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A clean bum and boat performance

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Hi guys 

I hope everyone is well and still enjoying boating! Great to see the forum still going strong. While I hear that your boat is supposed to get bigger as you get older, mine is much smaller and I am down to around 4m LOA with a little dinghy. I am sure I should own a fifty footer by now. But that's not why I am writing.

I am doing a little research into the correlation between a clean or dirty bum and boat performance.  I'd love to hear your anecdates/experiences and before and after statistics, for possible use in an online story. Also feel free to email me - zoe@wildemedia.co.nz 

Many thanks! 

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Just now, Fogg said:

No stats on current boat but 2 boats ago (AC - 35ft) with Yanmar 27hp at 2500 rpm I would do 5kts dirty and 6kts clean.

Thanks Fogg! 

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And for something different…. A friend with a Riviera 47 tells me that at his usual cruising rpm (~1800 I believe) he gets 18kts clean but is down to 14kts dirty.

No idea what the purpose of your study is but obviously the relative impact of dirty bottoms on fossil fuel usage (aka running costs) and carbon emissions is vastly greater with launches than wirh yachts.

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21 minutes ago, Zoe said:

Awesome! How long was it since you'd maintained the hull, and what did you notice exactly? 

measured before and after a full scrape and anti-foul.

Engine (Yanmar 2QM20) struggled to get the yacht (10m Spencer) up to 5.5kt at around 2,800rpm.  Now does 6kt @ 2,000rpm

Hull wasn't heavily fouled, but had the surface finish of a 15 year old schoolboy's face.  Its not exactly a baby's bum now, but much smoother than before.  The prop was probably the biggest contributor - lots of small barnies before, now smooth and prop-speeded


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Thanks for this guys. I have compiled it into some bullet points - all anonymous. The intention is to use it in a newsletter about marine biosecurity. If you'd like to see it before it is published, or are curious about where it's going, please just send me an email - zoe@wildemedia.co.nz - I'll be happy to show you. 

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