Hey all, I have an 89' Formula 242ls w/ a single 454/Bravo 1, and my problem is, this damn thing is too slow! Now I know these big ol' heavy things were never speed demons, but 50mph on gps, really!? Last year it was running a consistant high 50's (57-58 at about 4500 rpms), and that was with 5-6 people and 2-3 loaded up coolers in it every single time. This spring I had the whole lower unit rebuilt, new prop shaft, drive shaft, reconditioned the prop, the whole sha-bang, put a new impeller pump and thermostat and the usual **** in it, and now I can BARELY hit 50mph on gps, still about 4400-4500 rpms, and that's if I only have 1 or 2 people in it! Nothing else has changed, it is still the bone stock 454, and a Stainless Mercury Marine Bravo 1 22p 4-blade prop. I cavitates its ass off trying to get on plane, and I have to back it off big time to get it to stop, and then hammer down again, but I've been told that is kinda normal with these big heavy Formulas. I absolutely love the boat, and don't want to get something else at all, but I'll be damned if I'm gonna have to spend a literal fortune just to get this thing to run 60mph! Am I way off on the prop? Any recomondations would be greatly appreciated, I plan on building a Gen6 roller BBC for it in the future, but who knows how far off that is, so I'd like to get some better performance out of it until then. Still has stock silent thunder but that is about to be modified to a thru-hull set up real soon. Thanks again guys!

Try a different prop first to see if it makes any difference.
See if you can look in under the floor deck compartments for water. You might be carrying a lot of water that has leaked in and can't drain out.

Something is wrong here. At 58 mph you were at 7% prop slip which is almost impossible... at 50 mph you are at 20% which is very poor (in a perfect world you want to be 10-12% which puts you at 55 mph). Agreed that your boat may have gained weight but we are talking hundreds of pounds to drop your speed so much. Loss of compression would affect hp and your rpms--if you are sure rpm's havent dropped then checking compression wont help.

Since the only thing you changed is the lower unit I have to think that something didnt go back together correctly or it wasnt aligned correctly when it went back on. Do you know anyone with a spare drive you could bolt on? Its worth it to pinpoint the problem.

http://www.mercuryracing.com/propell...calculator.php

I hear prop reconditioned and think maybe that got messed up. Try to borrow a prop.

Formulas like a 3 Blade prop that gets the bow up a little as opposed to a 4 blade that lifts the stern. I would also check the hub on that prop you have to make sure it's not blown out and slipping....+1 on looking for water lurking around below deck also.

Thanks for the input guys, I have really been wanting to try a 3 blade out to see how it works... I have a 3 blade 23p, buts it's aluminum and a very small diameter, and it wouldn't even hold past 2800 rpms without cavitating it's ass off, wrappin up to 6000rpms instantly, and falling off plane. I have been cought in some MASSIVE rain storms lately, and been getting tons of rain here at the house where I store it, a few times before I could get home to get the cover back on, so water below would make sence, never really thought of that... Where would I check for it? I don't have a storage compartment in the floor, wouldn't it all drain to the engine compartment when I jack the trailor all the way up and pull the plug?

Try a Mirage Plus 21 pitch, I had the same boat and that was the best prop, you should pull 53-56 depending on if its a 330 or a 365. I had 525 hp in mine and it would do 68 all day long!

I think most Formulas you can lift the cuddy floor (walk way) out. Mine is just a 3/4" board that is removable. Take a peek down there as these boats are known for holding water in the front V. They can hold a bit of water, but most likley not enough to slow you down 6-8 mph. You said your prop was "reconditioned" I would be trying to borrow a prop and test out another one. Like everyone has said, the 21p 3 blade works nice. I have a little smaller boat with the stock 454 mag / bravo 1 and I run a 3 blade SS 21P @ 4600-4800 rpm around the mid 50s. Grab a GPS mph also, that will help eliminate any gauge problems.

Best prop on my 242 before building a motor was the old style Mirage 23P... not the Mirage Plus.

X2 on water.
I hauled my boat fro fl. To san diego ,always kept plug out -lost 10 mph and performance. Blamed a recent prop rehab.
Then one day after a disappointing run,pulled the plug and nothing, stuck my finger in the hole-a plastic cap had blocked the hole from inside! 45 min. And a couple hundred gal. Of fla. Rain water later. Problem solved
worst part is i hauled it 3000 miles that way