Glen-L.com

A few years back my Dad completed his barrelback 20. It took him four years to build and the boat turned out beatiful, with one exception, it tends to porpoise at just over 30 mph. He made no modifications to the design, other than going with the 20' option, and the v8 he put it in wieghs ~100 lbs more than the v6 that was specd with the 19' option. Since I'm not the builder I have limited knowledge of the details, but am working with my Dad (who is computer challenged) to try and figure out a fix. Any help or ideas would be most appreciated.

Darin

Welcome Darin

You might want to read through and follow this thread...Bruce is working on the same thing and will post his results

viewtopic.php?f=2&t=10325&start=0

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Yes, that thread is exactly to point.

And my first suggestion would be to install trim-tabs.

They are the best way (after the fact) to correct a slight imbalance in the hull, plus they improve the handling of the rig under numerous conditions which can not be factored into the design (like 300 pound "uncle Bob" sitting in the passenger seat).

Ok, I rig powerboats so I have some of my own interest at heart, but it's been my experience that just about every boat over 16' or so, running more than 90 horses can benefit from trim tabs...

_________________
Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

Yes, we've discussed trim tabs, but are considering other options such as the "stern elevators" dicussed in other threads. Since trim tabs will distract from the look of the boat (my opinion) we'd like some feedback on other approaches before committing. Thanks

Darin

Interestingly, I get a little porpoising over 50MPH when I have no riders in the rear seat. When I have weight from one person in the back, the ride flattens out with no porposing. So I am eager to see the discussion going on here.

_________________
Dave

My Riviera build - the Midnight Cry Project

Video of Midnight in Action
Blog

Few things in the world measure up to the thrill and satisfaction of boating in a boat that you built.

Actually one of the worse things that you can do is to shove the nose down when going at speeds that exceeds the hull speed too, Bow steering can and will take place depending on the loading which is not really that safe either. Find the sweet spot after you have run the boats a bit even if you do need to tweak the boats with some wedges or tabs,[ugly and not becoming to these boats IMO] and enjoy them. I iwll add a few more comments on tweaking with some photos following up on another thread of what may also work for you. Of course you are on your own since all these modifications are a crap shoot without viewing and riding any hull.

The problem with a permanent, non-adjustable trim solution on an inboard installation is you can only correct to a very narrow window of operating conditions.

With an outboard or sterndrive you can alter or wedge the angle of the lower unit/outdrive, to give you extra "trim in", but you still have the control of the power trim to give you a range for different circumstances (running bow heavy sometimes etc).

So as "ugly" as they are, power trim tab units are one of the very few ways to give you variable control on an inboard unit so that you can adapt to changing conditions - and really, the only time you see the tabs is when the boat is sitting on the trailer - so park it "bow out"

_________________
Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it