what is the difference between a longtail prop and a surface drive prop? what makes the prop stay in the water... or how can I create more downforce? I have a prop that I got new from glen hopkins last year but when I ran it you cant hold it in the water, or it tries to surface and blows out. same thing happens with a big surface drive prop I tried. just wondering what the difference is and what makes it surface rather than dig down in the water. I just shipped him my original prop and the one I bought from him and I know he'll fix it up but just for my info what's wrong here?

How about entering this.....http://www.mercurymarine.com/propellers/

into this

http://www.googleisyourfriend.com/

any legit answers? put one on a 100mph+ bass boat and I know what I'm talkin about. I thought yall knew the answers. I guess not. maybe somebody who actually knows will make a post.

I had a 31 godevil long tail. I tried a 11x10 surface drive prop on it. It dropped my speed by 3mph and my rpms by 400. But I had no problem keeping it in the water.

The main difference is the amount of pitch it has. Since it runs half out of the water, it can have twice the pitch of a long tail prop.

Well not much info on that big ole Preditor longtail has been posted....

But - on the average 25 hp LT - the big difference is that there is
no reduction gearing so a smaller diameter lower pitch prop is used - where
a SD has a 1.2 to a 1.4 gear reduction and a much larger higher pitched
prop is used....

As far as lift - even the smaller LT props will develop lift - but the bigger
SD props develop even more lift - but lift more as they wear out and as
your RPMs go higher and higher....

My LT devoloped max speed when "surfacing" the prop - but you have
to expend a lot of energy holding it in the "sweet spot" so that tactic
is only good for short bursts of speed across shallows....

No factual idea on how to fix your blowout - but possibly stay with the
more rounded prop designs - consider a set of "lower fins" similar to the
GDSD design which hold the prop at a predetermined depth and angle
of attack....

you cant hold my motor in a sweet spot. it goes where it wants to. it has a stop on the way down then it finds its own sweet spot. I dont have any trouble turning the higher pitches, just wonder what cupping where makes it want to surface.

have you asked glen about it? that guy really knows his chit and could prolly tell you right off the bat.

yeah he made me a prop last year for it and he should have it back at his shop tomorrow. I sent that one and one that works good back to him. he'll tell me when he sees what my problem is- I was just wondering for my own info (I dont like to bother him too much. hes a busy dude) hes a legend in the prop industry- kinda like the hero of every go fast boat guy. he's the best there is at designing props and casting techniques.

Yeah he made me a prop for my baja i had. i called him with the weight, hp, and current rpm and speed and he spouted off numbers for size/pitch right off the top his head, i love it knowing somebody who really knows what the hell theyre talkin bout

yeah you get into an outboard (or I/O in your case) and whatever prop you got he probably designed.

It might be ur transom height which would put the shaft at the wrong angle. I know the props on a gd longtail aren't what keeps the prop in the water, it's the cav plate that is bent up that creates a downward force on the motor. I don't know anything about the predator but there might be something u could bend up to create the downward force or add something to make the effect.