Advice on upgrading from Honwave 3.5

[RayWilde]

I currently have a Honwave 3.5 with a Mariner 15hp motor that I use in the sea around Harlech and Holyhead, subject to good weather. I have got the bug and want something bigger and more sea worthy. Generally using it to cruise around finding Dolpins or taking my 8 and 10 year olds Knee Boarding.
I have a budget of £7000ish and needs advice.
Thanks
Ray