Prop dia-v-pitch effects

Hi all...

So I was given a 15" 17P 3 chopper from a friend of mine.
I'm currently running a 14", 19P.

Boat specs in my Signature...

So a couple of questions. Assuming this clears the trim tab, what will the performance difference be? I'm not using this as a primary, but rather a backup/spare.

I'm under the impression that a 15" 17P will be close to the 14" 19P...close?

Thanks in advance!

Re: Prop dia-v-pitch effects

Disregarding the boat and motor and its present performance. If the same brand and model.
Rpm may increase about 300 to 400.
It's normal for diameter to go up as pitch goes down. !" is a bit extreme.
And may temper the change. There are anodes that will increase room for
larger props.
Assuming same brand same model The 17" should behave like a 17".
Usually a reduction in pitch will improve holes hot, may be easier to keep on plane at reduced throttle.
may lose some top end speed.

Re: Prop dia-v-pitch effects

You didn't spec the engine type. I have a 90 hp Merc with a 4 1/4 gear housing diameter. It runs props in the 13 to 14" category. The 135 and up V6 Mercs run a 4 3/4 gearbox (I may be off on my fractions, but point here it is a larger box for the larger engines) and turn a 15" or thereabouts prop. Additionally, the outer diameter of the hub is larger also which can and did cause an interference problem with the gearbox housing resulting in part of the mods necessary....other part was prop length addressed below.

I have run a large gearbox prop on my engine but it took some modifications to get the distances worked out. The diameter was 14" and just barely fit under my anti-vent plate, like I had a 1/4" of clearance or thereabouts. I ran it once. I had been running 13+ diameter Ballistic SS props and this was a Turning Point Hustler alum. I obviously was comparing apples to oranges and some of the change was diameter and the rest was blade shape/area/thickness and maybe OD tube size, as I had the same 21P in both instances.

My SS rpms were too high (not the prop I usually run but I had it and ran it), like over 6k at WOT and installing the Hustler alum cut them to 5000....too low to suit me. After the test, I put my 24P Ballistic back on and that's what I run.

However the hole shot was stellar with the alum as was just above planing speed control of the boat. The alum did have ports and was cupped, high rake blades, unlike most alum props and for $100 I just wanted a data point. So, there is definitely something to a lower pitched larger diameter giving you more (available) "thrust" at the lower speeds.

HTH,

Mark

Re: Prop dia-v-pitch effects

I'm under the impression that a 15" 17P will be close to the 14" 19P...close?

Click to expand...

Ayuh,.... Pitch is Important,.... diameter not so much, to none...

I'd expect a 200/ 300 rpm difference...