Prop upgrade - how to choose

region4

Cadet
Joined
Aug 12, 2013
Messages
29
Re: Prop upgrade - how to choose

I am considering the LaserII 25P, model # 48 16550A46, which may be discontinued shortly, per Mercury Marine.

Any other prop ideas?
 

region4

Cadet
Joined
Aug 12, 2013
Messages
29
Re: Prop upgrade - how to choose

For skiing you do want a prop that pushes you passed that top end. That gives you the hole-shot you're looking for. Your current prop is pretty much a standard 'Vengance' style prop. But I believe it is pulling too many revs, hence the great response out of the hole.

If skiing is what you're primarily doing, consider a Laser II or even a High-five. Both these props have vent holes in the prop, allowing the engine to spin up without load before taking a bite... Hole-shot is unbelievable. I put a Laser II on my boat years ago, just to see what it would do... Talk about 'light the blue touch-paper and retire'... :eek: And the High-five is even more aggressive! One of the best props I ever used was the old 4 blade SS, 'Offshore' series. I believe it's now been replace by the Revolution 4. VERY difficult to make that prop ventilate (which is what you are getting, not cavitation).

Ventilation is when air from the surface is sucked down into the blade area. Cavitation is when the water on the low pressure side of the blades boils and the blade loses grip. The end result is the same, the engine revs, the boat stops. But the fix is very different in each case, which is why you need to know which one it is.

Very difficult to find a single prop to do all things. I think the closest would be the Laser II if you want to ski and cruise. Just remember to put the vent plugs in the holes before you go cruising... And I would definitely go up at least 2"... And yes, with the bigger prop, your top speed will increase..

Chris........

I water tested a Laser II 25 pitch (48 16550A46), PVS vents plugged, and was pleased with the results. Initally, I thought the aggressive pitch would overpower my engine, but I was pleasantly surprised. My tachometer seems to creep (upward), and thus is not accurate, so I need to solve that issue. Anyway, the results follow (with unreliable tach):

4500 RPM / 51.4 mph (per GPS), - Load was one person and full tank (as before). Hole shot was not as good as with 21P, but still on a full plane in two boat lengths. Overall, WOT boatstpeed increased 2.4 mph.

What is a 'typical' slip, for a setup like mine? And how does one fix a vintage tachometer?
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Prop upgrade - how to choose

At 4500 rpm slip is about 20% I feel that you're right the tach is reading high.
Typical slip is 8 to 12% If we use 12% your rpm is about 4100.
You can go through all the tach related connections make sure they are clean and tight.
Start with the selector switch on the back of the tach. Note its position and operate it a few times to clean the contacts.
My limited experience on here the 165 has a relatively low rpm range and isn't fond of over revving.
Perhaps you can borrow a shop tach to evaluate your rpm.
 

dazk14

Ensign
Joined
Jul 22, 2008
Messages
966
Re: Prop upgrade - how to choose

1st - nice to see an hwsiii post.

To OP. You need a reasonably priced inductive tach.

Actron CP7529 Digital Timing Light is what you want. from Amazon $66.27 free ship or 2 day prime. ridiculously good value.

We stumbled on this ~4 years ago when we dropped our Snap On off the back of an outboard boat on a Sunday and needed something quick - paid much more. Works great - verified. Have a few now, including a Snap On.

This does it A LOT with digital read out.

Inductive Timing, Inductive tachometer, 2 or 4 stroke setting. digitally set advance - this is important to check total timing which can be more important than idle timing - although that's where you begin.

Also has a flashlight mode, which helps finding marks.

I may have missed it, but what specifically are you hoping this prop will do/improve?... besides rpm adjustment and a dinged up prop.

What happened to the " just want to do it once" Are you getting great deals on these props - which is a smart way to go.

Our "One and Done Prop" is anything Solas. LOL
 
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