Prop Upgrade Pitch Question

[tboltmike]

I have a 2009 130 ETEC on my 17.4' by 7' beam trihull. Total weight engine, fuel, persons, gear is about 1700 lbs.

I am using the prop from the original 1975 115 HP Johnnie, 13" x 17"p, 3 blade stainless. That engine WOT was about 5200 rpm and 38 mph.

This prop on the ETEC pushes 45 mph at 5800 rpm.

Used a propeller wizard program it is recommending a 13.25 dia with either 23 or 21 inch pitch.

This seems like a drastic change.

Most of my cruising is between 30 and 35 mph, but do enjoy occasional speed blasts.

Do you have a diameter and pitch recommendation?

Thanks, Mike

 

[steelespike]

Re: Prop Upgrade Pitch Question

Your numbers don't add up.You can't go 45 with a 17" prop at 5800 rpm.
Is the speed by gps? I'm guessing with the tri hull your speed is probably around 37 to 40 mph.
And the 17 is darn close to what you need.
Are you using the old tach?
Is the motor mounted with the anti vent plate a ltitle above the bottom of the transom?

 

[tboltmike]

Re: Prop Upgrade Pitch Question

My mph's are gps on two units.

The tach is an omc but is the same used on my old 115. Dealer said it was compatible with the new engine.

The water line, when rubbing is above the cavitation plate and nearly to the small plate just above it, but is flush with the bottom of the keel.

Thanks for the input.

 

[jimmbo]

Re: Prop Upgrade Pitch Question

6000 rpm 8% slip puts it pretty close to 45mph

 

[jestor68]

Re: Prop Upgrade Pitch Question

Let's see; an Evinrude 130 Etec rated at 130 hp at 5750 rpm. WOT range of 5500-6000 rpm.

Motor is turning 5800 rpm, 50 rpm over rated horsepower; 200 rpm below max rpm, with a light load. Not much to play with there.

It would appear that you have a near optimum set up for good all around performance. Subtracting 1 inch of pitch would put you at max rpm; idea with a light load, but probably not worth the trouble.

Sometimes the propacalculators are way off, as they do not(and cannot) take into consideration the design of the boat.

Bottom line; don't change anything. You lucked on the near perfect set up.

My boat speed calculator shows 44.83 mph. Not that I trust them.

Using his old 115 at 5200 rpm, it shows 38.09 mph. Hmmmmm?

 

[steelespike]

Re: Prop Upgrade Pitch Question

One of us may be wrong, probably me. I'm using a gear ratio of 2.25 from the etec site,17" prop.
Calculator says you can't make 45 at 5800 rpm.
Calculator says 9% slip with the 115 at 38 mph.reasonable.

 

[steelespike]

Re: Prop Upgrade Pitch Question

My mph's are gps on two units.

The tach is an omc but is the same used on my old 115. Dealer said it was compatible with the new engine.

The water line, when rubbing is above the cavitation plate and nearly to the small plate just above it, but is flush with the bottom of the keel.

Thanks for the input.

If water is up to the small plate the motor needs to go up to a point just before venting becomes a problem.

 

[jimmbo]

Re: Prop Upgrade Pitch Question

I used the 20in model which has 2:1, the 25in model is 2.25:1