I've got a 1985 21' Scarab with 350 chevy and alpha I drive. It has gone a best of 59 mph (on gps) at 4500rpms. At top speed I have to run the boat almost level and use hardly any trim out or the boat will start to porpoise. I had the blades cupped a little more on my Turbo 3-blade 14 1/4" x 22P prop, but that didn't help at all. Even at slower speeds I can trim the drive out a little and it will start to porpoise unless I tuck the drive in and run the hull flat. The prop should have enought lift to get the bow out of the water. I've got a set of Bennett tab on the boat, but I havn't got them working, the pump went bad and I need to order a new one. It seems to help if I turn either left or right right as the bouncing starts, and if I keep triming the drive out I can get the bow to lift pretty well but as soon as I hit a small wake it starts again. Is that just the nature of the hull, or am I doing something wrong?

I have seen this problem on a few 21 Scarab's.
Your speed seams about right my buddy has a similar set up running a 19 pitch laser that was sent out and labbed, 350 270hp. He has tried many other 3 blades from 19 to 23 with no luck.

He is running about 55 on GPS 4700 rpm I may be a little off on RPM it has been a while.

He to has a bad porpising problem. Really bad in sticky water.

Here are a few Ideas to kick around.

Try running a four blade maybe a Bravo.

A stand off box.

That stern jack from Land and Sea might be cost effective used.

More power and bigger tabs.

If all else fails go with a 24 Skater with twin 2.5's

Just kidding with you on the Skater, but I know where your coming from.

Good Luck

Nobudget!!

Have you checked the bottom of you boat for a hook? Take a straight edge about three foot long, put it up against the bottom of the boat from the transom forward , keep checking to as you move it toward the outside of the boat. you should not see a space between the straight egde and the bottom of the boat more than a 1/16. If you have larger gaps you have developed a hook. This will cause porposing . The bottom can be correct by any"" good """ fiberglass boat repair business. Check references. Basically you will be blue printing the bottom

I have the exact same problem with a Formula 20 Sc. 24" turbo, 330 hp/5.7. Someone told me that a cleaver prop may help, I will find out this weekend. I have a 23" cleaver that I am going to try.

What size 4-blade would be comparable to my 3-bladed 14 1/4 x 22 P Turbo prop? Should I drop down 1 or 2 pitches and keep the dia. the same? Will the 4-blade give me more lift and top speed?

I have a 18 foot Scarab Sprint that I put a 350 Chevy in place of the old 4cyl and it had a terrible porpoise. I use a high rake clever style prop. I could trim out all the way and the boat was balanced very well. The round ear props generate a lot of bow lift. The clever generates no bow lift. Four blade props made the problem worse.

Try to find several different style clever props. Someone stole my good clever last year and I tried another one it it doesn't work worth crap. So try several different clevers.

I moved the battery as far forward as possible and I can now run a round ear prop with some success, but still not as stable as it was with a good clever.

good luck try lots of differnet props

mike

fist thing id look at is the bottom................

i bet it has a slight hook.............

gotta get that out first..........get a long straight edge like blackhawk says.............you'll be surprised what you see.........


good luck

ez

I would play around with Props some and see if that takes care of it. Also as has been noted check the running surface to see. Now if there is a hook DO NOT assume immediatly that there is a problem. Some boats put it in there for a reason. So then call them up and find out if it is sapposed to be there.

Jon

Like Audio says, I remember reading a thread on here about a guy that removed the hook from I think a 240 Baha sport only to find it ruined the handling of the boat. He was then trying to figure out how to put it back in. I would either add power to support the bow lift or try prop changes.

BT

I'm with Jon, My 211 Liberator has a pretty pronounced hook and I was told pretty emphatically "Don't Remove". I am going to goof around a bit with it this summer, but as Jon said be very careful as allot of these were put in by the Manufacturer. Try the props first.

Les