Fortier 26 w/ Yanmar 4LHA/STP - Prop Question

[sealaw]

I ran into a fellow Fortier 26 owner recently - his boat has a Volvo TAMD41. He told me that he used to run the same prop as we have (Mich. 4 blade 17x18) and got about the same fuel efficiency we currently get (~ 8 gph @ 2750 RPM, pushing @ 16.5 kts).

He recently switched to a deeper pitched prop (I believe he said 19" pitch) and the result was that he cut his fuel consumption in half (!) while achieving the same speed. He didn't mention any change in RPMs for this speed range - but I assume it must change given the deeper pitch.

Does this sound reasonable? Should I consider re-propping? Will my Yanmar/Hurth 1.56 combo tolerate the increased torque? Will the resulting lower RPMs have a negative impact on the way the Yanny runs?

The fuel saving is irresistible - but sounds too good to be true.

Any comments/ideas? Thanks to all...

 

[dino]

All else equal 50% is excessive and probably is too good to be true. Pitch is not the only variable that might have changed. Diameter, surface roughness, shape, activity factor all could effect efficiency.

Dino

 

[delucat2]

Depends on the condition of the prop. Polish yours till it is nice and shiny then write down you speed and rpms from 2000 rpms to WOT and send to a good prop shop, they will tell you if you are propped right.

 

[Duke]

Call Rod Fortier and see what he says.

 

[captainlarry84]

The correct diameter prop for a 240 Yanmar 1:53 gear in a 26 Fortier is 19" next you pitch the boat until you get 3400 RPMs. Your wheel should come in at about 18" of pitch. Each 1' of pitch on your boat comes out to about 200 RPMs with that gear. If he gain all of that on the re-pitch did he clean the bottom & polish the wheel & was the original wheel out of whack? There is no magic bullet on this.

 

[sealaw]

Thanks for all the great feedback, gentlemen!

I'm doing a short haul this month - I'll try the polishing/cleaning routine, then clock the speed vs. RPMs and try asking Bosler & Sweezey here on L.I. - they have a reputation for perfect propping.

I'll keep you posted...

 

[Dr Dude]

I had the same boat and same engine and I ran a 17x20 dyna quad nibral and got 3350 at wot and depending on the elements got up to 29.8 mph. I cruised at 2800 (23-24 mph) and about 7 GPS.
Best boat I've ever owned.

 

[fortier256]

Check with Hale in Old Saybrook. He does the propeller work for Fortier and knows the boat well. Rod Fortier would send you to him.

 

[blackdiamond296]

The problem I would think you'll run into with that much pitch is cavitation in a sea. The boat is lighter with the Yanmar than with the older Izuzu or Volvo motors. Couple the reduced weight with the boat being higher out of the water when running 17+ kts and I think it's gonna lead to more cavitation.

Curious to see what happens though, keep us posted!