Time to change prop I reckon

[Vinny31]

We’ve had our 6m XS since February and on the few occasions I’ve got to use it full throttle I’ve noticed it’s not reaching the recommended rev range.

We’re running an optimax 150 of 2006 vintage and it’s pulling roughly 5200 flat out, seemingly we should be pulling between 5250 and 5750 and ideally I’d like to be towards the higher end of this as we usually run lightly loaded.

It’s currently running the prop seen below, any guidance or recommendations with regards to a replacement? I’m not so bothered about top speed, throttle response and ‘grunt’ would be preferable.

Thanks

[Iron Dials]

Are you trimming out to achieve WOT?

If it’s any use to you...
We have XS650 and Merc 150 4Stroke with 19in prop.
Trimmed out we get 42 kts at 5300rpm- boat feels a little light when trimmed out and fast though.
Recently changed from aluminum to stainless prop. Top speed pretty much the same but new prop makes boat much livelier above 20kts.
I’d still like more bite in rough weather so may try 17in 4 blade.

[spartacus]

Mercury Vengeance stainless steel propellers seem to to get a good write up, and importantly are available in 17 and 18" pitches. Normally drop down a pitch to increase hole-shot and grunt which theoretically will add another 200 rpm per pitch decrease to your current 5200 WOT.

Can you borrow a propeller to test first?

[Last Tango]

The 150 Optimax and Mercury's F150 have different gear ratios that equate to about an inch difference in prop pitch.
The Optimax's max revs are listed as 5000 > 5600 rpm
ref RPM/Gear Ratio Reference Chart

I think you can get Laser II with even number pitches. 18" ?

[Jeff]

Originally Posted by Last Tango

The 150 Optimax and Mercury's F150 have different gear ratios that equate to about an inch difference in prop pitch.
The Optimax's max revs are listed as 5000 > 5600 rpm
ref RPM/Gear Ratio Reference Chart

I think you can get Laser II with even number pitches. 18" ?

I think the even pitch laser props are for the small gearcase.. not the V6 optis. Vinny,,, its a shame you aren't nearer.. I have a 17" revolution 4 which I had tweaked to 18" ,,, now surplus. Wouldn't raise revs but would definitely give you more grip and whoosh [emoji6] Are you sure the engine isn't a hole too low... revs seem down for a 19" 3 blade on a 6m.

[Last Tango]

Originally Posted by Last Tango

The 150 Optimax and Mercury's F150 have different gear ratios that equate to about an inch difference in prop pitch.

Sorry.. This is wrong, they're both more or less the same.

[Pikey Dave]

Originally Posted by Jeff

I think the even pitch laser props are for the small gearcase.. not the V6 optis. Vinny,,, its a shame you aren't nearer.. I have a 17" revolution 4 which I had tweaked to 18" ,,, now surplus. Wouldn't raise revs but would definitely give you more grip and whoosh [emoji6] Are you sure the engine isn't a hole too low... revs seem down for a 19" 3 blade on a 6m.

The Rev4 prop is the best prop I've had on a rib, not the fastest or most fuel efficient, but it don't half grip.

[Vinny31]

Originally Posted by Iron Dials

Are you trimming out to achieve WOT?

If it’s any use to you...
We have XS650 and Merc 150 4Stroke with 19in prop.
Trimmed out we get 42 kts at 5300rpm- boat feels a little light when trimmed out and fast though.
Recently changed from aluminum to stainless prop. Top speed pretty much the same but new prop makes boat much livelier above 20kts.
I’d still like more bite in rough weather so may try 17in 4 blade.

I’m trimming out until she starts to get a bit ‘lively’ , which I presume is chine walking.

[Vinny31]

Originally Posted by Jeff

I think the even pitch laser props are for the small gearcase.. not the V6 optis. Vinny,,, its a shame you aren't nearer.. I have a 17" revolution 4 which I had tweaked to 18" ,,, now surplus. Wouldn't raise revs but would definitely give you more grip and whoosh [emoji6] Are you sure the engine isn't a hole too low... revs seem down for a 19" 3 blade on a 6m.

I’ll grab a pic of the keel and cavitation plate for opinions, if it was an option I’d be happy to cover p&p costs for a trial?

First things first though will see about engine height [emoji106]

[Vinny31]

Originally Posted by spartacus

Mercury Vengeance stainless steel propellers seem to to get a good write up, and importantly are available in 17 and 18" pitches. Normally drop down a pitch to increase hole-shot and grunt which theoretically will add another 200 rpm per pitch decrease to your current 5200 WOT.



Can you borrow a propeller to test first?

No sure borrowing will be an option but would be the ideal scenario. [emoji106]

[Vinny31]

Originally Posted by Last Tango

The 150 Optimax and Mercury's F150 have different gear ratios that equate to about an inch difference in prop pitch.

The Optimax's max revs are listed as 5000 > 5600 rpm

ref RPM/Gear Ratio Reference Chart



I think you can get Laser II with even number pitches. 18" ?

If I was getting into the 5500-5600 region I’d be happy enough tbh. Seems I have a few things to check first though.
Thanks

[Jeff]

Originally Posted by Vinny31

If I was getting into the 5500-5600 region I’d be happy enough tbh. Seems I have a few things to check first though.
Thanks

My quite heavy 6m cobra with 150 Opti was right at the upper end on a 19p laser so I'm almost sure you can tweak it by checking the engine height....

[Last Tango]

I'm running a 19" Tempest on my Merc F150 6.5mtr Coastline and that's revving to 5650rpm at 44kn. (Trimmed right out and getting "twichy") and the hole shot is very impressive.....absolutely no hint of "grip" issues)

Had a Vengence on my previous engine and changed it to a Laser II. The Laser was better.

[phantom 19]

You can get your current Laser2 worked to reduce the pitch, I had a 20” Laser2 worked down to an 18” for my Humber years ago.

[Vinny31]

Originally Posted by phantom 19

You can get your current Laser2 worked to reduce the pitch, I had a 20” Laser2 worked down to an 18” for my Humber years ago.

That’s food for thought, I’m going to have a look at engine height first and try to determine if it needs raised.
Thanks

[Vinny31]

Apologies for the picture quality, would have needed four hands to hold straight edge and camera etc.

From what I can see the ‘cavitation’ plate directly above the prop is iro half an inch above the bottom of the keel.

From what I’ve read I could probably raise the engine one hole and see how that affects things.
Advice/ opinions appreciated.

[Jeff]

Yep ,,, one hole up should be fine. [emoji106]

[Vinny31]

Originally Posted by Jeff

Yep ,,, one hole up should be fine. [emoji106]

Thanks Jeff

[Jeff]

,,, and then you need a Rev 4 [emoji6][emoji106]

[Pikey Dave]

Originally Posted by Jeff

,,, and then you need a Rev 4 [emoji6][emoji106]

Oh yes!