PORPOISING Chapparal HELP?

[jvcoconut]

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Hi,

I posted in Chapparal section, but maybe I can get help here too.

I own a 2005 232 Sunesta 5.0 gxi with a duoprop outdrive and double bimini from bow to stern. I notice when I look at some (not all) deckboats cruising next to me at all speeds, they ride smooth and nice, NO SLAMMING, NO PORPOISING.

I have tried everything.....Full Boat, empty boat, no bimini, both biminis, ice chest, no ice chest...I cannot get it to stop porpoising (even on semi glassy water). I currently trim the outdrive to just before the first line on the trim gauge and have tried all other settings below that and it still wants to porpoise. The only way I get it to stop is to back the throttle off momentarily and re-engage the throttle, then it smooths out for a bit.

WHY CAN"T MY BOAT RIDE LIKE OTHER SIMILIAR DECKBOATS????? The hull is deep enough and the boat is heavy enough, it should cut through chop smoothly and not porpoise on jetski wakes....RIGHT? I talked to my service guy @ Sun Country Marine in Onatario Ca and he rifled off several questions to make sure I was doing everything correctly in the operation of my boat, which he confirmed I was. I asked about trim tabs. He has some customers that installed trim tabs and it took away all porpoising. He also said they don't sit on the boat all that great due to the large swim step, but they can be made to function properly.

I purchased the boat because Chapparal claims to have the "best hull design years running" I think it is a crock of sh*t. I am happy with the boat, except for the ride.

Are trim tabs my answer?
Anyone experience the same problems and fix it with trim tabs?
Which ones will fit under my huge swim step?

Any answers would be appreciated

 

[tashasdaddy]

Re: PORPOISING Chapparal HELP?

is this your first boat? i think working with the trim should take care of it. if this is your first boat get and experienced boater to go with you and see if he can work with it. i have a Chris Craft 230 w 5.7 vp and have no problems.

 

[scoutabout]

Re: PORPOISING Chapparal HELP?

Something is driving the stern down and bow up. When the weight of the bow overcomes whatever that force is it settles back down and the cycle starts again.

I'd agree with TD that you should be able to trim out porposing as usually it's the angle of the propeller that's responsible for this. I'd put the second place culprit as an usually heavy stern due to overpowering, poor placement of fuel tank or other unusual factor.

Having said that, I have zero experience with deck boats but agree again that a test drive with an experienced boater (if you are not) might shed some light on your trimming situation. Some boats are just more prone to porposing than others. My SeaRay 170 would not porpose no matter how much the outdrive was trimmed up. The prop would just gradually lose bite.
The Scout on the other hand is very susceptible to porposing and I've got to walk a fine line between the optimum amount of wetted hull and a bouncing bow.

I have noted over the years that trim indicators are almost as inaccurate as fuel guages, so I'd learn to go by feel. It's possible it's out of adjustment and you are trimmed up much higher than it actually reads.

Something to try: Next time you're out, trim all the way down while underway at idle until you can hear the hydraulic pump change pitch to indicate you are indeed down. Then get up on plane to see what happens. If you are getting porposing with full down trim something is indeed amiss and I'd get the dealer out on the water for a look.

If you can cruise with full down trim without porposing, begin bumping up the trim in very short bursts until you can feel the bow lighten up. If you have non hydraulic steering you might also feel the wheel go a little lighter. You should also pick up a little speed (although perhaps not enough to read without GPS). While doing this exercise, ignore the trim gauge and concentrate on boat feel. If you can't trim up at all without some porposing I'd say things still weren't quite right.

You didn't mention passenger or fuel loading but the boat should run with any load from min to max rated and handle fine. Chapperal has certainly been around long enough to be able to design a hull that rides right.

Let us know the results of the above and folks can comment.

 

[jvcoconut]

Re: PORPOISING Chapparal HELP?

This is not my first boat. I definitely have tried the "feel" method and not relied on the gauge. From the down position @ take off, the prop is digging hard. With just a few taps of the trim control the outdrive "plowing" (as I call it) is gone and "smooth" power is felt. I'd be willing to bet the 56 gallon fuel tank may have something to do with it. The gauge is accurate when the trim is in the down position, but not at full gauge trim. The duoprop outdrive requires very little trim due to the amount of torque from the counter rotating props. I can assure you I know what I am talking about when it comes to this boat and have tried "all" possible fixes. The porpoising is not herendous, just annoying. This boat should ride alot smoother.

 

[jvcoconut]

Re: PORPOISING Chapparal HELP?

just bringing it back up. Any more takers

 

[CATransplant]

Re: PORPOISING Chapparal HELP?

You mentioned a 56 gal. fuel tank. Is that the standard tank for that boat? If not, then you're talking about 300+ lbs of fuel when it's full. That could definitely alter the weight distribution.

If it's the standard tank, then I'm sure the the builders figured that in. If it's not, then it could be the cause of your problem.

Here's a test: Run the boat with the tank only 1/4 full of fuel. If that solves your porpoising problem, then you've identified the source of the problem.

Again, if it's the standard tank, then I'm off base.

 

[QC]

Re: PORPOISING Chapparal HELP?

1) Porpoising is almost always caused by weight balance issues fore and aft. I see your notes about full boat and empty boat, but nothing about shifting weight fore and aft. If you have any heavy things in the stern and light things in the bow, switch them, tools, anchors, chain etc. may need to go to the bow with your boat. You need some significant weight shifted forward when they porpoise like you describe. Yes, the fuel tank could be the culprit, but I am guessing it is standard and staying put.

2) I don't care who designed the hull and what they designed it for, for me all V-hulls (tr-hull variants too) should come standard with trim tabs. I personally prefer helm adjustable tabs, but SmartTabs will accomplish this as well.

If it were me, I would play around with weight shifting fore and aft until I could only get her to porpoise at full trim and full speed. If I got to that point, then I would control the slight porpoise with the tabs. This combo should give you the fastest top speed, along with good drive trim control, and no porpoising at lower speeds.

Also, I had a boat that would not stop porpoising unless I put people in the bow. I shifted weight all over the place, I even fix mounted my Ice Chest in the bow. Frankly I think the fuel tanks were simply mounted too far aft and combined with dual batteries, I could just not get it right. Anyway, after installing trim tabs (Bennett's) she was a joy, and was very fast. On my latest boat, I think she is too heavy in the bow, and I could not get her to porpoise at all before I started messing around. I added tabs (see note about ALL v-hulls ) and I moved all of my heavy gear except the anchor to the stern, and have nothing but life jackets stowed forward. I can just get her to porpoise now in some conditions and I also get much more bow lift before the prop blows out. Again, I control all of this with the tabs. With a full bow of people I can run full speed with no down trim tab application and still use full trim without any blowout. If they all move aft, she is a little faster and I need a little down tab to control a slight porpoise . . .

 

[tashasdaddy]

Re: PORPOISING Chapparal HELP?

i also have a 60 gallon tank, but never put more than 30 gallons in it. why haul all that gas? i also never fill my onboard water tank.

 

[QC]

Re: PORPOISING Chapparal HELP?

why haul all that gas?

Uh, when you gotta go far . . .

BTW, IMHO that dealer sucks and I have multiple experiences with them. Great facility, some good people, but a lot of carp work and stories come outta there from my perspective and I have been involved (friend's boats) with three boat purchases from them. I think I related one of them in the Chap section . . . that thread might be somewhere else.

 

[rndn]

Re: PORPOISING Chapparal HELP?

I had a Baja that was a little sensitive to this and a five blade SS prop helped a lot. It really stabilizes the boat more than one would think. Under full steam, the prop is about the only thing in the water and it's better to have the additional suface area of a 4 or 5 blade prop than the standard 3 blade. So many people overlook this and if you don't want to pony up the money for the SS, iboats has four blaed aluminum props for about $170.00.

 

[jvcoconut]

Re: PORPOISING Chapparal HELP?

QC,

Thanks! I have tried everything. Moving passengers to the bow, leaving out my ice chest, taking down the double bimini (acts like a sail)....everything.

I wrote an email to a representative from Bennet trim tabs. He assured me the porpoising will go away. From what I also understand from the literature I have read on the net, PLANING times decrease and BOW SLAP over rough wakes goes away , does this sound correct to you?. The dealer tells me trim tab installation is a little tough. I looked at it and it is not going to be a big deal at all.

I think this is my certain fix. Like I said, for a 4,000 lb. boat it should ride a hell of alot better. I think the combo of the 56 gallon tank, 14 gallon water tank, dual battery and obvious engine weight contributes to my problem.

What do you think?