1988, 3807 propeller issues

[VicB]

I have a 88’ 3807. Rebuilt quadrajet carbs, electronic ignition, new plugs and timing verified last fall. 3 year old bottom job run only in North Alabama on the TN River. Runs extremely well. I can only get 3500 rpms out of her. She’s a chunky gal at 26000 lbs per last haul out. Bottom job 3 years old. All that to say, leaning towards being over propped. Trying to go through all my paperwork, hoping to find out what sizes I have. Any idea of what should be on there to get up to the 4200’ish rpms the book said I should get?

[buster53]

Need more info. What engines? What props? What did it run 3 years ago with fresh paint? A lot of growth can occur in 3 years. IF the engines are running at optimal performance AND bottom and running gear are pretty clean, then yes, it’s a good chance you are over propped.
Is this a new to you boat? Did it run like this during sea trial? Did the surveyor make any comments about the low RPM’s? Did you question the seller about it?

[VicB]

So this is our 4th season. During the sea trial the surveyor noted that it did not achieve max rpms at WOT. He acted like it was no big deal and I didn’t know any better at the time. Seller was not mechanically savvy and didn’t know much about the workings of the boat. Nothing changed from before the bottom job to after it was completed. I was surprised when we left that speed nor rpms had changed. I know there’s a good slime coat, as it hasn’t come out of the water in 3 years and the carp really work on it at night when we’re trying to sleep. I have twin 454 crusaders with quadrajet carbs. 1-3/4” shafts. Would that be the bore on the current props or would they be turned down at the prop?

[buster53]

3500 RPM’s is not good and you need to know the prop size (diameter and pitch) before you proceed. I would think that information can be found in your survey report.
How do you run the boat…what speed to you cruise at? I used to have the same boat and while cruising speed was in the 15-16 mph range, we normally ran at hull speed, about 8-9 mph to save on gas.

[VicB]

The survey report only said they were Michigan Wheel Dyna Quad 4 blade bronze props, so I’m guessing surveyor did catch the markings on them. We normally run 2000 - 2500 rpm which is 10-12 mph. If you look at the rpm/mpg chart for a 3807 with 454s, it falls right in line with rpms vrs speed. Now I’m nervous. Other people in the Carver Facebook forum are talking about how hard it is on the engines to be over propped. I’m not sure what’s currently on there. I assume they’ve been there the whole 32 year life of the boat. They are too expensive for me to be guessing on replacements. I’ve been through that with a ski boat. Sick feeling to buy a high dollar prop and it not perform. So I’m kind of stuck.

[VicB]

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[km1125]

The surveyor should have definitely noted the size of the props, especially if they went to the "trouble" of identifying the make and model!!

I would **NOT** suspect a prop size issue unless there was some indication they were changed previously (as in 'mentioned by the previous owner' or something like that), or I ruled EVERYTHING else out first. People wouldn't typically go to a larger prop on a boat like this unless they spent ALL of their time at hull speed and wanted more of a trawler.

When you checked the timing, did you check the mechanical advance?? Do your distributors have mechanical advance of is the timing advance done electronically?? Whether done mechanically or electronically there must be advance as you go up in RPM or you will NEVER be able to achieve rated power on the engines.

Checking the mechanical advance is fairly easy, as you just remove the dist caps and rotate the rotor. In one direction you should be able to twist it and have it 'snap' back to the original position. If you can't twist it or it doesn't snap back easily, then the mechanism is likely rusted. If it's electronic advance, there's usually a pin or connector that will disable it so that base timing can be set and if that pin or connector is not restored you won't have advance functioning.

You can verify how much advance by using a timing light and measuring the timing across RPM ranges to see that it increases with RPM and comparing with spec.

Also, not really related to this issue, but those anodes on the tabs should be on the TOP side of the tab. Putting them on the bottom just increases drag on the boat.

[bud37]

Maybe we can tell if you are over propped if you can tell us how fast are you going at about 1500 rpm.....how fast at 1200 rpm.

There are some members here with the same boat as you, hopefully they can be of more help as to speeds at certain rpm's.

[VicB]

So, somebody converted it to electronic ignition before I got it. Now with that said, I’m going to show my hand here. There are springs in the distributor and they are rusty. I liberally spray them with lubricant from time to time, but the points and condensers are gone. I’ve had the distributors out to remove the intake manifold on the starboard engine. When I put it back, I set initial and total timing and it fell right on the curve in the crusader manual timing chart. So if there is a 3 wire doughnut in place of points and condensers but still has springs is that considered electronic ignition with mechanical advance? Awesome catch on the anodes. One reason I don’t want it to be props is because the local place that did my bottom job and put the anode in upside down went out of business and the closest travel lift is 2 days away. BTW, I have always appreciated your posts and wisdom. You’ve been a huge help to me and many others. I need you to move to North Alabama.

[buster53]

10-12 mph is a very inefficient speed. If fuel economy is important to you, slow down to 1800 RPM’s and 8-9 mph. You will get a noticeable difference in mpg’s