|Topic Review (Newest First)|
|07-15-2007 01:51 PM|
Originally Posted by SEMIJim
Over 15 knots, I can't see any difference, but for typical high-summer sailing in Lake Ontario, that 1/2 knot gain is pretty obvious and is welcome, as is the perceptible acceleration now that there isn't a fixed prop.
When shifting gears at slow motor speeds, however, you have to rev the engine a bit more at first to get the blades to deploy...a small consideration, but it can affect your timing in a tight place.
|07-15-2007 07:29 AM|
On a long ocean passage, the speed difference could well matter... a speed difference of just 1/2 a knot is 12 nautical miles per day...and over a longer passage those 12 nm add up to possibly getting in a few days earlier than not having the folding prop.
Also, sailing in tidal currents... if you can make five-and-a-half knots against a two knot current, you're going 3.5 knots...if you can only make five knots, you're going 14.3% slower.
If the folding prop gains you a full knot, then the differences will be even larger. Over a ten-day passage, with a speed difference of one knot, your talking 240 nautical miles difference... that's two days worth of sailing in many boats.
Originally Posted by wine1959
|07-15-2007 01:31 AM|
Originally Posted by wine1959
|07-15-2007 01:15 AM|
Fix all the way
Remember, the more moving parts the more chance of a problem. I have NEVER lost a fixed prop but I did loose a folding prop in the middle of Sir Frances Drake channel two years ago. Keep the folding as a spare. The speed difference does'nt matter unless your in a real hurry.
|07-15-2007 12:36 AM|
Originally Posted by Giulietta
|07-15-2007 12:29 AM|
Good information there, Valiente. Thanks! 1/2 kt, eh? Didn't expect it to be that much.
Don't know what brands they are, guys. I'm guessing the fixed prop is probably original equipment, whatever that was. By the fact the PO has tended to put nothing but top-quality stuff on the boat, by way of upgrades, I'm also guessing he didn't skimp on the folding prop. I'll have to ask him what it is.
|07-14-2007 07:48 PM|
Originally Posted by ianhlnd
|07-14-2007 01:17 PM|
It really depends on the manufacturer of yor props.
Some folding props are really bad and crappy, and I'd rather have a good fixed than a bad folding.
Same the other way around.
So beware, just because it folds does not mean its good, same the other way around.
I vote for folding, off course, but a GOOD ONE, not a crappy one.
What brands are they?
edit...Val beat me to it
|07-14-2007 01:16 PM|
Out of curiosity, find out what kind of props you have. Some are better under power than others. A Pearson 30 is about as representative a '70s design as can be imagined (like a Catalina 30, but less common), so I have a good idea of your hull shape. Let's assume you have an Atomic 4 or a Yanmar 18 HP as a motor. The fixed prop will likely be a 12 x 6 or 7 Michigan Wheel two-blade, with about an inch of tip clearance. The folder will likely be a Gori or a Martec two-blade of about 11 x 8. This means you will need more revs to get the same speed with the folder, but you will have slightly more thrust and a finer control at low speeds. This is desirable in docking and maneuvering. Allow me to give you an example: With a fixed prop, my "dead slow" in forward was about 2.6 knots. Consequently, I learned to shift into neutral and coast into dock, depending on winds blowing me on or off. I could, however, make 5.6 knots in flat water at half-throttle. At full throttle I could make 6.5, but cavitation and the noise made it hardly worth it.
By contrast, my "dead slow" with a Gori folder was 1.5 knots, and my stopping and reversing power were increased by about 25%. I also suffered less from prop walk, which meant that I actually used the engine MORE with a folder, because I could maneuver with more throttle control when I had options under 2 knots of speed over ground. I would also reverse off the dock instead of simply pushing the boat backwards with the engine in neutral and then hopping on amidships and throwing the tiller over until my bow had cleared and I could push the shifter into forward.
As for sailing, I gained approximately 1/2 knot in speed under equivalent wind conditions. I actually had to mentally shift my sail changing "bands" in the sense that I would opt for a No. 2 sail if the wind was over 12 knots for a daysail whereas I would have waited for 14 knots with the old fixed prop. The reason? I had less resistance under the boat and its sailing characteristics became noticeably livelier (as did its acceleration) in light-to-medium airs.
My experiences with a folder contributed greatly to our decision to purchase a feathering VariProp for our ocean cruiser...the pluses greatly outweigh the few minuses in my view.
But don't throw out the fixed prop...if the folder is damaged, you've got a solution one hour in a TraveLift can effect.
|07-14-2007 09:23 AM|
Okay, I'll just leave it w/the folding prop. Thanks for the feedback. As usual: Sailnet's community comes through.
I really cannot imagine what this journey would've been like w/o Sailnet. Certainly I would've been a helluva lot more clueless than I am .
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