Merc 15 efi - Merc 20 efi Performance Difference.

[jeffstevens763@g]

If you have the money according to steel developments you can get 5% more out of a stainless prop for me the Sib hull doesn’t lend its self to fine tuning. Reading chipcos post my Mercury 365 hd with my engine topped out at 22knots with the 11 inch prop dropping to 20 knots with the 10 inch prop all this is in perfect conditions but not on the same days kind of agrees

[Steve509926]

I'd agree with "a SIB hull doesn't lend itself to fine tuning" at the end of the day I'm not trying to emulate Roflhat in a sausage keel SIB.
I've noticed on a lot of pictures I've seen recently 4 bladed props, why? What's the advantage/disadvantage?

[Pikey Dave]

Originally Posted by Steve509926

I'd agree with "a SIB hull doesn't lend itself to fine tuning" at the end of the day I'm not trying to emulate Roflhat in a sausage keel SIB.
I've noticed on a lot of pictures I've seen recently 4 bladed props, why? What's the advantage/disadvantage?

I’m a big fan of 4 blade props on RIBs.
+ more grip, lower planing speeds, better holeshot.

- increased fuel consumption, initial cost, slightly lower top speed.

For me, it’s the equivalent of putting all terrain tyres on a 4x4.

[Steve509926]

Originally Posted by Pikey Dave

I’m a big fan of 4 blade props on RIBs.
+ more grip, lower planing speeds, better holeshot.

- increased fuel consumption, initial cost, slightly lower top speed.

For me, it’s the equivalent of putting all terrain tyres on a 4x4.

So would you say a 4 blade prop would be good for a choppy / rougher sea with a heavier load ie: camping gear? and choosing a 4 blade prop, is it the same 9.25 x 10 but 4 blades?

[jeffstevens763@g]

https://www.boats.net/blog/3-blade-v...ade-propellers

Bit of info

[Steve509926]

Thanks Jeff

[chipko]

Whilst I’m well aware of the advantages of 4 blade props, why complicate the matter on super lightweight sibs with portable size motors…up to 25hp. Heavy boat hydrodynamics not applicable methinks.

After years of use with numerous sibs, run latterly with a couple of current 20 horse efi motors, stock 3 blade props run just fine. Not yet found any 3.5 to 3.8m sib (or even our little 3.4 rib) which doesn’t perform with OEM 3 blade 10 or 11” pitch props.

A moderately loaded sib certainly doesn’t need the extra lift provided from a 4 blade or benefit from any extra mid range grip so why lose some top end performance. The merits of any extra surface area from a 4 blade is just wasted imho.

Each to their own I suppose.

[Steve509926]

Originally Posted by chipko

Whilst I’m well aware of the advantages of 4 blade props, why complicate the matter on super lightweight sibs with portable size motors…up to 25hp. Heavy boat hydrodynamics not applicable methinks.

After years of use with numerous sibs, run latterly with a couple of current 20 horse efi motors, stock 3 blade props run just fine. Not yet found any 3.5 to 3.8m sib (or even our little 3.4 rib) which doesn’t perform with OEM 3 blade 10 or 11” pitch props.

A moderately loaded sib certainly doesn’t need the extra lift provided from a 4 blade or benefit from any extra mid range grip so why lose some top end performance. The merits of any extra surface area from a 4 blade is just wasted imho.

Each to their own I suppose.

The reason for the question was to gain knowledge rather than anything else chipko, as I didn't know what benefit could be gained by a 4 blade.