Re-pitching a Prop ?????

Baker said:

Tony, 1 inch and a little cup will likely not be noticeable to you at all.

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Yeee Gads Baker - 1 inch and a little cup!!

I've noticed your other threads with pictures...

Where you headed with this one!! :lol:

Al said:

Tony
Perhaps a review of the Christ Craft forum regarding "Connie 500" (I may have miss named this thread. The subject is the running on a single of twins. The point is both fuel economy and the effectiveness. You may learn a diffrent intent that will be supportive of the goal you seek.

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Al

I reviewed the thread "Constellation 500's" and this is pretty much what I am doing right now. I run on single when not in traffic. On post #38 I attached some charts that someone sent me. They did almost 6,000 miles and kept meticulous records using a flow scan meter. My experience locally closely tracks the same numbers. He had the same make, model and year as my boat. We generally run at 6kts (7 statute MPH) and get approx. 2 statute mpg. We can live with that and the Admiral really likes the slower speed.
The charts indicate that singles give better MPG than twins up to about 9 statute MPH at which point they equal out. By running single, I will hypothetically double the engine life of my boat.
My original post was to find out if I could get just a little bit more, not out of greed or cheapness, but 'just because'. I don't know how much HP I am using at six kts but certainly not anywhere near 270 on an single or 540 on twins.
I have velvet drive transmissions and I do not have to worry about free-wheeling with them.

regards

Tony B

Baker said:

Tony, 1 inch and a little cup will likely not be noticeable to you at all.

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I think you are right about that. There will obviously be a difference, but probably not noticeable under normal conditions.
I'll know for sure in a few days. Hoping to get out of yard by Wed. and back to Seabrook for a few weeks.
We are down at Hillmans. My wife likes to sit on back deck and relax. Up on blocks, she refers to it as the penthouse in the hood. Personally, I get nose bleeds at this altitude. I need to get back to sea level.

The plot thickens.

I am now convinced that 22-23 is the original equipment. I called the prop guy who was going to change my prop from 22-20 to 22-21 with a small cup for a totally different reason and rationale. This was before I just learned the original equipment was 22-23.
I called the prop shop back and the owner wasn't there - Dr's appointment. I spoke to his wife who is very knowledgible and explained the situation and was wondering if I could go to 22-23 and she said she would have to check the props themselves. must be bronze and something else had to be a certain way. She said that it was quite possible that the PO may have had the engines burn out prematurely and someone recommended the 22-20 for less stress on an older engine. She asked me what the manufacturers recommended max rpm was and I told her it was 4000 to 4400. Then she asked me what it was running at WOT. I told her that my Tachs were not accurate and so I couldn't tell her.. Unfortunately, I am unable to get with the PO.- changed tel numbers, besides he was about the 3rd owner. I do know that the engines were rebuilt in 2010. My model year is a 1986.
The owner of the prop shop will be back in a few hours and will call me. She recommended that maybe I ought to leave them at 22-20 but she will have him call me.
Another thing I just learned. - repair or replace the Tachs. Much more important than I thought.

Just got another post. Someone with the 22-23 had his engine rebuilt at 700 hours. Kinda early, maybe the ole gal knows what she is talking about.

At this point, I'm open to just about any suggestion that sounds good.

Tony B said:

At this point, I'm open to just about any suggestion that sounds good.

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Therein lies the problem.


Plus

1. Your tachs are not accurate and
2. you don't know the size of the currently installed props.

Take a deep breath, fix 1 & 2 and then decide if you really have any issues requiring redress. And ignore stuff like the guy who had his engines rebuilt at 700 hours - for all you know he may have run them with the RW valve closed. It is hard to imagine how a inch or so different prop size could ruin a gas engine. Yours have made it for a long time at with the present setup.

sunchaser said:

Therein lies the problem.


Plus

1. Your tachs are not accurate and
2. you don't know the size of the currently installed props.

Take a deep breath, fix 1 & 2 and then decide if you really have a problem.

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Fix 1: boat is out of water and props have been removed. Too late for tachs on this go around.
Fix 2: I do know the current size. They are 22-20's. The manufacturer has been installing 22-23's.
My props are presently in the prop shop ready to be worked on.
my real questions are
A). Cn the 22-20 be repitched to 22-23?
B). If it can be re-pitched to 22-23, do I want to?
c). Mybe somewhere inbetween? This is more likely, because I am not sure if they could re-pitch 3". I'm waiting for the call.

Thanks

I like experimenting and I am very interested in your results. I REALLY like experimenting with other people money.

My only concern is that you mentioned running full throttle after the repitch. Even though that is a minimal pitch change I would not run on plane if the engines will not turn up minimum rated rpm with the "new" props. If you are going to ONLY run a max. of 7 knots I think you would have a hard time hurting your engines with any prop. But, and this is a big but, if you ever want to run faster than that the ratio of manifold pressure to rpm must be considered and you don't have the instrumentation to do that safely. For that matter that information may not even be available for that engine. If you are going to run faster than 7 knots get a good quality strobe tach and make absolutely sure your engines will turn rated rpm at full throttle with the boat loaded for cruising.

I am willing to bet they can repitch it to 23. Sounds like you are working with Hood. Super good folks there and definitely straight shooters. If you're are doing something way out of line, Mike will tell you so. I do think that you are over analyzing here. Once you get the props on and nothing really changes, you will know what I'm talking about.... If you go to 23 then you might notice. But just 1 degree...not likely to notice.

If you are going to run faster than 7 knots get a good quality strobe tach and make absolutely sure your engines will turn rated rpm at full throttle with the boat loaded for cruising.

Great idea IF he is going to cruise at or near max RPM, otherwise any slight overload used for 20 seconds getting up on plane is never a problem.

Just watch any diesel sport fish pour out the black (overload) smoke every time it accelerates to get up and go.

If there is no engine knock from a gasser at accelerating youre fine.

Baker

I assume that is Mike Hood's wife that works there.
She explained how everything works and will leave the final explanation to a Mike when he gets back. IF, and at this stage it may be a big "IF", I can go to the factory spec provided 22-23, I might decide to go that route.
Right now, I posted this question on Yahoo Mainship Groups and here. This latest development about the prop sizes has burned me out. I'm done with thinking about experimenting. now it's all about getting it at or near the original factory spec......WHOAAAAAAAA.
In the middle of typing this, Mike Hood called me back. He said that he thought that 20-23 (the factory provided) was a bit much and thinks that I should stick with the idea of 20-21 with a slight cup. If any errors are to be made on this decision, it would be on the side of safety.
So if this is to be considered an experiment, it is on the safe side not the wild side.
Kinda boring outcome after all of this.
And yes, he said "get the tachs recalibrated or buy new ones"

Thanks everyone for all the help. I never would have thought this could be so complicated. I am starting to think that prop design is like hull design - mostly science but still a lot of art and experience involved.

Tony B said:

Fix 1: boat is out of water and props have been removed. Too late for tachs on this go around.
Fix 2: I do know the current size. They are 22-20's. The manufacturer has been installing 22-23's.

Thanks

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The only way you'll know the size is to have them measured. The prop shop should do this first. A PO could have. changed the pitch or they are not stamped correctly. Props 101 is to never trust the stamping until checked or bought new.

FF said:

Just watch any diesel sport fish pour out the black (overload) smoke every time it accelerates to get up and go.

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That is most likely an operator induced condition.

The Eagle Has Landed

I made it out of the yard and back to Blue Dolphin Marina (Seabrook, Tx.) today. Went in last Wednesday afternoon and left there this morning. I must say that out of all the yards I have been to in my lifetime, this was the most quick and painless time. Everything went better than expected.
OK, now for the prop thing. It worked out real well. I could definitely feel a difference. I don't know how much of the difference is due to a bottom job and repairing the prop to like new condition and how much is attributable to the 1" added pitch and cupping.
Here is the odd thing. Mainship equipped the boat with a 22-23 pitch. I had a 22-20 pitch on my props before my new re-work. The Prop shop told me that my 22-20 props were 22-23's at one time. maybe they were reduced for a reason.
Anyhow, I am a happy camper. Tomorrow is major clean-up day. Thanks again for everyone's help.