Go Back  Offshoreonly.com > Owners Forum > Formula
Porpoising - 311 >

Porpoising - 311

Notices
Formula

Porpoising - 311

Old 06-12-2017, 03:31 PM
  #21  
Registered
 
Join Date: Oct 2015
Location: Lake George, NY
Posts: 1,244
Received 3 Likes on 3 Posts
Default

Use the Tabs, Thats the reason they go down that far!
class6 is offline  
Old 06-12-2017, 04:06 PM
  #22  
Registered
 
Join Date: May 2012
Posts: 1,465
Received 8 Likes on 6 Posts
Default

Originally Posted by TomZ
FYI... Going to cross-post this in the prop forum. I'll keep both threads updated.
your original question asked if it was normal to run with negative trim and i answered yes, up to a certain rpm. You can over trim it till it porpoises then bury the tabs to tame it but it will scrub speed. Basically below 3k trim is slighty negative then goes positive more and more with rpm and speed. Not sure what other answer you are looking for?
Mr Maine is offline  
Old 06-12-2017, 04:34 PM
  #23  
Platinum Member
Platinum Member
Thread Starter
iTrader: (2)
 
TomZ's Avatar
 
Join Date: Feb 2001
Location: Virginia Beach, VA
Posts: 3,975
Received 1,224 Likes on 682 Posts
Default

Originally Posted by Mr Maine
Basically below 3k trim is slighty negative then goes positive more and more with rpm and speed.
At 3k RPM, the trim is negative. At 4k rpm the trim is still negative. If I try to move toward less negative, she starts to bounce.

At first, I thought this was normal because I was out in the 'Bay in some good rollers, porpoising, but still running 50-53-55 MPH at 35-3800. The porpoise seemed to fit the conditions, and I guess I just didn't know any better. Going on a run with some buddies onboard, their thoughts were she shouldn't be running like this for the conditions, and to back the trim off, which I did and she settled. Later, we measured everything because we wanted to figure the limits, and we were surprised that we were not able to gain anything close to positive trim at the RPM we were running.

So... running her back to the marina Sunday, I tried playing with the trim, and got a lot of porpoise in relatively smooth water. The drives were a tick and half off of fully tucked in... anything more than that, and I could just about get the whole boat out of the water due to the porpoise. During the run where Josh shot the video from the Chesapeake Bay Friends and Family event (included earlier), they could see my props coming out of the water... we weren't going that fast, and the water wasn't that rough. That was with the trim set at about neutral. I don't think that's normal, and I'd like to figure out why.
TomZ is offline  
Old 06-12-2017, 04:42 PM
  #24  
Registered
iTrader: (1)
 
Join Date: Apr 2014
Location: North Florida
Posts: 649
Received 121 Likes on 58 Posts
Default

It couldn't hurt to bum your buddies 26 bravos for an hour. Might help eliminate the uncertainty about what may have been done to your mirages. Beyond that, trim up until you stop gaining rpm. If the porpoise starts tab down until it stops. From here bump the tabs back up until you gain the rpms back but not more. More videos please!
ph1971 is offline  
Old 06-12-2017, 06:13 PM
  #25  
Registered
 
Join Date: May 2012
Posts: 1,465
Received 8 Likes on 6 Posts
Default

It seems weird that your neutral trim is around 6. Everyone i have seen is neutral around 3. Your speeds seem good, you spinning props out or in?
Mr Maine is offline  
Old 06-12-2017, 06:22 PM
  #26  
Registered
 
Join Date: May 2012
Posts: 1,465
Received 8 Likes on 6 Posts
Default

This video is right at 70gps, trimmed to about 7.5

this is in glassy water, probably around 2,
Mr Maine is offline  
Old 06-12-2017, 07:48 PM
  #27  
Registered
iTrader: (1)
 
Join Date: Aug 2007
Location: St.Louis MO
Posts: 1,038
Likes: 0
Received 0 Likes on 0 Posts
Default

Maybe ya need to try some 4 blades..I have a set of 24 pitch hydromotive I ran on my 330hp 311. I'm trying to trade them for a set of 24 bravos, but with your bigger motors they might work great on your boat. I can only spin them too 4000 rpm.
stlliberator is offline  
Old 06-12-2017, 09:24 PM
  #28  
Platinum Member
Platinum Member
 
mcollinstn's Avatar
 
Join Date: Sep 2001
Location: tn
Posts: 5,752
Received 133 Likes on 82 Posts
Default

My 311 with 502 Mags and Bravos with Mirages.
I always kept the nose light. Anything heavy was stored as far aft as possible.
Anything less than 40 mph, Drives "just up from full down" (like 1). Tabs at 4/5.

Glass water, 50+mph cruise, Drives 4, Tabs 4
Rough Chop 2'+, your choices are below 30mph or above 50mph. Above 50, use more tabs to keep boat level peak to peak, run drives close to neutral.
WOT - keep drives around 4, raise tabs as speed increases, when tabs are fully up, start bringing the drives up. Mirages will keep a good bite to around 7 on the drives, above that will lose a bit of speed and add rooster tail.
4900 rpm, 23 Mirages, 1.36 drives. 72 mph with <40 gallons of fuel and 2 or 3 people. Anytime it had over 75 gallons of fuel, in smooth water, it couldn't break suction on the outside hull chines and it hurt it a couple mph.

But once you START porpoising, you have to pull the drives in, or add tabs to kill it, then you can bump them back up some. You can be porpoise-free, and then 2 or 3 swells timed just right will START the porpoising.

If you put kids in the front bed, and tell them to brace their feet against the "ceiling", you can INTENTIONALLY porpoise for them. They love it. If the water wasn't rough, they would do it with no bracing, and float in the air as the nose comes down. You can exaggerate this a bit with the throttles... Wives don't care so much for that.
mcollinstn is offline  
Old 06-13-2017, 05:09 AM
  #29  
Charter Member #232
Charter Member
 
Audiofn's Avatar
 
Join Date: Oct 2000
Location: Carlisle, MA USA
Posts: 18,422
Received 6 Likes on 4 Posts
Default

I will try and get to this later but there is no way you should be having this issue. I had the same exact set up and it was rock solid. My guess is you have a prop issue but I will read this more later. For now i have to get to work.
__________________
Put your best foot forward!
Audiofn is offline  
Old 06-13-2017, 10:02 AM
  #30  
Registered
 
Join Date: Aug 2001
Location: Indy, St. Louis, LOTO
Posts: 1,333
Likes: 0
Received 1 Like on 1 Post
Default

Run a late generation 302, which I understand to be quite similar to the 311 that came the next year. While I didn't have the extent of the porpoising problem you have, things got all kinds of better when switching to Bravo 4 blade props. Nose came down, sub WOT speeds increased, and over all just a better SOTP feel. Did lose a bit at WOT, but that was still a good trade for me. Run TRS like yours, so have to be careful of not overloading the props on hole shots, but shouldn't do that anyway; it ain't a ski boat.
Chart is offline  

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.