Mother-of-all-invention

Volvo folding props spinning above 8 knots under sail?

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Having an issue with props spinning under sail on a 50' cat with twin Volvo Penta diesels, simple actuator controlled gearbox to shaft drive to 3-blade self-folding Volvo Penta props.  Recent haul out, full bottom job and pulled propshafts for cutless swaps.  Cleaned and polished shafts & props, replaced shaft zincs, and added plate zincs on struts.   Cleaned/sanded, polished props & shafts and applied PropSpeed coatings (with experienced team, proper prep-cleaning-phospho-etch-primer-2 quick but good smooth coats).  

After haul out maneuvering out of slip and harbor was fine, fwd/rev both clean thrust.  Motored an hour back home, was cruising faster than ever, plenty of thrust.

A couple weeks later out sailing and whoa...above 7 or 8 knots the props started spinning, and fast.  Engines were off.  Transmissions were Volvo Penta EVC'd into neutral, no way around that without manually disconnecting actuator linkage.   

I dove and checked smooth easy folding action on both a couple times and there seems to be no difference in folding action than existed before haul out/PropSpeed application.

Obviously the problem began after PropSpeed was applied.  Before I go sanding off the PropSpeed on the leading faces of the prop blades (outer faces when folded) just to troubleshoot, is it plausible that thin PropSpeed coating is creating an outward lift effect pulling the prop blades out far enough to catch the water and then the rotation keeping them out when above 7 or 8 knots? 

I added a 3" plate style zinc to the flat vertical plate of the inboard strut arm on both sides to add anode as there was a little pitting found on the gear.  Could that be adding enough turbulence to cause the props to kick out at speed vs the PropSpeed?

Here are the basic props per Volvo's site... https://www.volvopenta.com/marineleisure/en-en/for-owners/parts/propellers/folding-propellers.html

Pic is the polished setup with the added zinc on the strut arm.

Thanks in advance

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11 minutes ago, Mother-of-all-invention said:

Transmissions were Volvo Penta EVC'd into neutral, no way around that without manually disconnecting actuator linkage.   

Translating that to mean your engine is off, your transmission is in neutral by design. 

Surprising to project that the plate anodes would cause the props to unfold, but you could pull one off, and see if there's a differential effect. 

 

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Yeah, tried that about a dozen times last sail.  Both fwd and rev in low and high RPMs then quickly to neutral again.  Sometimes would help, but they usually started spinning again quickly if they did stop.  Tacking in a big cat slows down a lot and that sometimes stopped it if water speed dropped below the 7/8 knot zone, but usually it returned.  Was half tempted to tie a line around them with a remote release knot to hold them shut while underway, opted against that for safety reasons.   Could it be the plate/dish shaped zincs added to the strut arms creating turbulence over the folded prop blade on top?  The symmetrical dish/saucer shaped zinc on both sides of the strut arm were added during haul out too.  Here's a different angle pic...   It would be easier to pull those and retest before sanding PropSpeed off.

Capture2.PNG

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Can you put the trans in reverse when the engines are off and you're sailing? On my boat you have to do that to make the prop feather and quit spinning.

 

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24 minutes ago, kevinjones16 said:

Can you put the trans in reverse when the engines are off and you're sailing? On my boat you have to do that to make the prop feather and quit spinning.

 

It is possible, but not without disconnecting shifter actuator linkage while underway and manually shifting gearbox.  Doing so would keep force on the gearbox and thus rely on the engine compression to prevent rotation.  Could a warmed up diesel loaded in that way possibly "roll-start" itself in that scenario?  

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My rule of thumb when troubleshooting is "what did I change". I doubt it is the Propspeed. I'd bet on the turbulence from the zinc.

I know that a few very fast (20 knot) cats did manage to start engines via spinning props when sailing. But not at 7 or 8 knots. 

Remove zincs from one strut and re-test. Can you motor at 7-8 knots with just the opposite engine to simulate sailing speeds?

If the Volvo gearbox can't be left in reverse you could consider a shaft brake. Very clever and cheap home made one here:

http://www.zwerfcat.nl/en/propshaftbrake.html

Disc is just 8mm aluminum plate and brake is an electric parking brake from a car. Relatively light too.

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My old 42' Cross tri could start its Yanmar when sailing at a good clip. I always had kept the gearshift in reverse more to keep it up close to the pedestal to not snag lines than any other reason. Sure gets your attention when the Iron Genny roars into life and it is pumping the exhaust into the cabin since it is running backwards due to the gear box being in reverse. I thought the boat was on fire when the smoke started pouring out the companionway! 

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For my Gori folders, if I don’t put the shifters in reverse under sail, they won’t fold. Volvo’s recommendation is to either have the shifters in neutral or reverse while in sail, that is to say, with engines off, you do understand 

CE0BA333-78BC-491A-8EB0-289978841536.jpeg

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On 5/31/2018 at 3:45 PM, Rasputin22 said:

My old 42' Cross tri could start its Yanmar when sailing at a good clip. I always had kept the gearshift in reverse more to keep it up close to the pedestal to not snag lines than any other reason. Sure gets your attention when the Iron Genny roars into life and it is pumping the exhaust into the cabin since it is running backwards due to the gear box being in reverse. I thought the boat was on fire when the smoke started pouring out the companionway! 

Ayyy Carumba.  That would provoke a reaction from the admiral.   ...and me too, come to think of it!

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On 5/31/2018 at 3:45 PM, Rasputin22 said:

My old 42' Cross tri could start its Yanmar when sailing at a good clip. I always had kept the gearshift in reverse more to keep it up close to the pedestal to not snag lines than any other reason. Sure gets your attention when the Iron Genny roars into life and it is pumping the exhaust into the cabin since it is running backwards due to the gear box being in reverse. I thought the boat was on fire when the smoke started pouring out the companionway! 

things i never considered being a possibility... 

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That little adventure taught me that I could start the motor if my starter/house batteries ever got to low to turn it over by just going sailing with the gearshift in fwd and open the compression release to let the prop spin the whole drivetrain up. Took about 6 knots and then pop the compression release closed and it would start right up. Once I got the timing for that down, I was able to hand crank it with a little strop and ring that let me trip the comp release with my knee while I spun the hand crank for all I was worth.  Much easier to just sail off the hook and bear away in a puff and yank the strop leading out the motor compartment into the cockpit and it would fire right up.

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I had the same problem with that prop with a saildrive.  I would get the boat going forward to 5 knots shut off engine and then quickly put in reverse.   That seemed to correct the spinning issue.

 I eventually got rid of the prop due to drag - the blade tips when folded are facing forward and  catch stuff.  I found a black bag on the prop on day.  

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Self pitching autoProps with a similar shape will spin in neutral and will spin the Yanmar 4 cyl if left in reverse. Per their recommendation, I keep it forward and it behaves nicely. 

 

 

Id try zonker’s theory. What did you change? And go from there. Given your EVC, I’d be spending a set of shaft brakes soon. 

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Looking at the picture of the prop, it's hard to see why it wouldn't spin.

Unless you put it in reverse, you're relying on the minimal friction of the bearing, which is new.

With a clean hull you've changed the water-flow and maybe increased the speed.

Max was suggesting that you need to leave the gears in reverse when sailing.  He's right.

I've never managed to overcome compression with any combination of fixed / folding prop and horribly clapped out engines, I don't think that will be an issue.

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I'm pretty sure Propspeed has nothing to do with this. Put the engine in reverse.

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