Go Back   TeamTalk > General MasterCraft Topics > General Discussion

Reply
 
Thread Tools Display Modes
  #1  
Old 07-24-2012, 02:32 PM
Theomedic Theomedic is offline
TT Enthusiast
 
Join Date: Jul 2012
Boat: 2005 ProStar 209
Location: Irish Hills, MI
Posts: 450
Exclamation 1978 with a serious Porpoising problem

I just bought a 1978 Stars and Stripes that has a serious porpoising problem. It even does it with 3 adults int the forward seats and no one in the back. Any suggestions on how to get rid of this problem? It does it at speeds over 28mph and you can't go over 35mph because it feels like it will flip over backwards its so bad. I heard trim tabs may help? If so anyone know what ones would work. Please help. Thanks!
Reply With Quote
  #2  
Old 07-24-2012, 02:39 PM
old blue old blue is offline
TT Regular
 
Join Date: May 2011
Boat: 83 Stars and Stripes
Location: Northwes
Posts: 39
Stock prop size? RPM close to MPH 30mph@3000rpm?
Motor mounts solid?. Stringers solid?
Stock Velvet Drive Transmission.

Love the 78's. My first was a 79. Pictures help.
Reply With Quote
  #3  
Old 07-24-2012, 02:42 PM
Theomedic Theomedic is offline
TT Enthusiast
 
Join Date: Jul 2012
Boat: 2005 ProStar 209
Location: Irish Hills, MI
Posts: 450
I'll check those items. I know he said the trans was replaced. 3 years ago and it has a new prop, not sure on size or pitch, I'll check the rpm at 30.
Reply With Quote
  #4  
Old 07-24-2012, 02:55 PM
old blue old blue is offline
TT Regular
 
Join Date: May 2011
Boat: 83 Stars and Stripes
Location: Northwes
Posts: 39
Prop should be 13X13 LH I believe. 78 boat should have a 1:1 velvet drive tranny. Take a picture of the motor and Tranny and people here will ID it for you. Prop should be labeled on the end.

good luck
kent
Reply With Quote
  #5  
Old 07-24-2012, 03:15 PM
MIskier's Avatar
MIskier MIskier is offline
MC Fanatic
 
Join Date: Jan 2011
Boat: 2006 PS 190 w/ mini tower
Location: S.W Floarida
Posts: 603
While it is unlikely that the prop or tranny is the issue, if the engine was switched to opposite rotation at some point that may be a factor. What is the condition of the hull bottom and stringers like? If you have structual defects causing the hull to distort it can be a cause of porposing. Another possible culperate is forward loading causing the center of gravity to be shifted proportionaly farther forward than normal, while this seems counter intuitive, it is the most common cause of porpoising in boat designs. If it is just 3 guys than that should not be an issue, but if it is 3 guys, coolers, tower, speakers, empty fuel tank, etc. that may be enough of a forward shift to cause the instablity.
Reply With Quote
  #6  
Old 07-24-2012, 03:31 PM
old blue old blue is offline
TT Regular
 
Join Date: May 2011
Boat: 83 Stars and Stripes
Location: Northwes
Posts: 39
A lot of 78's have stringer issues that's for sure. I would want to eliminate that possibility first.
I have no idea about engine rotation. Your probably right about the prop, even if it provided too much lift, that's a lot of boat to lift.

Sounds like hull distortion...ouch!
Reply With Quote
  #7  
Old 07-24-2012, 04:30 PM
Theomedic Theomedic is offline
TT Enthusiast
 
Join Date: Jul 2012
Boat: 2005 ProStar 209
Location: Irish Hills, MI
Posts: 450
Prop is 13x13.

Prop is 13x13. Tranny is velvet drive 1:1. I can't upload pics today as I only have an iPhone. Our of isnt hooked up & I can't load pics from the phone. I noticed the motor mounts on the back only have bolts in the top & none on the sides.
Reply With Quote
  #8  
Old 07-24-2012, 07:30 PM
waterlogged882 waterlogged882 is offline
MC Master Poster
 
Join Date: Dec 2004
Boat: wooden, boat, 1908, putt
Location: lake
Posts: 10,930
..........
__________________
Barack Hussein Obama
Worst President Ever.
Elected by White Guilt.
66 Million Suckers.

Last edited by waterlogged882; 09-19-2015 at 04:21 PM.
Reply With Quote
  #9  
Old 07-24-2012, 07:35 PM
ctjahn ctjahn is offline
MC Fanatic
 
Join Date: Jul 2010
Boat: Own a 78 MC S&S
Location: Midwest
Posts: 626
?

I have a 78 and dont have that issue.... 351, 1:1, 13x14 prop.... (2 -3 -4 people in the boat)

but...

I do recall someone talking about adding a lip to the tail (and I have that).

cj
Reply With Quote
  #10  
Old 07-24-2012, 07:45 PM
thatsmrmastercraft's Avatar
thatsmrmastercraft thatsmrmastercraft is offline
MC Master Poster
 
Join Date: Sep 2008
Boat: 1977 Stars & Stripes
Location: St. Paul, MN
Posts: 17,867
Quote:
Originally Posted by ctjahn View Post
I have a 78 and dont have that issue.... 351, 1:1, 13x14 prop.... (2 -3 -4 people in the boat)

but...

I do recall someone talking about adding a lip to the tail (and I have that).

cj
Would like to see that. My '77 will porpoise a little when not loaded enough. Never an issue with a slalom skier or a footer behind the boat.
__________________
CUSTOM WHEEL & TIRE PACKAGES

$99 LED LIGHT PACKAGE - FREE SHIPPING
REBUILDING HOLLEY MARINE CARBURETORS - $249 DELIVERED
Email - tiresplease@gmail.com
Reply With Quote
Reply

Tags
1978, bouncing, porpoising, trim tabs

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


All times are GMT -4. The time now is 01:28 AM.