Classic 1963 21 Video and pics

[3rdday]

Denny,
How would a 4 blade 18P work? When you go from a 3 blade to 4 blade, do you go for a lower pitch, higher pitch, lower diameter etc.n How would one know what prop to go to when looking at 4 blade?

[Islandtrader]

Brian, I know nothing about props, however you might want to jump over to the Scream and Fly web. Maybe you can find some help there. They are into all that type of stuff.

[Bushwacker]

Brian - You have to know both pitch and diameter before you can predict what a given prop will do. Most props I've seen from a given manufacturer go up in diameter when you drop down in pitch with same material. On my old 115, OMC offered a 13 x 19P, a 13.25 x 17P, and a 13.75 x 15P. With Michigan, the 4B aluminum Vortex I started with was a 14"dia. x 20" pitch. The equivalent SS 4B Apollo was a 14.125 dia x 20" pitch, so with the same power input they could evidently turn the same rpm with a little more diameter due to less drag from thinner blades on the stainless prop. When going from 3 to 4 blades, the equivalent 4B props seem to be smaller in diameter, but you're still picking up quite a bit more blade area with the additional blade.

Suggest you check the various websites, such as Merc and PowerTech. Don't know what Yamaha has. On these websites you can plug in boat weight and type, motor, and max speed & rpm with an existing prop, and it'll recommend various props optimized for different conditions, such as max acceleration (water skiing), cruise efficiency, or top speed. I suggest you get more data with a heavy load and T-top before you lock in on a prop. Might also see if you can find a dealer that will loan used props to try, or come to one of the SeaCraft gatherings! Most of the guys probably have spare props they'd let you try! Denny

[3rdday]

What do any of you know about solid steel hubs on props(no polyurethane plastic insert) WHat are the advantages and disadvantages? I do understand if that prop hits something there is a greater risk of stripping/shipping gears in the lower unit?

[gofastsandman]

Blown spider gears at the least. Blown main shaft in the lower unit or worse! We used to blow 2 or 3 shear pins a summer in an old Rude 40 pull start on a little Whaler in Barnstable harbor as a child. One of the things I like about the mirage + is you can change the hub out in a jiffy if you dont drop anything in the water.... If you do spin a rubber hub, you can usually back off the pin and limp in.

Ron White called. How many Koopens for a ride at Long Point?
Sluggo wants a ride too.

The Merc prop selector on the site is pretty good for a starting point.
GFS
Looks like the chines are flying!