I have a 21 foot 1999 inboard/outboard cruiser with a 4.3 Chevy.  I would like to be able to get the boat on plane quicker when all the kids along with some adults want to get on the water (weight) and when pulling people on the tube.  The aluminum prop on it now is 14x23.  The lake here has all sorts of underwater hazards so I would like to stay with an aluminum prop.  

One person mentioned that I may want to go with a 14x21 prop.  

Thanks for any input.

Nowgrn4, as with rpm's, the tach doesn't work.  When the boat is used and as soon as it gets on plane I back off of the throttle.  I drive it to last and do not keep it "pegged".  And you guessed it on staying with an aluminum prop.

Thanks for reminding me alan73.  Yes I installed a hydrofoil (SE Sport 300).  Yes that did help.

Are you running the max rated engine RPM @ WOT with your average amount of weight (peeps,fuel,coolers) now? If not you could definitely reduce pitch. That would help your hole shot.

I assume you want to stick with aluminum because a dinged blade is easier to repair than a bent prop shaft?

would look into installing trim tabs or a hydrofoil, prop change may help a little but probably wont be much of an improvement.

Iirc 2" of prop = 200rpm
1 extra or less blade = 200rpm

If you reach full rpm with your current setup and passenger load then minus 2" and add a blade should do what you want.  Some places have a prop exchange program available.  

I have a 16' deep v fishing boat and lost a prop due to a submerged log in 8' of water.  I went from a 14x16 to a 14x11 but added a blade.  I wanted a slower trolling speed.  The extra blade and "lower gearing" was amazing.  Totally different boat.  But, i lost 8mph on the top end and .3 mps on the low.  Less slip with the 4th blade.

Just for shits and giggles i bought a 14x17 4 blade and now i cant tach out.  I will either buy a 14x15 4 blade or a new ecm for the merc outboard and just add power ( the 75hp is the same as the 90 and 115 with minor changes plus ecm)

Adding the blade is like adding grip. It helps with the hole shot and it grips the water when turning sharp at speed.  It is much less likelly to aerate when trying to see if the person on the tube can hold on while swerving and slingshotting them.  Adding the blade also adds drag which is why they take up rpm.


Michigan wheel makes a decent Al prop for not a ton of cash.  I got the vortex hub system with the 11" and now just buy the prop for around $90, so trying things is cheap and having a spare prop on board isnt a bad idea.

You really need a tach to correctly prop a boat. With that 4.3 you are running a huge risk of detonating the engine. Marine engines are designed to run in a specific RPM range at WOT. If you cannot attain that WOT RPM, the engine lugs and it will detonate and damage the engine. 4.3's are especially vulnerable to detonation.
21ft boat and a 4.3 I would start with a 19 pitch and maybe have to go down to a 17 to get proper WOT RPM.
You NEED  a tach!

<----boat mechanic.

Tabs? Hydrofoil? Meh. Gotta "prop" the boat correctly first. Tabs and 'foils are nothing but a crutch and cause lots of drag.