Which prop?

[daray]

hi all,

I'm looking for the right prop for my Slickcraft 279SL. It currently has a wrong prop fitted (15x17), so I'm looking for the right one.

Some specs.

Currently doing 50km/h (31mi) at 4200rpm (WOT)

Specs boat:
Mercruiser 5.7 V8 Alpha one
Beam: 8'9"
Length: 28'
Net weight 5200lbs

Your advice is appreciated.

Ray

 

[steelespike]

Re: Which prop?

Do you know your gear ratio? Sometimes it's on the outdrive.
I assume the boat spends a lot of time in the water.Is the bottom clean and smooth?
Any bottom paint?
A 15" prop could add about 300-400 rpm

 

[daray]

Re: Which prop?

The bottom wasn't clean when tested the current prop. Actually it wasn't clean at all. It is clean now, but it's layed up for winter now.

I don't know the ratio and there is no bottom paint.

 

[steelespike]

Re: Which prop?

Maybe in the spring you can look over the outdrive for the ratio usually on the upper portion.
and take a couple of lightly loaded test runs to get the wot rpm and GPS speed.

 

[phillnjack2]

Re: Which prop?

its a big boat for a single 5.7 engine
but I would of thought possibly 36mph if its running like when came from factory.
you have to think about what extra;s you have on the boat and what they weigh.
even fenders add weight plus anchor plus water tank,ropes, life jackets and anything else will add to weight =slower than makers specs.

so your not too far off max speed of around 35mph I would think.
is this a 260hp v8 or the higher output motor ?

.

 

[Bondo]

Re: Which prop?

The bottom wasn't clean when tested the current prop. Actually it wasn't clean at all. It is clean now, but it's layed up for winter now.

I don't know the ratio and there is no bottom paint.

Ayuh,.... Odds are, you'll see the rpms at Wot right in the sweet zone since it's been cleaned,...

 

[daray]

Re: Which prop?

Thanks for the advice guys. I also discussed it with my dealer and we'll do some testing next spring.
But it seems that 16x16 would be the right prop for my boat, we'll see...

It's the 260hp engine.

 

[dan t.]

Re: Which prop?

Thanks for the advice guys. I also discussed it with my dealer and we'll do some testing next spring.
But it seems that 16x16 would be the right prop for my boat, we'll see...

It's the 260hp engine.

As I was scrolling thru this post I was thinking 16x16 I have had some experiance with these props, they work very well for heavey boats, they have the "eliphant ear" blades and have lots of bite at low speed. You will find a hugely improved hole shot and better manuvering at docking speeds. Please excuse my spelling,spell check isnt working and I have come to kinda depend on it.

 

[jestor68]

Re: Which prop?

Well; according to the Mercury prop selector, the 15 X 17 is one of the choices for that boat.

Given that your results were obtained with a fouled(?) bottom, I wouldn't throw money at another prop until you test with a clean hull.

As Bondo suggested, a clean hull should gain a couple hundred rpm and put you about where you should be.

Your numbers indicate a 25-26% slip; possibly due mainly to a fouled bottom.

 

[daray]

Re: Which prop?

Thanks for the advice guys. I'll run it first with the clean bottom and see what she'll do.