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popusing problems

boatn70

boatn70

Well-known member
tell me something.....

ive got a checkmate 242convincor, with a 7.4 carb motor, everyhting runs good...........but at midrange speed, cruising at 28-32mph the boat porpuses terribly. i have to keep trim ALL the way down AND set my tabs down to 14, which is about 65% down. just to steady it. top end it runs real smooth.
ive run a 23 mirage plus, and had it redone by Darin at Houston with the accel. design. still porpuses.

any suggestions, is it prop,hull,or what
 
tell me something.....

ive got a checkmate 242convincor, with a 7.4 carb motor, everyhting runs good...........but at midrange speed, cruising at 28-32mph the boat porpuses terribly. i have to keep trim ALL the way down AND set my tabs down to 14, which is about 65% down. just to steady it. top end it runs real smooth.
ive run a 23 mirage plus, and had it redone by Darin at Houston with the accel. design. still porpuses.

any suggestions, is it prop,hull,or what
 
Boatn70,
This is A common problem With biger mates.I have A 251 that does the same thing but I dont have to run as much tab down.Pick up your cruise speed to 40+ with A little tab and they run nice.A nice 2 ft chop helps alot.I have tryed many props to correct this with not much change.I still want to try A bravo 4blade and A Hydromotive Quad 4.
Dave
 
Dave, it sounds to me like alot of others have this issue with the mates, ive heard some even say that the 4blades dont help it. imtrying to find a loaner Q4 or bravo to try though, just for shits and giggles, and piece of mind.
thanks
kevin
 
I have an 89 251. Using a Hydromotive quad 4 prop and a sea land stern jack. On smooth water, no chop trim down no tabs st8 as an arrow. This set up works for me.
 
If you are referring to gains in speed I really don’t know. I purchased the boat used with the stern jack installed. The previous owner said it was the best modification he did to the boat. He said it substantially improved the handling at all speeds. Alls I know is the boat runs level with no proposing or chine walk in varying water conditions. If I remember correctly Sea Land told him he could try the stern jack and if he didn’t like it he could return it for a full refund. Maybe you could get the same deal and give it a try.

I also purchased a couple of props with the boat. The previous owner said that the Hyromotive worked the best for handling but the Mirage plus was faster on top end. I haven’t had a change to compare the two. I have only run the Hyromotive.
 
sounds like what ive been hearing....
ive got a 22 Hydromotive to try now, just want the weather to cooperate with me here.
should be able to try it the next day or so.

kevin
 
well, i got to try the quad 4 sunday, worked well. seemed to reduce the propoising alot, however nnot completely, trim tab usage was much lower. i do like this prop for my boat.

time to plane seems less, porpoising seems less, top speed 58.1 gps vs. 59.8 gps with mirage 23 but i added 200 lbs of passenger too. midrange punch was good too.

all around.............two thumbs up for the hydromotive prop for all around usage!

now what should i keep or sell, i need to buy this hydro prop and sell my polished 23 mirage plus accelarator or a 23 mirage prop.........hhhmmmmmm.....

anyone?

kevin
 
I've been on three different 25' Convincers built in the early 90's. To date they have never showed any porpoising traits. Another friend bought a late 80's model with BB and Alpha drive. This boat was on Oneida Lake in upstate NY. It had a terrible porpoise from mid range to top end. He tried everything from props to Stern Jack with no luck. The boat continued to porpoise. He recently sold the boat with no resolution. I believe the hull developed a hook. I think Checkmate will concur that the boats should not porpoise at those speeds.
 
Boatn 70,
Its good to no something helps the porpoising at slow speeds.I have not found A quad yet to try .
Ing,
They must have took out when they came back out with the 251 in 98 because mine will porpoise at slower speeds.
Dave
 
dave,
i still get some porpoise with the hydro, but its better!! i can run low speeds with very, very little tab if any now.
satisfied for now, still looking for more HP though!!
 
Hea guys i thought i'd put my 2 cents in here.....not to many 24 degree single engine performance hulls like to run at slow speeds especially in smooth water.....just the nature of the beast! But you should check for a hook or most likely a rocker especially on the older ones. Hear this quite often on older 251's ..."it porposes at 30 MPH " or what ever low speed .... I tell them .......don't go 30 mph !
icon_wink.gif
 
Kip,
My 98 251 does not seem to have any hook in it (by eye)and it will porpose up to 45mph bad if I don't use the tabs.The boat runs great at 50 but sometimes I just can't run that fast and it is no fun bouncing up and down when my friends are running flat.
Dave
 
Check the bottom with a 4' level. Eye balling it will tell you nothing. Any more than a 1/8" gap is questionable. Over 1/4" = big problems. My ZT porpoises somewhat below 45mph, but I rarely see that speed for long and the tabs fix it. The 4 blade bravo helped quite a bit.
 
Dave ,
No hook in the bottom with 4ft sraight edge (my eye was good)
Eyecrazy.gif
I almost have my 502 done(I have been waiting for flyweel since march,Backordered) so I will wait before I purchase A prop.
Dave
 
man, you guys are makin me jealous, where can i find a 502 shrtblock or other, ive got the heads, intake, carbs and exhaust.
should i just order up a new shortblock for3900 or what?

also, how much of the hull should be checked, just at the vee or all the way out to the chines?

kevin
 
boatn70,
The other boats I have seen.The hook goes all the way across .I checked 4ft from the stern all the way acrossed.
Dave
 
I am a rookie and I am going to ask if somebody could better define the hook? Does it run parallel with the lines in the bottom or perpendicular? Is it a defect or abuse?
Sorry to be so....new?
 
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