I was afraid that might be the case. Is their any chance you can re bush the existing tube to take a 5 mm shaft? Otherwise you can investigate the removal of the whole tube and shaft. Heat applied to the tube with a mini blowtorch or soldering iron and giving it a twist with pliers or grips usually does it. Assuming you can get at it.
Or, maybe some older modeller will have a stash of old props. The cost of having props specially made is high and you have to consider buying couplings, so I doubt that is a practical solution. What type of model is it? we're mostly a nosy lot on here
Chas
Thanks Chas but that won’t work for this beast. It is an old Precedent f/glass 34” Huntsman which used to be petrol powered. The guy who built it knew what he was doing. The hull inside has been beefed up by laying down more glass and also adding core matt to reinforce various areas and then flow coated it. The prop shaft is fibre glassed into the hull. The result is a hull that weighs a tad under 2kgs.
He did a nice job, the only paint on the hull is a strip of blue where the deck joins. Otherwise it is a well preserved and polished gel coat hull. I don’t want to damage it if I can help it.
The problem is that it came with the remnants of a metal 52mm (!) prop and a spare 55mm plastic prop. I want to go electric with either a John Darke 780 series motor or brushless. For that I figure I need to reduce the prop to a 35 or 40mm one.
The hull might be in good nick but the superstructure is distinctly “sad and tired”.
What I might try is to regrease the tube and then fit a 5mm shaft in, leave it well ballasted, put it in the test tank and see how much water comes up the tube.