Pipe from deck to hull

[gotchiguy]

I remember reading in RIB international a couple of years ago about a janneau or beneteau merry Fisher style thing which had a pipe running from the deck down to the hull with the purpose of introducing air to the wetted surface and therefore reducing friction. Was just wondering if anyone had seen this done elsewhere or if crudely copying it on a rib would give any advantages in your opinions?

Merry Christmas etc...

[jyasaki]

The initial question would be more along the lines of "did it work"?

I know some of the US Navy ships have a system that bleeds small air bubbles around the hull and into the propellers, but those are designed to reduce sonar detection rather than to improve performance.

jky

[biffer]

Yep have seen this on race boats, had one in the yard a few weeks ago, the vents were behind the steps, they don't work how you would think they should, air is force out of them, have also dabbled with tubing around the prop area and this one does work by introducing air, unless you're trying to get an extra knot or two out of the boat it's not worth the trouble, race boats yes, pleasure ribs no


Sent from my iPad using RIB Net

[HughN]

One of James Dyson's first inventions was the Rotork Sea Truck that rides on a layer of bubbles to reduce friction.

Now, if you wanted to cover your hull in 'shark-skin' riblets* you might be onto something...

*No, not something you can eat!

[The Gurnard]

Do you mean a air stepped hull design ? its all explained in this video

https://www.youtube.com/watch?v=p6zFW9GNnbU

[C-NUMB]

As far as i understand, the general idea of the vents is to reduce unwanted vacuum possible developing behind the steps. On some racing boats the inlet is not even on deck.

Have the impression that the general idea with air vents and steps is not that much about reducing friction by adding bubbles to running surface, its more complicated than that.

Its not totally new idea adding steps in leisure boats, Flipper boats used steps on thousands of boats manufactured from 70's to roundabout 2005. The design was like a "stern" step.

The Beneteau design looks very complex and different from traditional steps otherwise, but the cut out close to transom is defo not a new thing, often just called a notch.

[The Gurnard]

Im certainly no expert on hull design.. but I know the traditional step hull has been around for years. The seaplane is a good example of the step hull as it made good use of the principle so it could break free from the water surface tension for quicker take off.

https://www.youtube.com/watch?v=Di-tShoowGo

I can only imagine the idea was then developed further to have intakes produce an airflow under the step on the hull similar to the Beneteau. One or two RIBs seem to use the same idea ? Like this Zodiac MACH 11. (MACH Military Air Chanel Hull)

http://www.powerboatandrib.com/boattests/683-zodiac-mach-ii

[Zippy]

Forced air step hulls have been around for ages with varying degrees of success. As biff said, mostly on race boats.

Beneteau used it with success on their Monte Carlo boats. (think the first was the 37 and then later the 32).

Of course the idea behind the step is to create disturbance in the water creating bubbles for the hull to ride on reducing friction and allowing same speed from less horses of more speed from same horses..

We have had a few stepped hull boats (both ribs and hard boats) and i didnt really like it. the stepped hull cruiser was a pig going backwards and the stepped hull rib was not for the inexperienced driver as it could easily catch you out.

i know Adam younger has developed his stepped hull designs quite a lot but for us, we will stick with non stepped going forward!

[C-NUMB]

This company: KND - Naval Design

have written a pretty understandable paper about stepped hull, interesting reading:

http://www.navaldesign.co.za/article...s-%20Feb07.pdf

Shape and number of vetted surface seams to be the dominating factor for improving speed and economy regarding stepped hulls.