3 or 4 bladed prop?

thorsby · 28 October 2011, 10:40

Im running a 6.5 chasecraft with a df140 on the back. Currently using a stainnless 3 bladed prop. It is a bit slow onto the plane but also revs high at top end. My question is, obviously i need a different prop but would there be any advantage of say a four bladed prop?

Cheers

Nathan k · 28 October 2011, 10:51

4 bladed prop would mean faster plane speed, also it can decrease your fuel consumption at cruising speed? i'm not 100% if that's correct though

jambo · 28 October 2011, 10:56

Yes u will get up quicker. But more blades equals more fuel at top end. I changed down from a high five to a basic 3 for that reason. A four would be a compromise.
J

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Bushrider · 28 October 2011, 13:21

Hi ,
I tried on my 18ft aluminium fishing boat with F100A 4 stroke both - 3 blade of different sizes and a 4 blade as well .
I went from a 19 pitch SS to a 16 pitch SS 4 blade . RPM @ WOT was almost identically but the boat went faster on plane with the 4 blade but I lost a bit of top speed .
Higher fuel consumption @ WOT I do not know - go seldom long distances with full speed .
I have changed the 4 blade now to a 17 pitch 3 blade Ballistic and that is the best prop for my purpose - great acceleration , good top speed and RPM @ WOT sharp 6000 rpm/m .
The 4 blade I want to try next year on the Yamaha 90hp on the SR5.4 with flooding hull .
As for now I would say a better acceleration I prefer rather than a few km/h more top speed which I cannot use anyway in the rough .

Ribochet · 28 October 2011, 14:22

Guess

Bushrider · 28 October 2011, 15:13

Quote:

Originally Posted by Ribochet

Guess

guess WHAT ?

thorsby · 28 October 2011, 18:29

Thanks for the info guys, would I go for the same pitch on the four bladed as I'm running on the 3 or would I go smaller?

thorsby · 28 October 2011, 18:30

Nice shiny prop in your picture there ribochet!!!!!

Bushrider · 28 October 2011, 18:40

Quote:

Originally Posted by thorsby

Thanks for the info guys, would I go for the same pitch on the four bladed as I'm running on the 3 or would I go smaller?

According my experience minimum 2x smaller !
That`s why I wrote on my boat the 16 pitch SS 4 blade had the same WOT rpm than the 19 pitch SS !! This is already 3x less .
Best would be if you find a dealer who will provide you a prop for testing before you purchase it !
Everything else I consider is either burning money on props which will not make you happy or looking in the magic "glass ball"

Regards - Jürgen

Bigmuz7 · 28 October 2011, 18:41

I think 4 only really had an effect when I got beyond 200HP. One things for sure .. it slowed me down

The best thing about the 4 was the bite it had on a hard corner, it gripped far better IMO, but that was it for me

.. apart from the black magic associated with props on high output motors, on the hp I suggested above, ... I'd keep the cash trousered for some other needy event and stick with the three blader tbh .. what ever benefit you get .. it will hardly be enough and far less significant, than an underspend on a decent auto bilge pump or new VHF hand held for example that you could have used the money on

I like your avatar thorsby... a nice downhill shot .. that gives me an idea

Ribochet · 28 October 2011, 19:11

Nice shiny prop in your picture there ribochet!!!!![

Thanks - 1 off 2
In my experience the 4 bladed props have give me a lot more grip - less slippage, more stern lift and better fuel fuel consumption at cruising speed

Thanks for the info guys, would I go for the same pitch on the four bladed as I'm running on the 3 or would I go smaller?

Changing from a 3 blade to a 4 blade prop will definitely reduce your WOT rpm - I would suggest by 250 rpm. Another factor to consider is how "agressive" are the blades of your existing prop in terms of cupping and rake in relation to your proposed new prop.

DOCTORSHED · 05 November 2011, 16:58

hi,

I have just resently gone from 19" 3 blade to 17" 4 blade stainless.

My thing is diving so involves pushing a lot of gear and people. The difference I have noticed is similar to what Ribochet is saying. I now have better stern lift and the boat planes at lower revs. Now when I am in a heavy sea I have noticed my boat doesn't get knocked back down off the plain as easy.

I don't use WOT very much but I gave it a 'blast' today and WOT throttle was almost identical in revs and speed as I was seeing with the 19".