Chapparal has trouble staying up on plane

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Aug 2, 2014
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I have a 1988 Chapparal 2350 SX with a 350 CI I/O Mercruiser that seems to have a difficult time coming up on and staying on plane when the throttle is below 4000 RPM. I changed the prop from a 20 pitch ti 16 and that didn't give a noticeable difference. The boat seems to take too much throttle and time getting up on plane and. again, staying there without much throttle. Any advice? Thanks in advance.
 

airshot

Rear Admiral
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Jul 22, 2008
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Excess weight from water saturated foam is a most likely culprit and difficult to remove. Next in line is proper engine performance, be sure it is tuned to the max.
One should not just change props without researching the problem first, by dropping 4" in pitch without knowing why, could be that the prop is now way to underpitched to get the boat on plane. Need to know a wot rpm to know whether prop is correct or not. But everything must be in proper working order before a realistic wot rpm can be achieved. Did the boat plane out well in the past with the previous prop?
 

edthearcher

Petty Officer 2nd Class
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Sep 22, 2007
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I have a 22 foot sea ray empty weight with out gear or gas is 3,200 i have a 5.7 350 merc. cruiser magnum, i have 2 props 17 and 19 pitch, my hole shot with the 17 was faster, than the 19, but my RPMs were high, called merc cruiser in wisconsin, they said try a 21 pitch my rpms would go down my speed whoul go up about 3MPH with a alum. prop. now why is your boat loosing plane when crusing, good question if i in my boat were doing 4,000 rpm and never touched the throttle lever it would back down slightly, there fore causing the hull to settle so once i get my boat up on plane, than watch to rpm guage, now tweek your stern drive slightly up and see how the rpms increase, this is the prefect setting. (not how much water you got in your cushion foam)
 
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Aug 2, 2014
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The "water saturated foam" is an interesting tip I had not thought of. The boat is a 1988 model. The performance did not change appreciably by changing the prop from 20 to 16, this was the recommendation of the folks at Midwest Propeller. I am confident the motor is tuned for max performance. How would one check for this foam issue?
 

airshot

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Older glass boats are notorious for absorbing water into the foam flotation under the floor, if you have no direct access to that foam then a hole needs to be cut in an area that would not be noticeable and check to see if flotation foam is water logged. If you can research the boat and find what the weight should be then you can weigh it at a truck scale. If it is saturated with water you could easily be adding 500-1000 lb of water. Many people cut a hole inside their hull someplace hidden where they can check for this condition, it is something that should be checked before purchasing a used glass boat. Trim could very well be part of the problem but at 4000 rpm the trim would have to be really, really far out. If you did not notice a change in performance by moving 4" in pitch then something is going on. If the boat sat uncovered outside or stored thru the winter without proper covering then I would be quite certain you have a water in the hull problem. Wish I had better news.
 

Watermann

Starmada Splash of the Year 2014
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Jan 12, 2013
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Is you're tach reading correctly? I would think a 21" p prop would be good, 19" should be the lowest.How many people are on board matters too, fuel loadout and gear. Are you correctly trimming the outdrive once on a plane? A 16" pitch prop on a healthy 350 should over revv pretty quickly even with a few hundred extra pounds of water in the foam. NADA may have your boats scale weight.
 

midcarolina

Chief Petty Officer
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Jul 16, 2013
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I'm pretty sure what I read said dry weight .......... I couldn't find the official specs of your boat so had to rely on several other statements of weight I found on the net.
 

ihearth2o

Petty Officer 2nd Class
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Aug 18, 2014
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IMO, you'd just be guessing if you took it to a truck stop now. Listed dry weights are just that. No gear, no gas, no accessories and may not even include the motor or at the very least the motor that you have on your boat. Don't get me wrong, getting a weigh is always a good idea but a better idea might be to weigh your boat now, then letting the boat sit for a while and do whatever you can to dry out (if that's even possible), then reweigh. Still would be a bit of guessing though.

I did a quick search and looks like some people have had some luck with removing seats off pedestals and then removing the plate to get a look at what's under the floor.
 

foodfisher

Captain
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Feb 18, 2009
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The "water saturated foam" is an interesting tip I had not thought of. The boat is a 1988 model. The performance did not change appreciably by changing the prop from 20 to 16, this was the recommendation of the folks at Midwest Propeller. I am confident the motor is tuned for max performance. How would one check for this foam issue?
Rusty colored bleeding from any thruhull penetration. Out of sight and easily patched drilling to check moisture content of what is pulled out. Why is this wet when it shouldn't be curiosities.
 
Joined
Aug 2, 2014
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Thanks to all for these tips. I will pull the passenger side front-back seats and see if I can access the inner hull and look around. I believe you are all probably right about the water saturation thing. This boat came from Kenosha, Wisconsin and sat over the winters in the previous owner's driveway. Even though he had it "winterized" every year, I wonder what effect a number of cold, wet winters would have had on it. Regards, the Colonel
 

midcarolina

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IMO if it sat uncovered for any real amount of time a whole winter or more, you can almost bet money you got water loggin going on
 
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It wasn't what I'd call "uncovered". It has what I believe is the original boat cover but it sags in the center over the front of the engine cover and holds a pocket if water after a rain.I store it with the bow elevated slightly and the drain plug out but not sure that was the case previously.
 

foodfisher

Captain
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Good luck! I've heard of moisture detectors out there but I'm not sure if they work through fiberglass.
 
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