checked my tach over the weekend.....seems like it is about 200 of above 4000 but pretty close below that. I checked it with my snap-on digital timing light that has a tach option in it. I cleaned my 21 mirage up took 2 hours with clr and steel wool to get all the growth that formed in just a few months. double checked both props the 21 mirage and 23 mirage plus ran both direction up river and down, jumped in changed in the water and reran. the 23 pitch netted me 44-45 mph at 3900-4000 rpm 21-23% slip the 21 pitch netted me 42-43mph at 4200-4300 rpm 23-25% slip both props have similar slip number when cruising around 3000 rpm getting 30-32 mph when i throttle up there rpms just sounds unloaded and free revingish almost the speed does not feel like it gain with rpms i figure with that much slip i cant beleive the rpms are not going higher once the numbers are crunched......makes me wonder if i get the slip down if i will still be able to turn that many rpms. during this rounds of test it was me and wife in boat 500 pounds and 1/4 tank of fuel 25 gal.

With both props i still could not trim very much before i started getting alot of slip. I was unable to get the trim gauge worked on to much going on over the holiday with family

there are a couple of rev 4 used props i can find on cl think i should stick with the 21 pitch or drop to a 19 pitch? doing the match seems like if i can the slip percent down i would have a better cruising speed at lower rpm with the higher pitch even in my test i was able to go faster at less rpms with a higher pitch prop. seems to me it would be better to run 50mph at lets say 4100 than to turn 4500 to get the same speed??

Hope everyone had a good 4th

Hmmm...the prop blowout doesn't make sense to me if you are really trimming that little, but I certainly believe you. Ran across this the other day and seeing your reply reminded me. Sounds like you may be able to get some ideas from it. Keep reading, the prop stuff is in there. It's a 251 Liberator, but I suppose it closer to your boat than mine is. His boat likes the 4-Blade.

http://www.speedwake.com/forums/showthread.php?t=72964

One more thing, how positive are you that you have a 1.5 drive ratio? That would explain a lot. It is possible it's a 1.65 ratio or something???

http://bluewatermarinesvc.com/pdf/me...ear_ratios.pdf

If you are unsure I think you can take the cover off the top of the driveshaft housing and count the teeth on the top gear. If the gear has 30 teeth, it's a 1:65, if it has 32 teeth it's a 1.5 and if it has 29 teeth, it's a 1.36. You only need a 3/8" twelve point socket to remove the 4 bolts. Some oil may leak out though. This may be worthless information if you already know for sure.

i have never counted teeth. the numbers on the sticker can not be seen. i was told it was a 1.5 next time the boat is out of the water i will pull that cover off and count....i would think if i had 1.65 gear i would be able to get more rpms out of it than 3900-4000 with the 23 pitch ans 4200-4300 with the 21 pitch. If i am thinking about about this the correct way the higher the number of the gear ratio the more easier it would be to turn higher engine rpm. and i would get less prop rpm. i guess i could pull my dist cap and put the boat into gear and manual crank the motor at the crank and count the turns of the prop. i should get 1.5 motor revs to 1 of the prop something not to hard to do in the water I am thinking about this the correct way correct? The motor turns faster than the prop just like gear ration in a gear?? engine revs is the first number to output revs as the second??????

The higher the ratio, the less the prop turns, so more rpm's to maintain the same speed. I guess what I am getting at is the 1.65 ratio puts your slip #'s more into the normal range. I can't believe all the props are slipping THAT much. Is the boat extra heavy and dragging in the water? Maybe waterlogged wood? Foam? etc. Is the motor NOT making full power, is it tired? and it's only getting the rpm's since it's got a higher ratio?

You've pretty much solved the prop question you end up in the 20+ range for slip on everything, now the question is why. If you knew the drive ratio 100% that may lead you down a different path. What I do know is that is a 50+mph boat, and something isn't adding up. You could do it in the water, but the different between 1.5 and 1.65 may be hard to see, not sure never tried.

You did have RPM and speed data from earlier though, the very first post says 4400 at 48MPH, that makes sense if your #'s are accurate and would indicate a 1.5 drive. The question is what changed...

By the way which way was your stock tach off, does it read high or low? I mean, are those #'s still valid since you now know the tach is off???

EDIT: Just thinking out loud.... i just don't have anything more useful for you at this point ;)

the boat does not seem water logged. I got good mph last year and it sat in inside storage all winter. My boat does sit in the water all summer but each week i do not get much water out of it in the bildge. If it does not rain some weeks even when i turn it on nothing comes out. What is a good way to check for this. The boat does not sit low in the water. it is down a little ing the back.....not as much as alot of other performance boats. it does lean to the starboard side....did this last year too....but both batteries are on that side....so is the fridge and the water tank.....just figured that was why

The motor seems strong, hold 40psi oil at idle and 60 when running. I actualy think the motor was changed sometime in the boats life. The oil dipstick is on the port rear corner where my other one was on the starboard front. Has over 150 cranking psi on all cylinders, never did a leak done test. But seems smooth and strong so i never looked into it.

Last year i checked the tach the same way and it was spot on this year reads 200 high so 4400 on my tach showed 4200 on the timing light

I will check the ratio this weekend. It should not be that hard to ID one blade put it straight up, put the boat in gear, pull the cap, referance the rotor location. hand crank the motor over till the prop blade get back to where it started and look to see if the rotor went 1.5 times around or 1.65( little more than 5/8) that should be very noticable on the rotor. I know alot of ppl run a 21 pitch prop on these boats and similar and turn 4200-4500 rpm with no issue.......using 1.5 ratio i would figure if i had a 1.65 ratio it would be easier to turn more rpms or a larger pitch prop. my rpms at 4200 with the 21 pitch and 3900 with the 23 seems very correct? but i will check

I agree it should be 50 mph boat i thought the prop had alot of slip last year that why i had the prop polished to get the scuzz off the try to help that hopefuly. The mirage and mirage plus are very similar style of prop so if for some reason my boat does not like that prop make since switching to 23 pitch from 21 would not change the world. I used the 23 just to try to figure out if it was my prop or not. I have also tried a 13 3/4 21 and 23 pitch 3 blade al props both had a hard time handling the rpms and power. they both blew out very easy and had a hard time even geting on plan and up to 30 mph I wish i had a 4 blade prop to try to see my last libby i ran a 14.25 4 blade 19 pitch and it seemed to work well. it came with a 13 3/4 21 pitch 3 blade stainless but would not even get on plane with it...........i tried that prop last year on my new boat and runned more rpms with less speed so i sold it

the boat is still very useable the way it is just not right. i will have some more answers after the weekend. But you have made a very good point about the gear ratio and will check it........not sure how to check to water logged

I do thank you for your time and thoughts on this issue you have brought up some good points and things to think about. I guess if i have a 1.65 ratio i need to find out why i cant turn more rpms....

I mean, everything you say about the engine makes me think it's fine too, have you checked the timing at say 3000rpm or up, to make sure it's getting full advance?

The best way to check for water logging is simply to weigh the boat...another not so trivial task....a whole bunch of extra weight would give the results you are describing though... Let's hope that's NOT it, because there isn't a real good solution to that one...at least not easy. If you don't have a lot of water in the bilge are you sure the front drain are draining to the back??? There is a hole in the bulkhead in front of the motor that allows for the front of the boat to drain to the bilge, can you stick your finger in it to see if it's clogged? Or a screwdriver or something?? Is a ton of rot around this drain??? If there is a lot of rot around this drain, that would be an indication there may be a larger problem. Though some softness immediately around this hole would be normal.

What is the bottom condition??? Since you keep it in the water???

You could always pull a valve cover to make sure you are getting full lift??? Now I'm starting to talk crazy....

Without actually being there I am about out of ideas.

the boat does not have tons of extra weight. i normaly run between 25-75 gal gas depending on where we are going but most of the time 25-50 gal. i have 2 13 pound anchors, about 250 feet of rope, 8 lifejackets, 2 al handled plastic folding paddels, 6-8 fishing poles, i normaly do not have water in tank, the potti does have 2 gal water almost in the nose. course the boat has the frdge, nothing in it most of the time

I do not know what these boats should tip the scales at. the four winns site says it 3105 but i know that cant be right...... I know a 454 is close to 600 pounds the manifolds and risers have to 75 a side so thats 150 750 the outdrive is close to 125ish 875 not sure what the housing and gimbal ring weigh maybe 100 so call that 1000 pounds on top of the 3100 four wins says 4100 350 for 50 gal gas i know my wife and i( normaly the only two ppl in the boat ) 550 neither of us are small. so say 5000 lbs running is a fair guess

Does anyone know what a 241 liberator with 454 and bravo should scale in at i do know the bravo is a little heavier than the alpha

last year i had 8 adult on boat and minus getting on plane the boat did not reall slow down any.....


I thought about something else too last year i was using a differant gps than this year wonder if maybe it read fast. My speedo on the boat did not work last year and this year it does seems to be about 2 slower than my gps....i did check it this year on both my gps and my iphone

I will check the drain hole too.......honestly never felt around down there.....would not be hard to run a something up through there just to make sure.......nothing ever seems wet but never know.... I will check all this out this weekend when i get up there.....all good points to check

I think i have the specs for the timing somewhere 8 for base timing and i think the module should give me 22 more or so by 3200 i think 30 total sounds right.

the bottom is clean got a fresh coat a paint this year with bioboost from sea hawk. i do keep the growth off the sides.....the water at the back of the boat goes about 3 to 4 inches of the paint......i had it painted up the factory tristrip did not want to make it look silly on the trailer by painting up that far. i can feel a little slick slime on the bottom that feels very smooth......but nothing big and hairy causing lots of drag

I could pull the covers.......but that means dropping those big heavy manifold and risers........if i was not gettting up the rpms i would think that way. i can get the rpms just not the mph besides if i pulled them off i would be very tempted to add 1.8 roller rockers and that starts a hole other issue i have........always wanting more hp in everything i have.....lol I have 3800 v6 making 400 hp as a daily driver and about 750hp 455 buick racecar......

I dont drive 50+ everywhere i can if it would just want things to be right just want to able to do it if and when i wanted and water was right and safe.....most of my boating is done at 30-35 mph just dont want to have to run extra rpms and gas to get there....

thanks for the help and info it always does good to get another brain or too involved might just uncover the snake sitting right in front of me.

Here is the 88' spec sheet: http://www.fourwinns.com/past_produc...20(p48-49).pdf

The 3100 is boat only, page 2 has total dry weight.

Check back in with what you find, you've got me curious...

Remember the rotor only turns half engine speed so 1 turn of the prop would be 3/4 turn of the rotor for a 1.5 to 1 drive. It would turn .825, or more than 3/4 turn for 1.65:1 drive. Kind of confusing.

Since that boat came with a OMC it probably came with a Raker prop. I have some friends with early 90s 221 Libs and they came with 20" Rakers. One has a stock 454/330hp and runs low/mid 50s with a 20 Raker. I think his drive is a 1.43 so that puts him at about 10 slip.

The could see high slip numbers on the standard Mirage 21 but the high slip numbers on the Mirage+ 23 are baffling.