thanks alot I will contact prop shop
info appreciated

HI daveo
The Waveney has a max speed of 13-15 knots. Uses a coarse pitch 3 blade prop. I suggest you speak to Simon at Propshop and seek his advice. A nice brass prop will make all the difference and 2.9:1 reduction on a 550 at 12v sounds about right. My 52" Arun uses a 4 blade 50mm Propshop blade direct drive from two speed 900's.
30mm seems a bit small, my guess would be nearer 40mm but as good props are not that cheap do seek advice before you buy. 😀
Good luck with the restoration.

hi
thanks for reply its actually two x 550 motors with 2.9 - 1 gear boxes not 9-1
the max prop size I could go to is 50mm

thanks in advance for any help

9:1 gearing is a bit high and will reduce the motor speed quite a lot, however pulling round a 30mm prop, would give little speed through the water I appreciate.
Depending on how much gap you have between the prop shaft ends and the hull will be your only restriction as to what is the best size props to fit, so if you can give us this measurement, it will help the forum in answering your question.