soma

Best folding prop?

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Once again, going to the hive for help. 

My boat came with 18” 3-blade Goris. They were in pretty rough shape (17 years old). I took them off and sent them to AB Marine for inspection/refurbishment. Bad news, not salvageable. Time to replace. 

I liked the idea of the Gori overdrive but folks say that it fries the transmission. Having just replaced the engine/transmission coupling (only 1200 hrs) I can believe the transmission doesn’t like them. 

Easy option is new Gori’s. Not cheap. Overdrive is maybe a solution without a problem.

Cheaper option is Flex-O-Fold. From reading some test results online the Goris are low drag but low pull/push. Flex-O-Fold get great reviews. And they’re cheaper! 

Tempted to go for a 2-blade composite version of the FOF. I have a shaft drive with a down angle so a 3-blade prop will be draggy (with 2 blades always dragging). But...it’s a cruising boat. Maybe low-speed maneuverability is more important (if that truly is a benefit of a 2-blade). 

Ive seen plenty of other manufacturers, but I feel like it’s a FOF vs Gori debate. 

Any advice?

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AutoProps! Great drive, great reverse, great regen (if that ever becomes an option), but goofy looking as hell with blades hanging all weird

Pitch themselves just right when motorsailing. Brunton product and they have been around forever.

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You'll have to resolve your racing vs cruising balance!  a 3 blade will always outperform a 2 blade, blade surface area reduces 'slippage' quite a bit, gives better performance into chop/wind & better MPG. No difference in top speed, esp in flat water. As to trans issues, I have always been told (esp by Yanmar) that is from shifting fast without letting eng revs spool down. I can't see too much difference in drag between 2 & 3 blades - maybe if you set the shaft to vertical the folded prop every time the 2 would be better, but absent that no real difference.

Auto prop - my contacts at PYI claim that because of the offset blades, the auto never fully feathers. I can easily believe that statement, it has to happen given the offset loading on the center of rotation.

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The AutoProp will not feather in the conventional sense at low speeds mostly because its pivot and center of gravity curse the blades to hang down looking like a seagull with broken wings. But above about 5 knots the waterflow gets them streaming aft into a semblance of feathering/folding and I'm sure the drag is not all that big a negative. At higher speeds they will assume an attitude to create the lowest drag possible but I would recommend shaft breaks to keep them from freewheeling because I'm pretty sure that they will always create some torque.  I ran a 50 electric hybrid cat for a year with a plain vanilla three blade on one shaft and a AutoProp on the other and was able to compare in many ways. 

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1 hour ago, Tylo said:

I don't know if you've come across this already but here's a pretty big test of many folding props in Yachting Monthly:

https://www.yachtingmonthly.com/gear/folding-and-feathering-propeller-test-29807

Unfortunately they couldn't bring themselves to name a winner but there's some valuable performance data in there at least. 

Yeah, I saw that. Gori was my foregone conclusion until I saw that test/article. Sure looked like FOF was the winner. 

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Has anyone heard about Aquateck feathering props? Picture:

 

2C75C3CC-CF91-499C-A2F3-49966C36DA00.jpeg

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I’ve got 2-blade Gori and I think they are good props. They were original to the boat (1992) and I replaced bc the newer model has a collar zinc that the old style didn’t. 

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FOF always seem to do very well in testing. Friends who have them speak highly of them.

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I cruised with a pair of FOF. I put them on when I bought my cat, on yanmar 3Gm30s with shafts, they worked just fine.

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I had a Gori fail when out in the Pacific Islands. They took months to answer my email by which time I'd given up and arranged replacement FOFs. They're saildrive geared folders. The failure was separation of the hub. Gori's answer when it finally arrived was essentially "dunno why, here's our price list." YMMV. I can't make out any difference in performance under sail or power between the Gs and FOFs. The FOFs are a bit easier to work on.

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The FOF are about $2500 less for the pair vs the Gori. That makes a compelling argument for them, too, beyond just the test results.

I guess it's decided. FOF FTW.

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I would go with a Gori 2 speed every day. If you have 5 kn of wind get one motor going in high speed and you are cruising at half throttle at 8 kn fantastic!!!

Just get one.

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Nice thing about a catamaran is that you can install slightly overpitched props (folding for minimum drag of course) such that you attain max speed in flat water with no wind on both engines. Then individually (with only one engine running) you will be well overpitched - BUT - you will be in great shape for extremely efficient motor sailing in light air, running only the leeward engine, particularly upwind - the cruising cats weakness.

The leeward engine will rotate the bows to windward and the small weather helm generated will help the boat lift to weather as the sails boost speed such that my boat routinely exceeds her balls to the wall two engine max at 3,600 with that one little (18 hp) Yanmar turning a comfy 2,800 where it runs over three hours on a gallon and helps advance the boat well over twenty miles.

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^^^ and double the expense when two overloaded engines expire at low hours. There is no situation where over-pitch is economically beneficial. 

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Well that's odd because after forty years of equipping and operating auxiliary powered sailing multihulls as described I never overheated or smoked out an engine.

I did fully rebuild the engines in my current cat after I bought it from a guy who was not even interested in raising the mainsail during our trial sail, the boat was wearing OEM fixed two blade props. I also reduced the diesel tankage by 75% - I am talking about SAIL boats.

17 minutes ago, El Boracho said:

^^^ and double the expense when two overloaded engines expire at low hours. There is no situation where over-pitch is economically beneficial. 

 

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Soma, we have FOF 3 blades and they're nice props although heavier than the Gori's. There are a few A57's with them and they get positive feedback.

The new composite prop from FOF is something I would definitely look into. Most probably what I'll stick on the next boat if it's permissible. I like FOF because their delivery times are good and they've got great customer service. I'll not rule out the Gori's though.

Charles had these on Leopard and loved them. I'll also take a look at these for the next boat.

https://ewoltech.it/en/

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Not a catamaran but I went to a FOF prop last spring, gained a full knot of boat spd over the last prop, excellent reverse performance and fuel consumption went down. It was everything they promised, from a timely quote , order and delivery was about 10 days. 

I cant say enough good, and they were nearly a grand  cheaper than gori. 

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I considered switching to FOF on a Catana 50 but I don't know what size/pitch combination to order. The C50 has Volvo-Penta four-blade propellers. So I don't know what the equivalent three-blade props would be.

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Just send them an email with the boat and engine specs and they'll let you know what size you need. Make sure you have enough clearance if you switch to a larger prop with fewer blades.

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Any opinions on the Kiwiprop?

Very light. But of course with a prop, that is not the only thing to look for. 

Paul 

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Kiwiprops have true believers, they are cheap and seem to work ok but they are not nor can they ever can as efficient as a well designed folding prop,

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