dropping a prop size, how much difference will it make?

[Pikey Dave]

I have a 9 1/4 x 12" prop on my DF20 on the Volaire. It's perfect with just 2 of us & I hit 6K rpm at WOT. However with 4 up & some fishing/ picnic gear on board, it struggles to get up on the plane, although it does get there eventually. We're heading down to Portugal soon & there will be 4 of us on the boat, so I'm looking to downsize the prop, the question is, how far should I go? I'm pretty au fait with propping bigger engines, but not down at 20hp-SIB level. Dropping 1" off a 12" prop is a much bigger drop percentage wise than dropping 1" off a 23" prop. Will dropping from a 12" to 11" make an appreciable difference or do I need to go down to 10", or is this too much?

Any input from the SIB gurus would be much appreciated.

Also does anyone have a 11" x9 1/4 Suzuki 10 spline prop for sale?

[jeffstevens763@g]

I run or have run three props on my 25 10/14 x 10,11,12 roughly on my 365m boat I got

22 knots from the 12 but sluggish WOT
22 knots on the 11 much better hole shot and recovery after hitting decent waves.
19/20 knots from the 10 but very good in the rough and recovering quickly.
Never hit the limiter on any the 11 ran at 5800 now you know I’m moderately slim Dave carry a lot of fuel and kit boat weight 100kg I think if you drop a pitch you will get better performance.
Just to add on the excel I get 18 knots out of the 10 WOT.

[Fenlander]

When I bought my new DF 20 the other year the dealer told me it was coming with a 12 inch Pitch which I refused. I asked him for a 10 as I guesstimated that would be right but he must’ve had an 11 hanging about because he refused to supply any alternative other than the 11. After I’d run the engine in I soon realised the 11 inch was still too much and I bought myself a 10 inch which was perfect. That was for my Aerotech with two adults and an eight stone teen plus dog 25 L of fuel and extra kit.

[Steve509926]

Hi Dave, I dropped an 1" on my Merc 15hp efi last year:-

9.25x9, WOT, RPM 5725, 15.6 knots.
9.25x8, WOT, RPM 6160, 16.2 knots and popped up on the plane noticeably quicker.

[Pikey Dave]

Originally Posted by Fenlander

When I bought my new DF 20 the other year the dealer told me it was coming with a 12 inch Pitch which I refused. I asked him for a 10 as I guesstimated that would be right but he must’ve had an 11 hanging about because he refused to supply any alternative other than the 11. After I’d run the engine in I soon realised the 11 inch was still too much and I bought myself a 10 inch which was perfect. That was for my Aerotech with two adults and an eight stone teen plus dog 25 L of fuel and extra kit.

Thanks for the info David, do you want to sell your 11”?

[chipko]

Also found a 10” pitch prop best suited the Suzi 20 for our use on various 3.5/3.8 sibs. Admittedly propped ideally for towing, would easily bounce off the limiter one up at a solid 21 knots, and give decent hole shot three/light four up.

We’ve also found 10” pitch works best for us on our current Mariner 20 efi.

[Fenlander]

You would have been very welcome PD but like the DF20A the prop is long gone.

[Pikey Dave]

Looking like the general consensus is a 10”.
Next question, I can get an after market one for around £45, a genuine Suzuki one is closer to £150[emoji15]. A Steel Developments (Solas?) one is £114.
Anyone have any experience/thoughts? Is the OEM one worth the 3x cost of the after market one?

[Wazzajnr]

If you're not 100% sure, you could buy 11 and 10 for 90 quid, sell the one you don't need for 30 quid and if it only lasts one season it's not the end of the world then you can buy a better quality one when you're sure it's right.

[Fenlander]

The only comment I'd make is that across brands, and considering budget aftermarket in particular, you can't rely on the pitch accuracy translating across. In my experience close to 2" error in some cases.

[jeffstevens763@g]

Originally Posted by Pikey Dave

Looking like the general consensus is a 10”.
Next question, I can get an after market one for around £45, a genuine Suzuki one is closer to £150[emoji15]. A Steel Developments (Solas?) one is £114.
Anyone have any experience/thoughts? Is the OEM one worth the 3x cost of the after market one?

I bought a cheep one from I think SSI £60 been ok for me Dave

[Pikey Dave]

Originally Posted by jeffstevens763@g

I bought a cheep one from I think SSI £60 been ok for me Dave

Yeah it’s SSI that has the aftermarket ones at £45, it’s worth a punt.

[Steve509926]

I bought an aftermarket one (Sodial on ebay) and it worked for me.

[jeffstevens763@g]

Originally Posted by Pikey Dave

Yeah it’s SSI that has the aftermarket ones at £45, it’s worth a punt.

End of the day if it works you can spend on a better one and keep the cheap one as a spare

[Pikey Dave]

Originally Posted by jeffstevens763@g

End of the day if it works you can spend on a better one and keep the cheap one as a spare

Yup, just ordered one from SSI, £49 inc delivery.

[Fenlander]

I have to admit to being shocked at the rise in prices for OE Suzuki props.... about 25% up since I bought mine around 2018. Yamaha OE props of a similar size are still available nearer the £110 mark... and much better made.

Re the aftermarkets despite my comments their pitch sizes might not be accurate I've bought a couple of Polastorm brand from these guys...

https://www.specialistsmallcraft.co....pellers/suzuki

They were a little out on their results vs stated pitch but better cast and finished than Suzuki OE. And as said above at a sub £50 cost being a third that of an OE probably worth going for one (or similar) and if it works out you're well in.... and if you need a second to refine the performance still in on the deal overall compared to OE.

[jeffstevens763@g]

Originally Posted by Fenlander

I have to admit to being shocked at the rise in prices for OE Suzuki props.... about 25% up since I bought mine around 2018. Yamaha OE props of a similar size are still available nearer the £110 mark... and much better made.

Re the aftermarkets despite my comments their pitch sizes might not be accurate I've bought a couple of Polastorm brand from these guys...

https://www.specialistsmallcraft.co....pellers/suzuki

They were a little out on their results vs stated pitch but better cast and finished than Suzuki OE. And as said above at a sub £50 cost being a third that of an OE probably worth going for one (or similar) and if it works out you're well in.... and if you need a second to refine the performance still in on the deal overall compared to OE.

Ali/titanium mix is interesting 33% stronger

[A1an]

Originally Posted by Pikey Dave

We're heading down to Portugal soon & there will be 4 of us on the boat

and I thought coming across the channel in a sib was hardy!

[Pikey Dave]

Originally Posted by A1an

and I thought coming across the channel in a sib was hardy!

Yes but….never mind…..[emoji23]