I've decided to buy Dick Morland's spare 23x23 props, which led me to wonder what the ideal size would be for my boat. 

I read this from Jim:

As to your question as to the correct propeller size, the 1966 through the 1968’s came with 23” x 22” x 4 blade Michigan Dynaquads.  The 1969 through 1972 models came with 23” x 21” x 4 blade Michigan Equiquads.  These were used on all installations with the Detroit Diesel 8V53N and the Cummins V8-300M engines riding on 1.5” shafts.  Difference in the pitch is attributed in that the early models only carried 275 gallons of fuel (the 1968 model was upgraded to 350 gallons) and the 1966 and ‘67 were equipped with the short fiberglass top.  The 1968’s were equipped with the extended wood hardtop.  The 1969 to 1977’s had a very heavy extended fiberglass hardtop.

I also read that Chris tried a couple of sizes and settled on 23x22 (I think), running n60 injectors.

I don't know exactly which injector I have, only that the previous owner told me they are "one size up" which makes me think n55. The PO also increased the props to 24x23. I can only think this was for a faster dinner cruise speed.

My no load speed is 2800 and 2850, so I'm thinking the high speed governor needs to be adjusted (or is the lower number correct for a larger injector?). Even so, it feels like the engines are working hard to move the boat if I try to bring the boat up on plane (which it doesn't do). I can hit around 2400 rpm and 16 miles per hour.

My boat is heavy @ 43,000 lbs. Many of the 1968 and older are closer to 35,800 lbs. Based on Jim and Chris' comments, I have to think that my current 24x23 setup is completely wrong.

We typically run @ 1300rpm and 9 mph. I realize I will drop speed at a smaller prop size for a given rpm, but I would rather not overload the engines and would love to see this boat get on plane. It sounds to me like I might want to re-pitch Morland's 23x23 to 23x22. That's possible, right?

The engines run great, with no smoke to speak of (except when I pushed them up to WOT, but that mostly cleared quickly after a couple of minutes, likely due to our typical slow cruise speed).

I know I touched on this last winter, but now that I have new props coming, I'd like to re-visit and get ideas from those that have been through this. I'd rather get the size right the first time so I don't have to pull the boat to try another.

Thanks!

Steve.

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Chris Craft did a lot of testing and were really pretty good with prop selection, better than other manufacturers. I’m running the factory 23x22. My props don’t have any bite around the dock in reverse. In forward they have plenty. I am not particularly afraid of using some throttle around the dock like some folks though, so it’s mostly a non-issue. I too have n60 injectors that run great, and the extra power is noticeable and appreciated when getting up out of the hole. Your engine governors are set wrong. To get a wot loaded of 2800-2850 you need to have a no-load of around 3000. Yours are set a few hundred rpm too low,

For what it’s worth, when you get this straightened out these engines will readily plane the boat. What’s your top speed now ?

The best I've seen is 16mph at WOT of 2400-2450rpm, and  it feels like it's hard on the engines.

Chris Wickersham said:

Chris Craft did a lot of testing and were really pretty good with prop selection, better than other manufacturers. I’m running the factory 23x22. My props don’t have any bite around the dock in reverse. In forward they have plenty. I am not particularly afraid of using some throttle around the dock like some folks though, so it’s mostly a non-issue. I too have n60 injectors that run great, and the extra power is noticeable and appreciated when getting up out of the hole. Your engine governors are set wrong. To get a wot loaded of 2800-2850 you need to have a no-load of around 3000. Yours are set a few hundred rpm too low,

For what it’s worth, when you get this straightened out these engines will readily plane the boat. What’s your top speed now ?

That’s almost exactly what you’d expect with those oversized 24x23 props. Rule of thumb is an inch of diameter is roughly equal to 200rpm, assuming a somewhat standard gear ratio, and an inch of pitch is equal to 100rpm, although the effect tends to increase as the prop size increases. Figure probably 150rpm. That would take you almost exactly to the 2800 you should be running WOT. 

You’re overpropped, buy those 23”s and have the pitch set to 22”. You’ll probably be spot on. If you tend to run a heavy boat, lots of people, fuel, water, and you want to err on the side of lower exhaust temps, then go with 23x21. You’ll lose a knot or so of top speed but your engine loading will be less dependent on conditions, which in the long run is good for them. I have a lighter boat than you, no flybridge and the single aft stateroom layout. The 23x22 are spot on for me. I would probably try the 23x22 first and see how you like them. That is the factory correct size, and CC usually tested several different wheels before picking the specs for production.


Steve said:

The best I've seen is 16mph at WOT of 2400-2450rpm, and  it feels like it's hard on the engines.

Chris Wickersham said:

Chris Craft did a lot of testing and were really pretty good with prop selection, better than other manufacturers. I’m running the factory 23x22. My props don’t have any bite around the dock in reverse. In forward they have plenty. I am not particularly afraid of using some throttle around the dock like some folks though, so it’s mostly a non-issue. I too have n60 injectors that run great, and the extra power is noticeable and appreciated when getting up out of the hole. Your engine governors are set wrong. To get a wot loaded of 2800-2850 you need to have a no-load of around 3000. Yours are set a few hundred rpm too low,

For what it’s worth, when you get this straightened out these engines will readily plane the boat. What’s your top speed now ?

I read a very interesting boat test with a new type of propeller from Sharrow Engineering. In the test from, I believe it was Boating magazine, the Sharrow propeller DRAMATICALLY out performed the best props on the market. They have propellers for runabouts up to large ships. It is well worth the time to read up on them. I will be doing further investigating for my next propeller purchase. I would love to hear the comments from all of our experts here in the club after you read the tests.

I've seen those, they look pretty cool.

Kevin Fitzpatrick said:

I read a very interesting boat test with a new type of propeller from Sharrow Engineering. In the test from, I believe it was Boating magazine, the Sharrow propeller DRAMATICALLY out performed the best props on the market. They have propellers for runabouts up to large ships. It is well worth the time to read up on them. I will be doing further investigating for my next propeller purchase. I would love to hear the comments from all of our experts here in the club after you read the tests.

I did buy the 23x23's and tried them - but they were horrible around the dock. Even the mechanic who drives many boats, but had not driven mine before, mentioned to the marina owner how poorly my boat felt around the dock with the 23x23's on it.

I don't mind using throttle around the dock, but the difference was staggering. I'm now thinking of re-pitching my 24x23's to 22 or 21 and am looking for opinions. 

Chris Wickersham said:

That’s almost exactly what you’d expect with those oversized 24x23 props. Rule of thumb is an inch of diameter is roughly equal to 200rpm, assuming a somewhat standard gear ratio, and an inch of pitch is equal to 100rpm, although the effect tends to increase as the prop size increases. Figure probably 150rpm. That would take you almost exactly to the 2800 you should be running WOT. 

You’re overpropped, buy those 23”s and have the pitch set to 22”. You’ll probably be spot on. If you tend to run a heavy boat, lots of people, fuel, water, and you want to err on the side of lower exhaust temps, then go with 23x21. You’ll lose a knot or so of top speed but your engine loading will be less dependent on conditions, which in the long run is good for them. I have a lighter boat than you, no flybridge and the single aft stateroom layout. The 23x22 are spot on for me. I would probably try the 23x22 first and see how you like them. That is the factory correct size, and CC usually tested several different wheels before picking the specs for production.


Steve said:

The best I've seen is 16mph at WOT of 2400-2450rpm, and  it feels like it's hard on the engines.

Chris Wickersham said:

Chris Craft did a lot of testing and were really pretty good with prop selection, better than other manufacturers. I’m running the factory 23x22. My props don’t have any bite around the dock in reverse. In forward they have plenty. I am not particularly afraid of using some throttle around the dock like some folks though, so it’s mostly a non-issue. I too have n60 injectors that run great, and the extra power is noticeable and appreciated when getting up out of the hole. Your engine governors are set wrong. To get a wot loaded of 2800-2850 you need to have a no-load of around 3000. Yours are set a few hundred rpm too low,

For what it’s worth, when you get this straightened out these engines will readily plane the boat. What’s your top speed now ?

Steve, my boat puts out enough thrust at idle if I put it in gear in the slip to make the boat 30’ behind mine strain its ropes. If I don’t do it in bursts until my own lines are taut it would pop the lines on my own boat. I do this to blow the barnacle babies off the props. That’s idle. 

What is your idle RPM set at ? I am starting to think your idle is set too low. I would take you a video of the wash behind my boat in gear at idle but my fuel and coolant hoses are all off the engines being remade at the moment. I will do it next week though. What you’re describing isn’t normal. The 8v53’s normally idle at around 550. I tried mine at 600 and liked it but when I had the new injectors put in they put it back to 550. A lot of guys used to working on 71’s and 92’s set them too low. What is your idle speed ?

Steve said:

I did buy the 23x23's and tried them - but they were horrible around the dock. Even the mechanic who drives many boats, but had not driven mine before, mentioned to the marina owner how poorly my boat felt around the dock with the 23x23's on it.

I don't mind using throttle around the dock, but the difference was staggering. I'm now thinking of re-pitching my 24x23's to 22 or 21 and am looking for opinions. 

Chris Wickersham said:

That’s almost exactly what you’d expect with those oversized 24x23 props. Rule of thumb is an inch of diameter is roughly equal to 200rpm, assuming a somewhat standard gear ratio, and an inch of pitch is equal to 100rpm, although the effect tends to increase as the prop size increases. Figure probably 150rpm. That would take you almost exactly to the 2800 you should be running WOT. 

You’re overpropped, buy those 23”s and have the pitch set to 22”. You’ll probably be spot on. If you tend to run a heavy boat, lots of people, fuel, water, and you want to err on the side of lower exhaust temps, then go with 23x21. You’ll lose a knot or so of top speed but your engine loading will be less dependent on conditions, which in the long run is good for them. I have a lighter boat than you, no flybridge and the single aft stateroom layout. The 23x22 are spot on for me. I would probably try the 23x22 first and see how you like them. That is the factory correct size, and CC usually tested several different wheels before picking the specs for production.


Steve said:

The best I've seen is 16mph at WOT of 2400-2450rpm, and  it feels like it's hard on the engines.

Chris Wickersham said:

Chris Craft did a lot of testing and were really pretty good with prop selection, better than other manufacturers. I’m running the factory 23x22. My props don’t have any bite around the dock in reverse. In forward they have plenty. I am not particularly afraid of using some throttle around the dock like some folks though, so it’s mostly a non-issue. I too have n60 injectors that run great, and the extra power is noticeable and appreciated when getting up out of the hole. Your engine governors are set wrong. To get a wot loaded of 2800-2850 you need to have a no-load of around 3000. Yours are set a few hundred rpm too low,

For what it’s worth, when you get this straightened out these engines will readily plane the boat. What’s your top speed now ?

My no load idle is right around 650.

Do your governors hold the 650 rpm when you put it in gear, or does it drop? At a 650rpm idle and the correct 23” props it should handle fine, if not bordering on excessive thrust, normal idle is 500, most people to with 550. I liked 600 but the 50rpm difference isn’t worth having the governors reset. 650 rpm idle on these size diesels is up there, I’m at a loss to understand what the problem is. Again I’ll untie the lines and take you a video moving around at idle once my hoses are done for comparison.


Steve said:

My no load idle is right around 650.

It drops a bit when put in gear, maybe to 600 or 625. Our boat is away for the year so I can't get a look for sure until spring.

Steve,

What is the transmission oil pressure at idle? Your problem almost sounds like transmission clutch slip issue. Several things could cause possible low idle trans pressure but at least close to or at proper pressure above idle engine speeds.

Steve said:

It drops a bit when put in gear, maybe to 600 or 625. Our boat is away for the year so I can't get a look for sure until spring.

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