Wow, lots of progress. Looking good.
How is the moisture level in the transom wood? Sure is a good time to fix and clean things now that the engine is out.
Looks like a FUN project!
I noticed that you're considering changing to a Bravo I. On a cruiser like that I am not sure you're going to get much of a top speed increase (3-5mph according to Merc) and due to the additional slip, it may not be as economical and certainly not as nice to maneuver as a Bravo III......
How many RPM do you expect out of the "new" engine? 5500 possibly?
if so, you might want to consider a 1.81 or 2.00:1 ratio.
Referring to the prop-slip calculator, http://www.go-fast.com/Prop_Slip_Calculator.htm
2.00:1, 28p props and 5500 RPM yields approx 65 MPH and with 30p props, you get approx 70 (both using a conservative 12% slip which may be high)
Using a 1.81:1 drive, you get approx the same performance with 26p props. With a 1.81:1 ratio you would approach 3000 prop RPM though..... which might result in cavatation. (Mercury Racing or other high-speed peeps might be able to tell you something about running a Bravo III at HIGH RPM........I have read that there's possibly an upper limit on how "fast" one should turn Bravo III propellers.....)
Wow, lots of progress. Looking good. How is the moisture level in the transom wood? Sure is a good time to fix and clean things now that the engine is out.
I'm glad you did talk to them. I have been hearing this for some time but we hear a LOT of stuff on the internet don't we? Mercury will have experimental data that we can rely on....Just called Merc tech support this AM and he says there is no limit for the prop of a B1 or B3. They have found no issues with cavitation and prop rpm. With that I was thinking of the 1.81 but may want to go with the 1.50, still trying to decide.
What is your drive ratio now?My top end now is running the 24's at 5200. I don't see any way my cruiser has a chance to get much above 50mph, it's just to heavy. If it hit 55 I would be very impressed. I'm thinking as the boat get closer to 50 there was be more prop slip starting due to weight, just guessing.
Hey Ted , found some soft wood on the transom down low. Starting a new thread in the restoration section. Going to have to cut into her and see what I find.
http://forums.iboats.com/forum/boat...hull-repair/8846856-formula-27pc-transom-work
HowdyTed!, how similar are the "PC" hulls to the "SS" hulls?Ouch. I hope it is not too bad. You can get a direct contact moisture meter at the big box stores for around $35. That may help in determining how much moisture the transom may have, versus buying the $400 marine moisture meter.
I'll check out your other thread as well.
HowdyTed!, how similar are the "PC" hulls to the "SS" hulls?
You should have previous engine performance to go on with all the different props and whatever ratio you have now (1.81, 2.00:1 or 2.20:1?)
I would lean to the 1.81:1 over the 1.5:1 in a big boat like that.......
but having said that, using 5200 rpm, a 1.81:1 with 24p props is approx equivalent to a 1.50:1 running 20p props..... using http://www.go-fast.com/Prop_Slip_Calculator.htm
What is your drive ratio now?
Ouch. I hope it is not too bad. You can get a direct contact moisture meter at the big box stores for around $35. That may help in determining how much moisture the transom may have, versus buying the $400 marine moisture meter.
I'll check out your other thread as well.
Ratio now is 2.0 and I get around 45 to 47 on a good day (light fuel and low wind) if I remember correctly
I kind of shooting in the dark, figure current WOT with 24 pitch and 5200 rpm. If I add another 150 HP I'll over rev using the 2.0 ratio. So I'm leaning toward the 1.81 but maybe the 1.50 would give me more room to be able to use some of my current prop sets
It's sort of the other way around......The 1.81 might give you more "room". If you MAX out at around 5000 RPM with the 1.5:1 + 20p props, going up in pitch will only lower your max RPM.
You're going to have a lot of excess power. I would probably do a 1.81:1 drive. But since you already have 20p props to play with, a 1.5:1 drive might work. (the B-III is available in 1.5?)
It's sort of the other way around......The 1.81 might give you more "room". If you MAX out at around 5000 RPM with the 1.5:1 + 20p props, going up in pitch will only lower your max RPM.
If you exceed MAX RPM with a 1.81:1 drive using the 20's, you can go to 22's or 24's or even 26's.......The 2003 Formula 370ss I looked at had 26p prop sets on it with stock MPI 496's, and I think I remember seeing 1.81:1 drives on it......(I could be wrong about that)
Do you know where your rev limiter is going to be set (or will there be a rev-limit?)
Ted, what ratio and props do you have on your 330?
I have 1.81 ratio and 26P prop sets on my 330SS. Different ballgame single engine versus dual engine though. I would think a single engine setup is going to be more sensitive to the right matchup of ratio and pitch.
Same here. 1.81:1, single 7.4L Mercruiser Bravo III and 26p Props. I get 4600RPM or so at WOT (approx 56 MPH)
21' Four Winns Liberator, total weight approx 4500-5000 lbs