Power to weight ratio

jools · 15 September 2002, 12:47

As always I smile when I read the comments about Mr Hart and his little boat....

Now it occoured to me tonight (as I sit in my Hotel room in Kuala Lumpur with a faster internet link than I get at home) people poke fun at Kieth, but maybe he has the most powerfull vessel on the forum (relativly speaking)

I have a 5.8m Ribcraft with a 90hp Mercury - Total weight (boat and engine 564Kg = 6kg/hp - Is that the right way round

Kieths SIB - well Keith can fill us in with the details

having seen him "Take off" in Cardiff Bay - this might be interesting.

Of course - this dosn't include the weight of the crew

Keith Hart · 15 September 2002, 14:01

Hi Jools

You are in Kuala Lumpur and I am in Birmingham!

Well I can answer your question anyway.

I wrote the following in a thread last year entitled 'Inshore' (try the search for the full thread):

Quote:

The weight of my boat is 35 kilos not 50. This makes the weight of boat + engine 73 kilos. Thefore the hp/weight ratio is in fact 4.86 kilos per 1 hp..

So in fact Quicksilver is more powerfull!

Keith (yes it might be small but it does get out there) Hart

jools · 15 September 2002, 14:05

Now its the turn of some of the "big boys" to own up.

Come on Brian - Is Cyanide any match for Quicksilver

Daniel · 15 September 2002, 14:58

Well...

Since i can't really compete with my current outfit i have designed a new one. It consists of my exsisting engine and a 4x2' peice of ply. Marine ply is desirable, but normal type will do.

The idea is tie ones self to said plywood, bolt engine to other side. Place small fuel container in a back-pack and see how fast you can go.

Me engine weighs 167Kg
Ply - lets say 1Kg
Fuel - don't need a lot of that - 1li = 1kg
Bolts, rope and stuff - allow another 1Kg

Total weight, 170Kg, 130HP, thats an amazing 1.3Kg/hp - anyone beat this?

I think we should call it a SNIB - Stupid Non Inflatable Boat

Brian · 15 September 2002, 15:05

I have got to do some estimating here as Cyanide is to big for ME to tow and has, therefore, never been near a weighbridge.
To the best of my knowledge it weighs about 3 tons. Call it 3000kg. With 450l of fuel thats another 450kg. Say 3450 all up (no crew). The engine is rated at 320hp (where; prop., flywheel, main shaft,-dunno). So divide 3450 by 320 equals, er, ehm, er....10.781kg/hp ? Er, which I think makes my power/weight ratio crap, right?
So as I said, how the hell Keith manages to handle all that (relative) power, I will never know!

Pete7 · 15 September 2002, 15:22

Daniel, thats a better power to weight ratio than the latest 1000 cc motorcycles, add some wheels and you could lap them at Silverstone.

As a point of interest you ned about 50 hp per tonne to make a boat plane (assuming its a planning hull) but this will only achieve between 15 - 20 knots depending on hull shape, eg depth of hull width in reation to length etc. If you want to go faster than this just add more power.

Daniel · 15 September 2002, 15:25

I'd only beat them when its wet though pete!

Since motorsport has dry and wet tyres does watersport have dry props? Prehaps one of those might help?

Keith Hart · 15 September 2002, 17:57

Quote:

Er, which I think makes my power/weight ratio crap, right?

Thanks for the offer of a boat swap Brian, but I couldn't get yours in my garage!

Keith (in your dreams) Hart

Flanker · 15 September 2002, 19:27

Who has a boat plane, I have not seen many about, is that classed as a rib with the rubber floats it lands on?

Pete

Alan · 16 September 2002, 12:00

Keith, I think you are only factoring in weight of boat and engine?
I think when you factor in the weight of the crew your power to weight ratio might be a little less impressive

Blue Ice weighs 890kg (boat and engine only) so with 200hp that gives 4.45kg/hp which is marginally better than BGLS (Britains Greatest Living Sibster)'s rig!

Course if I add fuel, kit and three heavy blokes then its 6.8kg/hp which goes to prove theres lies and damn lies and then statistics!!

Brian · 16 September 2002, 14:20

OK then Keith. Own up and tell us what your P/W ratio is with you and Bill on board.
In the interest of fairness you can do the calculation assuming you haven't had breakfast yet!

gaviotapete · 19 April 2006, 23:28

if you don't count total weight( that includes weight of passengers, fuel, anchor,surfboards/dive tanks/fishing kit etc..) then you will not get a relevant result.

ribit · 20 April 2006, 15:45

MM, not including all the water toys, and petrol, I would guess the 5.8 Ring and engine would come out around 525-550Kg, = 2.62-2.75KG/HP May be some years back even 2.38KG/HP, now all I need is a 2.5efi that should do the trick!!!