'Unusual' Brand New Shannon Class lifeboat design. .

My guess is the windfarm service boats stay in port on some days when the RNLI would respond to a distress call.

 

My son has got an adventure Motorbike, the BMW 650gs single, and it's a bit like a boat in that it has some major compromises. It's got a pedigree like the RNLI boats, and it won the Dakar rally several times.
It's a single for lightness, but isn't very light at 180kg.
Because it's a single it has to be long stroke to get the torque.
Because the stroke is so long the cylinder head sticks up into the petrol tank area.
..So they have moved the tank underneath the seat, and put a dummy tank in it's place with the airfilter, battery, electric gubbins etc..

So what's the point?
They have gone to the ends of the earth to produce the ultimate bike!!!

The Shannon design has used similar criteria, it could be adapted into the ultimate 'Adventure' boat for exploring the world, capable of 'looking after itself in all conditions' as the designer stated.

My ideas to make this concept affordable:
The aft hull form is a straight forward planing vee, a private owner would not need the beaching capability the the lifeboat needs. Dump the £200k jet drives and hang a couple of shaft drives on 'p' brackets in small tunnels: there will be a small draught increase but you will gain massive efficency at slower speeds over the jets.
Reduce the max speed from 30kts to the high teens, twin Cummins 250hp mechanical fuel injection diesel would be perfect, the brand new ones made in Mexico classified as reconditioned. Guess 15 to 18kts max.

The big problem.> the hull is foam sandwich bagged and cured with heat.
Any idea's?

 

THere's a guy on the MBM forum who was a Superyacht skipper, gave up his job and came back to the UK to skipper the the windfarm cats.

He goes out in Force 6, full throttles all guns blazing; he said he couldn't think of monohull that could achieve this, especially the stability when docked onto the base of the turbine.

Another Guy delivered a large commercial Cat from the UK to Norway, said it was fantastic in a head sea, but was constantly trying to broach in a following sea and needed very careful attention on the wheel; not exactly the ideal situation on a long trip.

The Shannon hull seems to have resolved these issues.

 

Being a full planing vee-hull it will not be efficient at the 8 knots you speak of, simply because you will have a lot of submerged transom. There is a substantial penalty in that. What you desire seems best satisfied by semi-displacement hulls, which will be capable of making the high teens when required, but be reasonably slippery at the 8 knots, though still not as good as a full displacement hull. There is also the issue of propellor and gear ratio selection, if you want that versatility in speed range, you will have to compromise a bit, and that won't help improve fuel economy either.

 

I take your point about s/d hulls, and there are many iconic makes out there like the original Nelson concept that started it all off.

But they all have large deep keels and massive skegs to give directional stability, which is the problem that the Shannon design has resolved.

Beneteau launched the Swift Trawler 34 a couple of years ago, a modern take on the the s/d hull, and the write up in MBM magazine stated that it was difficult to control in a following sea...........it has a long keel but somewhat reduced in depth.

Regarding the submerged transom, maybe it's a compromise worth paying at slow speed were the effect of efficiency has very little effect on total fuel burn consumption....reduce speed from 8kts to 7.5kts?

 

I think you will find it very hard to avoid the temptation to advance those throttles and get out of the slow-coach mode ! The way I see it, every boat has a fairly narrow speed band it does best at, maybe displacement cats not so much restricted. Running a planing hull at displacement speeds for the majority of the time seems like putting the cart before the horse.

 

The price of fuel has made big boats virtually obsolete for all but the very rich.

 

You might like the write up of the Shannon (prototype) class on test. It so happens I know the journalist and he had the qualifications to actually helm the beast. From talking to him, it became apparent that this boat is quite something. Let us hope it keeps the crew safe and enables lives to be saved for a long time to come.


http://www.telegraph.co.uk/motoring/news/9745940/The-Christmas-road-test-Shannon-class-lifeboat.html

 

Displ. 8kts cruise for normal use for good mpg.[2 mpg?]
Fast cruise option to run from bad weather.[17kts force 7: RNLI]

At 17K it might take 500-800HP , at 8K, 3 or 4 GPH would be perhaps 50 -hp or so.

The operation of a huge engine at idle for most of its life can cause under loading , slobbering and a very shortened engine life .

In yacht service it doesnt matter much , a 10,000 hour industrial marinization may loose 3/4 of its service life , but at the usual 200 hours a year a 2500 HR service life is still decades!

But that hull is designed for skipping from wave top to wave top so it would be a pity to see it underpowered!

 

I was just looking at the fins on the back of a surf board and comparing them to the arrangement on the Shannon design hull, and it all starts to make some sort if sense. A surf board is designed to be under total control in a following sea surfing down a wave, without the wave energy causing 'aft steer' and broaching....



A traditional s/d hull with a big central Skeg and rudder captures wave energy in a following sea that can push the hull off course because of its large surface area. if this surface area is not presented to the wave energy at exactly 90deg to the following wave, the hull will be pushed off to one side.

The two little fins that replace the big central Skeg on the Shannon design are positioned at an aft location right at the back of the hull, copying the set up on a surf board.........