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As detailed ad nauseum in "Atomic 4 replacement", Towser has now been fitted with a diesel engine, a Yanmar type 2YM15, 2-cylinder 14 hp. We knew right from the start that the 12x7 Flexofold folding 2-blade - which I recommend highly as a prop in general and specifically that size as an A4 prop - wouldn't be right for the boat, but put off replacing it until we could run the boat with it and determine a baseline for the new prop.
Part of determining the new prop's values will be done by logging present boatspeed as a function of engine RPM, but I'd also like to find out what others have. Please let me have engine type and horsepower, gearing if known, present prop's manufacturer, size and pitch. Oh, and whether you think it's on the money or if it is deficient in some way.
David Weatherston
Towser, Toronto
C&C 27 Mk IV
David Weatherston
Towser, Toronto
C&C 27 Mk IV
Offline
Hi David. If and when you do decide to replace that folder, I'd be interested for my A4. I can be reached directly at <A href="mailto:ken.pole@sympatico.ca">ken.pole@sympatico.ca</A>. Cheers.
Ken Pole
Santiva
Ottawa
Ken Pole, Ottawa
1975 Mark III Santiva
Offline
Dave, As noted in "Black Arts" I Went with a Max prop 13" Dia feathering prop set at 28 Degrees of pitch. This was per the Prop manufacturer's reccomendation.
I have found acceleration very good and the boat moves along at about 5 1/2 Knots @ 2800 RPM. 4 1/2 to 5 Knots @ 2200 RPM.
Ralph Ainslie
"Hyperion"
According to PYI, importers of Max-Props, 28 degrees of pitch equals 13 inches of pitch. -- Admin
Last edited by (2005-06-06 12:45:12)
Dave, Here's a sight you can have some fun with. <A href="http://www.image-ination.com/sailcalc.html
">www.image-ination.com/sailcalc.html
</A>
Scroll down until you find the prop calculator. This may give you some valuable info.
If I screwed up the address. let me know.
Regards
Ralph Ainslie
"Hyperion"
Last edited by (2005-05-25 05:06:50)
David,
How is the 2005 season for you?
Mine is dogged by MCA(Marine and Coastguard Agency) burocracy.
My Superseal 26, very like a C&C 27 mk V, has a Nanni (Kubota) 14hp saildrive which has 2:1 reduction.
Does 4.4 knts , smooth water. no wind, at half speed 1800 rpm with a folding two blade 12 x 8
If any of your members are in the UK for Holidays this summer ( except summer this year was a Saturday in April) get them to ring me on 01788 890648 and we could go for a sail
First pass results with the new prop:
C&C 27 Mk IV Towser
Yanmar type 2YM15, 2-cylinder 14 hp, 2.6:1 reduction
Flex-o-fold 14x12 rh
Two runs, flat water, with and against light wind
RPM Average speed
1200 3.8 kt
1600 4.7
2200 5.8
2400 6.7
At 2600 rpm, vibration becomes excessive. This didn't occur with the 12x7 blades left over from the A4, even at 3600 rpm when the noise became so oppressive that I lost interest in proceeding. I assume that the new blades (which are very heavy) aren't quite in balance. I will therefore have the prop dynamically balanced over the winter.
The engine is obviously working harder and this, curiously, has the effect of making it quieter, or at least shifts the noise into a less irritating part of the spectrum.
Reverse thrust is excellent, with surprisingly little prop walk at normal reversing speeds. The crash stop was a surprise, though. The first time I did it, going into reverse at 6.5 knots then goosing the engine up to 2200 rpm, I deliberately made no attempt to compensate for the boat's motion. In the course of a very fast stop, we spun 160 degrees. That made the people on the adjacent boat dock stare.
One last note - In addition to this bladeset, the Flex-O-Fold rep spoke also of the 15 x11 as a possible. Eventually, we decided it was iffy in respect of hull clearance, so I went with the 14x12 set. We never discussed the rudder as a limiting factor but it just might have been a hair too close when the prop is opening and closing (there might be 5/8" clearance at the closest approach, but I didn't actually measure it so then again, there might not have been). Of course, the first time the prop opened with a burst of power, it probably would have accommodated itself with a suitable excavation in the rudder's leading edge, but that's not hydrodynamically ideal.
David Weatherston
Towser, Toronto
C&C 27 Mk IV
David Weatherston
Towser, Toronto
C&C 27 Mk IV
Offline
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