Shopping of a Prop

[Seevee]

All,

I'm shopping for a prop, want a backup.

I've got a 5 blade, 26 in 19.5 pitch bronze prop and finding one is hard. Would like to pick up a used one, if possible.

Where are good places to search or prop shops that many have one?

And if I get one that's close, like the pitch is off a bit, how much can the pitch be changed?

Also, how valuable are cupped props?

[DavidM]

Does your current prop let the engine rev up to 3,400 rpm in gear at wot (accurate phototached rpm)? If not look for a prop with less pitch. A general rule of thumb is 1" of pitch will result in 100 rpm change. A prop can usually be repitched about 2" by a good prop shop.

That boat with the single is strictly a displacement speed boat- 8 kts or so. Running it harder will pick up a knot or two at a huge increase in fuel burned. I don't think that any modern props will do a lot for that reality.

For info on everything about Mainship 400s, look at Steve Cyr's website: Stella Blue Home.

David

[O C Diver]

5 blade are tough to come by used in a 26" diameter. Depending on the metal in the prop some can only be repitched an inch or two (Nibral prop), others maybe 4". A good prop shop is often associated with others that have both new and used. Find a good shop and see if they can find you one. You can always use a 4 blade as a spare. The pitch will be a little different.

Ted

[caltexflanc]

Not sure what is in the Tampa area. Over in Lauderdale, there is Lauderdale Propeller and Frankie&Jimmies. The surplus stores like Sailorman usually have various props around.
On line, these guys are good, give them a call if they don't show what you are looking for:
PropellerPlace.com

[psneeld]

This place in Ft Pierce for used props and other stuff....

Marine Connection Liquidators

[Rufus]

Originally Posted by djmarchand

That boat with the single is strictly a displacement speed boat- 8 kts or so. Running it harder will pick up a knot or two at a huge increase in fuel burned. I don't think that any modern props will do a lot for that reality.

David

That said, the hull is a planing design, correct?

[Seevee]

All,

Good replies, thanks.
The hull was sold as a semi displacement hull, however, with a single engine, it does very poorly at speed, getting about 14 knots, and just pushes a lot of water. Goal is to cruise mostly around 7 to 8 knots.

And, in talking to a few prop shops (that seem to be knowledgeable) they say a 5 blade is more appropriate for pulling, like a tug or fishing boat pulling nets. And for pleasure cruising I'd be better off with a 4 blade with a slight bigger pitch. Makes sense to me.... any truth to that?

4 Blade props are MUCH easier to come by.

[Nightsky]

Nothing says you have to stick with a 5 blade propeller. Typically five-blade propellers run smoother and quieter than 4 or 3 blade propellers.

[Nomad Willy]

Don’t see any comment about power.

Your prop clearence and power should determine how many blades you have. Best would be to find an easy to find three blade and try it. I suspect you’ll find it has the best performance. I’m assuming you have a typical blade design.

Got a pic of the 5 blade?

[Maerin]

Originally Posted by Seevee

All,

Good replies, thanks.
The hull was sold as a semi displacement hull, however, with a single engine, it does very poorly at speed, getting about 14 knots, and just pushes a lot of water. Goal is to cruise mostly around 7 to 8 knots.

And, in talking to a few prop shops (that seem to be knowledgeable) they say a 5 blade is more appropriate for pulling, like a tug or fishing boat pulling nets. And for pleasure cruising I'd be better off with a 4 blade with a slight bigger pitch. Makes sense to me.... any truth to that?

4 Blade props are MUCH easier to come by.

The fewer the blades, the higher the efficiency and transfer of power to thrust. More blades=smoother running, less noise. One of many compromises in the whole of boating.

You're getting information that's helpful, and you mention speed. Understand that you're dealing with a non-planing hull, so things like speed and cavitation, are moot. You don't mention your WOT, which in a displacement or semi-displacement hull is more important than speed. Your prop should be configured to allow the engine to reach its rated WOT. If it falls short, it's overpropped and overloaded. If it attains WOT rpm beyond its rating, it's underpropped.

You'll find differing philosophies regarding this aspect of propping a boat, but for the most part, there will be more agreement that overpropping/overloading a diesel is undesired, and can be detrimental to efficiency and longevity, in particular. An overpropped boat will make a higher speed, but at the cost of higher fuel consumption and increased wear & tear on the engine. An overloaded diesel will burn more fuel across the range of RPM. Refer to boatdiesel.com for in-depth information. LOTS of discussion about propping there. Says something about the importance.

If you want to max out speed, you're in the wrong boat. Sell the Mainship and buy a planing hull, get high pitch cupped props and go like the wind.

If you want to maximize your performance and economy on the boat you have, make some test runs and accurately chart speeds at WOT and various RPM's in between. Take the money you'd spend on a spare and have a prop shop computer scan your prop and tune it to your boat's rated WOT and enjoy the improved fuel burn and smoother run. Your diesel will be happier. There are no bragging rights associated with trawlers and top speed, it's incidental and shouldn't really have a bearing on the prop selection. That's for planing hulls.

It would be interesting to survey the actual trawler owners on the forum and see how many carry a spare prop, and how many have ever put one into service. I'm betting it wouldn't be many. I think the impetus for a spare is a carryover from the planing hull/twin engine world, and it's just a little misplaced in a single screw trawler world. But, that's my opinion and I was wrong once before.

[Nomad Willy]

Maerin,
Great post well written but are you sure an overpropped boat will have more speed? I don’t think so. The engine will be making less than max power.

[Seevee]

Steve,

My current prop is sized correct. I get full rpm of 3300 wide open, and not more or less. I have no issue with keep a 5 blade, except its availability and cost, especially if there's no performance benefit.

I need a prop, either get mine fixed or get another, and I'd like to have a spare.

And, has anyone gone from a 5 blade to a four blade and can report on the differences, and the specs of each prop?


Eric....Pix of current prop:

[Ski in NC]

Do you have a full keel protecting the prop? If so, the chances of damaging it are quite low.

Also, if you are running hull speed and under, you don't really need a 5b. 5b is often used when running a single engine boat with big keel, and running it fast. Fast, that keel puts a lot of disturbed water into the prop and it makes a lot of noise and vibe. Running hull speed you rarely have that problem.

A 4b will work fine at hull speed.

[Nomad Willy]

Seevee,
Quite a prop there. Must be heavy.
What’s the dia and pitch?
It’s great you’re propped good at WOT. The advantage of the 3b or 4b will be greater efficiency. But if your 5b is very smooth and you aren’t particularly interested in efficiency -I’d just get a 3b for a spare and run the 5b. Get a prop shop or Michigan Wheel to calculate the pitch/dia for the new 3b spare. I’ve never used my spare prop. Going to put it back on though as I like it better. And it’s perfectly propped at 50rpm under (50 more rpm) and then I can take an inch out of the MP prop I’ve been using for quite a few years (overpropped 50rpm).


Who put that 5b on? Can’t imagine it was Mainship due to the unnecessary expense. A remote issue could be keel turbulence necessitated the 5b for smoothness. Again do you know anybody w a boat like yours?

[Donsan]

Any chance the PO or a previous PO was pulling a tender? That might explain the 5B prop.

[Maerin]

Originally Posted by Nomad Willy

Maerin,
Great post well written but are you sure an overpropped boat will have more speed? I don’t think so. The engine will be making less than max power.

That sentiment stems from the (mis)concept(ion) oft heard around trawler discussion where the thinking is that if the boat runs say, 7 kts @ 1800 rpm, then increasing the pitch of the prop will make 7 kts @ 1600 rpm. Better, not? I think it's a throwback to gasser props with planing hulls. I mistakenly bought into that idea until an experienced prop guy schooled me on WOT and the concept of loading a diesel engine. His answer to my assertion back then that it would be more economical to make higher speed at lower rpm was "if you wanna go faster, push the throttle forward. Don't overload your engine."

He took 1-1/2" of pitch out of my (3 blade) prop, computer scanned and balanced it. My speed at 1800 dropped, WOT at rating, but my fuel economy increased by 20%. He predicted as much. He made a believer out of me!

[DavidM]

Your prop guy is a wise man .

David

[Thinback]

I also have a Mainship 400 T with the same prop. The standard prop from the factory was a 4 blade. The 5 blade pro was an option. When shopping for my boat I saw more 5 blade singles engine Mainships.

[Seevee]

Originally Posted by Ski in NC

Do you have a full keel protecting the prop? If so, the chances of damaging it are quite low.

Also, if you are running hull speed and under, you don't really need a 5b. 5b is often used when running a single engine boat with big keel, and running it fast. Fast, that keel puts a lot of disturbed water into the prop and it makes a lot of noise and vibe. Running hull speed you rarely have that problem.

A 4b will work fine at hull speed.

Ski,

Yes I have a full keel, but managed to bang it up twice. Both times I let someone else drive the boat. Never again. I'll always be in command when docking, or entering a channel or area that's questionable. And both could have easily be prevented. This last one is costing me BIG bucks and BIG time delay for my Loop trip. Errrrrr!

I rarely run wide open, 99% of the time at hull speed... 7 to 8 knots.
Looking forward to a 4 blade.

[Seevee]

Originally Posted by Maerin

That sentiment stems from the (mis)concept(ion) oft heard around trawler discussion where the thinking is that if the boat runs say, 7 kts @ 1800 rpm, then increasing the pitch of the prop will make 7 kts @ 1600 rpm. Better, not? I think it's a throwback to gasser props with planing hulls. I mistakenly bought into that idea until an experienced prop guy schooled me on WOT and the concept of loading a diesel engine. His answer to my assertion back then that it would be more economical to make higher speed at lower rpm was "if you wanna go faster, push the throttle forward. Don't overload your engine."

He took 1-1/2" of pitch out of my (3 blade) prop, computer scanned and balanced it. My speed at 1800 dropped, WOT at rating, but my fuel economy increased by 20%. He predicted as much. He made a believer out of me!

Steve,

Whose your prop guy, would LOVE to call him.