Slimy question

Twister_Ken

Twister_Ken

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I accept that if you're a racer, you want a bottom that as smooth as a Kensington con man. And that if you're a cruiser, you don't really want to be dragging barnacles, mussels or weed around with you. But does that algae-like brown slime actually slow you down more than a fraction of a percent?
 
mmm - u r correct of course, but unless it is heavily crustated with long weed tendrils ......... I wonder

what do you think the drag really is, can you quantify it as a loss of speed ?

racing - yes every bit helps ..... but otherwise ?
 
Can't really think of many egs in cruising where even a few percent would make much difference.
Hang on - maybe Ken's bought one of those boat scrubbing thingies...
 
Difficult to carry out a controlled experiment under sail, as you cannot measure the drive and compare with the speed. Having a long keel and big wetted surface I reckon I can lose the best part of a knot just with slime and some weed.
Barnacles on the prop mean that measuring under power (in theory possible to measure power this way) is also not possible.
Sometimes I wonder if fouling reduces the measured log seed (even with a clean impellor) by disturbing the water around this area, so the effect may be less that it looks!
I remember coming back through the Kiel canal some years ago with slime and a bit of week, and only managing 3.8 knows with the donkey at near full welly. Got in 30 mins after dark and was ready to be fined by the over-zealous German police! This 3.8 was actual and not theoretical as it was with a trailing log!
 
cant give an example of a sailing boat and apologies about talking motor on this thread but, 3 years ago we built a 38' motor cruiser when finished with no antifouling just the polished gel coat thacked the thing down the river and over the measured mile recorded 29.5knots.
did this in both directions and took averages due to tide and wind 29.5 knots
on returning to the yard she was lifted out and her bottom washed, etched primed and antifouled with hard racing antifoul at the end of her treatment (allowing cure time etc)
re-launched and once more thacked down the river with a loss of just over 1.5 knots.
no other adjustments of additions to the boat were made!

So even antifouling causes friction through the water.

Why do windserfers and serfers alike was their boards!!!

draw your own conclusion!!
 
hi i can tell you . just took mine out to clean and antyfoul be fore done 3 to 4 knots motoring . sailing 5to7knts after 10 knts motor ing top sailing in last thee days 13 knts in 20 kts wind. 15 kts wind 8 knts under sail so yes it sure dose slow you down hpe that helps dave
 
Last year I scraped about two sq mtrs of small barnacles off the hull. I got an extra one and a half knots on the cross channel return trip.
I get a slime build up and reckon it costs me half to one knot, but I can live with that as LinR is in the water all year and I haven't A/F'ed for five years.

I plan to dry out and A/F this year. /forums/images/graemlins/cool.gif

Oh! by the way, I don't race /forums/images/graemlins/smirk.gif
 
In performance sailing they (Braithwaite) were experimenting to determine best hull finish and drag characteristic. They were dissapointed not to be able to repeat experimental results on a laser dinghy until they were advised it had been trailed to an event that weekend.

Cleaned off hull and replicated previous results. So even a thin coating of road grime can slow you down.

Braithwaite concluded the smoothest and most highly polished finish is best but in the Dinghy world many good sailors insist a 1200 wet & Dry finish encourages a wetted surface is best.
 
On our previous Westerly 33 under engine at constant revs slime reduced the speed by as much as 0.75/kt which is quite a bit. A quick dive with a sponge would have it back to normal again. I suspect the effect under sail in light airs however would be even more marked. I haven't checked our latest boat as we don't let slime get a hold, we either avoid it by using Optima or last year Micron plus two dive cleans. We just came out this morning BTW and the slime was very visible, boat unused since November, but came off easily with the pressurewash. The bright polished prop is already clean to start the re-polish, just with a bit of old plastic batten whilst the gunge was still wet. Barnacles present only in the root of the blades and easily removed.

Can you really afford to drop 0.75kt? Think what that is on a trip to Cherbourg!

Robin
 
X-402 (40 ft racer/cruisr) 1% of about 7 Kts per week of fouling in a flat calm under power.

Raced it a lot, so persuaded me that diver scrubs were worth having.
 
hi just afew small shells and brown slugy stuff no weed or build up . and few shells on prop no slugy stuff there. last time out i tryed common old tar on bottom i think if i had not left it for 18 months i would not have had a thing on bottom as it was it was realy better than ever before , and one things for sure it took every bit of old antyfoul with it . as i say if i had done it before xmas i dont think i would have had anything at all on bottom . as it was only over the last 8 weeks that she started to slow down . so if any one wants to get rid of old antyfoul do a season on good old tar. i tested a plate in the water for two years nothing grew on it only on the part i left free of tar (roofing bitumen) so ive done it again this time will take her out at!12 months see what i get but ill surely not use antfoul again dave
 
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