"Over the Hub" Props for Mercury 400/450 Single Engine Boats - Plane Issues?

[wagoetzmann]

Has anyone had success using "over the hub" type prop on large Mercury 400/450 4-Stroke Sportmaster, single engine boat?


Seeing all the exhaust has to go through the lower unit and "over the hub" of the prop, will it cavitate too much to get up on plane?


Something like the old Mercury Pro ET, Mazco R.E.4, BBlades Blaster, Hill Bullet 4,........of course only newer ones rated for the larger 4-strokes.


I'm in the process of prop testing a newer heavier 22 Talon with single 400R 2.6L and currently using Max-5 with no issues.


A Cleaver doesn't plane well for sure.

[LakeFever]

From the guys I run with it’s the diameter that’s the killer due to the lower unit. 14.75” minimum to work well. More than a few of these guys have openly mentioned dreaming of a lightning et prop for these new big four strokes

[JPEROG]

For your application, the best propeller for a holeshot and overall usability will be a thru-hub cleaver (offered by Mercury in a CNC, Hering in a CNC, and Hill in a cast)-run the tube 1 1/2 inches back from the blade root with very little or no flare. I can tell you that exiting the exhaust above the propeller on my cat improved getting on plane massively. It acts like an inboard with zero cavitation running overhub cleavers.

[LakeFever]

Most guys I run with run the through hub cleavers 26-28p for daily ripping and the 30+ over hubs for putting up numbers. Lots of hill props in the mix in my group

[wagoetzmann]

Thanks guys.

What is the difference between a cleaver with 15 degrees or 18 degrees rake for an air entrapment hull ...... always ran round ear blades no options so not familiar with a 3 degree rake angle effect?

I see Hill has two Signature 400 thru hub cleavers.....how much slip will these have up on the top.........I'm right at 10% or a bit less with a "worked" Max-5.

[powerabout]

might need a thrust washer with blowout ring that omc had long long time ago to help that issue

[racer]

Rake angle effects lift with higher rake having more bow lift at the same trim angles. Type of blade design needed IMO is dependent on the hull and its design/weight. Personally I like to run a prop that runs as close as possible to neutral trim. I have personally tested about 20 different props on a 450 in both over the hub and thru hub with multiple blade styles,

[billybob]

Contact a local good Prop. shop. For a little extra cash, they will probably have props. for you to try. Always test your props on the same day, or similar conditions. then record your info. for comparisons.