More prop or lower gear ratio?
 

I just blew up my drive and I'm considering going from a 1.5 to 1.36. I currently run a Bravo 28p but I should be running at least a 30 or 32. At what point does increasing pitch start to become less efficient?

You're going the wrong way ( ratio wise) if you want to be able to run a larger prop with the same amount of power

My question is, should I get a bigger prop or go with a lower ratio? The 1.36 gears are stronger than the 1.5, but what combination gives me the best efficiency? Since the drive has to be rebuilt anyway now is a good time to ask this question. If I go with the 1.36, I can probably stay with the 28, If I go with the 1.5 I will need to step up to a 30 or 32 prop.

Are you under propped ?....if the 28 pitch prop is letting the engine run in the proper rpm range with a 1.5 ratio drive, and you change the drive ratio to 1.36 ( less gear reduction, faster prop shaft speed than the 1.5), you'll need to drop DOWN at least 1 size in pitch to maintain the same engine rpm.

If you are under propped and have about 1000 rpm left over, you could probably go to the 1.36 and use the 28 pitch prop.

Bravo's start to lose their efficiency above 32" pitch

It sounds like what he is saying is he is over his RPM range on 1.5's so he would have to prop up. Instead of propping up he wants to change the ratio to 1.36 instead. It should work, but I have no idea what the difference in RPM would be.

a 28p to a 30p is about 400rpms difference, then 30-32 is about another 400rpms, so you are saying that you could be possibly over spinning 600-800rpms? what are you spinning now and what is your ideal rpm?

It is generally more efficient to spin a large pitch prop slower than a smaller pitch prop faster. I'd keep the 1.5 and step up in pitch as required to match engine max HP rpm.

Intresting I ask this sincerely why do 1/4 mile boats use such small props? One more if I may can a prop go supersonic in water? Ahh why then as one goes up in HP do mfg's go down in ratio???? 375 hp with a 1.98 final?

Ask eddie knox if anybody can he has. (supersonic)