Prop ???

[dbiberstine]

will changing to a smaller diameter prop of the same pitch increase hole shot?
I get no slip after mashing the gas.


motor 150 HP Mercury outboard
Mercury Trophy 4 blade 25 pitch prop 14 1/2" dia
Javelin 379Dc boat, prop is 3 1/2" below the pad.
4800-500 rpm 60 plus mph.

 

[Dhadley]

Re: Prop ???

Too much of a loaded question. Sometimes yes, sometimes no. It depends on the technology built into the 2 props you want to compare. It also depends on what motor it is. With an outboard you have the luxury of being able to raise the motor. Not so easy on an I/O. Not relevant on an inboard.

Generally speaking - very generally - on an outboard if you compare the same level technology and change the diameter only the larger diameter should - should - result in a better holeshot. And more top end. It should allow a higher X dimension which is less drag.

 

[j_martin]

Re: Prop ???

On a through hub prop, the latest, and quite effective gimmick is called "ventilated prop". A small hole dumps exhaust in front of each blade when it's going slow through the water, breaking traction somehwhat, which allows the engine to spool up into the power band. At speed, the moving water pulls the exhaust out of the hub, and also effectively closes the ventilating ports.

A high five prop, for instance, hooks into the water like an anchor into stumps. The ventilation allows my XR4 to spool up to about 3 grand when I mash it. Great combination for skiing, or hauling two phat phishermen and all their gear around.

hope it helps]
John

 

[TJEli]

Re: Prop ???

Depending on the model of Trophy you have, you may have adjustable vent holes (using rubber plugs) If you do, open them up to max and give it a try.

Is your boat very light? A 25P trophy is a lot of prop on a 150. Whats your WOT RPM and speed?

-Eli

 

[dbiberstine]

Re: Prop ???

prop has 4 fixed vent holes, boat weight is around 1300lbs only seeing 4800-5000 rpm depending on trim.

 

[TJEli]

Re: Prop ???

Sounds like you might try going to a 23P prop. What the WOT range for your engine?

-Eli

 

[dbiberstine]

Re: Prop ???

i think 5600 max by the book, but i see guys on line running 6000 with no issues.

 

[Dhadley]

Re: Prop ???

Have you tried raising the motor any?

 

[dbiberstine]

Re: Prop ???

I was thinking of trying 3" to see what changed.

 

[j_martin]

Re: Prop ???

I was thinking of trying 3" to see what changed.

Javelin 379Dc boat, prop is 3 1/2" below the pad.

Sounds a little deep. Try raising it. Without a Jack plate, 3 inches might be too much, but maybe not. If you don't have a water pressure gauge, get one before you raise the engine too much. Loss of cooling can kill yer engine pretty quickly, but not as quickly as you can see it on a gauge.

Are you checking your speed with GPS, or using the stock pitot driven liar?

hope it helps
John

 

[dbiberstine]

Re: Prop ???

I have a 4" plate and I will keep a close eye on water pressure. No GPS yet.Will raising the motor worsen chine walk?

 

[Dhadley]

Re: Prop ???

many times raising the motor improves the handling. Just keep an eye on the water pressure.