air flow hulls

[Nick_H]

Some smaller boats use this hull design technology (Beneteau is one), whereby air is injected through the hull just behind the planing waterline. The air mixes with the water to reduce friction on the hull, and probably helps prop efficiency as well. The performance benefits claimed are quite significant, particularly at high speed.

To date though i've not heard of any bigger boats using it, and its not immediately obvious why. It should be fairly easy and cheap to incorporate into a new hull, air is plentiful and, for the moment at least, its free (but don't tell Gordon)

IMO the motorboat industry will have to start showing its green credentials at some stage, to avoid being a convenient target for various pressure groups, and the options seem to be limited to drivetrain efficiency, hull design or usage restrictions. Best we focus on the first two before someone else starts down the route of the third.

 

[Wiggo]

MTB's during the war had underwater exhausts that dumped exhaust gas ahead of the props which had the same effect as stepped hulls, I understand.

 

[ajt]

But are you saying stepped hulls or forced air through a pump?

 

[Deleted User YDKXO]

Agree with you, houghn. Planing hull design has been stuck in a rut for more than 20 years with the last major innovation being the variable deadrise medium/deep V hull adopted by most major builders in the mid 1980's. If you looked at the hull of a 1985 Princess 45, it would'nt look much different in form to a 2006 Princess 45 and certainly would'nt be much different in terms of propulsive efficiency. I think the diesel engine manufacturers have done their bit with more economical cleaner engines and IPS is certainly, in principle, a major step forward.
I do think that there is scope for weight reduction in hulls maybe through newer lighter materials (kevlar?) but there is a limit as to how far this can go because, to an extent, seaworthiness is dependent on weight
I think eventually market pressure as a result of increasing fuel prices will force builders into designing better hulls but you always have to bear in mind that boat builders, even the largest ones, are relatively small companies with limited R&D budgets
I guess this is time to cue victoraspey to waffle on as to how cats are going to save the world

 

[Wiggo]

The MTB's were the equivalent of air injection, although stepped hulls do the same thing, drawing air in at the outside edges of the steps. Well, sort of.

 

[DAKA]

The last 20 years has seen tunnels evolve.

Stepped hulls wouldn't work on larger boats IMHO due to problems over antifoul, it is difficult getting it to stay on above 25 knts but to add hammer effect from bubbles will just about finish it off.

The smaller hulls that use it usually spend less time in the water and travel less so fouling and antifoul wear is not as much of a concern.

I thought I had seen a design recently of a larger craft with stepped ,which is what made me think of the above a couple of weeks ago.

 

[Whitelighter]

How about this:

That is a Fountian 48 BTW, 50' in length

 

[D3B]

Didnt Sealine try to address this with the fancy stepped hull on the S29. Designed by Ocke Mannerfelt. and the same on the T50???Allegedley causes a vacuum under the hull.
i can certainly stay on the plane in calm seas at 17/18 knots.

Doug

 

[Deleted User YDKXO]

Thats true but the efficiency gains are relatively small. Many builders have not adopted tunnels and those that did, have reduced their radius

 

[powerskipper]

I saw her the other day, but can't remember where.


The blade runner, tri hull uses air though the hull to create lift and therefore less drag, this helps her achieve the speeds she does.

edited when point out wrong. /forums/images/graemlins/blush.gif

 

[Whitelighter]

Web site for Fountain Powerboats

The boat above manages 40gph with triple Yanmar 440hp at 50mph - not bad, that over 1 mpg!

 

[ported0]

[ QUOTE ]
The blade runner, tri hull uses air though the hull to create life and therefore less drag, this helps her achieve the speeds she does.

[/ QUOTE ]

Good grief, what kind of life? aquatic /forums/images/graemlins/smile.gif

 

[Deleted User YDKXO]

V impressive figures for a 48 footer but even more impressive is the range 530miles @ 50mph and the boat just set some kind of record at 400 miles in 8 hrs. Dont know whether these are nautical or statute miles but pretty good all the same. Any idea what she costs? Looks ideal for GC1's next boat

 

[Whitelighter]

The one up on the hard at Cobbs Quay was a 2006 on with Ancasta for £650,000.

 

[Deleted User YDKXO]

Well I guess it's still there at that price!

 

[duncan]

yep - looked flash in Dolphin Haven earlier in the year but very very white everywhere!

it still had some plastic on it so it had only recently been shipped from somewhere - a lot of money though as already highlighted

 

[Nickb]

Biggest drawback of stepped hulls is efficiency itself!

As far as I understand they are great at high speed, in excess of 35knots? but until the steps are working all they do is create massive amounts of increased drag, think very big trim tabs!! and therefore more fuel!

If you fancy attempting to travel in solent and channel waters at 40 knots in UK weathers you are much more resiliant than I am!!

 

[duncan]

I can only do 35 knots - but do have a hard top!

Agree the wind in your hair bit associated with such speeds is best served in small doses!

 

[scej]

I think you will find that a lot of big boats have their exhausts out through the bottom on th ehull these days. the Maiora i am on certainly does. this also helps for noise reduction as well

 

[penfold]

The MTBs used the exhaust ejected forward of the props as a form of drag reduction, effectively an early manifestation of surface drive/ventilated prop technology. Hubert Scott Payne was a v. smart chap.

Perhaps some BigBoat Inc. could experiment with air injection using an engine driven compressor? Been tried before tho', and found to be more trouble than its worth.

cheers,
David