Propeller change

[osprey]

Result; a few year ago I bought a '82 46C with 8V92ti (650hp). Over the years I have done a lot of work on the engines, hoping to get as much out of them as I could. I rebuilt the blowers, turbos, intercoolers. pulled the injectors and cleaned , repaired, and replaces as required. and spent lots of time tuning the engines. (learning as I went, I have a manual ) And of course this forum. All in all I managed to get the old smoky engines to run pretty good (not sure how many hours on her, but guessing around 3K) (a little more info for fun, I bought the boat St. Petersburg and had a Captain, drive the boat around Florida to Ft Lauderdale to be put on a ship to SEA. The captain reported the boat ran well, cruising at 20 knots at 2100rpm) (note: I did not know anything about these boats or engines) Well, with all my efforts I managed to get the boat to cruise at 20 knots at 2100 rpm, but with a 90 percent reduction in smoke, which I felt was great, boat stayed clean and the engines are old. Hauling a boat out of the water where I live is not an easy event, and also not cheap, "O" how I wish I had the facilities you all enjoy back in the USA. (however, I only pay 80 cents a gallon for fuel) Any way; it came time to get the boat out of the water and do a bottom job. Big event, big bucks. with the bottom cleaned, repaired, primed and anti-fouled, I pulled out the spare set of props, they looked old, but came with papers claiming they had been tuned and balanced. The old props looked pretty good but I felt they must be out of balance as I was getting some vibration and had covered everything I could think of to reduce that. Original props, 3 blade 28" X 27" spare props 4 blade, 28" X 26". Test drive, Osprey (my new born baby) Pulls up onto the plane at 1750 rpm, cruises at 22knots at 1900 rpm, 27 knots at 2250 rpm, almost made 30 knots as it approached 2300 rpm, and I can manage to keep it just planing at 1350. there is almost no vibration, the little smoke I was getting is gone. The engines are running smoother, sound great and even smell different. I AM PLEASED. Old props to be tuned/balanced and pitch reduced by 1/2 inch, will let you know when I need to use them.

Enjoy your boat,

Pete

 

[jim rosenthal]

Nice to hear this- glad your boat is running well, and keep in touch.

 

[Finalee]

That's dramatic. Your new baseline for performance. Surprised you did not realize it was propped wrong sooner. Was the difference all props, or was a dirty bottom a factor too. That's a good surprise!

 

[Boatsb]

What's you wot rpm?

Does she spin up all the way under full load?

 

[saltshaker]

Your numbers sound great and pretty much what she should do. I thought the numbers were way too low reading the top of your post. Most don't perform as yours is now due to overloading the boat with gear or improperly propping the boat. Sounds like your engines are in good order if you're seeing those numbers. Run them at 1900-2000 and they will treat you well just make sure you stay on top of the cooling systems maintenance. The 46C HP is a great boat. Hope you have many years enjoying her.

 

[saltshaker]

BTW it sounds like the 3 blades need another inch of pitch added not removed. You typically run 2" less pitch on a set of same diameter 4 blades compared to 3.

 

[osprey]

It's all been a big learning curve, only boat of it's kind around this part of the world.
First off, I guess I assumed that if you bought a 30 year old boat it should already have
the correct props. Secondly, It was a combination, I started with a clean bottom and weak
engines and as I got to grips with the engines the bottom got more and more difficult to keep clean.
Hauled the boat, cleaned the bottom, changed the props. I can just manage to get to
2300 rpm on a smooth sea. As for the cooling system, surprise surprise, both engines now
run cooler, 185 degrees in a very warm ocean. The old props were definitely over loading the engines,
and the shop that does the props for the oil support boats recommend removing a half inch of
pitch (from 27" to 26 1/2") They said reducing by an inch would be too much... But I will not be
putting them on unless I have to.
And best of all, I'm a little bit wiser

Enjoy your boat,

Pete

 

[jim rosenthal]

More than a little bit. There is nothing like working on your own boat to really get you familiar with her. Good for you.

 

[Scope]

I just ran my 46 Hp on Saturday . 1850 rpm @20knts. I am currently running 28 x29 three blade propellers. The propeller sizes are not all the same. Besides diameter and pitch there is blade area involved, cup which will effect the engine loading. That said it seems you are very close on having the correct propeller under your 46HP. When a 92 series Detroit is tuned properly and loaded correctly they smoke very little to no smoke so you are good in that area also. I hope all the members have a great and safe boating season!!

 

[drburke]

This is excellent feedback--thanks for the OP for following up!

DAN