Porpoising

dimitris · 05 September 2001, 07:12

Is porpoising dangerous or just annoying ?

Is it the result of weight distribution or can it be the result of
overpowering as well ?

Regards

Dimitris

Keith Hart · 05 September 2001, 07:15

Okay, just to prove that I'm always the one to ask an apparently daft question, what exactly is porpoising?

Keith Hart

dimitris · 05 September 2001, 07:23

It is a continous up and down movement of the bow even when the water is dead calm

Dimitris

Keith Hart · 05 September 2001, 07:27

Thanks, I just knew there would be a simple answer. If it happens to me now at least I'll know what to call it!

Keith Hart

Keith Hart · 05 September 2001, 07:28

Oh, sorry, I forgot to ask....what does 'dead calm' mean?

Keith Hart

Paul Glatzel · 05 September 2001, 07:52

Go to Hotribs.com and there is an article within the section this link takes you to about the subject (features section)

http://www.hotribs.com/members/default.cfm

Paul

John Kennett · 05 September 2001, 08:05

To save you arriving at HotRIBs then casting round wondering what on earth to click on next, here are some direct links:

Porpoising article
Trimming devices part 1
Trimming devices part 2

If your RIB is porpoising it generally means that it is not set up correctly, and is not running as efficiently as it could. It may simply be a matter of having the engine trimmed too far out, or it may be something more fundamental in the setup of the boat.

At lowish speeds it's not a big deal (although annoying) at high speeds it can become dangerous as the oscillations grow in size and more control is lost.

John

batfalcon · 05 September 2001, 10:38

I don't think that over power could have this result.

Michael

dimitris · 05 September 2001, 19:05

Thanks for the responses.

The links to hotrib provided me with an understanding of the phenomenon and it's posible solutions.

As of next week, I am starting the project of re-distributing weights on my boat.

All the problems started when I added a second 90 liter tank.

Regards

Dimitris

batfalcon · 06 September 2001, 11:19

Where did you installed the 90 lit. tank ?

Michael

dimitris · 07 September 2001, 07:10

I have two 90lt tanks both under the deck.

The first is in the middle of the boat.

Later I added a second 90 lt tank just after the first and towards the back of the boat. It is between my back bench and the console.

I think I already found the solution. I am planning to present later a case study of the problem, and make it an example of bad weight distribution on a small RIB.

Dimitris

batfalcon · 07 September 2001, 07:57

From the full lenght of your boat and the positions of the tanks, I assume that the total weight is far towards to the stern. I know that it's rather immpossible to relocate the tanks, so I think that you should have to live with it. The exact triming AND the correct speed is the answer.

Michael

dimitris · 07 September 2001, 08:03

Michael,

I am planning to take out the second 90lt. tank and replace it
with a new 50 lt tank positioned in front of the middle tank towrds the bow of the boat.

Dimitris

batfalcon · 07 September 2001, 08:31

That's the best thing to do. I have one 120 l installed just behind the anchors locker, 45 cm behind the very bow.

Michael

batfalcon · 10 September 2001, 06:39

Where do you launch your rib usually ?
Most of the time I sail in Saronic gulf, Gaidouronisi, Egina or Makronisos at the oposite side etc.
Michael

dimitris · 10 September 2001, 17:11

Michael,

I usually launch my boat in the south evoikos gulf, but I would not
mind trying the saronikos gulf.

If you want we can arrange going out for ribbing together through
private messaging or e-mail.

Dimitris