Need prop suggestion - 20 ft SeaRay Bowrider

[ejnichol]

I have a 20 ft Sea Ray BR. 5.7L finj rated 250 hp Mercruiser with Bravo1.

Operating weight is 3600 - 3800 lbs. .
Prop is a 19p, and reads Quicksilver 48-16316A4-19P

Owners manual says 4600 - 4800 maximum rpm rev limiter suppose to come in at 4880. Rev limited didn't come in on first run. On another run it came in intermitently. scratching my head.

At WOT its runs 5700 - 5800rpm and goes 51mph on gps.

Want a prop that gives good hole shot for ski and tubing as well as good mid range fuel economy. ALso don't want boat to over rev if we 'overstuff' the throttle by accident.

Was thinking about a 4 blade stainless based on heard of superior tractability(?).

Which prop would you reccomend? Thanks

 

[Bondo]

Re: Need prop suggestion - 20 ft SeaRay Bowrider

Ayuh,... I'd suspect the tach might be Off,...
Test it against a knowm shop tach...

I'd also Guess a 21" pitch might be a better prop, depending on just how off the tach is.....

 

[45Auto]

Re: Need prop suggestion - 20 ft SeaRay Bowrider

As Bond-O says, you may want to check your tach. Also, a Bravo 1 is kind of an unusual drive to have on a 250HP 20 ft bowrider. You may want to verify what your outdrive ratio is.

 

[jkust]

Re: Need prop suggestion - 20 ft SeaRay Bowrider

As Bond-O says, you may want to check your tach. Also, a Bravo 1 is kind of an unusual drive to have on a 250HP 20 ft bowrider. You may want to verify what your outdrive ratio is.

45Auto, I haven't seen you around for a long time. I thought you dropped off Iboats. OP, I'm thinking that particular v8 wouldn't last more than a very short while at rpm's that high. Ignoring the Rev limiter even, 5100 rpms would make me cringe.

 

[ejnichol]

Re: Need prop suggestion - 20 ft SeaRay Bowrider

Is the gear ratio stamped on the outdrive? The dealer said same about, odd, bravo 1 on this boat. I tried my early 80's sears diagnostic but it flake out at 3500. Tiny tach was for garden tractor and it did the same.

I feel lucky the motor didn't blow. Should have read owners manual. Not having owned a v-8 and being 15yrs newer I assumed they had gotten to where they handled much higher revs. I was wrong.

It think the dash tach guestimate its reporting 400 over and actually it read 6000-6100. The rev limiter started working secound time out but sporatically. Yesterday took it out and didn't let it go over 4800 by dash tach trying to get a reference tach to work. I'm going to order something new. Sears in trash. Tiny tach going back on gt.

Motor runs fine. I feel bad about it. This prop on it looks so small. Looks like a 19 pitch like what I use on my 1981 Century with 140 hp. I have a 21p & 23p for the 140. Would that work on this boat?

Thanks


EDIT: Ordered a new portable tach. I'll post up new numbers when I get back on the water.

 

[ejnichol]

Re: Need prop suggestion - 20 ft SeaRay Bowrider

Finally got out with new portable tach, gps and full load of fuel.

The factory tach is way off. At full throttle engine was turning 4730 - 4750. The wind was running guessing 5 mph - 6 mph.

Running with the wind I got 55mph on the gps. Against the wind 53mph. I'd say the blade thats on their is good but would still like 4 blade for better hole shot.

All the while the factory tach is almost pegged at 6200 plus. Relieved about the tach being so far off.