Best propeller for more speed in a Lagoon 42

[Peregrine1983]

We've had good luck with our PYI MaxProp Classic folding prop. It has tons of thrust in both forward and reverse and folds to lessen resistance while sailing.

They make a sail drive version, which I believe you would need for your Lagoon, called the Easy.

[DragonflyBob]

Originally Posted by Montanan

The line cutters become invaluable if one gets tangled, but they will degrade somewhat the performance of the propeller that is located downstream of the turbulent flow of the cutter blades.

One is unlikely to have doubly bad luck to get lines tangled around both of your widely separated, twin sail drives of catamaran and one can operate with just one propulsion system operating until you can untangle at a place of convenience.

We recently installed a Shaft Shark on our Flex-O-Fold folding prop used on the SD25 on our Dragonfly 32 tri. There are LOTS of crab traps where we sail to the point you cannot enjoy night sailing/motoring without the huge worry of fouling a crab trap.

I really have not seen a degradation in performance of the boat under power with the Shaft Shark installed, if so it has to be less than a 1/2 knot. We’ve had the Shaft Shark on for about 3 months now and so far have not had a fouling incident to be able to report how effective it is. Our boat uses a 3YM20 engine and with the engine speed at 2,400 - 2,600 rpm, the boat will move at 6-6.5 knots in flat water with minimal wind and current burning 1/2 to 3/4 gph of fuel.

[Montanan]

Possibility???

This Sacrificial Anode Line Cutter Assembly (SALCA) solves two major problems: line entanglement and galvanic corrosion. The Zinc metal helps protect the marine craft from corrosion in salt water, fresh water, and brackish water while the stainless steel cutting edge slices through lines guarding the boat against propeller entanglement.

Designed by divers for divers this sacrificial anode is a convenient and economical alternative to other line cutters because it doesn’t require mounting by professionals.

It is composed of two-sized halves that fasten around the propeller shaft which eliminates spinning under pressure. Conformed to the highest Mil-A-18001 standards for the world’s best cathodic protection.


https://anodeshack.com/salca-sacrificial-anode-line-cutter-zinc

[DragonflyBob]

Originally Posted by Montanan

Possibility???

This Sacrificial Anode Line Cutter Assembly (SALCA) solves two major problems: line entanglement and galvanic corrosion. The Zinc metal helps protect the marine craft from corrosion in salt water, fresh water, and brackish water while the stainless steel cutting edge slices through lines guarding the boat against propeller entanglement.

Designed by divers for divers this sacrificial anode is a convenient and economical alternative to other line cutters because it doesn’t require mounting by professionals.

It is composed of two-sized halves that fasten around the propeller shaft which eliminates spinning under pressure. Conformed to the highest Mil-A-18001 standards for the world’s best cathodic protection.


https://anodeshack.com/salca-sacrificial-anode-line-cutter-zinc

Great concept but it looks like this is only available for shaft drives and not sail drives.

[JimsCAL]

The most important thing to maximize boat speed when motoring is having a correctly sized prop. That usually means the largest diameter that will fit properly in the opening (not too little tip clearance) and the correct pitch so engine makes rated RPM when at rated HP. Make and model of the prop is secondary to this.

[MicHughV]

Not to state the obvious, but a clean hull and clean prop will do wonders for boat speed.

[CarlF]

Propeller sizing is still more art than science. Many boats are either over-propped causing strain on the engine and sometimes black smoke or under-propped limiting top speed. Over-propping a little bit can be a good thing but too much causes real problems. I would talk to other Lagoon owners to see what speed they can do with which props (including pitch and diameter). You'll likely find that there is a "best" for the boat.

I had Flexifolds on my previous monohull but went with Gori on my Leopard 50 cat because it was recommended that I needed a stronger reverse with a cat to maneuver in a marina. The Flexofold reverse is quite weak - wasn't really a problem on my monohull with a bow thruster. The Gori's will spin me in my own length with reverse bursts on one engine and forward on the other. The other prop recommended for strong reverse is the MaxProp.

The Gori's "overdrive" lets you add some pitch (I think 2"). This let's you go faster at a lower RPM but that's a mixed bag as you are over-propping the engine. You won't use less fuel because fuel use is determined by load not RPM. And the lower RPM wlll put the engine under greater strain - in an extreme case increasing wear on the engine and causing smoke/carbon buildup. It's also quite hard to "get into" overdrive as you need to get the boat to come to a complete stop to get the blades to reverse into overdrive. This is hard to do at sea. The Overdrive is very useful when motorsailing as the sails are carrying more of the load so you get more speed at a low RPM without overloading the engine.

The other route is to simply get a higher pitch propeller which would be like a constant overdrive in the Gori. The problem is that you are then likely to be "overpropped" and won't be able to reach engine maximium RPM. This would be a problem during survey when you sell the boat.

A folding or feathering prop increases speed under sail more than just about anything else you can do. It's worth doing just for that reason. You might find that you sail much more with a boat that sails better (and points higher). Most catamarans reach higher speeds under sail than power.

I looked at Brunton before getting the Flexofolds on the monohull. It's problem is that it has much more drag when sailing. Not as much as a fixed prop but way more than the Gori or Flexofold. They also require a lot of maintainance and have a reputation for losing a blade underway.

[Cheechako]

Originally Posted by patolega

Hi everyone,

I’m trying to choose a reliable propeller that will increase the speed when motoring on my Lagoon 42 catamaran, with a Yanmar 57 and SD60 saildrive, and would really appreciate input from fellow cruisers—especially other multihull sailors.

We usually do long raids of 6 to 8 hours mainly on motor.

I have been looking for options like Gori and Bruntons.

What would you choose again (or avoid)?

With or without ropecutter?

Thanks in advance for any help or experiences you’re willing to share!

Fair winds,
Patolega

Well, either you are propped right or you are not. Propped right you should reach hull speed, regardless of propeller.
I had Max Props on my 42 ft cat and 3 other boats. They are good powering into a chop when it's tough going and in reverse also. I shy away from any props that rely on centrifugal/centripedal force opening them like an Auto Prop etc.

One thing you will find is motorsailing with the lee engine is fast and efficient and stable and you will point up maybe 15 degrees better.

[barnakiel]

A well sized and geared (pitch) prop makes wonders.


I have seen boats identical dragging their feet at 150% of our hp while consuming 2x the fuel.


A well matched engine hp / prop / hull is a marvel. A marvel. Saves fuel, noise and makes for knots of "free" boat speed.


Very well worth the effort in study and (less) testing.


barnakiel

[MicHughV]

After reading " the Propellor Handbook" I took it on myself to see if I could improve the motoring qualities of my boat.
After reams and reams of calculations, formula's, etc, etc, the conclusion I came to was quite clear.
For most any sailboat, unless the inboard diesel is off sufficient power, fiddling around with props will gain little, if anything.
It doesn't require much horsepower to tootle along at 5 knots or so, but as one approaches " theoretical " hull speed, the horsepower requirements jump up exponentially. Then too, one can't expect any given diesel engine to operate at 100% duty, so an even bigger engine is required to bring that to around 75% duty.
In real life terms, while around 20 hp is sufficient to tootle along at 5 knots, it will require around 50 hp to do hull speed, and probably around 70-80 hp to ensure the engine has a reasonably long life.
Then there is the issue of the prop. While a big 3 blade prop can provide the thrust, so to will it provide gobs of drag.

At the end of the day, if you want to motor everywhere, get a power boat, which likely has the correct engine, or engines, to power you along, but for a sailboat some or other happy compromise is in order.

[patolega]

Originally Posted by Loredo

The OP asked a simple question, six worthless replies thus far...
I'll give it a try. For me the Autoprop by Bruntons works. Better speed, 30% less fuel consumption. The prop really shines when motor-sailing. I couldn't ask for more. They're pricey but you get what you pay for. Maybe this helps a bit?

Thanks

[skipperpete]

If the OP’s still around…. Patolega, what are the details of your existing propellers? Fixed or folding? Feathering? Pitch? Diameter? It would help a lot to know what you have that is currently unsatisfactory.

[drdoyle]

Some issues you may have to consider. First is what size propeller diameter is the maximum size the saildrive will allow. The saildrive reduction may be defined and not changeable. If you are planning motoring much of the time you should use the maximum propeller diameter that will fit and is compatible with the shaft on the drive unit. Pitch is determined by the speed through the water you are moving plus 10-20% slippage. And the rpm of the shaft at cruising speed. Without an engine change and probably a heavier rated drive unit don't expect much improvement in cruising speed. The 42 lagoon should cruise at about 8 knots in calmer seas. But in sufficient seas and not greatly submerged the drive mechanism may not keep a steady bite on the seawater to produce a speed above 5 knots. Get a 3 blde fixed prop of maximum practical diameter and pitched to match the cruising speed (or max rpm full throttle rpm pitch) , this is about all you can do/expect from your current propulsion system. It easier to get a new boat than to try repowering with twin internal hull mounted engines.

[maine50]

2nd or third vote for flexofold - assuming they make ones for saildrives. Great increase in boat speed at lower RPM's.

[Cheechako]

Originally Posted by MicHughV

After reading " the Propellor Handbook" I took it on myself to see if I could improve the motoring qualities of my boat.
After reams and reams of calculations, formula's, etc, etc, the conclusion I came to was quite clear.
For most any sailboat, unless the inboard diesel is off sufficient power, fiddling around with props will gain little, if anything.
It doesn't require much horsepower to tootle along at 5 knots or so, but as one approaches " theoretical " hull speed, the horsepower requirements jump up exponentially. Then too, one can't expect any given diesel engine to operate at 100% duty, so an even bigger engine is required to bring that to around 75% duty.
In real life terms, while around 20 hp is sufficient to tootle along at 5 knots, it will require around 50 hp to do hull speed, and probably around 70-80 hp to ensure the engine has a reasonably long life.
Then there is the issue of the prop. While a big 3 blade prop can provide the thrust, so to will it provide gobs of drag.

At the end of the day, if you want to motor everywhere, get a power boat, which likely has the correct engine, or engines, to power you along, but for a sailboat some or other happy compromise is in order.