Glen-L.com

Guys - As you know, I have been trying to resolve a few issues with Midnight. Specifically, I wanted to reduce my max RPM WOT down from 5800 to 5000-5200 per manufacture recommendations and also remove the singing I am getting from the prop above 30mph

I am pushing using 343 ponies on a 1.23:1 tranny. My torque curve is pretty high. With a 2600# unloaded boat I theoretically could use a 13x21 or 14x18.

I started with a 13x16 three blade, recommended by the manufacturer. The revs approached 7000 in a heartbeat on that one. This was changed to a 13.5x16.5 four blade.

Singing started and got pretty loud above 30mph. RPM's matched the speed consistently but the RPMs still reached 5800 and I was able to reach 60mph.

So I called the ACME plant and spoke to them about the issue.. The singing is caused by the trailing edge of blade not being square and sharp. They asked if I had run the prop thru some sand. WHAT????? So they agreed to resquare the trailing edge for free. They also recommended to recup my existing prop to .190 and give it a try.

I had my first opportunity this weekend with the revised prop.

I just responded to Kens about the performance in a PM so I am just going to copy my response.

""I actually did run it yesterday for the first and I am not too fond of it.

Bullet points
1. I lost 1300 RPM.
2. I lost mph. My max speed now is 48. I was able to hit 60 before.
3. I have a minor prop vibration
4. But I did lose the singing sound
5. I have great midrange efficiency. I am cruising at 30mph on 2300 rpm but the power curve starts falling rapidly from there. At 48 mph, I am pushing 45RPM and that is all there is. I need to max WOT between 5000-5200.
6. I actually have some side torque to the left now when backing up. Found this out when taking the boat off the trailer. It caused my boat to scrap along a bracket on the side of the trailer and I now have a 18" long scratch just above the water line I have to repair. This was a very shallow ramp. I had to literally have all 4 wheels of my truck in the water so the trailer was unusually shallow. Previously all ramps allowed the trailer to drop away underneath the boat but not this one. So that clamp is now moved and won't cause a problem anymore.


So what this is telling me is that my original 13.5x16.5 4 blade was really really close. I am going to send the prop back to have them reduce the cupping in half. It is rather aggressive at .190.

I am going to try out the 3 blade 13x16 I have today just for a whim now that I have the porpoising issue resolved.""


Isn't boat building fun!!!!

dave

_________________
Dave

My Riviera build - the Midnight Cry Project

Video of Midnight in Action
Blog

Few things in the world measure up to the thrill and satisfaction of boating in a boat that you built.

Not always a bad idea to go back to square one. I'm sure you will get optimum results eventually.

Roberta

_________________
Roberta
Built Zip "Oliver IV" and Super Spartan "Jimmy 70"

I had a prop re-pitched or cupped to just 1" more to drop the RPM's some and hated the results....Bought a different brand of the pitch I wanted, but haven't tried that yet

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Dave swote,
"This was changed to a 13.5x16.5 four blade"

How much cup was on this one?

_________________
God Bless our Troops; especially our Snipers

started with a .08 and increased to .19

_________________
Dave

My Riviera build - the Midnight Cry Project

Video of Midnight in Action
Blog

Few things in the world measure up to the thrill and satisfaction of boating in a boat that you built.

Acme has a common cupping of .13 on their listings, that may be the one for you.
I am very surprised you lost so much speed. Something doesnt seem to compute.

_________________
God Bless our Troops; especially our Snipers

Tell me about it

Anyway, put my original 13x16 three blade on today. Criminy, the difference. No vibration and no singing.

But at 55mph I was doing 5800 RPM. I did not stay there. And I still had a lot of throttle.

At least I have my porpoising totally resolved. The boat is not porpoising at all and not plowing either at high speed. It is just perfect.

I wanted to do some trial runs at various speeds and start charting some various props but got cut short. The marina gave me some bad gas and I had to limp back to the dock. Anyone want 10 gallons of something that does not like to burn?

dave

_________________
Dave

My Riviera build - the Midnight Cry Project

Video of Midnight in Action
Blog

Few things in the world measure up to the thrill and satisfaction of boating in a boat that you built.

Dave,
After much trials with different props and detailed tracking of each; they sent me a prop to be the end all of trials.
Well, that thing was a dud. I couldnt turn it at all. They said it was a 16x12 heavy cup, and if I'll be damned, it was a 17 pitch if i ever saw one. I know, I own a couple of 'em.
I discussed this with the shop and I even allowed them all the caveats.
It was someone else' prop mistakenly shipped to me
The computerized measuring machine needed a daily calibration
Their technician had a bad day
they would have none of this and adhered to their 12 pitch theory. I made them eat their 12 pitch. They took it back and paid the shipping.
Sometimes a wheel just dont work out.
I guess you just got one of those duds with that 4 blade there.

_________________
God Bless our Troops; especially our Snipers

I know a Riviera ain't a Monaco,but have you PM'd Garrys and asked what he is running,specs, performance etc?

He's got an EFI SBC motor in his

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Well, for one thing, there isnt any standard measurement for cupping.
Michigan wheel states their cupping on a scale from 1-10; 10 being the heavy cupping. Most prop shops that support Michigan equipment rate cup from #2 thru #8.

Acme props show on their website cupping from a low of .030" up to a high of .130"
well what the hell is a cupping of .080" on Acme??
Dave said he got a .180 cup from Acme, well what is that?? That must be a mysterious super cup.

How does a #4 cup from Michigan compare to a .080" cup from Acme?

Prop sizing is less of science than the manufacturers tell you.
It is a whole lot of VooDoo & Black Majic.

_________________
God Bless our Troops; especially our Snipers

You GOT that right

_________________
Dave

My Riviera build - the Midnight Cry Project

Video of Midnight in Action
Blog

Few things in the world measure up to the thrill and satisfaction of boating in a boat that you built.

I sure hope you get the proper size and combination down pat. I don't have enough time left on the planet to do this when my time comes for my own day in the "barrel".
But seriously this stuff is interesting to me and can be very benifical for a lot of folks later on, kinda like those volunteer pioneers for drugs. Of thats right this is what these projects are anyway.

So you are saying this whole boat building thing is a "drug fix" for us addicts.

_________________
Dave

My Riviera build - the Midnight Cry Project

Video of Midnight in Action
Blog

Few things in the world measure up to the thrill and satisfaction of boating in a boat that you built.

Ya but only temporary.....then you need more....and more....and....

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

I thought it was psycho therapy, but I'm not sure it is helping or exacerbating!!!

Roberta

_________________
Roberta
Built Zip "Oliver IV" and Super Spartan "Jimmy 70"