F20 WOT 4800rpm Propshift?

[merc200dalarna]

With a simple induction tach I got the reading Idle: 1030rpm
And with fully loaded boat at WOT: 4800rpm

Yamaha F20 2013. Manual start. Long shaft. Tiller.

I think my revs are to low at WOT. It sounds like low rpm's and the tach confirmed it (despite it being a cheap tach, gives a general idea)
The tach was almost steady at 4780rpm's WOT.

Yamaha original propeller "9 1/4 - 12" - 3 blade.

Should I try lowering the pitch 1 or 2 inches?

Is there any benefit for me to try a 4-blade prop at lower pitch?
(Speed is rather low, heavy boat and heavy fishermen onboard, 14 knots on WOT) (~480lbs glass fibre boat, 15ft) (manufacturer claims 19knots w 20hp and 2 persons onboard)

Should I settle for 4800rpm at WOT?

Swedish fisherman.

[boscoe99]

The idle RPM specification is 1050 so your tachometer appears to be correct.

Your WOT RPM is low. Too low. Bad for performance and could be bad for the motor. So no, you should not settle for 4800.

Ruff rule of thumb is for every inch of pitch change the WOT RPM will vary ~ 150/200. I would try the standard propeller in a 9 pitch. I suspect that you will be very pleased with the added performance. Ideally you want the motor to try and run at or near 6000 RPM if and when the throttle is wide open.

[merc200dalarna]

The idle RPM specification is 1050 so your tachometer appears to be correct.

Your WOT RPM is low. Too low. Bad for performance and could be bad for the motor. So no, you should not settle for 4800.

Ruff rule of thumb is for every inch of pitch change the WOT RPM will vary ~ 150/200. I would try the standard propeller in a 9 pitch. I suspect that you will be very pleased with the added performance. Ideally you want the motor to try and run at or near 6000 RPM if and when the throttle is wide open.

Yes, I saw this video after I posted, a Yamaha tech guy explains it very simple: https://www.youtube.com/watch?v=vJr-_aeIgUw
(Even though my engine is only 20hp, I can still see it is designed to reach upper half of WOT-range 5-6000rpm) It has benefits throughout the whole range if the end "WOT" reaches top rpm. And I could almost hear it by ear that my engine wasn't reaching it. Yes, 9.25x9-pitch will probably do the trick. My local dealer with "American auto parts" (imports to Sweden, mostly engineblocks, but also marine blocks and props) sells "Turning Point Propellers", cheaper than solas amita 3, supposedly good propellers? They have 9x9 and 9x10-pitch for yamaha f20, I guess a .25 less diameter won't hurt me much? Or should I go for Solas Amita 3 substitute for original 9.25x9? The turning point did look well engineered...

BTW, I rarely use WOT longer than 12-15 minutes to reach fishing areas (~5km, 3,5mile)

Many thanks as always from across the globe!

[panasonic]

Yes, I saw this video after I posted, a Yamaha tech guy explains it very simple: https://www.youtube.com/watch?v=vJr-_aeIgUw
(Even though my engine is only 20hp, I can still see it is designed to reach upper half of WOT-range 5-6000rpm) It has benefits throughout the whole range if the end "WOT" reaches top rpm. And I could almost hear it by ear that my engine wasn't reaching it. Yes, 9.25x9-pitch will probably do the trick. My local dealer with "American auto parts" (imports to Sweden, mostly engineblocks, but also marine blocks and props) sells "Turning Point Propellers", cheaper than solas amita 3, supposedly good propellers? They have 9x9 and 9x10-pitch for yamaha f20, I guess a .25 less diameter won't hurt me much? Or should I go for Solas Amita 3 substitute for original 9.25x9? The turning point did look well engineered...

BTW, I rarely use WOT longer than 12-15 minutes to reach fishing areas (~5km, 3,5mile)

Many thanks as always from across the globe!

I would try the 9x9 and see what happens. What are you measuring the RPM with?

[merc200dalarna]

I would try the 9x9 and see what happens. What are you measuring the RPM with?

It is a cheap tach/hourmeter, but it gives consistent results.
Idle flutters +-10rpm
WOT flutters +-50 rpm initially, after 10 seconds it flutters +-10 rpm's

I ran for atleast 30 seconds WOT and it remained at 4780rpm.
Decreased throttle and let go of tiller, it stayed at a specific value.
I take into account that the specific value may not be exact.
It points me in the right direction.

Maker of tachometer is "Hardline" I think.

Have you got any experience with "Turning Point Props"??
Are they a serious brand in America?

[boscoe99]

I see that an 8" pitch propeller is also available.

If you have a Yamaha brand propeller made for the F20 and you switch to a different brand/model (particularly with a different diameter) then all bets are off with respect to what the end results may be. There are many many variables other than just pitch and diameter that engine into the propeller selection equation.

Propellers are available from this website. How do they compare pricing wise to what you are seeing in Sweden? Many folks from your side of the pond order from the US to get better prices.

63V-45947-00-00 YAMAHA PROPELLER (3X9-1/4 X

63V-45945-10-00 PROPELLER

[merc200dalarna]

I see that an 8" pitch propeller is also available.

If you have a Yamaha brand propeller made for the F20 and you switch to a different brand/model (particularly with a different diameter) then all bets are off with respect to what the end results may be. There are many many variables other than just pitch and diameter that engine into the propeller selection equation.

Propellers are available from this website. How do they compare pricing wise to what you are seeing in Sweden? Many folks from your side of the pond order from the US to get better prices.

63V-45947-00-00 YAMAHA PROPELLER (3X9-1/4 X

63V-45945-10-00 PROPELLER

Yes, the original are as low as 8 inch pitch, and I do not mind original at all. But the price of Turning Point was attractive, after that comes Solas who are the main "Alternative brand" in Sweden.

Propeller prices are pretty similar, a great drop recently due to internet competition. No benefit due to shipping cost.

On the other hand I do not shy away from aftermarket brands, as long as they have serious reviews from multiple sources. I'm not panicing, I can still fish as is. But I'm going for a new prop with similar top end speed, but at different revs that will improve overall handling, and probably be more benefitial to the engine itself.

EDIT# So mister Boscoe, if YOU were to choose a pitch, as a first try, using yamaha original propeller, based of the data of my revs, you would first try the 8inch pitch? (Calculation ~4800 rpm minus 4 inch, from 12 to 8 pitch, at plus ~200 rpms per inch equals ~5600 rpm's?)

[panasonic]

Can you buy a prop to try and see if they will take it back if it is not right? The shops around here will do that.

[boscoe99]

Yes, I would try an 8" pitch. Either Yamaha, Turning Point or Solas brand. You are so far from being at the desired WOT RPM that the rule of thumb with respect to pitch change does not apply so well as it would if you were close.

See if the seller will let you try it for about an hours time and then return it for an exchange if (assuming no damage or wear and tear) for a 9" pitch if that would be more beneficial. 8 or 9 I think you are going to like what you see. It will make the motor feel more powerful.

[merc200dalarna]

Can you buy a prop to try and see if they will take it back if it is not right? The shops around here will do that.

Yes I've found one propeller spe******t dealer that lets you "try before you buy". He deals with the Solas brand only for lower end engine sizes/aluminium props. Suits me fine, even though correspondance via postage would drag on for some days.

Yes, I would try an 8" pitch. Either Yamaha, Turning Point or Solas brand. You are so far from being at the desired WOT RPM that the rule of thumb with respect to pitch change does not apply so well as it would if you were close.

See if the seller will let you try it for about an hours time and then return it for an exchange if (assuming no damage or wear and tear) for a 9" pitch if that would be more beneficial. 8 or 9 I think you are going to like what you see. It will make the motor feel more powerful.

My own lack of knowledge leads me to believe you are right, 8 pitch will be my starting point. I have no desire to over-rev, I'm not looking to make my boat a racer of any kind. So if it would occur with 8 inch pitch, I would not let it stay. I will ask the genuine yamaha store if they have props on the shelf as they will be checking my valve clearance wednesday. Unfortunately they are specialized in motocross and road bikes, their outboard section is basicly just the service mechanic....

But I still greatly appreciate your input.

[panasonic]

More than likely your engine has a Rev limiter..so you can't over Rev it. Cuts in at 6000-6200 RPM.

I am no expert on this at all...just an educated guess.

Mr. Boscoe will be able to give a definite answer if it does or not.

[boscoe99]

The F20 certainly does have a rev limiter. It starts misfiring cylinders at 6200 RPM to try and protect the engine from an over speed event when the operator is not doing his business.

[merc200dalarna]

More than likely your engine has a Rev limiter..so you can't over Rev it. Cuts in at 6000-6200 RPM.

I am no expert on this at all...just an educated guess.

Mr. Boscoe will be able to give a definite answer if it does or not.

The F20 certainly does have a rev limiter. It starts misfiring cylinders at 6200 RPM to try and protect the engine from an over speed event when the operator is not doing his business.

Just to conclude the thread: I went for the Amita 4 and took a gamble that I would need to go down to 9-pitch. Well, it wasn't perfect, I could probably reach over rev if I had pushed it (my tachometer became unreliable at 5400rpm, started showing strange results, so I went "by ear" after 5400 rpm) But the boat handled like a dream, and boy did the Yamaha F20 feel strong. I reached 15knots with max load.

But in the back of my mind I felt I should try a 10-pitch too, and now I have.
I have nothing but praise for 4-bladed props now (for smaller boats)
19 knots with full load, 2 adults and fishing gear, battery and 6 gallons of fuel.
Now I know how the manufacturer reached the promised speeds.

I had no idea how much I would gain by pairing my workload of my boat with the right propeller. Despite the small engine size and a fiberglass boat, the right propeller is a must.

Many thanks from a very thankful swede.

[boscoe99]

I had no idea how much I would gain by pairing my workload of my boat with the right propeller. Despite the small engine size and a fiberglass boat, the right propeller is a must.

Many thanks from a very thankful swede.

Most folks don't. The propeller is the key to converting horse power to thrust. It can be the weak link in they system if incorrect. As you now know very well.

Thanks for the feed back. Motor on before it gets too cold. Autumn is coming soon over there.