Four Bladed Props

Simon B · 16 June 2004, 13:45

Forumsters,

We have a dive RIB a Delta 5.5 with a 100 hp Yam on its performing poorly Delta have said the engine is a might heavy and our prop is a bit too big. Steel developments said the same and reccomended going for a 13" prop possibly a four blader. Does anyone else run a dive rib like ours or have experience of four bladed props.

Nick Hearne · 16 June 2004, 14:30

Hi I have a similar set up to you 5.75 Osprey Viper with 100ho Johnson (which I have been told is the same engine as the Yamaha)
Whan we first got our boat it was for diving & the prop that came with it was too higher pitch at 13" X 19 pitch it struggled to get up on the plain & would not rev to max RPM with all that weight! So we changed to 13.25" lower pitch (can't remember will have too look it out!) we sold top seed but it was happy with all the kit & divers! I now run on the original prop as I do not get too do any diving these days!

What pitch prop have you at the moment & what seed will she do?
Nick

Simon B · 16 June 2004, 14:36

Nick,

Currently we are running a 17" pitch 3 blader. We have never got anything better than 4500 unless its been dead flat and lightly loaded. With only 2 on board and a flat sea we got 5200. Fuel consumption has beeen horrific you think it was 2 stroke.

Nick Hearne · 16 June 2004, 14:41

I will did out my old prop & check the size tonight & let you know!
What size did Steel D. recommend?
Sorry have just read the above scrap that question!

Nick Hearne · 17 June 2004, 09:23

Simon the size of the prop is 13.75 X 15 it worked for me!
Nick

Simon B · 17 June 2004, 09:33

Nick,

Steel Developments had reccomended the next one down, 13" allowing our motor to in theory rev from 5500 to 6000 in normal sea conditions. Julie was fairly sure about this as well, saying it was a combination of a heavy motor 168kg and us putting a lot of weight in boat. Can you remember your max RPM?

Nick Hearne · 17 June 2004, 10:37

Hi my engine is a 2 stroke so lighter me thing ks! max revs 5500 and we got about 5400 so it did the trick for us!
Steel Developments do know that they are talking about! I can only speak from my experience & if it dose not queer the problem I would have thought that they would exchange it! Worth asking.
Nick

Simon B · 17 June 2004, 10:47

Its starting to compute now, still not to sure if 4 blades are right for us instincts say yes, divers dont need top speed. Well C'xs like it and end up battering the life out of people in heavy kit sitting on poor seats.

I think 4 blades gives better torque and more rapid acceleration up to a slightly lower top speed.

Thoughts please

Nick Hearne · 17 June 2004, 10:54

Yep as far as I know the 4 & 5 bladed props are used for water skiing to get you up & on top of the water quickly.
Nick