Positioning of helm station on RIB?

Hocus-Pocus · 28 October 2012, 04:05

I am installing a helm station on my AB 9.5AL RIB but have found no details on the correct positioning regardless of make of RIB or helm station.

The best I've come up with researching this are the general guidelines for the "Unihelm" which falls short of what I'm hoping to find. Basicaly, what they say is to position the helm forward of the transom enough to allow the engine to be fully tilted up then "field adjust" the final position for optimum trim.

I'm thinking that there must be a more scientific approach to this and am hoping to get some direction from AB in this regard, but I'm not optimistic that it will be forthcoming.

Assuming that I can't get any help from AB, my logic is that the helm should be positioned so that the centre of gravity of the boat will be maintained for optimum planing speed with the boat at it's expected average load. This would include engine, fuel, operator and passengers and freight. I would expect that this C of G would be at a position some distance forward of the transom.

Can anyone provide me with any guidance on this?

Screaming04 · 28 October 2012, 04:16

"Field adjust" here is key. Ideally you need to run the boat before you install the helm station. Anything else would just be a guess.

Locozodiac · 29 October 2012, 22:23

Was wondering same, assume middle deck will be a starting point if boating solo or with a mate sitting up front to ballance boat correctly. If opting for perfect field tuning will need lots of remote and steering cables sizes to test best console position and drive engine untill the sweet spot is found on deck.

Out of this world possibility. Let's hope some efficient ribber will chime along to share proper rib rigging information...

Happy Boating

Hocus-Pocus · 30 October 2012, 01:14

I still haven't got any reply from AB on this, which is a bit disappointing. They do make RIBS with fixed consoles so I would assume that they have engineering data as to where the optimum balance point would be and how much "wiggle room " you are likely to have on either side of this point. Certainly the best position can be determined by trial and error but I was hoping to get some reasonably close guide lines as a starting point.

While searching this I did come across one interesting short article in which Dave Gerr, a well respected marine architect suggests that for all planing boats, the Centre of Gravity as well as the Centre of Buoyancy should be located at a point of between 60% and 65% of the length of the boat measured from the bow. I'm not sure if RIBs deviate from this general guideline or not. I suppose that this might be a starting point but still subject to "field revision".

On a relatively small boat like mine, I suspect that about 200 mm either side of a starting point would make a big difference.

Locozodiac · 30 October 2012, 13:16

I think that 60% would be a good starting point, to achieve correct rib/engine ballance, assume that will depend entirely on the type of console you plan to install. What type of console is it : a jockey seat, central standing console, console and seat ?

Happy Boating

Hocus-Pocus · 30 October 2012, 15:18

I will be installing a "Eurohelm" by St Croix Marine. Here's a link to their web site:
St. Croix Davit Euro Helm Seating

The other contender for the job was the "Unihelm" The Unihelm is the all-in-one helm and seating system for your rigid hull inflatable boats.
The Unihelm is quite a bit lighter than the Eurohelm, which is good, but the helm is fixed in position and does not swing down for storage. This presents a problem for the davits I'll be using.