need some prop advise

[idylours]

I have a Catalina 36 with a 21 hp universal currently it has a folding prop but I'm thinking of switching to a fixed 3 blade will this give me better handling under motor

[DougR]

It depends whether you have a folding two or three blade.

If you have a folding two blade, then the fixed three blade will have better drive in both forward and reverse, but significantly more drag under sail.

If you have a folding three blade, you might not find much difference in thrust in forward or reverse, but again more drag under sail.

DougR

[GordMay]

Fixed propellers are the least expensive and, when correctly sized, will provide the best forward propulsion under power with reasonable astern ability. But they will also create the greatest drag under sail.

You might be interested in:
➥ http://www.sname.org/HigherLogic/Sys...8-e1cb8ed62310

[GrowleyMonster]

If you mostly sail, and do not have electric propulsion, you want folding or feathering prop. If you motor a lot, a fixed prop is worth considering.

Just remember bigger diameter, higher pitch, more blade area, more blades, all load the engine more, and vice versa. It is possible to re-prop to outside your engine's optimum power envelope, or to spin the prop faster or slower than its optimum speed. There is a whole lot of wiggle room, but if you motor a lot then you want things more tightly optimized than if you only need the prop for docking and stuff.

Folding props are optimized for folding and trailing with low drag. In pursuit of a more slippery folding prop, propulsion efficiency is obviously going to suffer a little bit. You can't have everything. But a prop designed to push the boat efficiently is going to have considerable drag. You can't have everything. Even freewheeling the prop doesn't eliminate drag, only reduces it somewhat.

If you can re-prop cheaply, you might want to try it and see if it suits you. For instance, someone gives you a prop or you see a used one of appropriate size for sale cheap and you are fixing to haul the boat out anyway for bottom job, etc. Otherwise, and especially if you don't motor very much and loss of a half knot or so under sail is important to you, I would stick with the folder, at least for now.

[akprb]

I'm a big fan of a large fixed blade prop. Take the time to pitch it properly to your engine.

Read "motoring" on our blog for more thoughts :-)

[UNCIVILIZED]

You need to define what you mean by "handling". Since a feathering, reversible pitch prop like the MaxProp will probably give you the best ability to manuever in close quarters. Owing to it's generating almost as much thrust in reverse as in forward. But a fixed 3-bladed prop will probably give you the most power transferred to the water for motoring straight ahead, forward.

Keep in mind that if you find an inexpensive, used, fixed prop, the cost of the haul out & changing it, will run you more than the expense of the prop.

As to prop efficencies, there's no shortage of tests; here on CF, as well as online. Which it'd be wise to look for yourself at them.

Also, most any prop can be reconditioned, & or tuned to best suit your boat. Whether that's having the pitch on a fixed prop altered, or a MaxProp reconditioned. And with the latter, you can alter the pitch, in various increments, while it's on your boat, in the water.

[wesevans]

I am a fan of the maxi prop or a feathering prop. minimum drag under sail and good power both forward and reverse.

[Cheechako]

Many of the older folding props are terrible. poor thrust and especially bad in reverse. Is that what you have?

[Island Time O25]

My 36 footer came with Universal 5432 and a fixed 3 blade prop. Happy with both. Have once been thinking of changing to a maxi-prop or some such but was dissuaded by my more knowledgeable marine pro buddies. Their uniform advice is basically - don't fix what's ain't broken.

My 28 footer came with a shot Universal 5411 which I replaced with a Yanmar 2QM15. The Yanmar's prop was in bad shape but nevertheless the guys at the yard handling the removal of Yanmar from its old boat have misplaced it in their pile of junk stuff (stuff even they don't think will not sell but they still keep it just in case) and I have no patience to go through it as I'm not sure it was properly sized anyway. The prop which came with my boat was surprisingly made of plastic and on the last sail of the last season (on the way to the haul out) it chipped a corner the size of a quarter. It was far from ideal for the Yanmar anyway and I was going to replace it anyway. So over the winter I looked for a used 2 blade prop which would have the factory Yanmar specs for this engine and my shaft - 15X9X1RH. As I was having a hard time locating a used one in my $$ range (under $150 preferably around $50-100) with exact specs so I decided to look for a 3 blade as well, which for this engine/shaft was spec'd at 14X9X1RH. So I told the yard manager of the change to my search parameters and he directed me to a 3 blade section in their used props area. Bingo - a shiny, like new 3 blade which I installed in 10 minutes. They wanted $200 for it b/c of its condition but gave me a break of $50 as a credit for misplacing that old POS prop last year. Sure it'll degrade my speed under sail but I don't race and the boost in motoring performance is more important to me, especially control in reverse. Will update once I splash and check out its performance this season.

[idylours]

Originally Posted by Cheechako

Many of the older folding props are terrible. poor thrust and especially bad in reverse. Is that what you have?

yes it is and it's a 2 blade

[Island Time O25]

Originally Posted by Cheechako

Many of the older folding props are terrible. poor thrust and especially bad in reverse. Is that what you have?

I found that out during my search for a prop. The yard has dozens of these old folding props but none are fully functioning without this or that part which they are usually missing. And the boatyard guys were uniform in their opinion that even if I got one for free not to install it as it'll cost me more to replace it mid-season either b/c I wouldn't like its performance or some pin would break yet again.

[grjfield]

I replaced my Gori prop 3 years ago with a Flexofold 2 blade folding prop. I found a prop study that showed the folding props were in many cases better than the fixed props. To this point I have had no issues and it pushes my boat fine.

[Lancerbye]

I switched from my big three blade props to Campbell Sailor props, three years ago. l am very satisfied with the change. Greatly improved sailing speed.

[a64pilot]

Especially for a smaller boat, I see no need to haul the boat to swap props?
If uncomfortable with doing it yourself it may be less expensive to hire a diver as opposed to hauling

[sv.antea]

I have had a 15" old cruising style Martec on my Yankee 30 and love it. Had a chance to compare the motoring performance with similar fixed two blader when I swapped them for for going through the French canals once upon a time. There seemed to be no difference forward (I was hoping for improvement). The reverse was better with the fixed two blader, but I am quite happy with my 35 year old Martec, once I learned not to be shy with the reverse RPMs. Practical Sailor once ran a tank test comparing fixed and Martec folder and found no loss of performance in forward for the folder.
My take on Max Prop is: spectacular reverse, nautical disc brakes, but there may be slight penalty in forward, because the blades are flat, no twist. The few boats I repowered ended up slower at the same RPMs when the same pitch was dialed up.