no power with weight in the boat

[scottberry]

I am having some performance issues with my 5.7 mercruiser. It is a 25 ft regal with a bravo III. WHen there are four or five people in the boat, it seems to run fine with plenty of power. Yesterday I went out with 10. Max capacity is 12.
The boat had no power at all from the start and wouldn't plane off. It acted like it was just loading up. After I dropped a few people on the shore, I took it out and opened up and it seemed to regain the power. I was able to tube and ski no problem wiht 3 or 4 in the boat. But as soon as I put everyone back in the boat it struggles.

Any suggestions??

I changed the water separater and it was clean. At this point I can't tell if it is fuel or spark related.

 

[45Auto]

Re: no power with weight in the boat

Sounds like it's marginal on power. What year is it, how well is it maintained (last impellor, etc), when was the last complete tune up done, have you ever done a compression check on it?

 

[mkast]

Re: no power with weight in the boat

Any suggestions?

A basic course in physics.
XXXX in weight.
XXX in horsepower.
XX in speed.
Increase weight, speed will be reduced because the horsepower stays the same. Ever notice how fast the hull is when you're on board alone, with a near empty fuel tank?

 

[WizeOne]

Re: no power with weight in the boat

If you cannot hit your max rpm, at WOT, with the load you are carrying, you are under propped. You may need to have a couple of different pitches to switch back and forth depending on the load you will carry that trip.

 

[scottberry]

Re: no power with weight in the boat

The motor was pt in a little over a year ago. So it has little hours on it. It is in a1998 Regal 2500 LSR.

Last week I put in a new impeller kit and went out for a test drive with my brother and daughter. We tweaked on the timing with it in the water at WOT. It was screaming with top speed around 45.

A couple of days later we went out with some friends and the boat ran perfect the entire day. It's just when we loaded her down she started bogging down.

Since it is a bravo III, the props are not cheap. Any idea of where I should start with pitch angles?

 

[mkast]

Re: no power with weight in the boat

As the weight of the load increases, the WOT rpm will decrease. As the pitch of the propeller decreases so will the top speed of the boat. Your options at this point are, live with it or start buying propeller$ for the range of weight you plan on carrying.

 

[scottberry]

Re: no power with weight in the boat

My back prop is stamped 26.
My front prop is stamped 26 but also has a 24 just below the factory 26 stamp.

Do these sound like the correct pitch for my boat?

 

[Maclin]

Re: no power with weight in the boat

There is a method in determing the proper pitch for the boat.

But, you need accurate info to start with, and you need to be very certain that the engine is running the best it can for your WOT (side open throttle) test run.

Do a WOT test run...:
WOT rpm (accurate as possible) at normal loads (full of fuel, number of people, etc.)
Speed (accurate as possible) at that rpm

Then be sure of these items...:
Drive ratio
Top rpm range for the engine from the MFG.

With that info you can tell if the pitch is too high (over-propped, engine not reaching max rpm) or too low (Over-propped, engine is revving way past the top rpm range).

The prop forum here can help.

 

[mkast]

Re: no power with weight in the boat

Do these sound like the correct pitch for my boat?

What size did the hull come with?

 

[45Auto]

Re: no power with weight in the boat

We tweaked on the timing with it in the water at WOT

You adjusted the timing while running WOT? Not surprised it's not running right and it needed a new motor. Don't expect this one to last long either

You may want to take it to someone for a compotent tune-up and check out rather than spend literally thousands on B3 props you don't need. 26 pitch B3's on a 5.7 in a 25' Regal should be right unless you're way up in the mountains somewhere.