6mph but with new prop. at 7.2 mph at 3100 rpms the motor sounds good and not loud.
I haven't done a fuel test yet but the engine doesn't work as hard with the 9 pitch.
The higher rpms means more HP ,why I got almost 2 mph faster. The winding noise I will live with as I will be doing 2800-3100 rpms cruiseing were there is no singing or 1800 rpms were I still move 4.8 mph.
Dave

Dave,
I run a 3 blade 12 1/4 x 10 prop. I get about the same speed as you, maybe 1 MPH slower, at WOT 6300 rpm. What would be the advantage of going to a 4 blade prop? My fuel consumption is about 3.5 nm/gal at speeds over 10 kts. The motor is a 50 HP 4S Johnson/Evinrude.

Roger

[DaveB]

Rodger,
The general rule is if useing a 4 blade prop. you go with 1 inch less prop., the 4 blade has a better grip and less cavatation. It also gets out of the hole faster.
I have tried at least 5 diffrent props. on my boat with small diffrences. Your 12 1/4 diamiter prop. would not fit on a BF 50 (would fit but cause cavitation) max. is 11.8.
I am surprised you get 6300 rpms on your size prop. but that could mean you have no cup in blades and they are narrow.
Also how much weight do you have aboard.
With other prop. I was getting 9mpg @ 5.5 kts. Wide open 3-4 mpg. @14.5 mph.
With a 90 hp Suzuki cruiseing at 22 mph I would guess useing 3 mpg.
Why the Suzuki 90 makes sence if one was to cruise fast. Victor or others that have installed the 90 hp would have more detail fuel consumption.
Dave

Dave,
I run a 3 blade 12 1/4 x 10 prop. I get about the same speed as you, maybe 1 MPH slower, at WOT 6300 rpm. What would be the advantage of going to a 4 blade prop? My fuel consumption is about 3.5 nm/gal at speeds over 10 kts. The motor is a 50 HP 4S Johnson/Evinrude.

Roger[/quote]

[rwmiller56]

Rodger,
The general rule is if useing a 4 blade prop. you go with 1 inch less prop., the 4 blade has a better grip and less cavatation. It also gets out of the hole faster.
I have tried at least 5 diffrent props. on my boat with small diffrences. Your 12 1/4 diamiter prop. would not fit on a BF 50 (would fit but cause cavitation) max. is 11.8.
I am surprised you get 6300 rpms on your size prop. but that could mean you have no cup in blades and they are narrow.
Also how much weight do you have aboard.
With other prop. I was getting 9mpg @ 5.5 kts. Wide open 3-4 mpg. @14.5 mph.
With a 90 hp Suzuki cruiseing at 22 mph I would guess useing 3 mpg.
Why the Suzuki 90 makes sence if one was to cruise fast. Victor or others that have installed the 90 hp would have more detail fuel consumption.
Dave

[/quote]

Dave,
Thanks for the reply. My previous prop was an 11 3/4 x 9. It had alot of cavitation damage from the PO. I replaced it with a 12 1/4 by 9, but different manufacturer (Michigan Match). It was turning too fast RPMs, way above max, so I went with the next larger size Michigan 12 1/4 x 10, and it seems to be dialed in nicely for the RPMs. So I think you are right, the shape of the cups are different.

I've only noticed about a maximum of 200 RPM decrease when I add weight to the boat (gear & people) for a long cruise, or if I am fighting a heavy current.

I'd like to try a 4 blade prop, if it gets better bite. It gets pretty snotty at times here on SFO Bay, and I would like to get better bite from the prop when coming off a wave.

Do you mean 1 inch less prop diameter for a 4 blade? Or less pitch?
Thanks,
Roger

[DaveB]

1 inch less pitch for a 4 blade.
Dave

Do you mean 1 inch less prop diameter for a 4 blade? Or less pitch?
Thanks,
Roger[/quote]