broke down, coming in on one
 

Made a 6 knot 11 hr trip back and had a lot of time to think about how to avoid that again. I've always been told not to run over about 1500rpm when on one because anymore would be hard on the overpropped drive. I've also heard of boats that will come up and plane on one... not sure if the good drive breaks minutes later, but interesting anyway.

So, the question is --could I run a little faster, say enough to get 10 knots if I put a different, smaller prop on? If so, what prop (normally running 17 3/4 X 21p) and what rpm would be safe (Bravo 2)?

I have driven my 33' donzi on one outdrive at speed. Think about it some boats only have one drive.

That's true.

Look at the bright side, at least you had two engines:D

Believe me, I'm happy to do 6 over nothing, I drive big boats where 6 isn't too bad. My question is will running faster hurt the good drive. Yes, there are lots of boats with one outdrive, but they are propped correctly, the drive is centered, and they don't have a dead drive dragging.

If you have a smaller prop, I would have pulled the prop off the damaged one and put on the smaller prop and see if you can get it on plane. There would be less drag on the hull at speed and with the smaller prop, it wouldnt have been a drive breaker. Now with the large prop, if it didnt come on plane, because you didnt get into the torque curve of the motor, I think you would still be ok.. but it would put a severe strain on it getting on plane. Now if you have a torque monster motor and you try it,, you could possibly limit the power as you came on plane. But all the beer and heavy women in the front, etc..

There again it all depends on what drive and how heavy a boat?.. I would try it with a Bravo, but not an Alpha (unless you have the right size small prop).

The only good way to know is to find someone that tried it with your combo.. or when you get the one drive fixed, experiment till you break the other one and then you will know.. :( sorry.. couldnt resist being a smart as_...

Dick

unless its an extremely heavy boat with a diesel I doubt you could damage a B2 by getting up on plane with one engine, it just may not do it because overpropped/not enough low end power. My cousins Magnum has three powerstroke diesels, the outside two have B1 drives the center engine has a B3, it will get on plane with just the center engine and that boat weighs over 20,000lbs..

It is a heavy boat (near 20K) with Yanmar 6lps (315hp). Lots of torque... I'm not necessarily looking to get on step, just to get a more reasonable speed out of it. If I were to take the broken leg's prop off, what size/pitch prop would you recommend trying on the other? Thanks for the help. This is interesting.

If it was me I would carry a spare prop 4" of pitch smaller and you should have zero problems getting on plane with a yanmar.
At minumum planing speed you should be around 16-18mph, I think anything in between would be innefficient seeing as much more than 6mph off-plane you start pushing water and the bow would start going skyward.