When do you know you've got the right prop?

[bestman]

Further to advice gleaned on this forum - I've significantly improved the performance of our 4.8m Ribcraft powered by a Suzuki DF60a by changing props.

With the previous 11 1/2 x 13 prop I got a max speed of circa 25kts and easily hit the limiter at zero trim.

With the 15 - Four up I can get 29kts - and I can now get 32kts one up and trimmed out, and still hit the limiter.

Seems to be performing well but how do you know when you've got the 'perfect prop' is it when you can't hit the limiter?

I can't hit it with zero trim but can when I start trimming, but I guess one might always be able to achieve this, if you get the prop out of the water?

Could I have gone for a 16? Hole shot still seems good.

[Highland Haggis]

Hi bestman your Yamaha F60a has an rpm range of 5000 / 6000 rpm you want to be close to the top of the rev range give rib craft a call and ask for Charlie he will tell you the best prop for your set up HH [emoji106]

[jeffstevens763@g]

If your hitting the limiter you need to pitch up you should have a manufactures recommended max revs which is 6000 rpm on yours I keep mine down to 5750 rpm ish so I'd say from what your getting a 16 pitch will work IMO

[Limecc]

Is the perfect prop a three blade or a four blade?
I'm going for the latter..

According to Solas prop selector a 13x17 four blade is right in the middle for your 60hp, 13.1/4x15 one lower, 13x19 one higher.

Seems to me you have been using 50hp dia props which are 11.x" so you'll be having higher slippage compared to 13.x" which is what they list for the 60, also for the three blade. My DF50 has a 11.5/8x14 as standard so I'm not surprised you hit the limiter.

Having said the above, something might be off with your numbers. 32knots@6000rpm with a 2.27:1 gear ratio? and a 15" pitch calculates at 1.9% slip which seems an unrealistic expectation. I'm new to this though. Your 13" pitch at 25 knots calculates at 11.6% which is expected.

[spartacus]

Running a Solas stainless steel 17 pitch prop on mine. Could have probably settled on 16 pitch, but done now. 15 pitch is a great all rounder, and still have my aluminium prop as a back-up. This is on Tohatsu 60hp tweaked to 70hp.

You need to look at your boat weight with everyone onboard, hole shot and what exactly you want. I'm running with 2-up normally, 75 litres of fuel, a 4hp auxilliary engine, Avon 8 tender folded in a bag and the usual assortment of safety and leisure kit.

Tops out at about 5,200rpm.

[Limecc]

Originally Posted by spartacus

This is on Tohatsu 60hp tweaked to 70hp.

How was this done?

[jeffstevens763@g]

Originally Posted by Limecc

Is the perfect prop a three blade or a four blade?
I'm going for the latter..

According to Solas prop selector a 13x17 four blade is right in the middle for your 60hp, 13.1/4x15 one lower, 13x19 one higher.

Seems to me you have been using 50hp dia props which are 11.x" so you'll be having higher slippage compared to 13.x" which is what they list for the 60, also for the three blade. My DF50 has a 11.5/8x14 as standard so I'm not surprised you hit the limiter.

Having said the above, something might be off with your numbers. 32knots@6000rpm with a 2.27:1 gear ratio? and a 15" pitch calculates at 1.9% slip which seems an unrealistic expectation. I'm new to this though. Your 13" pitch at 25 knots calculates at 11.6% which is expected.

you can do the math but there's so many factors including prop design that the only way is in real time with a few scenarios weight, weather etc to get a good alround prop.

[Pikey Dave]

Originally Posted by jeffstevens763@g

you can do the math but there's so many factors including prop design that the only way is in real time with a few scenarios weight, weather etc to get a good alround prop.

As Jeff says, there’s theory & then there’s real world. The theory is a good starting point (you have to start somewhere [emoji848]). As in most things boating related there will be a compromise somewhere along the line. One man’s perfect prop might be bottom of the list for the next bloke. I usually run 4 blade props, I find they suit heavy RIBs better, they hang on in the rough & offer better grip. The flip side is increased fuel consumption & slightly reduced top end. I prefer to err towards the “underpropped” end of the Rev range, this gives better holeshot, throttle response & puts less stress on the engine. That said, I always max out on the engine capacity.
Ideally try to beg/steal/borrow props to try beforehand.

[jwalker]

I agree with PD, it's all a compromise so finding the perfect prop is subjective. However, from what you say in your post I reckon you've got a good match. One up trimmed right out you hit the limiter, trimmed in you don't. Still only loosing a few knots with four up. Sounds ok to me.

[bestman]

Cheers for all your thoughts Gents,

Rev limiter kicks in at 6300 on my engine.

Suzuki WOT RPM CHART DF 60A 2010~ 5300-6300 2.27

Is idea to get as close to this without exceeding?

Or should I aim for WOT somewhere in the middle of the range?

[Pikey Dave]

Originally Posted by bestman

Cheers for all your thoughts Gents,

Rev limiter kicks in at 6300 on my engine.

Suzuki WOT RPM CHART DF 60A2010~5300-63002.27

Is idea to get as close to this without exceeding?

Or should I aim for WOT somewhere in the middle of the range?

Personally I’d aim to be at the higher end of the WOT range as previously mentioned. I’d be aiming at 6krpm

[Limecc]

Did you make a typo with the diameter or are you happy to run with the undersize prop?

Someone care to explain what the effect would be? If the blade design is the same and the blade area is less you could pull a higher pitch to max revs and go faster?

If it's a light boat maybe the holeshot would be good enough and the strategy would work. In that case why not get a small dia four blade with high pitch and get the best of both worlds? This is my dilemma for my own 'perfect' prop.

[jeffstevens763@g]

IMO as Dave says get it off the limiter around the 6k mark not sure if you're hitting the limiter with 4 up and the 15 pitch personally i would talk to steel developments before buying another prop or propeller EU it might be you need two props for best performance in all scenarios thats what i do running 10 & 11 pitch for my needs having said that top end speed isn't what i'm after.

[bestman]

Hi Limecc,

I'm not sure why you think I've been running undersized props?

My understanding is both the 11 1/2 x 13 and the 11 1/4 x 15 are suitable for my Suzuki DF60A.

Suzuki Propellers DF40,DF40A,DF50,DF50A,DF60A 11 1/2 x 13 in

Suzuki Propellers DF40,DF50,DF60A 11 1/4 x 15 in

I'm trying to figure out if there would be any advantage to going to a 11 1/8 x 16 in which should theoretically bring WOT RPM down by 150-200 so circa 6100RPM?

ATB

Nick

[beamishken]

Originally Posted by bestman

Hi Limecc,

I'm not sure why you think I've been running undersized props?

My understanding is both the 11 1/2 x 13 and the 11 1/4 x 15 are suitable for my Suzuki DF60A.

Suzuki Propellers DF40,DF40A,DF50,DF50A,DF60A 11 1/2 x 13 in

Suzuki Propellers DF40,DF50,DF60A 11 1/4 x 15 in

I'm trying to figure out if there would be any advantage to going to a 11 1/8 x 16 in which should theoretically bring WOT RPM down by 150-200 so circa 6100RPM?

ATB

Nick

I think hes confusing your engine with the 60 suzuki which shares the larger 70hp gearbox I've had the same issue ordering an impeller it came huge & turned out it was for a different year engine which used a larger box

[bestman]

Ah - thanks beamishken.

[Limecc]

Originally Posted by bestman

Hi Limecc,
I'm not sure why you think I've been running undersized props?
Nick

Beamishken is correct I understood the 60 to share the same prop size as a 70 so yours must therefore be a three cylinder not the older four and probably the gear ratio is also different.

My DF50 is running the same size prop as yours but 14" pitch and it came with the engine.

Originally Posted by bestman

I'm trying to figure out if there would be any advantage to going to a 11 1/8 x 16 in which should theoretically bring WOT RPM down by 150-200 so circa 6100RPM?

If you went with a four blade (sorry to keep pushing this )
that also reduces the revs by a pitch. Depends what matters most to you.

[bestman]

Understood - my gearbox is 2.27

Spoke to Charlie at Ribcraft this morning - he suggested there would be benefits, aside from speed, by going up a prop size and bringing down WOT RPM.

He suggested greater efficiency and less wear on the engine.

ATB

Nick

[Limecc]

Originally Posted by jeffstevens763@g

personally i would talk to steel developments before buying another prop or propeller EU

Thanks Jeff
I had a look at that EU site https://www.propeller-shop.com/ and a prop I am interested in is branded 'BS.Pro' which is attractive compared to an alloy Solas because of price. Do you think they have cloned the Rubex or is it worth paying the extra for Solas?

[jeffstevens763@g]

Originally Posted by Limecc

Thanks Jeff
I had a look at that EU site https://www.propeller-shop.com/ and a prop I am interested in is branded 'BS.Pro' which is attractive compared to an alloy Solas because of price. Do you think they have cloned the Rubex or is it worth paying the extra for Solas?

most go for solas, IMO if you know what you need id buy the best as a final prop, a SS prop will give around 5% more but is it worth the price. on my rib i ran an ali 14 x 19 & a 13 1/2 x 21 SS and got the same performance from both on my 90df suzuki for info