It does'nt add up.

[burgundyben]

It does\'nt add up.

200hp diesel boat engine, from a truck, 6 litre weighs about half a ton, uses about 5 gallons an hour

200 hp petrol ford cosworth sierra engine, 2 litre weighs about, well not alot cos me and a mate can lift one and were both wimps, now, say, sierra on motorway doing 70 mph, and maybe 35 to the gallon, thats 2 gallons an hour, so why are petrol boats so much thirstier than diesels?

plus, porsche 911 engine, at 3000 revs, mine was doing 90 mph, say 30 to the gallon, so say 3 gallons an hour, but, no water cooling blocked strainers frost damage knackered impellers etc and light as a feather, and 250 to 300 hp, so if I took the ton and a half of engines out of my boat and put in maybe 200 kgs of 911 engines that do only 3 gallons an hour each I am winning right?

I just wondered...



<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[BarryH]

Re: It does\'nt add up.

Bugger you've just made Newton's law redundant........if only it was as easy as that!

<hr width=100% size=1>

 

[ccscott49]

Re: It does\'nt add up.

Only one problem, it's rather more difficult to push 3 tons of boat, through the water and in contact with it, than one ton of car through the air on wheels! Back to the drawing board my lad!

<hr width=100% size=1>

 

[ballena]

Re: It does\'nt add up.

I know exactly what you mean, I have 5 litre EFI V8(250hp) in the boat, 2 .5 tonnes, 40 mph max and 2.5 mpg and weighs 500kg with drive.

Car 2 litre 5cyl turbo(180hp), 1.3 tonnes, 150mph(i tested it in Germany)and 28mpg

Its all about DRAG, boats look nice and slippery, but they sure aint.

<hr width=100% size=1>V8's rule!

 

[burgundyben]

Re: It does\'nt add up.

he's my great great great great grand father (according to Aunty Alice who was a bit nuts), anyway, why have I made his law redundant?

for every force there is an equal and opposite force and F=ma

accept colin point, so fuel economy might be higher due to greter work load but also save a thrid of the weight of the boat remember, I am sure this is worth investigating......

<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[ccscott49]

Re: It does\'nt add up.

I think you will also find torque raises it's ugly head, along with gearing, how many boats do you know with five gears?

<hr width=100% size=1>

 

[BarryH]

Re: It does\'nt add up.

Dunno, sounded good at the time.

<hr width=100% size=1>

 

[burgundyben]

Re: It does\'nt add up.

ok, so I need to keep the props little cos there is not much room to swing a big one in a huntsman, and the porker engine revs high which is ideal for an ickle prop, prop can be suited to torque output by getting the pitch right? dont need 5 gears, just a boaty type gear box

iumagine the sound, and if using a pair of 911 turbo engines at 300 gee gees each then 45 or so knots, woo har!!

<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[hlb]

Re: It does\'nt add up.

It's Frankinstiens law of relitivity I think.

Anyway they were alot cleverer in the olden days cos it only took one horse to pull a barge with hundreds of tons of coal in it, so with Muckies 400horses power and only 8 tons, it should do about 1600 mph, Told you Volvo's were crap!

<hr width=100% size=1> <font color=blue>No one can force me to come here.<font color=red> I'm a volunteer!!.<font color=blue>

Haydn

 

[Deleted User YDKXO]

Re: It does\'nt add up.

Is'nt it about torque not power? You need loads more torque to accelerate a few tons of boat onto the plane compared to a ton and a half of car down the road. I'm guessing but I bet a 300hp turbo charged diesel has far more low down torque than your 300hp 911 motor

<hr width=100% size=1>

 

[ccscott49]

Re: It does\'nt add up.

At the revs you'd need with ickle props, they'd have to be surface action two bladers, then you'd need trim blades to lift the stern and then.....etc. But yeh! what a noise, open pipes!! Yahoo!

<hr width=100% size=1>

 

[burgundyben]

Re: It does\'nt add up.

at last hlb you have said something worth while "Told you Volvo's were crap! "

<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[Baltimore_Bill]

Re: It does\'nt add up.

try sawing one of the prop blades off - less drag, easier on the engine.




<hr width=100% size=1>

 

[Bejasus]

Re: It does\'nt add up.

He already tried that one....................../forums/images/icons/crazy.gif

<hr width=100% size=1><A target="_blank" HREF=http://www.arweb.co.uk/argallery/h00>http://www.arweb.co.uk/argallery/h00</A>

 

[ccscott49]

Re: It does\'nt add up.

That was uncalled for!! tee hee

<hr width=100% size=1>

 

[Dave_Snelson]

Re: It does\'nt add up.

I have often thought of this...

I've read some of the replies but they don't explain the HUGE disparity of the two transport types. For example, my car is a Frontera which weighs 2 tons and is powered by a 100HP 2.2L diesel. It does 35mpg and therefore uses 2gph at 70mph.

My boat is a shakespear 17ft bowrider with 100HP Suzuki and I think that weighs just top side of 1 ton, lets say 1.3 tons with 5 people on board. It drinks 6gph at 4000rpm (the frontera at 70mph is doing 3000rpm).

This isn't just a little different, its a magnitude of 3X different.

Do marine engines have to work *that* much harder? Is water drag such a huge factor?

I still cough up the cash every weekend though!!

<hr width=100% size=1>Madoc Yacht Club
<A target="_blank" HREF=http://www.madocyachtclub.co.uk>http://www.madocyachtclub.co.uk</A>

 

[ccscott49]

Re: It does\'nt add up.

An engine driving a boat, is like a car permanently going uphill, a steep hill, see what your fuel consumption is like then, or better still, drive your car through heavy mud, for a couple of hours and check your fuel consumption. Also isn't the suzuki petrol? You have to take into consideration calorific fuel values. But I'm afraid it is a physical and scientific fact, so get used to it.

<hr width=100% size=1>

 

[Dave_Snelson]

Re: It does\'nt add up.

Oh, I'm already used to it - I'm just trying to rationalise it.

...now, about Teflon coated hulls...

<hr width=100% size=1>Madoc Yacht Club
<A target="_blank" HREF=http://www.madocyachtclub.co.uk>http://www.madocyachtclub.co.uk</A>

 

[Bejasus]

Re: It does\'nt add up.

A basic but very important thing to take into consideration, is the relationship between tyres and tarmac and propellors and water. Huge amount of efficiency loss due to slippage means that your propellor is trying to act like an automatic gearbox which can never get into lockup, no matter what pitch you run.

<hr width=100% size=1><A target="_blank" HREF=http://www.arweb.co.uk/argallery/h00>http://www.arweb.co.uk/argallery/h00</A>

 

[Chris_B4]

Re: It does\'nt add up.

The petrol vs diesel thing is down to calorific values as ccscott49 suggests there's basically more energy contained in a gram of diesel than in a gram of petrol so the engines get same power from less fuel

Air cooled engines ? where are they gonna get their air from, like you say in the Porker there's a 90mph airflow rushing by to use for cooling, shame that



<hr width=100% size=1>