Yes and no. On a 40 foot performance design like yours a really dirty (read that as hairy) bottom would likely be 2 knots. That is extreme though. A little slime would likely be .3 to .5 knots
Cleaning the bottom probably also cleans the impeller as suggested by others. I have often calibrated my speedo in the fall and then found the boat extremely fast the next spring when first launched. Usually the speedo is reading 0.3 knots or so fast The other question is how often do you haul the boat? In southern climes where boats are left in the water year round I would guess that without regular cleaning the bottoms would be very foul and very slow. In northern climates even if we don’t ever clean mid season they are always out for the winter so at least clean for the start of every season … From: CnC-List [mailto:[email protected]] On Behalf Of Jim Watts via CnC-List Sent: Thursday, May 21, 2015 1:35 PM To: 1 CnC List Cc: Jim Watts Subject: Re: Stus-List Scum Drag A knot and a half seems extreme, but I'm guessing it's your instruments. I usually pick up less than half a knot in reality, once I have recalibrated the knotmeter. There seems to be a lot of speed trickery going on with slime and other stuff down below, so throughout the season I keep recalibrating the knotmeter to reflect reality (as seen by my GPS in slack water). Once I have a clean bottom again, I reset the knotmeter to the base value. Jim Watts Paradigm Shift C&C 35 Mk III Victoria, BC On 21 May 2015 at 08:53, Josh Muckley via CnC-List <[email protected]<mailto:[email protected]>> wrote: Doesn't sound atypical. Other powerboaters and sailboaters alike have stories far more extreme than that. Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD On May 21, 2015 11:45 AM, "Tom Buscaglia via CnC-List" <[email protected]<mailto:[email protected]>> wrote: OK. I get that our boats are faster with clean bottoms. But I just had Alera hauled and pressure washed and the speed jumped back good knit and a half. I got to wondering if this is typical. Well, is it? Tom Buscaglia S/V Alera 1990 C&C 37+/40 Vashon WA 206.463.9200<tel:206.463.9200> _______________________________________________ Email address: [email protected]<mailto:[email protected]> To change your list preferences, including unsubscribing -- go to the bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com _______________________________________________ Email address: [email protected]<mailto:[email protected]> To change your list preferences, including unsubscribing -- go to the bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com
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