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  Folding Prop Advice (pura vida)
Posted: 9:46:23 pm on 3/6/2005 Modified: Never

Any advice on folding props? Pura Vida is a 1974 MKII with a Yanmar 2GMF. When the boat was purchased a year ago she had what I suspected to be the OEM prop designed for the Atomic Four. The boat moved pretty well with this prop but seemed to hit hull speed and squat pretty quickly. Recently the yard replaced everything from the transmission back and now I have a nice three bladed parachute dragging under the boat. She powers better, but 1/2 a knot is 1/2 a knot. Obviously some math needs to be done to fit the right pitch to the boat/engine combination so what I'm hoping for is comments on brand performance from those of you who are using folding props now. One other thought, if any one has determined when to stop spending money on these boats please let me know .

Mike M
SV Pura Vida
Galveston  Bay

  Re: Folding Prop Advice (rsengland)
Posted: 11:07:56 am on 3/6/2005 Modified: Never
Yesterday I was browsing around on the Internet and came across a knowledgible-sounding discussion of folding props on a discussion group.  I can't remember the URL, but a bit of looking may turn it up.  The gist of the comments was that the Martek props so common on C&Cs aren't very good -- they have "sloppy" tolerances and, the blades not being geared together, often don't close properly.  Someone said that one blade hanging down can cost 0.5 knot boatspeed in light air.  The Gori and Flex-O-Fold props were considered to be better props.  It was mentioned that there is a small difference in drag between the brands, but I can't remember which way it went.  The Maxprop sounds like an interesting way to go, since it feathers reliably and allows the pitch to be adjusted (while out of the water) to get your engine loading right.  My opinion based on owning several diesel powered boats is that the ability to adjust pitch without a trip back to the prop shop is a valuable feature.  (My boat has the geared Gori (13x8 if I remember correctly) and is a little over-propped given the way I load it down with tools and gear!).  The downside of the Maxprop is cost and a requirement for annual maintenence (greasing), and some operational complexity -- you can't shut down your engine while in reverse or else the prop won't feather.
  Re: Folding Prop Advice (davidww1)
Posted: 12:30:26 pm on 3/6/2005 Modified: Never
I know the feeling of having a 3-blade. The boat feels out of balance and hobbled.

I have a Flexofold 2-blade that I've had for 2 years now. It works well in both directions, opens and closes smartly, and was competitively priced. The only caveat that I would offer is that it, as with all geared folders, probably generates a fair bit of drag compared to the old Martec style. Because it requires room for the blade gearing, the hub is almost twice the diameter of my old Martec and the folded blades are about 3/4" apart, so there's probably a fair bit of turbulence between them.  If I raced the boat seriously, I'd be concerned; but I don't, so I'm not.

However, if I did race the boat seriously, I'd consider a Martec (again). They do get sloppy over time as the pivot holes wear (but a machine shop can fix that), they have negligible reverse thrust (but you get used to that) and one blade does hang down if you're careless (but you paint a line on the prop shaft and right before every race, someone goes below to make sure the line faces up and the blades will fold). On the absolute plus side, they have the smallest cross-section, hence least drag of any prop save a 2-bladed Max and they never fail to fold, while Max-props very occasionally decide not to feather. If I cruised more, I'd carefully weigh the $1,000 premium of a Max-prop.

Ralph Ainslie of Hyperion bought a Max-prop when he switched to a diesel (see his comments in Black Arts) – perhaps he will tell us how that's worked for him.

As to when to stop spending money –  when you've got the boat that's exactly right for you, be it gold-plater or floating slum, you go into maintenance mode.

David Weatherston
Towser, Toronto
C&C 27 Mk IV
question Re: Folding Prop Advice (Cameron)
Posted: 12:37:10 pm on 3/6/2005 Modified: Never

I have a Gori 14RH9 on my 1987 MKV boat which seems a little big but it only cost $100 so I went with it. The boat will only do about 5 knots with the iron lung operating at about 2500 - 3000 rpm. How fast does a 13RH8 make the boat go?  Perhaps I will get mine cut down if possible.  The old fixed prop was better at 12RH9 for speed which pushed the boat along at about 5.5 knots.





  Re: Folding Prop Advice (pura vida)
Posted: 7:27:23 pm on 3/6/2005 Modified: Never

Thanks for the quick response. I looks like still have some homework to do so any other thoughts are appreciated.

One thing of note which may be a bit off topic is that the Flex-o-Fold comes in Whitworth shaft sizes. Growing up in a garage full of British morotcycles makes this standard familiar, but I didn't know anything was still build to the spec.

Mike M
SV Pura Vida
Galveston  Bay

  Re: Folding Prop Advice (Jim W)
Posted: 10:12:17 pm on 3/6/2005 Modified: Never
I have a flex-o-fold on my MKV - it has a Yanmar 1gm.  It works like a charm,  with much more drive in forward than the 2 blade fixed factory prop, and way better in reverse.  I race the boat, and we're fast, so the folding part seems to work ok too.
  Re: Folding Prop Advice (rsengland)
Posted: 11:55:17 pm on 3/6/2005 Modified: Never

Here are some measurments of RPM vs. boat speed (knots) by GPS in relatively flat water, replications run on 180d recriprocal courses.  The boat is a 1985 27 Mk5 with the Yanmar 1GM10 and a 13x8 Gori prop.  The engine cannot achieve 3600 RPM in gear, so I think this prop is too big, or else the boat is overloaded with gear.

0 0
800 1.75
800 1.65
800 1.60
1000 2.00
1000 2.10
1000 2.20
1200 2.60
1200 2.70
1200 2.70
1500 3.10
1500 3.10
1500 3.20
1700 3.70
1700 3.80
1800 3.90
1800 4.00
2000 4.30
2000 4.50
2000 4.40
2250 4.90
2250 5.00
2400 5.10
2400 5.20
2500 5.30
2500 5.40
2500 5.60
2600 5.60
2600 5.70
2600 5.50
2700 5.80
2700 5.90
2800 5.70
2800 5.90
2900 6.10
2900 6.00
2900 5.90
3000 6.10
3000 6.30
3000 6.20
3100 6.30
3100 6.50
3100 6.40
3100 6.30
3200 6.20
3200 6.40
3200 6.50
3200 6.40
3200 6.40

If one fits a linear regression to this data, the equation is

Speed (knots) = 2.1 * RPM/1000


  Re: Folding Prop Advice (wbsmith)
Posted: 10:35:12 am on 3/7/2005 Modified: Never


I had a Maxi-Prop on a 42' foot boat with a universal diesel - worked great once you got the pitch right (could take several tries), but requires annual lube and replacing the internal anode.   Also once spent a good amount of time on a boat with a 2-blade folding - really inefficient - not good for extending motoring, not to mention the horrors of trying to use reverse.

By the way, when she "squats", you're really at your hull speed.  If it's less that 6.5/6.4, you've got a dirty bottom or something.  Mine tops out around 6.2/6.3 in level motoring which I can make at well under 1/3 throttle in flat water with the 8 hp Yamaha, but I am dragging a strut with shaft (no prop) and need a bottom job. Heeled under sail I can make 7 - 7.1 if conditions are perfect.  That is 2 direction avg. with GPS by the way.  I am not sure why the big difference. 

Oh, if anyone needs an original folding prop for a Mk I I have an available spare.

Warren Smith
Galveston Bay, Texas

  Re: Folding Prop Advice (Ralph Ainslie)
Posted: 3:27:12 pm on 3/8/2005 Modified: Never

When I changed fron the Atomic four to a Yanmar 2GM20 I switched my folding prop for a max-prop feathering prop. My old folding prop would not open properly and as a consequence, with only one blade out the boat would vibrate until you thought it would come apart.  I e-mailed an outfit out in Seatle giving them all the criteria I could think of  I.E. Displacement, length of boat, Engine HP. and the amount of available space from the shaft to the hull. They came back with a 13" prop to be set at 28 degrees of pitch. I usually run the Yanmar at 2800 RPM as this is where it seems most comfortable and the boat will go all day into the wind and swell at 5 1/2 knots. In reverse I get plenty of thrust. My cost 2 years ago landed in Dartmouth N.S. was approx 2200.00 Cdn. Hope this helps.                  P.S.  B O A T  stands for Bring On Another Thousand.


Ralph Ainslie


  Re: Folding Prop Advice (RodMillar)
Posted: 8:43:50 pm on 3/20/2005 Modified: Never
I installed a new Gori 13RH9 on my 1985 MkV and it seems about right.  Yanmar 1GM10 with 2.62:1 gearbox.  Will rev to 3600 giving boat speed about 5.5 knots or so.   Would continue to accelerate if I let it (which I don't!).  Am told not all these boats may have same gear ratio, and that matters a lot with prop selection. Dragonfly C&C 27 Mk V


  Re: Folding Prop Advice (sociopath)
Posted: 10:07:02 am on 7/14/2013 Modified: Never
Hi All.. I came across a cheap Martec folding prop 15X12.. I know that Martec recommends a 14X11 for the 1GM10.. Is the 15X12 going to be too big? Any thoughts?  

Kerry Marsh
Charlottetown Yacht Club
C&C 27 Mark V - Sociopath
  Re: Folding Prop Advice (sony2000)
Posted: 11:57:56 am on 7/15/2013 Modified: Never
Kerry you can cut it down your self. I suggest 1/2" of each end at first. Trace the cut with a pencil and make a cardboard pattern of the to be cut piece. Then use the cardboard to draw the line on the other blade and start cutting. Then file the cuts.
Not necessary, but you could weigh each blade after the cut.
You could send me the outline of the blade and I could suggest a line to cut.
If it is still to big, next haul out, cut more off.