Porpoising - 311
 

Morning folks!

Another great weekend in the books! We went to Harborfest, and enjoyed friends, food, and boats; fireworks for the finale! Yesterday was set up for cleanup and rest. Surprisingly, the boat stayed pretty clean despite three young kids with food and drink, as well as guests coming onboard while we were anchored for the show... we had a full boat!

So yesterday I had the boat to myself (we overnighted the boat local to Harborfest), and got to play around some without having to worry about the kids getting banged up. Overall I had fun, but man does she porpoise! Trying to get her trimmed out is where I'm running into problems.

I have marked my indicators so that know where neutral is with regard to trim and tab position. Neutral trim is at 5/6 mark, and tabs are on 3. These indicate a position that is on the same plane as the hull bottom.

Typically, I'll leave the drives tucked in and tabs set at 3 unless I need to get on plane quickly (I'll drop them to 9 and bring them back to 3 once going). Generally. she gets on plane without much trouble (though dropping the tabs. Keeps the bow low so I can see). Once on plane, I'll bring the trim to 2/3 and leave there because she'll start to bounce as you go up in trim. The porpoise gets so bad that the boat will leave the water (see pic below).

Is it normal to run the 311 with negative trim most of the time? I would think she'd want a little positive trim to run best. Negative trim puts the bow in the water leading to bow steering (a very unsettling feeling).

502 MPIs with CMIs, 300 hours, TRS drives with nose cones, 27P Mirages. RPM at WOT is 4700-4800 depending on load.

Should I add some weight up in the bow?

At what speeds are you talking about when porpoising?

Cruise... 3K to 4K. I've been running on the ICW here lately so running WOT hasn't been an option because of traffic.

TomZ,

These are the same props from the CBFF run, correct?

My 292 (Modified 454 Mags w/ Bravo's and 26P B1 Props) loves to porpoise and will do so if not constantly adjusting trim/throttle during operation. I have been able to find the "sweet spots" and the corrections needed to quickly calm her down. Although your 311 is obviously longer and heavier, both boats have a lot of weight towards the rear. The following is my typical "settings"

Tabs - Never used them, ever. So i can't give any input here.

Planing - Drives tucked in, on plane around 2600 RPM in very short time.

Cruising with some chop - Drives at 2, engines at 3000 RPM

Cruising (95% of the time) - Drives at 3.5, engines at 3600 @ 50 MPH

WOT - Drives trimmed out a hair off the indicator and one blip back In on the switch, engine at 4900 @ 70 MPH (Fully loaded yesterday, 135 Gallons, Coolers, 7 people)


I will use 3600 RPM as my example because I am typically at that RPM..

My porpoising occurs if I trim up too fast without clicking up the throttles a bit (up to around 3600). I alternate a burst on the trim switch, with a click on the sticks until I reached my desired trim and RPM. If I trim from full tucked to 3 or 4 without moving the sticks, she starts jumping pretty good. If I start to feel the porpoise while I am cruising, I will raise the RPMs by a couple hundred and bring it back to 3600 or trim it IN briefly then back OUT.

Porpoise Mode is activated more easily if I trim anywhere past 5 below 4000 RPM. If i am above 4000 RPM and I trim out from 3.5, the boat really opens up around 5/6 on the indicators and pulls hard to WOT.

Apologies for all that information, but that has been my experience so far. My 292 takes some driving to keep the ride smooth but I enjoy making adjustments while cruising. I have put ~30 Hours on my boat so far this season so I have had a lot of seat time to get everything figured out with my setup. Coming from the 223 to the 292, there was a little bit of a learning curve but I am sure others will post their experience with these old birds.

At WOT in chop I can trim her out and run hard for the most part, but even just under WOT the porpoise is there. Video link below is running about 43-4400, trim about 5/6 if I remember correctly.


https://m.youtube.com/watch?v=UBOqoD...ature=youtu.be

If all the way down is zero neutral shouldnt be at 6, its about 3.5 on mine, same with tabs.

anyway, for me 3k i run about 1.5-2 on drives, no tab. From there its more trim with more rpms up to about 7 or 8 wide open still no tab.
if im running through heavy chop and rough water i put the tabs at 3 or so maybe more if real rough, also may use one tab in strong crosswinds.
no porpoise issues.

Josh, your experience is similar to mine. And yes, same props as the run. Stacy and I got 69.8 out of the GPS speedo and Navionics spinning to 4800 so I'm pretty happy with them (though they do need a little cleanup).

My thing is that once the porpoising starts it's hard to get her to stop without tucking the drives back in a good bit. Perhaps more seat time will help.

My understanding is that the 311 has rocker built into the hull. Maybe that's contributing to the negative trim needed for cruise. I'll need to read up on that aspect.

We used a straight edge to gauge neutral trim angle... the cavitation plates were in plane with the hull's running surface at 5/6.

Maybe I'm wrong with what's considered neutral?

Interesting question...

Is drive trim angle set by the hull's running surface, or by its waterline? And how does the 311's rocker play into this? I'm guessing the porpoising has a bit to do with it.

The 311 doesnt have rocker, its a straight bottom hull. The 272, 242, 206 have it.
Do your indicators read zero when the drives are tucked in? Both my 272 and 311 all were neutral at about 3-3.5 both tabs and drives.
I do think you are over trimmed thats why you are porpoising, with a gps nudge them up till you stop gaining speed you should be good to go. Some water in the bow tank can help the ride.