High RPM
 

Well I bought my first Mariah last Tuesday and today was the first outing. It is a 1995 Talari 180 with the Mercruiser 4.3XL/Alpha One. I am pretty excited with my purchase after today. It seemed a solid and smooth as a new boat. Rides great compared to all the boats i have ridden over the years. Engine starts so quickly and idles so smooth you have to check tach to make sure it is running.

There are tons of posts about props and I have read a lot of them. I am pretty sure i need a 19" pitch and a 14" or 14.5" diameter. The prop that came with it is a 13.75" diameter and 21" pitch.
I was afraid it might lug the motor too much and assumed someone was trying to get speed.

I am not certain of the accuracy of the original gauges but with three full size adults in the boat it easily planed out at 50 MPH and the tach was at 5,000 rpm at WOT. I am a little concerned about the rpm level. Not that i will run at WOT but it tells me the prop is probably wrong.

Do you think the prop is too small diameter? I am thinking a 14.5" with 19" pitch might be better.

Any advice? Is 5 grand at WOT seem unusual?

Thanks

Re: High RPM
 

5000 RPM with a 21" pitch prop at WOT is unusual and normally I'd say that a 21" pitch prop would only get you in the 4600 - 4800 rpm range at WOT. Rule of thumb is you increase your RPM at WOT by 200 for each 1" decease in pitch so effectively a 19" pitch would put you up around 5400 and that aint' good. But increasing the prop diameter should reduce your RPM's slightly too. Sounds like something isn't quite right.

First off check the tach. Lift up the seat back cushion in the bow area in front of the driver and access the backside of your tach in the console. There is a small wheel in there which you should spin a few times and then make sure it is set to "6 Cyl".

It's also possible that the gear set ratio in your Alpha 1 isn't quite right for where you are using it. That's an expensive proposition to change so most boaters would just change the prop to control the RPM's.

Then, depending on what you plan on using your boat for; a 21" pitch is a good 'cruising' pitch and a 19" is a good 'all-around' pitch prop. IF you do a bit of tubing / water-skiing / waterboarding etc, then i would suggest a 20" pitch with a 4 blade prop for that little extra 'bite' in the water. AND if you have a few extra $$ in your pocket, that 20" - 4 blade in stainless steel works very well on the 180's.

Re: High RPM
 

Thanks much for reply. I think I may have discovered part of the problem. I think someone has “dressed” the prop edges to get rid of some dents and bends. I would guess diameter has been reduced to less than 13.75. Maybe as much as 1/4 inch. I will measure this afternoon.