3 blade feels like its gonna kill me

[no_manatees]

i just bought my 18.5 shockwave tunnel a few months ago and its running a 2.4 bridgeport and came with a 23 pitch high5 thats been cupped. i was wanting more speed so i bought a 28 pitch turbo stainless prop off ebay and went to run it yesterday and at 65-70 mph the boat actually kicked to the right pretty hard so i got out of it and tried a run back across the lake and same thing so i eased out of it and ran it up slowly through the speed it was doing it at and got through it and it seemed ok but started jerking all over the place bad enough for me to get out of it and load up the boat and go home. is this from prop too high? or some other reason?
is it a problem in setup going from a high5 to a 3 blade?

[staylor]

...which is odd since the Hi-5 is fairly small diameter, and most Turbos would be something like 3/4 to 1 inch larger in diameter. Thus, I don't think it's the height. The key may be in the prop's cup- look at the Turbo and see if the tip of the cup is rounded, not sharp. Turbo's are electropolished at their factory and usually have the sharp edge of the cup etched away to a rounded edge. This alone can be the problem- and a good prop shop could fix it.

Three other factors come into play. One is that the more blades you have, the better the boat will handle, and Hi-5s are known to be a very smooth, good handling prop- although not often used on performance boats. The second factor is the the Turbo probably has a much higher rake angle than the Hi-5, rake angle being how the blades angle back when viewed from the side. High rake gives bow lift- and tunnel hulls are very sensitive to how much bow lift they have- too much and they have weird handling. Lastly, you don't say exactly what Turbo you bought. Turbo is a very old company and has built many different prop designs over the years. Some may look great, but are not very good performance props.

I'd suggest you borrow another 3 blade to try, preferably a Merc Tempest- also a high rake prop, but one with very good cupping. If this acts up also then it's probably the high rake angle- or the 3 blades- that your rig doesn't like. If you do a search on propeller pitch blocks on Google, a company called Rundquist comes up. Go to their site and look at their pitch block catalog- it lists rake angle for most all well known props. Pick another prop in 3 or 4 blades with about the same rake angle as the Hi-5 and find one to borrow.

A wild card is to borrow what's called a "flats boat prop" from a fisherman. These props have low rake, and usually top out at about 23 pitch.
Doug

[rchevelle71]

Yup, 4 blade, probably trohy plus would be the way to go. We run a 600+ HP Big Block in the 24 Pantera raceboat with a 3 blade, and it leans to the left like mad, but gets up to the limiter quick coming out of turns.

[CLIMATEMASTER]

Most tunnels like to run pretty flat. With slight lift. Depends on how heavy your boat is. Try to track down somone with a boat like yours and ask what works for them.

True the more blades the smoother, and quicker hole shot for a given pitch. If speed is what your after a 3 blade will be it.

I run a vast array of props for my tunnel but unrigged it wieghs about 450lbs. I change props for holeshot, solo, 2 person, 2 person with a full cooler and 3-4 people.

Also you need to know you gear ratio.

Some boats will experience prop blow out at high speed, high propshaft height, and high trim. Blow out may cause the boat to slow rapidly and pull very hard to one direction or the other.

Good luck

[stokernick]

sounds like blowout to me,engine too high!??

[Juggernaut]

sounds like blowout to me,engine too high!??yep..

[no_manatees]

first thing there is noone within 500 miles with anything like this. so im on my own here . ive read alot of things on here that have already helped me out so thats why i joined. i am adding very minimal trim just enough to get the front end to stop digging down and it just starts to fly then WHAM it kicks to the right. almost enough to throw me out the first time it did it. i'm on the second holes from the bottom of the mount on the motor on an 8" setback plate so only one more set to move up till its topped out. should i try to move it to the bottom holes to bury the prop a bit? oh ya its a 14.25 x 28 turbo ss anchor staylor

[no_manatees]

possibly not blowout it still gains speed after it does it

[no_manatees]

wheeliejones has a 26p clever will that be worse or better than my turdbo 28?

[Juggernaut]

cleaver props are designed for surface drive. i dont have much (any) experience with then, so i dont know. but by the way you're describing this "hook", its sounding like blow out to me. a friend of mine has a 16 baja with a worked 135 merc putin out about 150 horses, and spinnin a 25 chopper i think. i took it for a ride, and jacked the plate up about 2 inches from all the way down, and at 62 mph, it hooked hard to the right, and threw me out of the drivers seat and across the boat it was soo severe. scared the $h!t outta me the 1st time it did it. once i put the jack plate 1/2 inch lower, no problems.
i imagine the mopre pitch you run, the worse blowout will be. im not quite sure though.. good luck!

[BAJA SS]

looking for a little help, i have a stock 115 merc on my 16 foot baja ss, it tops out around 50 and gets there really quick, i am trying to get the most out of top end that i can. what would you recommend for the best prop. Motor is 86 115 merc outboard, boat is 16 ft baja, currently running a 13" with a 21p stainless 3 blade
thanks,
greg

[staylor]

..I ran a Baja 184 SS with a 140 years back and it ran best w/ a 3 blade small hubbed Raker- the small Raker which is very similar to a Merc Laser in blade shape and rake angle. This boat ran fastest with the old OMC V-4 chopper, but took a while to plane. I don't know if they make a small hub Laser to fit your lower unit, but several manufacturers offer similar props- and this may well be what you've got now. Baja's seem to like a lot of blade rake angle. Another "wildcard" for your rig is a Merc Trophy-Plus or the similar Turbo 2+2 OT- these are small hub 4 blade V-6 props that should your lower unit OK, but you may have to go to a flat plate to replace your trim tab- about $20. at the dealer. Have you checked your rpm at top end to see if you just need more pitch? Reason I ask is that I was just setting up a 19 ft aluminum fishing boat with a 115 Merc, about a 2000 model, and this beast with full livewells was turning max rpm with a 19 inch pitch aluminum in 13 inch diameter. We gained 4 mph with a Turbo 2+2 OT in 20 pitch, but rpm was down to the low end of the suggested range from Merc.
Doug