'Unusual' Brand New Shannon Class lifeboat design. .

Hi All,

In the Uk the RNLI have just launched the latest jet drive 44' lifeboat with a very interesting hull form designed to operate in extreme weather conditions.

Displacement: 17 long tons (17 t)
Length: 13.6 m (44 ft 7 in)
Beam: 4.54 m (14 ft 11 in)
Draught: 0.75 m (2 ft 6 in)
Propulsion: 2 × Scania DI13M, 650 hp (485 kW)
2 × Hamilton HJ 364 Waterjets
Speed: 27 knots (31 mph; 50 km/h)
Range: 250 nmi (460 km)
Complement: 5

Draught only 2'6"..................:eek :


When the RNLI were designing their new Shannon class lifeboat, they tried out the Safehaven design and rejected it as being too hard a ride for safe use in rough seas, and they had to totally adapt the hull shape to make a softer riding hull.

Here's the Irish Seahaven patrol boat that was rejected:

And the new Shannon class: : http://www.rnlivideolibrary.org.uk/getvideo.aspx?vid=WteGPo7M

Some design drawings:http://rnli.org/newlifeboatappeal/design/PublishingImages/cad300.jpg
the designer:https://www.youtube.com/watch?v=2wvMv4nKV7U

RNLI site:http://rnli.org/lifeboat-building/the-shannon/Pages/the-shannon.aspx#.Uzs-I_QW01I

It's hard to believe, but this appears to be a planing hull design!!!!!
Photo of hull:
https://www.google.co.uk/search?q=s...rst_superlifeboat_jets_in_for_duty%2F;480;360

 

...and here's the totally crazy launch system:https://www.youtube.com/watch?v=cmBU6n5gy7M

 

Nothing in this is too crazy at all, the launch systems are obviously dictated by the given conditions in the location of deployment. The German DGzRS has utilized Unimog trucks to deploy its smaller mobile units for quite some time now. But the conditions on beaches are no-where comparable with the ones in the UK, and the units are way smaller.

I can easily see why the Safehaven design (as awesome as its capability of taking on big seas is) would be deemed too hard in slamming.

Regarding the planing hull: In the video you linked Mr Eyre explains that, obviously, this is a requirement for the boat maintaining its 25kn speed, adds a huge amount of stability and makes it easier to control in adverse wave conditions, or through rapid turns.

And yes, those boats are made for shallow coastal areas, operation near beaches and in river mouths, and is even made to withstand beachings at high speeds, so limited draft is obviously always at a premium.

But really, holds up well in tests, no? https://www.youtube.com/watch?v=5BID7406gEs

 

As you say the design seems to fulfill it's role perfectly, but if I told you a few years ago that I was going to design an offshore life boat with a draught of 2'6" , waterjets and wide flat aft section, you would have asked if it was a catamaran?

Which makes me think that this is a real milestone in boat design, a shallow draft boat that is seaworthy. All previous lifeboats that I can think of are semi/displ. designs with big keels and skegs for stability and massive 4' or more draught.

So this boat will go up shallow canals and rivers, and offshore across rough sea's in gale force winds...........

 

Here's a better view of the hull form in the roll over test:https://www.youtube.com/watch?v=4WxLTKk3Deg&list=PL3D9E8F471CCF8034#t=49

 

I wonder at what stage those big twin keels were added. Looks like it would be broaching without them.

 

Looks like a classic 'botch job'.

Am I correct in saying it looks like a classic fine entry bow section a la semi~displ. hull [compound curved section], a standard planing hull section all the way back to a low deadrise vee section....

And as you say two bilge keels bolted on to cure the 'squilly' side to side motion
surfing down the back of waves.

......I'm amazed!!!!!

 

I don't know if they were an afterthought, or factored in as an integral part of the package. It's a very deep footed boat, sometimes they don't broach too bad in fast boats if the higher part of the bow isn't very heavily flared, the "bog" factor when they ram into the back of waves is less, and that means they have speared through the wave before a broaching action can happen. Judging by the copious amounts of water coming over the front, there is not much flare.

 

As you say, there appears to be very little buoyancy in the bow section.
I know from commercial catamarans that service offshore windfarms that the skippers complain that the they get severe 'bow steer' in a following sea, a classic problem with very fine bow entry, esp. on cats.

...I can't quite understand how bilge keels on the aft section would solve that problem?

 

They offer a fair bit of surface area to resist sideways movement, and in a boat barrelling along like one of these things, would be effective in keeping it on track, like flights on an arrow.

 

That makes perfect sense.

I'm interested in the concept from a home building aspect, and was wondering if this hull form could be adapted to steel.
A 45' boat at 17 tons is in the right ballpark for steel, and a single engine would save nearly another ton...

..the bow section would be the only tricky bit, maybe a straight vee section without the compound flare would perform as well?

 

Home build ? Seems very ambitious ! Perhaps a little downsizing to meet your finances ? I would imagine the fuel bill is daunting, the boat is likely built like a brick outhouse, and with jets probably not the most economical alternative. I think the people inside are supposed to break before the boat does.

 

I've already built a 60' steel boat so have a bit or experience, so much so that I would never do it again! You can get a steel hull fabricated for about £1000/foot which makes much better sense.

I was looking for the ultimate hull for my next project, the proof is in the successful application of a design concept, and I think this hull took 7 years to develop by an institution of the very highest integrity.

My criteria are very different to the RNLI:
Displ. 8kts cruise for normal use for good mpg.[2 mpg?]
Fast cruise option to run from bad weather.[17kts force 7: RNLI]
Shallow draft of 2'6" for river use.
Less than 15mtrs for cheap mooring fees.
Off shore capability.
500 gals fuel.


Twin 600hp gives 30kts, so I was thinking a single cummins 410hp would give a 15 to 17kts fast cruise?

 

How are you going to keep it down to 2'6 draft ?

 

Other recent RNLI boats have them including the Mersey class which the Shannon class will replace. Photo of Mersey class stern

My guess is the bilge keels serve several purposes including directional stability but the primary function is support so the boat stays upright when it is grounded or on a slipway. The Shannon class was designed for beach launching and recovery (return) which can include running the boat onto the beach.