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Convincor 251 owners advice!!

S

seth0687

Member
Hey guys I just picked up a '93 Convincor 251 with a carbed 502, bravo 1 drive, and 24p prop. Looking for any boat specific advice that you guys may have for this particulare make and model.

I called checkmate and they sent me the "brochures" for this boat/year/model, but they said they didn't ever come with owners manuals, do you guys have an owners manual or know of where I can get one, I try to do all my own maintance on my vehicles and toys but this marine engine thing is a new world to me.

Also, for some reason the boat is porpoising (Sp) pretty bad. When I bought the boat, the previous owner had 70lbs of weights in the front storage underneath the sleeping area towards the front of the boat in the cuddy cabin, if that makes any sense at all. When I bought it I took the weight out and went out on the lake, the porpoising was so bad it was rediculous, cruising, on plane, WOT, didn't matter it was horrible.

Then I did some research on Offshoreonly, and found that some folks put wieght in the bow to fix the porpoising so I put the wieghts back in and went out the next day. It was tons better, almost no porpoising at WOT, but while cruising/just on plane, it would still do it pretty good.

Here' s the thing, the second I try and trim the motor up to get up to speed it porpoises so bad, so someone said drop the tabs down a bit, I slowly work the tabs down and all it does is get much worse. I have to trim the drive back down and make tabs nuetral in order to get it to go away. The only amount of tab that wont make the boat go nuts is if I use just a little tab on the right side down to level off the boat, anything else and it porpoises so bad I get scared and back off the throttle.

I was running next to a guy in a Nordic, who said I was porpoising so bad the boat got out of the water twice at WOT. I am a new boat operator, but I have been doing exactly what everyone has been advising me to do.

Lastly, I live in Colorado, elevation 5280ft. I cannot for the life of me get my RPM's above 4200-4400 at WOT. The max speed I have been able to achieve according to my wifes GPS on her smart phone is 45.9mph at 4200ish rpms. Is this right? People keep telling me that I should be going much faster than this, and I have to admit I was expecting at least 50-55ish even at this altitude.

Any help and advice would be much appreciated, as well as things you have learned regarding this particular boat and articles that relate to this particulare model as well.

Thanks so much and if there are any Colorado owners out here I would love to meet up with you guys and get on the water, or grab a beer in the off season.

Cheers,

Seth
 
:bigthumb:Welcome to the 'Checkmate bounce'.
The 251 likes very little trim at lower speeds. Trim all the way down and anything more then a bump or two up will have you bounceing. Once your say 40 you can trim it up as much as you like. Your right on the tabs, they really only level the boat.I never touch them unless I;m leveling. Just leave them up. You should be seeing at least 10 more mph and your rpms are low, but with your altitude I,m not sure whats going on there. No owners manual for the boat, but I have manuals for motor, drive etc. Basically anything you need to know is on this site if you do a search or just ask, It will get answered.


Its just gonna take some seat time to learn your boat.
 
yeah like keith said if your gonna do maitenance and want manuals get a merc sterndrive manual and a merc motor manual for your particular setup just get ready to get hosed they are not cheap i think i bought my stuff on ebay
also with your altitude you probably lose some hp might want to get the boat dialed in for your area and then possibly think about a smaller prop
 
regardless of the altitude, you should never have porpoise at "wot" .....also not sure about what altitude will do to your boat but that speed at that rpm is right....
 
ross said:
regardless of the altitude, you should never have porpoise at "wot" .....also not sure about what altitude will do to your boat but that speed at that rpm is right....
Click to expand...

less dense air at higher altitudes means less air in the air/fuel ratio which means richer engines and less power
 
jazzy said:
less dense air at higher altitudes means less air in the air/fuel ratio which means richer engines and less power
Click to expand...

my point being, at "wot" NO BOAT SHOULD PORPOIS at "WOT" i dont care if its a fishing boat! something is wrong here! the altitude has nothing to due with this issue;)
 
At that elevation you have a 15-17% horsepower loss.

What prop do you have on the boat now?


edit: Also, imo- the altitude might affect this boats performance with this prop. If he's not able to get the power outta the motor to turn the prop, he might be in a bad range for it. My mirage props porpise pretty bad running at midrange speeds (which is what he's running). Dropping the tabs cures it for me- not sure what is going on there.
 
not enough trim will make it porpoise at wot the wrong angle of the drive forces the bow down kinda like skipping a rock jams the whole boat into the water and then buoyency does the rest it pops back out and the cycle repeats he needs to find the point where the drive is at least neutral and then work up from there
 
i got a 251 not that long ago, it porpised real bad at 32-38 ish with a 3 blade mirage, i barrowed a 24 bravo from gimmie fuel:thumb: and it helped tremendoulsy, it still does a little, but not nearly as bad.

As far as the tabs i pretty much leave them alone. i started a thread on that a while back. http://checkmate-boats.com/forums/showthread.php?t=21788

i got a bone stock 454 in mine, (which im sure is a little tired) the best ive seen yet is 58 on the gps. with the 24 bravo.
 
Mine bounces like a basketball too. Can't cruise at any even speed under 40 or so with any trim out at all. Porpoising at WOT doesn't sound right though.
 
The only way I can cure the porpoising at WOT is by putting the tabs down. What could be the potential cause of this? How can I trouble shoot it and fix it?

Thanks guys,

Seth

PS-I borrowed a 21p 5 blade from a friend and that got my rpms up to the 5200-5400 range at WOT, also appeared to get me just over 50mph...Still need to get a handheld GPS for a final accurate top speed number.
 
i would have thought by now one of the 251 owners would have told you where they kept their trim setups at for cruising and wot but just so you know checkmates are infamous for their porpoising thats part of the hull design and part of what makes them fast thats a real good hull and probably one of my all time favorites but like ross said if properly trimmed there is no reason it should porpoise at wot
 
jazzy said:
i would have thought by now one of the 251 owners would have told you where they kept their trim setups at for cruising and wot but just so you know checkmates are infamous for their porpoising thats part of the hull design and part of what makes them fast thats a real good hull and probably one of my all time favorites but like ross said if properly trimmed there is no reason it should porpoise at wot
Click to expand...

and i dont know how to drive a boat:shakehead:
 
wtf dude you have the same boat the guy is asking for help as to where to set his drive/tabs you comment on his thread like three times but still no setup advice what are you keeping some trade secrets under wraps with that boat :poke:
 
What I found is to trim it up till the rooster tail is about 4' tall. Let her eat and hold on! That's where I got the best speed from the 251. That is the point where it pulls the hull out of the water and breaks loose from the suction cup effect. You should not have to drag tabs with the right prop, setup. Just be careful being this is your first boat. Its nothing like driving on a road.

However I am thinking you got to replace your transom assembly from your other post. Sounds like the gimble, king pins, and arm has some slop and that will severely screw up the boats handling. Price out replacing the entire unit and the labor. From what I hear, its cheaper to replace the entire thing vs just the parts. Also hyd steering, even if only a add on system will help save the new parts from the same wear as well as be a safer setup!
 
1st ch looseness at the drive....then dial in the RPM WOT trimmed out about 5300 max 24 bravo 1 should be close, thats the best prop for the bounce but will aways want to in cruise..just have to get used to dialing in the trim...but once you do should not be bad...the WOT should not at all..unless real choppy water..at sea level that boat should run 65 with no problems, at your alitude should be close to 60..I have a 24 bravo 1 if you need one...Rob
 
OK guys, I went out the other day and can get the boat smooth as glass NO PORPOISING at 22 mph, 30mph, and 40mph. HOWEVER, when I try and hammer it, I cannot get trimmed up very far without porpoising, and I have to drag tabs the entire time I try and run WOT.

If my wifes GPS on her cellphone is right, it seems as the best I have been able to get is just over 50mph. I feel like the boat should do more than this but can't figure out how to make it happen.....My engine trim gauge and trim tabs gauges do not work....so I am flying blind so to speak...

Any help/advice/etc... would be much appreciated. Do you guys work the throttle a lil then trim a lil? do you start with tabs down/up? Anything ?? BUELLER?

Thanks,

Seth
 
Gauges are not that big of a deal with trim. You shoul be starting out of the hole with the trim all the way down (hold button down until you hear the pump change tones....try this with the motor off so you know what you are listening for). You will run with trim all the way down until you get above 40 mph to avoid slow speed porpoising (in general). With the trim all the way down, hammer the throttle to full and see what happens. Let the boat top out if there is no porpoising now. Start bumping the trim button up until you feel the boat break loose from the water and speed increases. As you trim up at WOT, you will find a spot where you have the greatest speed. Once you go past that you will see your speed begin to drop, the boat may porpoise, blow out the propeller, or the drive gimbal/u-joints start to vibrate. If any of those things happen you are over trimming your boat. Your trim lavel will vary with your speed. WOT will be full trim to the point I described earlier. Slow cruising speeds will use little to zero trim.
 
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