New boat seems underpropped on paper...what is your experience?

[gixxerjim]

So I bought a new to me 1992 Century Mustang II 19.5' Bowrider. I have not run it enough to have a feel for the prop, but on paper it seems like I could easily go up in pitch. The loaded boat weight will be 3000lbs. The 4.3L v6 was rebuilt a few years back and the paperwork shows some go fast hopups, .040 over, roller rockers, flat top pistons for higher compression with moly rings and so on, but no cam numbers or quoted compression or hp. I have no idea how much hp she makes. I am guessing it started with 175 from the factory in 1992? I also don't know the drive ratio, assuming 1.81?

So without enough data, I know, what would you try first if you had no prop with the boat?

(FWIW I do have a Michigan Wheel 17P 3 blade aluminum on the boat now, with a fancy newer version of the old whale tail on the lower unit. The previous owner and his wife and two grown kids combined weight I would estimate at 500lbs more load than my small wife and I and small kids, and they ran 35mph without opening the boat all the way up but only used it for tubing at 25-30mph).

 

[Bondo]

Re: New boat seems underpropped on paper...what is your experience?

So I bought a new to me 1992 Century Mustang II 19.5' Bowrider. I have not run it enough to have a feel for the prop, but on paper it seems like I could easily go up in pitch. The loaded boat weight will be 3000lbs. The 4.3L v6 was rebuilt a few years back and the paperwork shows some go fast hopups, .040 over, roller rockers, flat top pistons for higher compression with moly rings and so on, but no cam numbers or quoted compression or hp. I have no idea how much hp she makes. I am guessing it started with 175 from the factory in 1992? I also don't know the drive ratio, assuming 1.81?

So without enough data, I know, what would you try first if you had no prop with the boat?

(FWIW I do have a Michigan Wheel 17P 3 blade aluminum on the boat now, with a fancy newer version of the old whale tail on the lower unit. The previous owner and his wife and two grown kids combined weight I would estimate at 500lbs more load than my small wife and I and small kids, and they ran 35mph without opening the boat all the way up but only used it for tubing at 25-30mph).

Ayuh,... With that many unknowns, how can you figure it's under propped on paper,..??

Go Run it, 'n get the numbers needed, 'n asked for in the "Read this First" thread at the top of this forum...

 

[gixxerjim]

Re: New boat seems underpropped on paper...what is your experience?

Ayuh,... With that many unknowns, how can you figure it's under propped on paper,..??

Go Run it, 'n get the numbers needed, 'n asked for in the "Read this First" thread at the top of this forum...

I did read that, thought maybe somebody might still have some insight despite the admitted lack of complete information. A response like 'I had a 19' boat with a 4.3 from 1992 as well, about that weight and it ran 45mph with a 20p aluminum 3 blade prop' etc....

Am I correct that a 1992 4.3 made 175hp base and 190 efi? Is 1.81 the normal correct drive ratio for a 4.3 Mercruiser?

Thanks
Jim

 

[gixxerjim]

Re: New boat seems underpropped on paper...what is your experience?

Also the underpropped suspicion comes from using a 19P on my old 19' SeaRay 3.0l that was only about 400# lighter but had just 130hp, along with Mercury estimating 19-21P prop for good all around use on the new boat. Just asking for some opinions, not going to hold anybody to within +/- 50 rpm or 1mph etc...

 

[Maclin]

Re: New boat seems underpropped on paper...what is your experience?

The 190hp was a 4bbl carb version back then I think. 175hp was 2bbl.

 

[Bondo]

Re: New boat seems underpropped on paper...what is your experience?

Also the underpropped suspicion comes from using a 19P on my old 19' SeaRay 3.0l that was only about 400# lighter but had just 130hp, along with Mercury estimating 19-21P prop for good all around use on the new boat. Just asking for some opinions, not going to hold anybody to within +/- 50 rpm or 1mph etc...

Ayuh,... I understand, but You have to understand the personality, purpose, 'n mentality of this forum...

Comparin' boats like this is really irrelevant, as the variables are incalculable...

Here at this forum, if you simply answer the questions posed in the "Read This First" thread,..
You'll get an answer that'll put yer motor/ drive/ hull in it's closest to Perfect situation that's humanly possible...

Look for the Bullship, 'n banter you're wantin' at yer local lakeside waterin' hole, or down at the dock....

 

[ufm82]

Re: New boat seems underpropped on paper...what is your experience?

To add to Bond-o's words, you yourself also noted the additional "performance" work on the engine and the mystery of how much HP. Or even if the WOT range is different now due to the engine work? And then you compare two completely different boats.
The only way to properly ascertain what you need is to run the boat at all ranges, take measurements, times, speeds, rpms and handling characteristics and then determine what prop to use. And also take into consideration that you can easily have two 19 pitch props with widely varied performance. Waaaaay to many variables as stated above.

 

[gixxerjim]

Re: New boat seems underpropped on paper...what is your experience?

To add to Bond-o's words, you yourself also noted the additional "performance" work on the engine and the mystery of how much HP. Or even if the WOT range is different now due to the engine work? And then you compare two completely different boats.
The only way to properly ascertain what you need is to run the boat at all ranges, take measurements, times, speeds, rpms and handling characteristics and then determine what prop to use. And also take into consideration that you can easily have two 19 pitch props with widely varied performance. Waaaaay to many variables as stated above.

okay okay. I am just dying to run it again and need a way to pass the time bs'ing until I get to be on the water again!

 

[Bondo]

Re: New boat seems underpropped on paper...what is your experience?

okay okay. I am just dying to run it again and need a way to pass the time bs'ing until I get to be on the water again!

Ayuh,.... That's what We're doin',... ain't it,..??

I'm headed down to the river now,... probably go for a ride in my tinbarge abit later tonight,...

 

[444]

Re: New boat seems underpropped on paper...what is your experience?

A 19p stainless might do well on there, but don't get too excited until you get out there and run your boat again. Right now anything is a shot in the dark. Take note of your top speed and max rpm. Your boat may only weigh 3000lbs loaded. It may weigh more(unless you've scaled it to confirm). Otherwise you're just going by published #'s and you have to allow for 20 years of use, waterlogging, etc. Props seem to half way be a trial and error thing, which sucks considering their cost.