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[surfer71]

HI guys


ok so I have a question that I know the basics but I value your input on ..


We all know not to fit the prob shaft tube below the water line other wise water comes in.. but how can you be 100% sure your in the safe zone??


I have pegasis boat I think the tubes just might be abit below or certainly dam close to the water line, so before i do the RNLI trent boat I want to make sure i have checked them..


so any tips please advise I am all ears 

[KitS]

With the few boats I've built from scratch (about 3 maybe....) I've marked the waterline on the outside of the hull with tape, and then dunked the hull into the bath (after the Local Authorities have issued the necessary approval....) and watched to see if any water came aboard.

I got it wrong with one of them and had to de-install the prop tubes and have another go, not much fun but better safe than sorry at your stage of the build I reckon.

[surfer71]

which is why 100% I am asking ok.. dunk tank sounds a good idea.. I will get on to that.. float it and add some weight like a 12v battery from the motorbike I have for my other boats as the super structure and all the kit must be around that weight if not less and see if it's all ok..


I understand the grease will keep some at bay as well..

[Hotglove]

I bought a boat ready built, it is a Dumas Chris Craft 1930 runabout and the propshaft is well below the waterline. The Dumas shaft is a plain brass tube with a stuffing tube and a 3/16 shaft running in it. There is noticeable play in the shaft/tube, when the boat was demonstrated by the seller we had a minor problem with the coupling being loose and it was quickly tightened, I bought the boat and tried it out at our club lake. It let in about 2 dessert spoons of water in a 40 min session. I made a few changes, one of which was a short length of fuel pipe on the shaft, reassembled and the next time it let in less than half as much.
I have just changed to brushless with a new shaft (same tube) and coupling. The old setup was badly out of line due to the size of motor fitted. The new setup features a very adjustable mount and the alignment is just about perfect, with a plain coupling fitted the shaft could be slid into the tube then into the coupling without any binding. The plain coupling was swapped for a heavy duty rubber variety and the prop and shaft were assembled and packed with Molykote 111 Silicon grease, with the familiar piece of silicon tube stretched over the shaft. On its last outing it ran much sweeter, with less noise and no water leaking at all. The idea of using a short (4mm approx) length of silicon tube slightly compressed came from elsewhere on the forum and is very much appreciated.
Hope this is of interest.