9x13 propellor

[Guest]

I have an MG Spring 25 with a Yanmar 1GM and a rather insignificant looking propellor that was obviously put on with racing in mind. A forthcoming trip from Lancaster to South Brittany has prompted me to re-prop the boat. I am told by several people that I need a right handed 9x13 propellor but dont know whether the shaft is imperial or metric. Does anyone know off hand and/or better still has anyone got such a thing surplus to requirements.

 

[dickh]

The size of the propellor is stamped on the boss - this will give you a better idea as to a replacement prop. If your engine gets up to full revs or just below, then you probably have the right size prop - what is the gearbox reduction ratio? Speak to one of the prop manufactures and they will be able to compute the correct size - alternatively see if there is an owners association and pick their brains. If it is shaft drive you should be able to measure the shaft accurately and this will determine whether it's imperial or metric - if it is about 15 yrs old it is probably imperial. If you get a new prop, send the old one to them and they can copy the taper. So many ifs... - anyway good luck.

 

[Guest]

It sounds to me that at first look that the diameter is too small and the pitch too much.

The small diameter and big pitch is fine for the planing high reving power boat stuff. But like gliders, and our foresails, we need as much 'luff' as we can safely and efficiently use. If the pitch is too much the prop will 'stall' - like our sails and planes do.

Folding props are mighty expensive when you could buy a two blade with decent area for about £140. You might have to put up with a bit of vibration - but hey man ! You own a yacht