question about setting up my boat

[settle1]

hey guys i have a question about my 99 nitro 882 with a 175 merc 25 pitch trophy prop....my boat runs around 70 with speedo not sure gps but it is slow to plane and with 2 people and full live wells it may take 100 yards to plane and once it gets there its hard to keep it on plane under 30mph.....i tried lowering the motor and it may have helped a little.....but not enough.....i bought the boat used and you can see were someone has been messing with the jackplate....when someone says the prop shaft should be 3 inches below the pad what is considered the pad? is it the very lowest point of the bottom center of the boat? and what is the best method to measure this use a level or something.....thanks for any help....also my rpms are around 5200

[cart7t]

Yep, lowest part on center of the bottom of the boat.  You can use a Drywall t-square or any long straight object to measure with.  Lay it on the very bottom of the pad so it extends out to the engine. The engine should be trimmed to a 90 degree angle of the measure. You'll measure the distance from the top of the cavitation plate (that flat plate just above the prop) to the ruler or measure you're using.

Does your Trophy have the vent holes with plugs in them?  If it does you may want to try removing some of those plugs, that low RPM doesn't seem right, sounds like the prop needs to be freed up.

[fireandice]

Don't get me wrong, I think the measurements are important, but with your low rpm and your crappy hole-shot, I'd say you need to just free up that prop and then see where you end up.  Find the recommended cruising rpm for your motor and try to hit that.  When we say free up the prop, what we mean is that you need to step down in pitch.  If your boat has a 26p, then step to a 24 or 25, etc.  The props dimensions are written on the hub area if you look forward into your prop from the back of the boat.  You may have to experiment to find a pitch that works well for your setup, but it sounds like you could go down in pitch, because you don't need to go 70mph, and in the meantime you're going to dramatically improve your hole-shot and planing.  Just be careful not to exceed the engine manufacturers recommended rpm.  

[ernel]

One way to check the measurement below pad is simple. All that is needed is a level, tape measure, and a level spot in the driveway. Place the level on the pad, and raise or lower the tounge on the trailer until the pad reads level. Next place the level on the cavitation plate and trim the motor up or down untill the cavitation plate reads level. Measure the distance from the ground to the bottom of the pad. Then measure from the ground to the center of the prop shaft. Subtract the prop shaft distance from the pad distance and this is your distance below or above pad.

Before buying new prop, I would try the PVS plugs first if the prop has them. If you do not have the plugs to replace the ones that are in the prop, they are not expensive to buy from the dealer. It almost sounds like you could remove all of them to begin with anyway. If the prop does not have the vent holes, you can have them added by a good prop shop for around 40-60 bucks.

[Way2slow]

Vent holes should have no affect on WOT rpm.  If the motor is only turning 5,200 rpm, you have a problem.  This could be in the form of the motor being over prop'd (too much pitch), the prop has blade/s rolled, or the motor is down on power, could be as simple as throttle cable out of adjustment and not opening the throttle plates fully.

For some reason, many people think if they go to a bigger prop, they will get more speed, but usually the reverse happens.   My first check would be to get on some web sites and ask others with your same outfit, what pitch prop they are running and what their WOT rpm is.    If several say they're running the same motor, hull and prop and turning close max rpm, then I would suspect a bad prop or weak motor.  If they're turning a smaller pitch to get the rpm, then you will need to also

[fireandice]

Very good points 2slow.  I hadn't even thought about a misadjusted throttle cable or linkage, or timing for that matter.  It would be a good idea to make sure the motor is sound and tuned properly before spending $350 on a new prop.  Good info.

[settle1]

good info guys my prop is the trophy plus with the vent holes....2 are in and2 are out....i have checked and found guys with the exact same rig with the same prop....and i have checked the throttle cable its ok....im preety sure my engine is set to low...it has marks were it was set at one time maybe from the factory and someone lowered it before i bought it and then i tried lowering it somemore to see if it helped with my hole shot.....could the motor being to low hurt the hole shot also?i raised it up today just a little above the what looks like factory settings but havent tried it out yet...thanks for the tips on measuring the distance i wasnt sure on how to go about that...im going to do that before i take it out this week...

[fireandice]

The motor being too low could hurt your performance somewhat especially if your cavitation plate is riding below the waterline.  If your throttle cable, linkages, timing are all correct, then I'd be back to looking at the prop perhaps.  Did you notice when looking at the boat like yours if the prop was the same size?  How about the amount of weight in the boat, etc. ?  Did you question the owners to see how their boats performed, avg. rpm, etc?

I think if I were you, I'd adjust the jackplate to the preset height if you can tell what that is, take it out and try it.  If your boat chine walks, or the roost is above the cowl of your outboard, then your motor is proabably riding too high.  Adjust it down a couple notches and hit it agian.  Take the tools to the lake to do this and see if you can get it fine tuned with passenger, gear, and such.

[cravenfish]

With 2 men, livewells full and plenty of gas in the boat its not going to pull but so good of a hole shot. Check your motor and see what RPM's you should be running, then go from there. Aloso check and see what prop they recomend you run.

[settle1]

well i raised my engine up to prop shaft 3 inches below pad and went out this evening...the boat had a great hole shot it comes up with ease with live wells full and it got my rpms up but it chine walks like crazy now and i could never find a comfortable ride at high speeds also i have alot of torque steer now just about any were i trim it....i think now that my prop might just still be biting to much and i can really fill it with the engine raised....im gonna try to remove the other 2 plugs in the prop and also maybe borrow a 24 pitch and see what happens.......craven i know it will be slower to  plane with the added wieght but this thing was taking 100 yards or better it was sad

[fireandice]

Sounds much better already.  I think even before trying that 24p. I'd drop it back down about 1/2"-1" and try it then.  My buddies new Champion did the same thing until we lowered it back down a little.  You'll still be in good position to plane and get good speed, but chine walk can be very dangerous.  Did you happen to look back at your roost?  It was probably above the motor.  It shouldn't ever be higher than the top of the outboard.  You should also be able to trim it back down when the chine walk kicks in.  I know it slows it down a bit, but it's much safer to have more boat in the water and be more stable.

[settle1]

yea i looked back and it was probably just below the cowl or even.......yea i thought about lowering it back down a bit and pulling the other 2 plugs from the prop.....i just hope i can get rid of that torque steer....i know ive just got to find that sweet spot...i dont mind sacrificing some speed for a better hole shot as long as its stable at high speeds