Wellcraft Excel 26SE Propeller Size

[jfrdcl@gmail.com]

Hello All,

I was wondering if someone knew some info regarding propeller size, WOT and cruising RPMs and speed for a 1996 Wellcraft Excel 26SE with a Volvo Penta 5.8FL setup. I previous had a 14.5x19p prop but I'm told it wasn't reaching the RPM spec for WOT (4200-4500?). Now I have a 17p prop. I believe it's a 15x17p. With the current prop, I achieved the below RPMs and speeds.

I understand the prop should allow achieving the rated WOT RPM, but these speeds seem pretty low. Conditions were 2 people with 1/2 tank of gas. With the 14.5x19p prop last year I recall cruising around 24kts @ 3200-3300 RPMs but I do not recall what I got for WOT. I'm also being told my tachometer is reading about 200 RPMs low, but that doesn't seem to make sense from the below data as that would imply a 3600RPM (seems high) for just a 20.5kts cruise.

GPS HEADING Notes RPMs "GPS SPEED(KTS)" "SPEED(MPH)"
215 M Against Tide 3000 12.6 14.5
219 M 3200 17.7 20.4
210 M 3400 20.5 23.6
219 M 3600 23.8 27.4
200 M WOT 4200 27.8 32.0
201 M WOT 4200 27.9 32.1
058 M With Tide 2800 12.5 14.4
059 M 3300 19.9 22.9
046 M 3400 22 25.3
063 M 3600 24 27.6

Any feedback is much appreciated!

Thanks,
John

[DaveKamp]

I'll disclaim any detailed knowledge of the V-P 5.8L... but I can tell you a few things that'll probably help;

The 26SE is not by any means a 'small' hull for a 5.8L V8.

IF the engine or drive has a designed max operating RPM that is HIGHER than what you're attaining with the current prop, you're either dealing with too much hydraulic or aerodynamic drag, or you've got too much prop pitch, or not enough SLIP to get it to max RPM.

Before you go too far, check the hull, make certain it's clean of marine growth (water inlets, too!)... then focus on your WOT performance numbers. Make certain you adjust the drive trim to get highest plan as possible at full on throttle.

Prop PITCH is only part of the propulsion performance formula. As you noted, your higher pitch prop has a smaller diameter, the lower is larger. The lower pitch presents more leverage for thrust, and a larger diameter blade, with larger surface allows that prop to generate higher thrust, but you'll have more blade drag, and you'll be limited by ultimate RPM (or blade cavitation, whichever comes first).

Trimmed out, the full-on throttle point will yield a maximum prop RPM, and that will be your guide to getting the proper setup. Choose the propeller that gets you closest to the engine/drive RPM without exceeding the engine/drive max RPM.

The drive system has a gear reduction. your drive PROBABLY has about 1.5:1 gearing. With the power input, I'd expect you to be around 29mph max.