Fuel Consumption KAD300's

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Fuel Consumption KAD300\'s

During the next few weeks I plan bring my boat (37ft sports cruiser fitted with twin KAD300's) from the Medway to her new berth in Gosport. Total distance is approx 150miles. My tanks hold 600lts. I reckon on a cruising speed of around 20knots (maybe higher depending on sea state/weather etc) My Volvo Penta manual states best economical crusing RPM is about 10% off Max RPM which is between 3700 and 3900 so lets assume i'll be cruising at 3400RPM.
My manual does not mention fuel consumption so i'd be interested to know what fellow forumites think as to what kind of fuel consumption I can expect.
 
Re: Fuel Consumption KAD300\'s

My experience with engines is the WOT less 10% thing is in the real world not the most econominal speed. I had a pair of KAD43's hooked up to a fuel monitoring system and found that for mid revs on the plane fuel consumption was pretty constant - around 2mpg on a 33ft boat weighing about 6000kg.

Push the boat into the top 20% of the revs however and the mpg figure dropped of dramatically to WOT which returned a little over 1mpg.

I would suggest a cruise for you with the KAD300's would be between 2300 and 3100 rpm. If the consumption curves exactly mirrors my KAD43's (which it wont, but I expect it will be close) then your most efficient engine speed will be around 2900 rpm - though the differences through the mid range are not really enough to worry about.

As for your actual fuel consumption, this will be dictated by the weight of the boat, hull shape and condition (slime, fouling etc), drive and prop condition and sea state. In perfect conditions in the efficient range of 2400-3000 I would expect to be getting around 1.7 mpg, so your trip should use around 90 gallons, or 410 litres of the red stuff. Poor condition hull or an unfriendly sea, or string tides against you will drop this figure and can do so dramatically. You should have enough range if your tanks are full, even with a 20% reserve.
 
Re: Fuel Consumption KAD300\'s

I agree with the above.

If you have any doubts due to bad fouling, poor conditions etc etc, you could call in at dover or brighton for a top up.

I did a similar trip ( I came from Ipswich) called in at dover for a top up an it worked a treat.
 
Re: Fuel Consumption KAD300\'s

I d estimate 150miles at 25 knts at 75 lph= 450 litres.
And assume it will be more for the reasons Jez mentions. 450-550 litres.
 
Re: Fuel Consumption KAD300\'s

Agree with others. I think VP's suggested cruising speed of WOT less 10% factors in that if you bought a fast boat you probably want to go fast in it, so they suggest dropping off 10% to get a balance of speed, economy and engine wear. If you are only interested in economy, then for most planing boats its probably less.
 
Old thread but worth adding to it rather than starting a new one. I want to ask the opposite question.

Whilst I've owned my FL Targa 40 for 7 yrs I don't know the answer. Summer 2024 I want to travel to Scilley Isles and taking 3 months off work as a sabbatical. As such I'm in no hurry and want to chug as much as I can at say 1,000 revs doing about 5kts amd wanting to estimate fuel needs and refueling stops. Gonna approach journey as a sailing trip using tides. Appreciate at times I will need to blast for exercising engine, certain tides and conditions and any urgency reasons.

I haven't got fuel flow meters though was going to have fitted few years ago but other costs came up. My fuel assessments ignore chugs and focus on hours on the plane. I burn 80L per hr at 3,200 revs achieving 27kts with SS props. In principle this gives me 7hrs cruising with full tanks.

My question is, does anyone know what the fuel burn per hr would be for a 40 ft twin Kad300 10 ton cruiser @1,000 revs?

Edit- oops 27kts at 3200 revs

Many thx
Simon
 
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Hi, My old boat 38 feet and 9000kg have 2*kad44. Fuel consuption is about 80 litres/ hours 23 knots speed 3400 rmp.

NBs
 
Interesting
The 10% below WOT is quoted time and time again. Without doing any measurement it’s always felt that just on the plane and a little bit more kind of feels comfortable with less engine strain. My definition of cruising. @Portofino data sheet bears this out from a fuel usage point of view. Also the dbA readings are interesting from a comfort aspect.
Conclusion
Cruising at 10% below WOT is just marketing
 
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DavidJ said:
Interesting
The 10% below WOT is quoted time and time again. Without doing any measurement it’s always felt that just on the plane and a little bit more kind of feels comfortable with less engine strain. My definition of cruising. @Portofino data sheet bears this out from a fuel usage point of view. Also the dbA readings are interesting from a comfort aspect.
Conclusion
Cruising at 10% below WOT is just marketing
Click to expand...
Volvo say "cruising speed should be at least 10% below WOT".

We prefer to cruise slightly over supercharger cut-out speed and where the boat angle of attack has levelled off.
 
Portofino said:
What do you both mean by WOT?
That piece of paper or your boats real figure ?

Can you even attain that figure quoted by Volvo ?
Click to expand...
WOT is “wide open throttle” which even back to my motorcycle days means there is no more to be had out of the cable (Yes my KAD43’s are cable) The wide open bit will be the butterfly on the traditional carb.
So from the Volvo description. Levers fully down say gives 3700 rpm then 10% less would be 3330 rpm.
I take my boats max rpm not Volvos (KAD43) which is 3900
 
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Little update from a friends targa34 with KAD300.
Always felt i got 1.5mpg in my T40 cruising so data should be transferable at slow chug 1,000 KAD300 fuel use data.jpg
 
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