Good morning i have a 1994 celebrity 240BR status with a 7.4 and a bravo 1. I have been trying to figure out what i have going on . and maybe its just how the boat is. Other people claim they are getting 60mph out of there same boats and the fastest I have seen is 41.

so here are some details

others claim anywhere between 55-60 mph top speed (GPS checked) with a 21-23 pitch prop at 4400-4800 RPM

I currently have a 22pitch 4 blade stainless and can see 40 at 4000RPM

I have changed to a 21 pitch 3 blade and seen 41mph at 4100
also did a 19 pitch 3 blade it would hit red line but at a slower top end

I did a compression check and it was 120 at the lowest and 125 at the highest. engine seems to be running good and smooth.
plugs look good not to rich and not to lean.

I do have trip tabs but I wouldn't think they would slow it down 20mph compared to the next guy
it gets up on plane good and cruises nice at 28-30 mph at 3,000-3,200 rpm just getting the extra 10mph definitely takes some good effort.

I'm wondering if anyone else has any ideas what might be going on or if anyone has the same boat as me and how your boat reacts compared to mine?

Check the weight of the boat - if it's heavier than it should be there may be some hidden water somewhere in the hull. Not unusual in a 30+ year old boat.

Are your tabs dragging? When out of the water, do the tabs stay above the level of the bottom of the boat, if you put them there?

Is the bottom clean?

Basic tune-up stuff - plugs, wires, cap/rotor, should all be inspected and/or replaced.

Use this prop slip calculator to try and make sure the numbers make sense. I did a couple quick calculations for you from your posted numbers. I am using 1.50 for the drive ratio as that is the most common. Although 1.65 is also out there.

Others claim(using averages) prop size 21-23 = 22, rpms 4400-4800 = 4600, speed 55-60 = 58....results 9% slip...unlikely with a V hull.
Your results props size 22 4 blade, rpms 4000, speed 40 = 28% slip....that is high, like high enough something is wrong
Your results props size 21 3 blade, rpms 4100, speed 41 = 25% slip, still to high

Another example for you is my boat. A twin engine 35 fountain straight bottom.
props size 28 4 blade, (4000-4100) rpms = 4050, speed 60 = 16% slip

My guess is these "others" are blowing some smoke. 9% is cat type slip. But also your slip is to high. You just need to figure out why the slip is so high. I don't think this is engine related. Could be something with your coupler, your prop hub, the bottom of the boat, excess weight in the boat. Are you trimming the boat out enough? Are you sure your trim tabs are up all the way?

John

It should run 53 to 57 on gps with a 21 or 23. 3 blade prop. You are 500 to 700 rpms down. motor is down on power. Check the timing first. I think it is should be 8 degrees. May also have bad spark plugs, cap rotor ect. . All cheap DIY stuff

Chris

Drfeelsgood i will have to go check the weight of the boat. (hope theirs not hidden water anywhere) i will have to cheack

The tabs are about 3/4 higher than the bottom of the boat when all the way up

the bottom of the boat ov very clean looks new

and did a good tune up last fall and double check when i was at the lake last an it all locks good

Jadento Thank you for the awesome info on prop slip. what amount of prop slip should i have?

i have put diffrent props on with different prop hubs an had the same results
all my max spped has been with just me and my 8year old.

do you think if i had a coupler issue that i would fill it or hear it? i have been trying to figure this out for about 200hrs of boat run time ( thats how long i have ownd it)

my trim tabs when all the way up are about 3/4" above the bottom the boat do you think that high enough?

Thank you i will double check timing what do you think total timing should be?

Can you share a photo of the trim tabs on the back of the boat? I have the same boat but the cuddy cabin version that I am working on for someone and they asked me the same question you just did. However they said they see 45 ish.

That boat has no good location for tabs and when I looked at the boat I have in front of me, the tabs are mounted 3/4” up above the water line, but they are always dragging on this boat when they are fully retracted, about 3”.

Tredav39,

For reference, we had a Rinker 236 SportCuddy that ran 60-61 GPS with a mildly warmed over 465 (454, .040" over), turning a 23P three blade of unknown make, taching out right at 5K RPM with a 1.5 ratio BravoOne drive.

Thanks. Brad.

Here are my trim tabs and how they are mounted