Propellor

[BC Mike]

Sometime soon I need a new prop and strut. The strut has cracks so I will get a new one built. The prop is a two bladed Martec folding with longer than average beaver tail blades. I get a steady tromp tromp at higher revs with this prop. It could be the condition of the prop, or the slightly longer blades, or it could be from when both blades are behind the keel. There is enough hull crearance. So I have a decision to make about a new prop. A two blade geared prop or a three bladed feathering like the NZ made prop or the three bladed geared Gori prop. The prices in order in Canadian dollars are $1300- $1600- unkown. Any opinions are welcome. Eventually I will be motoring around Vancouver Island ( when not sailing ) and there are places with some strong currents. I want to minimize drag. BC Mike C

[Steve Rust]

Mike
For years I used a two blade folding prop on my 40 ft 12,000 lb trimaran. With only a 17 hp diesel this proved just adequate. Cruising speed was 5 knots, max was 6.5 Reverse was terrible. This last summer I swapped to a fixed three blade prop that had been lurking in the bilge for years because I was going to be doing some river travel. Cruising speed went up to 6 knots at 2000rpm and max was 7.5 at 2700rpm. This prop had a little to much pitch as I could not reach 3000rpm. Much better control in reverse. I plan on purchasing a folding three blade probably from Flex-o-Fold. My thoughts on feathering verses folding are with the folding prop you have cupped blade shape for highest efficency and they are less expensive but you hope that the supplier gets the diameter and pitch right. With the feathering adjustable pitch props you can fine tune them for your engine and boat but they generally have flat blades. Not the most efficent shape. Either one would be a vast improvement over the two blade and the 3 blade should have better balance and lessen vibration.

[BC Mike]

Thanks Steve. First I have to get a new strut. Flex O Fold was kind enough to reply to my e-mail, they are a bit more money for me in Canada. A friend owns North By West propellor so I think I will try a two bladed geared folding prop and If it is not smooth enough then switch to the three blade feathering. Still waiting for a price from Gori for a three bladed folding. I have a 15 hp Yanmar in my 7400 pound 29 foot boat so I have plenty of power for hull speed of about 6.5 but I usually back off a bit as it is waisted power at that speed. 6 is more than adequate, I think a feathering prop will be efficient enough. Michael Casling

[Jeff H]

Unless you have a tiny aperture, there is no reason to even think about putting a three bladed propellor on a 15 hp Yanmar or on a 7400 lb 29 footer for that matter. That is an ideal application for a Martec which are good, reasonably priced, very efficient propellors. I had a Gori on my prior boat and was dissatified with their reliability and with their product support. One of the biggest problems with thier service support was with their North American representative, Jensen, who is the person you are stuck dealing with if you buy a Flex-o-fold. Martec provided great support in reconditioning my current 20 year old Martec. Martecs are very rebuildable and Martec does this quite cheaply.

Jeff

[BC Mike]

Thanks for the input Jeff. The Martec prop I have at the moment is not geared so one blade can open without the other, so if I got a two bladed folding it would be a geared prop. I looked at a Varifold 2 bladed geared folding $1200- Canadian, it has lots of blade area and appeared well built. The blades closed nicely together. www.spw-gmbh.de Michael

[Steve Rust]

I came across an article in Feb 04 edition of water sailing">Blue Water Sailing about props. Here are a couple of additional points from the article.

Feathering props will generally provide more power in reverse than folding props because they present the same leading edge whether in forward or reverse. And as stated before folding props will generally provide more power in forward due to the more efficent blade shape.

Folding props are superior if reduced drag under sail is your goal with one exception. If your prop shaft is at a considerable angle from horizontal then a feathering prop with independently rotating blades will deliver less drag as each blade can weathercock to the water flow. Folding or ganged feathering blades will be pulled through the water at the same angle as the prop shaft. Kiwi Props and Autoprop were two listed as have independent blades.

[Robmaas]

We have a 46' aft cockpit Morgan we purchased about a year and a half ago...last year we dropped a new engine in, redid the wirering, plumbing , holding tanks and now electrionics...whew....The boat has an 18"dia 3 blade fixed ,,but when we bought it we were given a 3 blade AUTOPROP featherin prop....the question is should we install it???...its designed for this boat but our marina is telling us it is just another thing thats going to break....

Whats your opionion???...we are just family cruisers and not racers...and hardly ever back into our slip just use reverse when backing out of the slip and down on the anchor....so what do you think is it worth putting it on or is it destined for EBAY??

Rob

[Jeff H]

If Autoprop's claims are correct, they are supposed to deliver significantly higher efficiency when motoring than a fixed prop. Of course they also deliver greater distances run in a given time under sail in moderate conditions which also means less motoring time. With that in mind I would install it and enjoy it, and keep the fixed prop as a spare.

Jeff

[CSY Man]

Jeff:

I thought, perhaps wrongly, that a fixed prop was the most efficient for motoring as the blades are shaped without compromise as in folding or feathering, but that same fixed prop is of course the most ineffienct at sailing.


???

[delmarrey]

I've run both, and the feathering prop really makes a differance. Once you learn the personallity of the feathering prop you'll forget all about the fixed. They do need to be kept in good shape or they'll vibrate.
................._/)

[irwinsailor]

They sure know what they want for them! I would like to get one but I would need to mortgage the boat. If I remember correctly it was about $3500. for my boat.

[Sonosailor]

After asking many questions of many local sailors, and checking out the prices of the options, I opted for Flex-o-Fold, two blade for my small catamaran, to be powered by my Yanmar 2GM20 engines and SD20 saildrives. I replaced the two-blade fixed props before launch yesterday, and was expecting a poorer performance with these shorter blades. I was wrong. At 1800 RPM, the boat normally moved along at 5.5 knots. The new props pushed the boat to 6.5 knots at the same RPM. Response to higher RPMs seems good.

The company brags that they worked closely with Yanmar to get a good product. I have to assume that they worked harder than Yanmar did with the original props, and better optimized the shape and pitch. Still, it could be that my particular boat (35' cat) is better matched to the props, and others may not experience the improvement.

I cannot wait to try it sailing. I imagine the 4 big, long fixed blades (2 props) working like a built-in drogue system as my sails try their best. Anyone want to suggest a % improvement?

[captjohn360]

hey for whats its worth. i have the same engins and sial drive on my athena 38. i put on gori folding props love them. picked up 1 to2 knots powering and sailing. and great in reverse also. only 650$ each jt

[Jeff H]

I had a Gori prop on my last boat. The props were not terribly reliable (the polyurethane connection between the hub and the shaft socket failed several times and a hinge pin failed once as well) and the factory support was farf worse than awful. I would never buy a Gori prop again and would consider it a deal breaker on a larger boat if it required one.

Getting back to the original question, my boat made a very distinct 'thunk thunk' at speed. I had been concerned that it was a problem with the Martec prop and had it rebuilt and the noise did not go away. This spring I replaced the cutlass bearing and it is amazing how much quieter the engine and drive train became. The thunk thunk is gone.

Also, CSY man, for many years I thought as you did but as it turns out not all props are made the same. Many folding props are actually made so that they are more efficient in motoring in the forward direction than a fixed prop because they do not have to have the compromized shape to reduce drag when sailing. Like many things in sailing the improved efficiency in forward sometimes results in a reduced efficiency in reverse. Autoprop claims a higher efficiency than other props because the pitch changes with load. That said, I have come across some negative comments on the Autoprop when used in rough conditions.

Regards,
Jeff

[Alan Wheeler]

And just to add a little something. Sometimes a prop lock in position can create less drag than one left to rotate. Why? well it depends on water speed, but at some point, the water is cavitating behind the locked prop. This produces a result much like a spoiler on a car. The turbulence behind the prop reduces the drag. A blade that is left to free spin can infact create more drag at certain water speeds. In other words, the cavitation is reduced, but the prop is not spinning at full water speed due to friction in the drive train. Thus the drag behind the prop stays for a larger range of water speeds. How it affects a boat depends on so many factors that as stated above somewhere, trail and error is the best method of seeing which is best. As also stated, how the transmision is lubricated is most important to whether the prop should be locked or not. IF the oil is good quality and clean, then there should be little additional wear to the transmission. The box will remain much cooler. The only concern is the shaft seals and bearing of the propshaft itself. Doesn't matter if it turns under load of the engine or from turning in the water, it still has a limited number of turns for its life. But that is a long life in most situations.