Where have my knots gone?

[A2THEK101]

Hi. Relatively new to boat ownership and had my boat since marchfrom brand new. I have managed to get 45 knots out of the little bugger with a friend aboard in April which is the listed top speed. Yesterday on my own and with relatively low fuel, the bugger would only max out at 37 knots. Can that all be growth under the hull or am I missing something, tide current etc. Boat is a Jeanneau cap Camarat 7.5wa with a 300hp Yamaha. All advice appreciated. Thanks

 

[jrudge]

Growth on hull and props.

Go swimming and give it a scrub

 

[A2THEK101]

It's bloody freezing

 

[ari]

Growth on hull and props.

Go swimming and give it a scrub

Agree with this (apart from the swimming bit perhaps!) Even just a little slime on the hull can make a huge difference.

 

[jrudge]

It's bloody freezing

I agree. The sea today is 21 degrees and really should be warmer at this time of year !

In Mallorca that is !

 

[MapisM]

Can that all be growth under the hull or am I missing something, tide current etc.

Yes it can. But you could also be missing something.
A boat like yours is likely to have a GPS-measured speed, which means that it is affected by current.
In other words, if you would reach a SOG (=speed over ground, i.e. GPS-based) or 37 kts while cruising against an 8 kts current, your STW (=speed through water) would be exactly 45 kts.
An 8 kts current would be huge though, hence very unlikely. But it could me a mix of current and hull+props growth.

 

[A2THEK101]

Thanks all for the advice