Fuel costs per 100 miles?

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NealB

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My 'next motor boat buying' saga continues.

As I get closer to making offers, I get more nervous of possible fuel costs.

Having not yet made any definite decision as to which boat to go for, I'm interested in getting a rough feel of the scale of what I'm taking on (after decades of sailing, this is a new, scary world for us).

We're probably looking at: 40 foot -ish, semi-displacement type hull, twin 250 - 300 hp.

One owner tells us he gets:

3 mpg at 6 knots
1 mpg at 14 knots
.7 mpg at 19 knots

If I budget on this basis, am I likely to be at least barking up the right tree?

Assuming fuel costs say, £0.9 litre, I then reckon that a 100 mile trip would cost:

(100 x.9) / (3 x .22) = £136 at 6 knots

(100 X .9) / (1 X .22) = £409 at 14 knots

(100 x .9) / (.7 x .22) = £585 at 19 knots

Has anyone got the time, knowledge and inclination to either confirm these broad assumptions, or to point out the flaws?

If so, many thanks!
 
neal, is it properly a semi d hull (like a nelson) that wont plane, or will it level out at speed?

From your descriptions it sounds like they are older non planing hulls, so the figures look right that the faster you go, the worse it gets.

Haydn is talking about planing boats and those rules dont apply to the type of craft you are looking at.

The figures look about right. I would actually expect slightly better fuel consumption at fully displaced speed and a bit worse at top whack.

Thing is, with boats of that age engine condition, prop condition, hull condition, extra weight and kit will all make a difference so its a question of sucking it and seeing. but I dont think your figures are way out.

On a boat like that, the general rule will be the slower you go the better the mpg figure will be.
 
The two boats we've narrowed our list to are a Broom Ocean 42 and Princess 414. I'm guessing you'd call them both semi-displacement (my ignorance of motor boats is still deeply profound)?
 
Those figures look about right for the Broom but I think they're a bit pessimistic for the Princess. The Broom is a a big lump of a boat with a SD hull and a big keel to drag around so I'm guessing 19kts is near flat out so 0.7mpg sounds about right. The Princess was designed as a planing hull although it won't be as efficient as a modern planing hull but it should give better mpg than the Broom, say around 0.9mpg @ 18kts
Yes, your costs are about right too. I reckon £6/mile for my own boat. Nobody said motorboating was cheap /forums/images/graemlins/frown.gif
 
Hmm, looking at an add, it seems that the 414 is a semi displacement boat, the add I looked at was an 85 model with aft cabin. I cant see that ever making 19 knots, mind it did not mention the engines.

Think the .7 might be about right.
 
Good question as so many talk of MPG.

I'm running a Fairline Targa 40 on outdrives and D6 350s'. Obviously, it's a quick planing hull. As hlb & Jez mentioned earlier, if you're planing it doesn't make much difference to mpg or litres per 100NM.

I can cruise at 24 -35 knots in the right conditions and 100 nautical will use about 300 litres. The fuel burn per hour increases of course but running time is reduced at the higher speed for a given distance.

If I push her to over 40 knots then I can say goodbye to economy as you would expect, highest speeds just waste fuel.

Hope that helps.

I
 
"1985 414 with aft cabin"....yes, that's the one.

I'm reliably informed that both it, and the Broom, will achieve 19 knots (mine won't, if I get one, but it's nice to know the potential is there).
 
It might just reach 19 knots, with the biggest engines. Who designed it, the info I've found so far is very scant. Probably Bennet.

Olsinki came along just after and moved the goal posts.

Yep My P35 will achieve 25 knots in perfect conditions, though it's supposed to do 27.

In reality 22 is good, though I once got down to 13 knots, with a bit of weed. /forums/images/graemlins/frown.gif

I'm 8 tons P35 though to be honest it's a bit longer. V41's 200HP. Plaining hull. Cruise these days about 18 knots, though used to go a bit faster. I once checked it at 1.3 MPG. But I use 1 mpg as a guide.

I'd try to find an Olsinki designed boat if you can, there worlds apart from Bennet.

P414
 
I think the 414 was a Bennett planing hull albeit with a small keel. Should do 20kts+ with the right engines IMHO

414.jpg


Doesn't look much like a SD hull to me
 
Going by a trip over to the island last night even though the water was as flat as a babys bottom speed and fuel cons. was down by 25% . The hull was last cleaned off in august. Im seriously thinking about not bothering to a/foul anymore but use the sealift twice a year.
 
I'd say these figures are about right. we have an atlantic 38 with s/d hull and 2x 225 engines and get hese kind of figures although considerably better than 3mpg at 6 knots. you will pay dearly for every knot over displacement speeds. ours is good up to 8 knots and then starts to get more thirsty. 14 knots figure mentioned is actually perhaps a tad optimistic
 
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And your point is?

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I daren't tell Searush what my Princess burns, Roger - he'd have kittens.

(there arent any smiley faces that have tears so I'll have to use this one instead and think of something else /forums/images/graemlins/wink.gif)
 
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