Boat porpoises above 30 mph

[TahoeBears]

I have a 2006 Ski Centurion V Drive Wave Warrior, with fuel injection with Perfect Pass...above 30 mph, the boat porpoises irrespective of whether PP is on of off. There is no prop or hull damage. The Fixed trim tab is in good condition. Boat is located in Lake Tahoe at aprox 6000 foot elevation. Any thoughts on what can be causing this? I'm thinking either some type of binding in PP or fuel flow regulations. ????

 

[DBreskin]

Re: Boat porpoises above 30 mph

I can't answer your question, but I wish my boat got 30 mpg. I'm lucky to get 3 mpg.

 

[NHGuy]

Re: Boat porpoises above 30 mph

Porpoise...if it's porpoising you might have it loaded wrong or water logged. Does it have ballast water bags? Are they full when they ought to be empty? Or empty when they ought to be full? Is there something overweight in the boat? Like is the bilge loaded with stuff and/or a bunch of water?
Is the trim tab stuck down? Could someone have set it wrong to bust your b___s? I have some punk friends, maybe you do too.

 

[QC]

Re: Boat porpoises above 30 mph

I fixed the typos . . .

I have NEVER heard of a tournament boat porpoising. Define what you are calling porpoise, and why would you suspect fuel? Do you mean surging? Would that be more accurate?

 

[TorchedGT]

Re: Boat porpoises above 30 mph

There are certain speeds when my friends Checkmate 230BR does this really bad, usually around 30mph or so as well. I believe by porpoising he means bow "jumping" up and down in ~2 sec oscillations. Once you give it some throttle she flattens out and really takes off, but it looks awkward while it's happening! From what I can tell, it's simply a result of a certain hull design and weight distribution.

 

[QC]

Re: Boat porpoises above 30 mph

a result of a certain hull design and weight distribution.

And typically not inboards . . .

 

[Ned L]

Re: Boat porpoises above 30 mph

Inboards certainly can, but yes, it is usually the result of hull design and weight distribution.
Check out some videos of Jersey Speed Skiffs if you want to see it on inboards.

 

[metriccrescentwrench]

Re: Boat porpoises above 30 mph

There are certain speeds when my friends Checkmate 230BR does this really bad, usually around 30mph or so as well.

Totally different hull design from TahoeBear's. While that condition can be cured on Checkmates with trim tabs (I can mostly make it stop with just engine trim) most prefer to fix it by going faster.

As for TahoeBear's issue, yes, something just doesn't seem right.

 

[sschefer]

Re: Boat porpoises above 30 mph

Throttle is the most common solution because.... What the boat is trying to do is hold the bow up. It can lift it but it can't hold it because there's not enough power applied. Add a little more power and it stays up. Getting up on plane means getting the boat up and on top of the bow wake and keeping it there. This means keeping the bow out of the water or lifted. If it the current power applied can't keep the bow out of the water, the boat slows and falls off the bow wake causing a sudden lift of the bow. The cycle continues until enough power is applied to keep the bow out of the water and the stern on top of the bow wake.

Too much forward weight can make it difficult for the boat to keep the bow lifted so if you have passengers up there you might experience this. If you have too much weight in the stern if may also have difficulty staying on top of the bow wake. There are stern lifting props that help to overcome that but you have to be very careful in your pitch selection when you go with a stern lifter like a high-five, etc.

Hydrodynamics also throws one at us in that a boat can only travel to a speed where the bow wake meets the stern. In the case of a drag boat that might be the last 1/4" of hull. After that you have to be lifted out of the water completely or the boat will fall to the water and do the infamous end over end routine. That's just an example to give you a better perception of how it works. Think of the bow wake as a sort of pedestal and the boat doing a fine balancing act almost on top of it but not so far on top of it that it slips away out the stern.

 

[rallyart]

Re: Boat porpoises above 30 mph

TahoeBears, I suspect you mean surging if you are talking about the PerfectPass. Running at Tahoe's altitude will change things but your relatively new engine should be able to compensate. I would check fuel issues, like your Mercruiser's fuel water separating filter. (looks like an oil filter in the fuel line) I haven't seen a newer Centurion porpoise, where the bow is starting to bounce, but if the wake tab is up and you have a lot of weight in the stern that might cause the problem. Just trim down or have a passenger move forward and porpoising should stop on your boat.

 

[sschefer]

Re: Boat porpoises above 30 mph

TahoeBears, I suspect you mean surging if you are talking about the PerfectPass. Running at Tahoe's altitude will change things but your relatively new engine should be able to compensate. I would check fuel issues, like your Mercruiser's fuel water separating filter. (looks like an oil filter in the fuel line) I haven't seen a newer Centurion porpoise, where the bow is starting to bounce, but if the wake tab is up and you have a lot of weight in the stern that might cause the problem. Just trim down or have a passenger move forward and porpoising should stop on your boat.

This is all true except that the fire triangle (oxygen/fuel/heat) is what it is. It doesn't make any difference how new the engine is or what type of fuel delivery system you have, you will experience a loss of power at higher altitudes. It's just physics. You do bring up a good point about the fuel filter. For a few years there were a lot of problems with the Water Separating style filter systems. The had a problem at high altitude with cavitation. They solved it with a longer threaded nipple that the filter screws on to. That gets it deeper into the filter where the cavitation is not occuring.

 

[QC]

Re: Boat porpoises above 30 mph

I don't think any of us know what he is actually reporting yet. However . . . a August 2011 post from the OP says: At approx 28 mph or above, the bow of the boat tends to continually rise and lower, even in fairly smooth water. Is there a means to stop this, possible by manually adjusting the trim tab in the back? Is this a common occurance?

This does in fact sound like porpoise, and I agree with those that mention weight balance and possible bag issues. If the bags are empty, this should be controllable with the trim tab though.

Also, I should not discount the porpoise possibility with a "tournament boat". I wasn't really considering V-drives, and of course they have more weight aft which is the typical culprit.

 

[TahoeBears]

Re: Boat porpoises above 30 mph

I have a 2006 Ski Centurion V Drive Wave Warrior, with fuel injection with Perfect Pass...above 30 mph, the boat porpoises irrespective of whether PP is on of off. There is no prop or hull damage. The Fixed trim tab is in good condition. Boat is located in Lake Tahoe at aprox 6000 foot elevation. Any thoughts on what can be causing this? I'm thinking either some type of binding in PP or fuel flow regulations. ????

Everyone...thanks for feedback...to be clear... what I meant by popusing was the bow continually rising and falling over....say...3-5 sec intervals. There is a fat sack in middle but it is empty....There are no other weight issues as all I have in back quarter lockers are life preservers, etc. I've tried to trim out by disengaging the perfect pass and manually adjusting throttle but this was not successful. I also tried to add weight to the bow....2 12 year old boys....so say 200 lbs but that did not reduce the condition. To date....per the feedback maybe it's the fuel filter which flow might be restricted at higher speeds???? Makes a little sense if only form the point having the Perfect Pass engaged or NOT would not resolve a fuel flow issue. The only action that stops the porposing is reduce speed below 29-30. If I then rise the speed slowly back up above 30.....phenomenon comes back. Any other thoughts??

 

[QC]

Re: Boat porpoises above 30 mph

Is your tachometer moving? Do you hear the engine revving up and down? If not, then I would not suspect an engine issue at all. If I did hear it "surging" then that's where I'd concentrate.

Any other thoughts??

Severely "rockered" hull.

Have you adjusted the "trim tab" down?

 

[64osby]

Re: Boat porpoises above 30 mph

I had an old OB fish n' ski that would porpoise at 28-30mph. I tried several different things to fix it. I ended up sticking 2 sand bags up under the bow, about 70 lbs. The boat didn't porpoise any more.

Maybe try some weight up front and see what happens. Yours may require more weight. My .02

 

[metriccrescentwrench]

Re: Boat porpoises above 30 mph

Maybe try some weight up front and see what happens.

I also tried to add weight to the bow....2 12 year old boys....so say 200 lbs but that did not reduce the condition.

Is this a new to you boat?

Another thought - Anyone? - This is a wakeboard boat, right? WAKEBOARD boats aren't designed to go fast, just to throw a good wake at 20 miles per hour or thereabouts. Is it possible that this phenomenon is inherent to the hull design?

 

[rallyart]

Re: Boat porpoises above 30 mph

^^Bubba has the right idea. I think there is a turnbuckle adjustment on your plate. This is not a normal condition for your hull. You might want to look closely at the back of the hull for any flaws in the shape, especially a more rounded line where the hull meets the transom. Experiment with weight to see when the bounce goes away, also. Your boat should cruise well at 30-35 without full throttle, even at your altitude.

 

[TahoeBears]

Re: Boat porpoises above 30 mph

^^Bubba has the right idea. I think there is a turnbuckle adjustment on your plate. This is not a normal condition for your hull. You might want to look closely at the back of the hull for any flaws in the shape, especially a more rounded line where the hull meets the transom. Experiment with weight to see when the bounce goes away, also. Your boat should cruise well at 30-35 without full throttle, even at your altitude.

The trim plate in the back does have turnbukles but the plate appears to be attached rigidly to the hull of the boat. I didn't test the "tightness" of the turnbukle last year. Even though the plate is relatively fixed to the hull, do you still beleive "loss turnbuckle" might allow the plate to flex sufficiently to allow the phenomenon to occur. The reaminder of the hull is in perfect condition.