Top End Speed

[MarieK]

My (new to me) boat was coppercoated last year but I havent lifted her out this year (yet) to give her a scrub and get rid of the build up of scum.

I am comparing my performance with an identical boat freshly antifouled. At 3000 RPM we are both getting 20 knots but at 3800RPM he is getting 28-29 knots whereas I am only getting 24-25.

My question is would the excessive growth on my boat show itself this way and would a bit of scum on her (nothing excessive) be enough to account for a 5 knot top end difference?

 

[Nick_H]

Are the props clean? A layer of algae can lose you a few knots, but fouling on the props will lose you more

 

[MarieK]

She is on shafts so not really sure what state the props are in. I did put down an underwater camera and they looked ok.

 

[David of Essex]

Whats the best treatment for stopping the props fouling up.

David

 

[DavidJ]

I've found the biggest influence on speed is barnacle build up on the priops. After a quick clean up with "Starbright pads", which is easy with raised stern drives, it's pretty much back to normal reguardless of hull crud.

 

[MarieK]

How much might you lose when they are bad David?

 

[DavidJ]

[ QUOTE ]
How much might you lose when they are bad David?

[/ QUOTE ]
A lot! It feels like there is something seriously wrong with the engines. Normally I can get up to 30 knots with ease but with only a small build up on the props I'm struggling to get 24 knots. Can you hire a diver to give them a clean up?

 

[neale]

I had a 25ft boat powered by a V8 petrol lump that would get up to 35knots with a clean bum. I launched it with a clean hull, left it on a swinging mooring for 3 months and then took it for a run. Max speed.....11 knots. Boat would not get up on the plane. Took it out of the water to find a serious build up of fouling. Had it cleaned and re-launched. Back to 35 knots.

 

[MarieK]

OK great info thanks guy, will lift her out and give her a scrub.

 

[oceandrive]

A few barnicles on the props will knock the speed down and also send the consumption up. Also very important shafts and the underside of trim tabs anodes etc.

Copper cote works quite well with sailing yachts but motor yachts "planning" need clean props and and tabs. so you still need to either lift or get under with a scrapper, and a 3M pad.

As said if your on stern drives you can get a good idea by lifting the legs to beach and have a feel around.

Have a look at the thread a few days ago re: antifoul similar problems. Think it was from hlb .

 

[billskip]

"Whats the best treatment for stopping the props fouling up"





Dont let them get wet!

 

[hlb]

Anything, but anything, will slow the boat down. You might not be even able to see it. But it's costing you money. Just how much, before it's worth having lifted, is hard to tell. Probably a good power wash and clean up every six months on boats doing a hundred hours a year.