Fuel Economy: Clean v Dirty Hull

beejay190

beejay190

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Does anyone have any information/records as to whether and by how much their boat is more fuel efficient immediately following a power wash of the hull, outdrives and tabs. Particularly interested in something about the 30-35 foot mark.

Thanks
 
My P35 used to do about 22/24 knots. But one year, about September time, it got down to 12 knots flat out. After an antifoul it was back up to 22 or more again.

So that was a 50% saving, if it helps.
 
There is a forumite whose boat was used by MBM for their comparison, he will arrive soon.

12 months the reduction in mpg was 29%.

I keep mpg figures for my boat with every refuel and you can clearly see it after a wash off or after a wash and antifoul.
 
I noticed a huge difference on my old P35, that used to loose about 8 knots afyer 6 months of being in the water, my new boat, a princess 43 footer lost around 5 knots after being in the water for 6 weeks, had her bum cleaned and she was fine, this will of course make a difference to the MPG
 
Blimey, reading the responses so far we must be lucky with our anti-foul or maybe fouling isn't such a issue in the muddy waters of the East Coast. We used Cruiser Uno on our Fairline Targa and apart from an easily brushed off occasional 'beard' around part of the waterline we didn't get any serious fouling or reductions in performance.
 
Think we must be lucky too. We rarely get any growth other than a thin layer of slime at the water line which brushes off with a long handled brush. We dont use expensive antifoul (Premier Paints) so it must just be that we are in a very low fouling area. Plus the boat rarely stays still long enough for growth to occur :D
 
Greg2 said:
Blimey, reading the responses so far we must be lucky with our anti-foul or maybe fouling isn't such a issue in the muddy waters of the East Coast. We used Cruiser Uno on our Fairline Targa and apart from an easily brushed off occasional 'beard' around part of the waterline we didn't get any serious fouling or reductions in performance.
Click to expand...

I am also on cruiser uno (softer than many and erodes faster above 25knts)

Every now and then I deliberately run through chop @ 30knts knowing that a thin layer of cruiser uno is coming off leaving fresh UNO.

When I have lifted after 10-12 months the hull has been just about clean but the props and shafts have been covered with 'felt' like covering.

After a scrub of these and a jet wash hull I have noted a 1.5 to 2 knot increase.
well worth a scrub but nothing as bad as being reported above.
The cruiser uno is repainted after two years, I try to erode the uno off before reapplication so that there isnt a build up of layers.

Cruiser uno is recommended up to 25 knts, my boat is faster than this but in all honesty I seldom cruise above 25knts, I doubt I cover more than 20 miles a year @ 30 knots , KevB recommended it to me years ago, thanks Kev. :)
 
Broom 38

On a sea trial prior to purchase of our Broom we achieved 12 knots in place of the 25 knots claimed.
The broker claimed it was down to hull fouling. I did not believe it could be such a reduction.
The boat was slipped, pressure washed and returned to the water within 2 days. New trial gave 25 knots!!
The hull and undercarriage were badly fouled but even so ........!!
QED, if it makes this much difference to speed, what is happening to fuel consumption!!
 
Thank you for your replies.

My Bav29 was pressure washed last April ,but within two months there was lots of green and brown stuff growing on the drives and tabs, and the hull felt like it was covered with a thin coating of slippery jelly. I put on my wetsuit and tried to clean it off myself, but that was a waste of time.

So, BOBBY will shortly be dry berthed and from now on she will always have a clean bottom. I am looking forward to better acceleration up onto the plane ; maintaining a mid 20s cruise speed but at lower revs, and of course greater fuel efficiency.

In case you are wondering where the name BOBBY came from, it was the name of the previous owners favorite dog. Wonder what his wife thought of that .
 
I am due to have the boat out for a wash after 10 months in the water. I have accurate fuel metering so I will do some before and after figures. It has lost about 8kts over that time.
Might do some planing / displacement figs too for the other thread. I did do some a few weeks ago and the cons at 8kts was about 2mpg and at 16kts 1.7 - didn't get a lot worse up to 22kts.
LPG injection soon, with a clean bottom should be 2 - 2.5 at 25kts then!
 
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