prop size conversion

[Rod Holder]

Hi all,<br />I have a 1978 21' Glasply (average weight V hull) and a 470 Merc.<br /><br />The prop that is on it is a 15x18 beater that has been repaired more than a few times and is in sad shape (I want to use it as a spare)<br /><br />I get to my 4,200 rpm max.<br /><br />1) Will the year of my drive limit my selection ?<br /><br />2) Is 100 rpm per inch dia and 200 rpm per inch pitch a good formula ?<br /><br />I was thinking of 14 1/4x19.<br /><br />Any info would be great...........Thanks

 

[Doug Durako]

Re: prop size conversion

Should be about an even swap. See if you can borrow a stainless steel prop that size from a friend or a prop shop and try it out. Newer props are often "cupped" and every rig reacts differently to cupping on either the leading edge (to lift the bow) or trailing edge (to lift the stern) of the blade.<br /><br />I spent about $600 on prop rebuilds with my former boat before I made the jump to stainless---with a little care, and no rocks or concrete, you will get many seasons out of a good stainless prop.