Cutting Diffuser off Merc Maximus 5 blade

[RiverDave]

I haven’t machined anything in over six months because if my ankle injury. Sean needed the diffuser cut off his prop late last week, and it was nice to fire up my lathe.. Thing was pretty stuff originally from sitting so long, but a quick clean up on the ways and it was right back to normal.

Other than it being fairly “sketchy” looking it is a pretty basic job. Go in with a part off tool and chop it off than clean up edges.

Had to move the tool post a bit to clear the blades on the prop and the table..

Indicating the tool post to make sure the part off will be perfectly straight.

Closer shot

You can see I slid the tool post over quite a bit. If you see that little protrusion underneath the tool post and about halfway across the table. That initially would have hit the blades.

Always make sure you check clearance through the stroke of the cut! Because it didn’t hit initially and would have hit the tips of the prop right about the time it was getting close to parting off.

Clearance

Power steering fluid

Parted off and deburred with a file and a rat file.

Part that was removed.

Quick cell vid

 

[Headless hula]

Thanks again Dave!

 

[spectras only]

I'm surprised you didn't use a Bravo prop shaft to mount the prop on. I used Merc propshaft, splined insert and nut to mount the prop, but, no matter how many positions I've tried the props weren't running true. Both of my props were like that.I guess the cast Bravo S/S props are no match to SNC made props.Are those props you have here are for OB or IO? Seeing went plugs, I assume OB?! If so, I would have left the diffuser on.
My prop on the lathe running pretty ugly.

Why didn't you turn the tool post 90 degree and have a J shape bit to go in?

 

[spectras only]

Ps; I'm gessing that you were using dial indicator to true the prop on your lathe before cutting the diffuser, holding the prop by the jaws. i'd be interested to find out how concentric the prop mounted on shaft , instead of the hub. Maybe Maximus props are better than the Bravo 1's as manufacturing go.

 

[Bucketlist]

Hoping Im not going to get flamed for asking this question............ what is the reason for cutting off the diffuser?

 

[28Eliminator]

Thanks again Dave!

Not interested in transom lift?

 

[Headless hula]

Not interested in transom lift?

Between the sportsmaster gearcase, and those big azz blades on the maximus, theres PLENTY of sternlift.

 

[Headless hula]

Hoping Im not going to get flamed for asking this question............ what is the reason for cutting off the diffuser?

The particular Maximus propeller that I have, came as a long-tube version.
I just needed a standard for my particular application, and the long tube is what was available to me, and as you can see by the video it is fairly easy to modify.

They can be ordered three ways, long tube, standard, and short.

I found a smoking deal on this one and it happened to be a long tube.

 

[Headless hula]

So Dave did me a solid and cut my prop off for me, and now he has some winter boating content for the site.

That's a win.

 

[Flying_Lavey]

Between the sportsmaster gearcase, and those big azz blades on the maximus, theres PLENTY of sternlift.

How'd it run once unloaded?

Sent from my LM-G710VM using Tapatalk

 

[Headless hula]

How'd it run once unloaded?

Sent from my LM-G710VM using Tapatalk

Solid!

 

[spectras only]

Hoping Im not going to get flamed for asking this question............ what is the reason for cutting off the diffuser?

You can read educated guesses/ opinions on OSO, by BBlades, ThrottleUp, Ed and others. It all depends on what hull, x dimension and other scenarios.
https://www.offshoreonly.com/forums/prop-talk/105876-diffuser-rings-what-do-they-do.html

 

[Racey]

I get the chills any time i put something in the lathe with arms like that... doesn't matter how many times i've done it, it sends shivers down my spine every time.

 

[spectras only]

I get the chills any time i put something in the lathe with arms like that... doesn't matter how many times i've done it, it sends shivers down my spine every time.

Dave's using Coors Light as lubricant, cutting S/S

 

[spectras only]

Hula, 82.17 is a nice number. Did you gain some speed with the diffuser removed?

 

[Headless hula]

Hula, 82.17 is a nice number. Did you gain some speed with the diffuser removed?

I gained midrange acceleration, and a bit better handling on the big end.

More importantly, I didn't lose anything on the bottom. Still planned really well. It gets right up.
I'll run it more when I get back.

It went 84 with a 26 standard length.
I only had enough time to run it for a little while, and was not able to do much mid-range cruising around or anything like that.
This particular 24 Maximus will plane the boat with six adults and full of fuel.
It is very very very rare that I have that much on board nine times out of 10 it is usually just pop tart and myself with maybe a medium-sized cooler..

 

[Shlbyntro]

View attachment 820084

View attachment 820085


Brand new Coastal Marine Export prop?

 

[RiverDave]

I'm surprised you didn't use a Bravo prop shaft to mount the prop on. I used Merc propshaft, splined insert and nut to mount the prop, but, no matter how many positions I've tried the props weren't running true. Both of my props were like that.I guess the cast Bravo S/S props are no match to SNC made props.Are those props you have here are for OB or IO? Seeing went plugs, I assume OB?! If so, I would have left the diffuser on.
My prop on the lathe running pretty ugly.

Why didn't you turn the tool post 90 degree and have a J shape bit to go in?

Didn’t have a prop shaft laying around on a Thursday night.. lol

As well it all cleared (albeit tight) so no reason to change setups. If he wanted to take more off than I would have had to start getting creative or get some tooling.

 

[RiverDave]

I get the chills any time i put something in the lathe with arms like that... doesn't matter how many times i've done it, it sends shivers down my spine every time.

As Sean said... Coorslight helps. Lol

It’s more the filming with one hand and using the other to plunge that makes me sketchy. Lol.

Risking life and limb for the entertainment of others.

 

[spectras only]

Didn’t have a prop shaft laying around on a Thursday night.. lol

As well it all cleared (albeit tight) so no reason to change setups. If he wanted to take more off than I would have had to start getting creative or get some tooling.

Dave, anybody with a lathe should have a prop shaft laying around. I took about 5/8 off from my props, looks to me you did about the same or just maybe a tad more.

 

[Go-Fly]

Does this really help anything or is it, I think it feels better then last week? I've seen small things make a big difference but, this is inside the maximum wash of the prop. What forces are on that little .625 ring you cut off. Asking for a friend.

 

[Headless hula]

Does this really help anything or is it, I think it feels better then last week? I've seen small things make a big difference but, this is inside the maximum wash of the prop. What forces are on that little .625 ring you cut off. Asking for a friend.

Time I ran this boat in Wisconsin I had the chance to run two 26 pitch Maximus props. the only difference from one to the other was there was one in, not 5/8 of an inch but one inch of the tube cut off. The boat ran 4 miles an hour faster with the prop that had the shorter tube.

You know, we are always learning things. Taking an inch off of my prop just to see what it does? Sounds like it's a good exercise in education to me.

 

[spectras only]

When you have nothing else to do, watch this video. You must have patience to finish something like this.Even if it is useless per se, it's still fun.

 

[Go-Fly]

Time I ran this boat in Wisconsin I had the chance to run two 26 pitch Maximus props. the only difference from one to the other was there was one in, not 5/8 of an inch but one inch of the tube cut off. The boat ran 4 miles an hour faster with the prop that had the shorter tube.

You know, we are always learning things. Taking an inch off of my prop just to see what it does? Sounds like it's a good exercise in education to me.

Is this a drag issue? You're on plane, lift is no longer in play. Did you gain RPMs?

 

[Headless hula]

Is this a drag issue? You're on plane, lift is no longer in play. Did you gain RPMs?

Drag and leverage.
That extra inch was acting like a wheelie bar. I want to pry that bow up just a tiny little bit.

If the tube is shorter, maybe the slip% would go down a tick too...

 

[QC22]

When you have nothing else to do, watch this video. You must have patience to finish something like this.Even if it is useless per se, it's still fun.

Crank's bent and I'll need to see dyno numbers to take it seriously.

 

[Go-Fly]

Interesting. Can you cut the tube back to the blades to reduce slip and use trim to control the bow? Do you lose pull out of the hole? There is always give and take.

 

[monkeyswrench]

I can see possibly removing the bell shape portion of the diffuser changing the thrust angle, or vector...cone of spinning water? and making it more focused. The prop equivalent of adjusting the beam on a Maglight.

 

[Headless hula]

Interesting. Can you cut the tube back to the blades to reduce slip and use trim to control the bow? Do you lose pull out of the hole? There is always give and take.

Cutting another inch off it may create difficulties planing..

If you're interested, here's some reading to get you up to speed with what I have done to the boat so far...

https://www.riverdavesplace.com/forums/threads/23-kryptonite.182381/

 

[Headless hula]

I can see possibly removing the bell shape portion of the diffuser changing the thrust angle, or vector...cone of spinning water? and making it more focused. The prop equivalent of adjusting the beam on a Maglight.

But only half of the prop is in the water at any given time. This is a surface-piercing application which kind of changes up the ball game a little bit.
At this point I am basically chasing a popcorn fart through a keg of nails...

 

[spectras only]

Crank's bent and I'll need to see dyno numbers to take it seriously.

Yes, he spent a lot of time to make this conversation piece. Yet once it's assembled and turned on , it wobbles like a Mecruiser Bravo 1 prop on a lathe. I think he just wanted to demonstrate the concept of using solenoids to make a shaft turn.

 

[monkeyswrench]

But only half of the prop is in the water at any given time. This is a surface-piercing application which kind of changes up the ball game a little bit.
At this point I am basically chasing a popcorn fart through a keg of nails...

Ahh....That does change my theory quite a bit. In that case, the diffuser area is no longer counter acting itself, if just the lower portion is submerged. It would be drag either way, but partially submerged it would push down...creating hull lift, I think...

 

[Go-Fly]

Cutting another inch off it may create difficulties planing..

If you're interested, here's some reading to get you up to speed with what I have done to the boat so far...

https://www.riverdavesplace.com/forums/threads/23-kryptonite.182381/

Cool build. It's going to take a little to read through it all, just read the last part. Having a hard time getting my head around this. Seeing how it works in real time testing makes me wonder why, not if.

 

[Headless hula]

Ahh....That does change my theory quite a bit. In that case, the diffuser area is no longer counter acting itself, if just the lower portion is submerged. It would be drag either way, but partially submerged it would push down...creating hull lift, I think...

Stern lift, but yea you get the idea. The prop blades bashing the surface of the water picks it up plenty.

 

[Taboma]

Yes, he spent a lot of time to make this conversation piece. Yet once it's assembled and turned on , it wobbles like a Mecruiser Bravo 1 prop on a lathe. I think he just wanted to demonstrate the concept of using solenoids to make a shaft turn.

I'm fascinated by the process and the amount of dedication to precision and amount of time to produce something that does essentially nothing.
In a way reminds me of childhood friends who built model cars as if they were future museum pieces, spending weeks on a single model getting everything exact.
I, on the other hand, would slap those fucks together then blow the shit out of them with cherry bombs I honestly tried to emulate my friends, to enjoy the build, not just blowing up the finished product --- couldn't do it.

What I am most curious about in this project is how with only a two wire connection to a single power supply, he's getting the adjacent solenoid cylinders to fire @ 180 degree intervals.

 

[HydroSkreamin]

In a way reminds me of childhood friends who built model cars as if they were future museum pieces, spending weeks on a single model getting everything exact.
I, on the other hand, would slap those fucks together then blow the shit out of them with cherry bombs I honestly tried to emulate my friends, to enjoy the build, not just blowing up the finished product --- couldn't do it.

Haha! That’s me and my cousin at age 10-12. We’d both buy the Revelle snap-together ‘55 Chev and I’d trim all the parts, file the edges, lube the axles and get all the decals on straight.
He couldn’t wait to cherry bomb what he snapped together as fast as he could. I couldn’t blow mine up...

Today he’s a successful body man in a Dodge garage (lifelong Dodge guy) and I work in engineering doing detailed work with tight tolerances. Guess we both met our calling.

I’m guessing you’re a giterdone kinda guy. I probably build more fixtures than necessary

 

[HydroSkreamin]

RiverDave, nice work on parting the diffuser and saving the part in case HeadlessHula needed to add back.

Fortunately, I don’t think that’s happening anytime soon.

 

[monkeyswrench]

I'm fascinated by the process and the amount of dedication to precision and amount of time to produce something that does essentially nothing.
In a way reminds me of childhood friends who built model cars as if they were future museum pieces, spending weeks on a single model getting everything exact.
I, on the other hand, would slap those fucks together then blow the shit out of them with cherry bombs I honestly tried to emulate my friends, to enjoy the build, not just blowing up the finished product --- couldn't do it.

What I am most curious about in this project is how with only a two wire connection to a single power supply, he's getting the adjacent solenoid cylinders to fire @ 180 degree intervals.

At about the 17m mark, he put 4 micro/reed switches in the crank case, mounted to the base.
I can't say I'd ever build one, but damn, I wish I had the skillset.

 

[Taboma]

At about the 17m mark, he put 4 micro/reed switches in the crank case, mounted to the base.
I can't say I'd ever build one, but damn, I wish I had the skillset.

AHHH, OK thanks, went back and sure enough. You see it's that patience thing again, got near the end and I kinda sped things up a bit and hadn't noticed those were reed switches --- now it all makes sense

Best get back to the diffuser discussion before Sean boots our asses out of his prop thread.

 

[Mandelon]

Drama Free!

 

[CoolCruzin]

Dang
I was holding my breath for you as the cut off blade was starting to cut .

 

[BDMar]

Here's a very short Readers Digest version of the effect it had on my boat (Daytona 28LP) about 3 or 4 years ago. I was testing props and a friend with an F29 had a set of 34 Bravo Ones with the diffuser cut off. I had a standard set of 34's. His F29 loved them, my boat hated them. Nearly impossible to get on plane. Getting on plane, the diffuser ring also feeds water to the blade tips helping the props stay loaded. Once it actually got on plane, it also didn't like not having the transom lift. It felt like it was dragging an anchor. The boat was about 7 mph slower and needed way more trim to get air under it and get a little transom lift. Even though the props are "surfacing", the diffuser still creates tail lift.

 

[guest hs]

When you have nothing else to do, watch this video. You must have patience to finish something like this.Even if it is useless per se, it's still fun.

That was a really interesting video thanks for sharing.