Volvo D6-370 fuel consumption. What changed ?

[Petrolia]

I’ve got one of those Volvo engine monitoring things where I can get real time data on fuel consumption & the like. At 2550rpm and around 20knots she used to drink fractionally over 15gph which was pretty much what I had expected before buying the boat so I was happy.

Recently however the boat got lifted for a bottom clean, anti-foul and new anodes. After going back into the water at the same rpm the speed seems fractionally down but worse the consumption runs at about 19gph. What can have changed ? The weight of gear on the boat pre and post bottom clean was the about the same.

Another thing is that before the bottom clean I never had the opportunity to run at WOT so don’t know what max fuel consumption was. However after the bottom clean at WOT the consumption was 40gph. Is it actually possible to use 40gph when the quoted figure for flat out is 34gph ? The engines did achieve max quoted 3500rpm at WOT. Also the boat did 32.5knts against quoted max 33knts which isn’t bad considering we had our cruising gear onboard, nearly full water and about 1/3 fuel.

So it gives max revs & good speed but the indicated fuel consumption is higher than before & at WOT way higher than Volvo specification.

Am I really using more fuel than before ? Could it really be using 40gph flat out ? Can I rely on these instruments ? Is there a Volvo tech help number ?

 

[Dave_Snelson]

The answer to all this could be in the anti-foul. A lot of new boats are tested without anti-foul and the difference when anti-foul is painted on is alarming. A different anti-foul could cause extra drag and hence more fuel consumption. It did on my Windy until I sanded and polished the hull and hey-presto! 4 kts more and 2gph less at cruising speed.

 

[Petrolia]

Thanks,
Funny you should mention this. When the boat first came out I commented on a kind of 'stippling' effect on the hull. The people who were going to do the work said, "poor application of antifoul, we will give it a sand down".

I don't think I paid enough attention and I don't think they did much of a sand down. Also I had it in my mind that they put these stipples or dimples into golf balls on purpose to make them go further. Seems that it doesn't work for boats.

The main thing that still confuses me is that the boat did achieve max revs & good top speed. Could it have done this with poorly prepared hull creating excessive drag ?