Funny - prop walk seems to be as little understood as sail drive. I have read three different explanations - 1) the pressure on the water on the lower blade is higher (the deeper you go the higher the water pressure); 2) the angle of the prop shaft and 3) the upward and downward flow of the thrust. Of all the last seems the most probable. It is explained as follows:
Transverse thrust is of much greater significance when using an astern movement. The helical discharge from a right handed propeller working astern splits and passes forward towards either side of the hull. In doing so it behaves quite differently. On the port quarter it is inclined down and away from the hull whilst on the starboard quarter it is directed up and on to the hull. This flow of water striking the starboard quarter can be a substantial force capable of swinging the stern to port, giving the classic kick of the bow to starboard. Read more at http://www.ybw.com/forums/showthread.php?341281-Prop-walk-Pysical-reason-why-does-this-happen/page5&s=9d5e1334410d8aca0215750337644810#proEkO42zUH4PEgp.99 -----Original Message----- From: Chuck S via CnC-List <cnc-list@cnc-list.com> To: cnc-list <cnc-list@cnc-list.com> Cc: Chuck S <cscheaf...@comcast.net>; Jeremy Ralph <jeremy.ra...@gmail.com> Sent: Wed, Oct 26, 2016 4:18 pm Subject: Re: Stus-List Folding Prop won't open FWIW, I heard it explained that propwalk originates because the shaft is at an angle to horizontal. The more angle the more prop walk. Also, more surface area of the prop causes more prop walk. Sail drives have the least prop walk because their shaft is horizontal, not at an angle. Power boats with outboards have very little propwalk. Powerboats with inboards and angled shafts have the most prop walk as their props are huge, too. Propwalk is not a problem but a sideways thrust that if used wisely, can be very helpful at times. When docking stern first, I get the boat moving where I want it and shift into neutral. I leave the throttle at idle and shift into reverse just long enough to keep her moving. To slow or to stop, I place the shifter into foreward only long enough to stop. Impulse power vs warp power. Chuck Scheaffer Resolute 1990 C&C 34R On October 26, 2016 at 1:20 AM Jeremy Ralph via CnC-List <cnc-list@cnc-list.com> wrote: I had issues with my 2 blade Martec though not as bad as you describe. I would open with a clunk, sometimes stick when opening, and have some bad vibrations. A surveyor informed me it should be be rebuilt, which is in the works. I replaced it with a 3 blade Campbell Sailer prop, which I'm happy with, although reversing with the Martec had way less prop walk. Hey guys, with all of the discussion on props it reminded me that I'm having an issue with my 2 blade folding prop. Pretty sure it's the Martec that you all are mentioning. I continue to have issues with one blade not opening after we've been out sailing. Once we drop the sails and go to engage the engine and prop it fails to open one side and I get severe vibrations. Is this a normal thing with these props? It truly makes me want to just get a fixed prop. Unfortunately that's not in the budget right now though. So far I've tried: - to come to a complete stop and try again - Kick it into reverse and then back to forward - short kick to full throttle. The last time we were out nothing worked. We ended up limping along back to our slip. Afterwards I checked it by rotating it from the inside and it sounded like both blades would open when it was facing down because I heard the clunk. Occasionally it will open but it's not a first time thing. On departure from the slip I don't have any issues, it's only when trying to reengage the motor after a sail. It's really frustratin _______________________________________________ This list is supported by the generous donations of our members. If you wish to make a contribution to offset our costs, please go to: https://www.paypal.me/stumurray All Contributions are greatly appreciated! _______________________________________________ This list is supported by the generous donations of our members. If you wish to make a contribution to offset our costs, please go to: https://www.paypal.me/stumurray All Contributions are greatly appreciated!
_______________________________________________ This list is supported by the generous donations of our members. If you wish to make a contribution to offset our costs, please go to: https://www.paypal.me/stumurray All Contributions are greatly appreciated!
