Flex-o-fold 3-blade SPEED CORRECTION, SS Shaft, Bullflex coupling

[Noah]

Had a successful haulout last week. Bottom job and running gear work. I replaced original bronze shaft and coupling with Aquamet 22 SS shaft and Bullflex2 flexible coupling and Flex-o-fold 3-blade 15 x 10. Replaced original stuffing box with new, but stayed with traditional wet box and GTU packing. All install went well (after some usual yard BS).  Engine aligned pretty easy, although one of my original motor mounts ended-up bottomed out with no more room to adjust,without fear of breaking it. Fortunately, it was right at desired alignment. Overall VAST improvement on both vibration and boat speed motoring. Haven't sailed yet. On the way back to my slip, I achieved 8.4 KTS. @ 2800 RPM  up the channel at slack tide, in slight chop with 10.5 KTS true wind on the bow!!!! Engine ran smooth at all RPMs!! SUCCESS!!!

[Noah]

One more pic. Speed climbed to 8.4 kts after this photo but had my hands full single handing with lots of traffic around.

[Stu Jackson]

Congrats, looks great.  Heck, 8.3 vs 8.4, but who's counting???   

[Mick Laver]

You'll love the Flex-o-fold, Noah. We've had a 15x9 for a few years. But 8.4??? We've only got that surfin'!

[Noah]

Yeah, Surprised me too!  Speed was confirmed by knotmeter/paddle wheel and GPS SOG. My prop is a 15 x 10. No smoke from engine either, however, I haven't tried it yet outside the bay in any sea chop.

[WTunnessen]

What engine model do you have and about what as your top speed before?

[Noah]

Previous top speed on same course and conditions was 6.7 kts. with old Michigan Sailer 3-blade 15x9 (not Campbell Sailor).

[Jeff Tancock]

8.4 knots!!!
Are you kidding us?
How many horses are you whipping? What engine do you have?
How is that possible? Have you gone out again and repeated those numbers?
How much ($$$) was that steroidal prop?
Thank sounds too good to be true......
I've never been able to power at more than 6.5 knots. I can only get those numbers if motor sailing on a broad reach.

[Noah]

Surprised me too. I have NOT reconfirmed (yet) running a measured mile with a stop watch, but will. My paddlewheel knot meter and my GPS (SOG) were reading within 0.2 of each other and I was single-handing (in a hurry, LOL!) so not able to do further testing that day. I haven't had the boat out since then, but I intend to double check soon and will post results. I am running an M25XP 23 hp with a 15 x 10  -- 3-blade Flex-o-fold at full throttle of approx. 2,800-- 2,900 RPM. 

Meanwhile, if for some reason I totally screwed up, brain faded and my speed was some how bogus:  At least I do know it goes faster with the folder!! The boat moved through the water 1.5 KTS faster wth the 15 x 10 folding prop than my original fixed 3-blade Michigan sailer 15 x 9 -- this I know because I used the same instrument and course conditions going to and from the boatyard. Fixed prop going to yard 6.7 KTS. retuning from yard folding prop 8.4 KTS.

[John Langford]

When I used the 15x10 configuration on my new flexofold the stern submerged at my normal cruising revs of 2200 rpm and I couldn't get to 2900 at all.  For the MK II at least, 15x9 is the right combo. It's a great prop in forward and reverse.

8.4 knots with no current...the stuff of dreams!

[Noah]

I am planning on running measure mile a recalibration next weekend so I may be "eating some seagull" if my previous Kts numbers were off. The 15x10 spins up fine to 2900 and no burying of stern on my MKI. Different gearbox, engine and stern config than your newer boat, I believe. 

[Noah]

Ok, here is an official "Mia Culpa". I reported BAD info previously. Today I recalibrated my knot meter and ran the measured mile course---and I LOST a full 1.1 knots off my last reported "wishful-thinking speed." Now, my actual top speed at 2,900 RPM (caveat, tach not yet checked with laser), in smooth water at slack tide is 7.3 knots. My previously reported 8+ knots should have been red flagged by me in light under the old tenant "if it sounds to good to be true..." But... Meanwhile, with no smoke, albeit my stern was buried, I am happy with my 15x10, 3-blade F-O-F prop, and I am especially happy with the Bullflex coupling, and its resultant lack of vibration. 

[Roc]

I think the max hull speed (theoretical) of a C34 is around 7.3 knots or so (displacement hull can only push through water and go a certain speed.  Any faster would render it very unstable). Any faster is probably due to surfing down a wave, currents, etc. 

[Ken Juul]

Correct.  A displacement hull speed is found using this formula.  1.34 times the square root of the water line length.  For both the mk1 and mII the water line length is 29.83 ft giving us a theoretical max hull speed of 7.3 knots.  That is speed though still water.  Surfing may give momentary speeds above this because gravity and wave action is helping and currents may give a speed over the bottom faster.  Weight also pays a big factor, when I first got the boat I could easily motor all day at 6-6.5 knots.  Now loaded down with toys and additions 5.5 is closer to standard.