steves86ta

Hi all,

I have a 1980 Bahner mini day cruiser. I just built a new 350 for it, with what im guessing is around 425-450 hp. It has a "pre-alpha" or i think its actually a MR1 drive.

Took it out to the lake saturday and the new motor pulled about 1000 more RPM than the last engine. Im looking to get more top end or a better cruising prop.

Currently the boat is pulling right at 5,000 RPM at WOT with a 21" Mirage plus prop, and a 1.5 ratio drive.

I also have a 21 pitch Mirage propeller that got dinged prettyy badly and needs to be repaired. I bought the propeller used and it was worked (according to the laser etching) by bronson propellers. With the last engine the boat seemed to like the Mirage more than the Mirage plus.

My question is there a prop that would be better suited? i seem to have a lot of stern lift, and the boat seems to chine walk right around 60mph. I think the boat has more MPH in it, the above was with 40 gallons of fuel and 3 adults, 1 child, and all of our crap for the day.

Should i stay propped for 5000 RPM or should i shoot for higher RPM? Ive read to keep these older drives at or below 5k and they will live longer.

Thanks

bbladesprops

Steve,

Cool old boat! You should have a original Mercruiser stern drive. It probably says MerCruiser on the side of the upper.
I think you might be experiencing a bit more bow lift than you think as well as overall lift at 60 mph. This combo tends to give the rocking from chine to chine.

Yeah, rolling that drive too far past 5K can slow its life quickly. Especially depending on its past usage. Where is the engine designed to run at WOT? This is a important starting point.

You are running very efficient right now as far as the propeller being hooked up. We can offer some test props or other input if you like. Call us anytime and we'll do what we can to help you moving forward.

Thanks,
Brett

steves86ta

Hi Brett
I was hoping you would reply. I've never had the engine dynoed but knowing my combination and off of what desktop dyno said my peak torque comes in right around 4000 with peak HP in the 5800-6200 range.

I was thinking that the mirage has way to much bow lift built into it. I think I need something with more stern lift. I believe the boat/motor has more in it but with the chine walking I don't like pushing it to far.

I'd be interested in a labbed prop I'm also thinking about a 22-23 pitch prop. This will be a cruising/top end prop. I have a stainless 19 pitch for skiing/tubing.

Its an mr1 I belve. And I have two of em (for when one dies).

To be honest. I would really really like to see 70 or so on GPS I tthink I'm close. Especially with less weight in the boat.

What prop or props should I be looking at? Is a labbed one good for my combo? How does it work having you guys do the work?

Thanks!

bbladesprops

If the engine is making peak HP at 5800, you'll probably want to prop at the 54-5500 range. Typically the last few hundred rpm don't produce much power and the trade off with smaller pitch to get to the higher rpm is mid range cruise speeds and fuel economy. Also we have the high rpm versus drive life to contend with.
4 blade props actually create more stern lift that the 3 blade props do. However, I think a 14.75 diameter Bravo 1 raked pretty heavy would work well.
If the 21 M+ is at 5000 rpm, it could be the right prop to work with. As much seat time and performance info you can give us the better we can be with our recipe for the Lab process.

Brett

steves86ta

Hi Brett,

Ive been thinking about what you had said earlier, and i really believe that i need more stern lift than i do bow lift. When i was at the lake i was able to swing the M+ to 5400 but didnot GPS the run, and it was chine walking badly so wasnt going to mess with the GPS.

Are you saying you can tweak the Mirage to have more stern lift?

IMO i believe that the tirm/prop are lifting the bow so easily that its causing me to have to much air underneath the boat at speed. its a closed bow boat, and there really is no weight over the bow. Except for a couple of liffejackets and a deflated tube. Almost as if the prop is "intensifying" the trim

bbladesprops

Ok,

We can try a 4 blade prop with more stern lift and learn from that. We wouldn't want to adjust the 3 blade till you do some 4 blade testing.

Brett

steves86ta

Okay sounds good. What about going with a Cleaver route?

What are your hours? i work 8-5pm PST and i cant call during the day. How does the "try out" program work?

bbladesprops

Probably no on the cleaver route.
Here is a link to our test prop program info on our web site. Our standard hours are 8-4 Mon through Fri.

http://bblades.com/propeller-test-program/

steves86ta

Thanks Brett

I will take you up on this

thanks

SB

iTrader: (1)

Same issues on my boat. Hit the trim button, the drive stays the same compared to the water, but the boat lifts up. Like....right up !

Not the same boat, but a little very light 20ft'r also.

Tried many, many different props (non labbed) and kept coming back to my stash of old Cleaver's.
Mirage, Mirage +, Turbo, Turbo+4...to name just a few. Most props designed for big block boats have too much diameter for the small block small lightweight boats. From what i noticed anyway. My 23" Mirage + was hilarious on the boat it was so unsafe trying to shoot me to the moon and all. LOL.

Anyhow, over 50mph the boat when trimmed just a little but would very airy. Give it more gas and it would scare you...even with more trim left.

Almost touching 70 with the clevers and it's non eventful.....unless aimed for a big wake of course....lol.

Anyway my drive is real deep (propshaft over 7.5" from bottom of boat) and supposedly won't work well with the cleavers, but it does.

I'm sure better props out there for my boat, but after seemingly a couple million I went back to what worked.

You are probably in the correct direction looking for more of a sternlifter.