Seamaster 27 Performance

[3rdday]

I have a Seamaster 27 Flybridge with a Bravo 1 outdrive, Mercruiser 454, and a 15 pitch Power Tech prop. I am looking for better cruise mpg,cruise is at 2800-3100 RPM and 17-19 mph. I contacted Power Tech and they tell me this prop was designed for load pushing, workboats, pontoons, etc. It is a 3 blade large petal shaped prop. I believe 15 is not enough pitch, what do you folks think? Power Tech recommends 4 blade with more pitch;; ""OFS4-Blade Offshore Propeller: Has a constant 15.25 inch diameter regardless of pitch, available in every inch of pitch from 14-30. It has a polished finish, right- or left-hand rotation, moderately high rake, full tip cup for excellent lift and grip. It is excellent for V-bottom Off-Shore style boats; single, twin, triple and stern (I/O) drive applications.""

[Ryank]

Maybe a 17 -19 pitch? not sure but I would check with a few prop shops to get a general opinion What is the engines maximum RPM rating and what are you achieving at WOT?

[Bushwacker]

Brian, what is your max rpm @ WOT with typical load? What's the max diameter prop you can run with the Bravo 1 drive?

Jeff McAnally, who we spoke with when I stopped by your house last spring, said he ran a 20" diameter prop on his Seamaster/454/Mercruiser No. 2 + Marine transmission rig that Frank Brown set up for him in the late 60's. Will ask him what his optimum cruise was, but I think it was faster than yours. Jeff did not like to run slow! I just saw Jeff at a luncheon on Monday - he's in his mid-70's but is driving a 2011 Shelby Mustang that he's souped up to 600 HP with a reprogrammed computer! Once a gearhead, always a gearhead!

Maybe Fr. Frank is familiar with that old powertrain set up.

I run a 4B PowerTech with the old SST profile blades and it seems to be a pretty good prop. I think they're a good outfit to work with and should be able to get you dialed in if you can feed them enough info. Denny

[Fr. Frank]

I like the old 370 hp 454/BW tranny/Merc TRS II setup. With regular maintenance, it was bulletproof. We had a customer with that setup in a 27' Searay. He turned an 18.5" diameter bronze prop, but I don't recall the pitch.

With your 454/Bravo 1 setup, I'd have to know your current HP, max RPM rating for the motor, current max RPMs at WOT, and which gear ratio drive you have before I opined about the pitch you should be turning behind a 7000 lb boat.

If the max RPM range for your motor is 4600-5000 RPMs, you want to be propped so that you can turn 5000 RPMs with the boat at maximum gross weight.

That's called propping for Max of Max at Max. Yes, it does mean that you can slightly exceed the max RPM rating if you're lightly loaded, but it also means that in an emergency or otherwise, even at max weight, you can apply plenty of usable torque.

Trust me on this: that is a VERY good thing to have in bad situations.

[76Red18]

Sounds like you just have a "push boat" prop with no cup . I have no experience with i/o's but if you use the trim (I don't even know if you can trim i/o's )do you get any bow lift? If not, I would have cup added to the blade tips (Bow lift) and trailing edges (Stern lift ). I bet 15 pitch is on the money, you just need better "grip" i.e cup.

[Islandtrader]

Give these guys a call...they know there stuff...

Brett @bblades 920-295-4435

[76Red18]

I run a 4B PowerTech with the old SST profile blades and it seems to be a pretty good prop.

Theres something about that old style SST blade profile and the SeaCraft hull. Sandy might chime in on this also.

[seafari25]

he ran a 20" diameter prop on his Seamaster/454/Mercruiser No. 2 + Marine transmission

Hey guys,

My knowledge is limited as we have always had our 25 marine serviced, until recently, however I think the setup that Denny mentioned is similar to ours. I'd actually like to learn more but I'm pretty sure our drive has been refered to as a 2 or II drive and the diameter of the prop is at least 20". It has been a while since I bought a prop but I think it is 17p. It is a 327 chev and I believe I heard a mechanic say 288hp at some point but my grandfather always said 280 or 290...

That said our performance numbers are exactly the same as Brian mentioned at cruise and wot is 32mph at 4200rpm.

This is the original setup from 76.

Brandon

[gofastsandman]

My 20 came with a house mouse eared prop and I hated it.
It was an old Mich. match. A 1978 prop on a `96 motah?

I now run an old style SST and like it. `96 150 rude.

Denny`s Powertech and Apollo 4b were the bomb when we went a testin`. Great cuhsion lock hub design. Less thunk and smoother feel through the wheel and binnie. Great bite and lots of trim with the 4 blades.

I have a 15.380 x 17 Mirage + if you want to try it.
This is a sweet prop, but I just can`t spin it up.

Big was right when he said it screws through wood.

As an added bonus, George and Denny have said that if you spin the flo torq hub, you can spin it to 3 k and re-weld the plastic after 45 seconds or so. Not sure if you want to go above displacement speed though.

We need more info.

Cheers,
GFS

[3rdday]

Thank You Everyone.
I am supposed to get 4200-4600 RPM WOT, It is a 310 HP 454.
Bravo 1 Drive indeed , I believe my max diameter is 15.5 or 15.25. I Believe I get much more than the 4600 max rpm maybe 5000RPM I WILL TAKE IT OUT & RUN IT THIS WEEK and report back.

Sandy that is exactly the prop I have House Mouse Ear style blades. Thank you for the offer i may take you up on it.
Sandy Is the Mirage a 4Blade?