Correct Prop?

Nickgriff · 19 July 2010, 11:37

Ribtec 535 (2007) Yamaha 80hp (2007)
2 People, 50lts of fuel.

@3000 rpm 13kts
@4000 rpm 20kts

These were the best speeds after playing with the trim.
The top speed is around 35/36knts (@6000rpm I think!!)

The acceleration is mindblowing, but I would rather have a higher speed at a lower RPM. Any suggestions, or is this normal?

Kernow Buoy · 19 July 2010, 11:41

Had a 535 with a mid 90's 90hp Evinrude, fitted a ss 17" which gave a top speed of 40kts, acceleration and pull for wakeboarding was still good.

9D280 · 19 July 2010, 16:04

Inevitable 2 questions:
- What prop is on it at the moment?
- What is the max RPM you get at WOT? (and I guess the speed at WOT would be handy to know)

Nos4r2 · 19 July 2010, 16:13

Quote:

Originally Posted by Nickgriff

Ribtec 535 (2007) Yamaha 80hp (2007)
2 People, 50lts of fuel.

@3000 rpm 13kts
@4000 rpm 20kts

These were the best speeds after playing with the trim.
The top speed is around 35/36knts (@6000rpm I think!!)

The acceleration is mindblowing, but I would rather have a higher speed at a lower RPM. Any suggestions, or is this normal?

'snot normal hitting 6000rpm at WOT. You're underpropped. If 6k rpm is corect, what size prop is on there?

I assume it's a 2 stroke not an F80?

Nickgriff · 19 July 2010, 16:24

Sorry, but I have to ask, what is the meaning of "snot and WOT"?
Cheers

Mollers · 19 July 2010, 16:47

Quote:

Originally Posted by Kernow

Had a 535 with a mid 90's 90hp Evinrude, fitted a ss 17" which gave a top speed of 40kts,

martini · 19 July 2010, 16:53

Lol I think snot is short "it's not"

WOT stands for "wide open throttle" aka balls out; flat sticks etc etc...

Max rpm for a Yamaha F80 is 5000-6000 rpm so your right at the top end of the range there. Every 1" increase in the pitch of your prop should reduce your max rpm by around 200-250. Using your current prop you need to decide how much more pitch you want based on the different weight loads you encounter on the boat.

ie. if you're getting 6000rpm with an empty boat and no fuel then you could increase prop pitch by 4" making your WOT rpm around 5000. But if you then add a tank of fuel & half a dozen divers you may well be down to 3000 rpm and not even getting on the plane. Not to mention the damage to the engine making it work so hard.

The more props you can beg, borrow and steal to try out the better for finding what works best for you, the boat and the motor.

GJ0KYZ · 19 July 2010, 17:19

Martini's right; try as many props as possible - it can make a big difference. I just moved from a Raiker 14.5 x 22 to a four-bladed Cyclone 14 x 21 and there has been an improvement in all areas with no loss of WOT speed or fuel economy. I'll be trying a Cyclone 14 1/8 x 19 this week sometime and I'll let you know how I get on.

Kernow Buoy · 19 July 2010, 18:13

Quote:

Originally Posted by 9D280

Inevitable 2 questions:
- What prop is on it at the moment?
- What is the max RPM you get at WOT? (and I guess the speed at WOT would be handy to know)

Dunno, I sold it.

I think WOT was about 5800, that was the 40 kt mark, at that point I had to look behind me to see Mollers cussing panting and sweating whilst his 150 Opti wheezed up to it's max speed of 39.5 knots, I tend not to mention that very often though.

Kernow Buoy · 19 July 2010, 18:18

Quote:

Originally Posted by Mollers

Just helping a guy out

Your, uh, 250 Etec running OK ?

Mollers · 19 July 2010, 18:24

Quote:

Originally Posted by Kernow

Your, uh, 250 Etec running OK ?

Yes, very well thanks, your XR3i?

Kernow Buoy · 19 July 2010, 18:37

Quote:

Originally Posted by Mollers

Yes, very well thanks, your XR3i?

It's not the 'i' model, real men have carbs.

Nickgriff · 19 July 2010, 20:44

Quote:

Originally Posted by Nickgriff

Ribtec 535 (2007) Yamaha 80hp (2007)
2 People, 50lts of fuel.

@3000 rpm 13kts
@4000 rpm 20kts

These were the best speeds after playing with the trim.
The top speed is around 35/36knts (@6000rpm I think!!)

The acceleration is mindblowing, but I would rather have a higher speed at a lower RPM. Any suggestions, or is this normal?

Ok, just checked the prop, 13.25x17k. Just something to add, this was on a freshwater lake which is where the boat is used. It is an 80hp fourstroke.

Mollers · 19 July 2010, 23:16

Quote:

Originally Posted by Kernow

..... real men have carbs.

Killer carbs.

Kernow Buoy · 20 July 2010, 08:46

That can't be me

I've sold the Red boat.

jyasaki · 20 July 2010, 16:06

Quote:

Originally Posted by Nickgriff

Ok, just checked the prop, 13.25x17k.

Hope it's not 17k... 17" is the correct number.

FWIW, the pitch is usually selected by the WOT rpm. Select a pitch that gives you somewhere near the top end of the manufacturer's suggested max rpm range.

Playing with props differeing slightly from that will give you different mid-range and bottom end performance, but the pitch as selected above should generally remain about the same.

jky

Nos4r2 · 20 July 2010, 18:47

17K suggests a K series prop.

jpn · 21 July 2010, 18:03

selecting the pitch when near maximum/maximum rpm range is obtained...should this be done in calm water with the motor fully trimmed out?