need help with prop selection!!!

[flatboy]

Hey guys! I have an 18ft flat bottom with a 92 115 merc.I have a 3 blade 20pitch prop and my boat will not launch like i think it should. When i nail it all it sounds like is winding out and my props not in water.Several people told to run a 4 blade 19 on it.With 3 adults gear and ice chest i can get it up to 52mph before it starts slamming in the front and i still have about 1/4 trim left.I need better trim tabs but i think i need prop?

 

[jevery]

Re: need help with prop selection!!!

Problem with buying props is that you usually can?t return them if they don?t perform as expected. There is Prop Shop in my area that will loan you 3 or 4 props to try before you buy. A dealership might do the same. If you?re near a metro area call around. You do need to know if your 20P prop is allowing the engine to run within the recommended RPM range at wide open throttle before buying another prop. 52 MPH with three adults and gear with a 115 doesn?t sound bad for top end. Is the ?slipping? that you describe occurring at low or high speeds and does it decrease when you trim the motor down?

 

[Irv964]

Re: need help with prop selection!!!

Hey guys! I have an 18ft flat bottom with a 92 115 merc.I have a 3 blade 20pitch prop and my boat will not launch like i think it should. When i nail it all it sounds like is winding out and my props not in water.Several people told to run a 4 blade 19 on it.With 3 adults gear and ice chest i can get it up to 52mph before it starts slamming in the front and i still have about 1/4 trim left.I need better trim tabs but i think i need prop?

Welcome to the site Fatboy, first of all you need to provide a lot more info.
What is the max rpm your motor is rated for? What is the max rpm and speed you are now reaching with a moderate/average load? And also tell us what you mainly use your boat for, heavy loads? Fishing? Water sports?

Mods, I think if a new sticky was added above telling peopl to please provide this info while posting, it would save a lot of members from having to ask all the time? Just a suggestion...........Irv964

 

[steelespike]

Re: need help with prop selection!!!

A given boat setup may not run at full trim for any number of normal reasons.
A "flat bottom"can you be more specific is it a Jon boat?aluminum?Glass?
specifically made for speed.A flat bottom boat usually will tend to get up on the water a scoot.Even so I would say your speed is exceptional.
What kind of prop are you running?Is it in good shape?Aluminum,stainless composite?How is the setup?The antivent plate (just above the prop)even with the bottom is considered a starting point may be able to raise it more.
if you only have venting problems on hole shot it is probably a prop problem and the motor could be higher.A 4 blade can improve low end performance but usually at the cost of top speed.
A stainless prop might solve your problems also certain aluminum props do well the Hustler turning point is one.As suggested;if you could find a dealer to let you try before you buy thats the best way to select a prop.

 

[flatboy]

Re: need help with prop selection!!!

Sorry for the lack of input! First i use my ALUMINUM boat for salt water fishing.I have a quicksilver laser II prop now and its in good shape (not all dinged up) the slipping im talkin bout is only went i try to take off once i get on step i can trim up and run at about 5200rpm before the boat starts to bounce when it does i have to trim down. The boat should run about 5800-5900 rpms. I tried a sting ray II fin on my motor (junk) but pulled it off cause it was throwin water in my boat. Really if i can get bottom and mid range ill be happy to lose alittle top end (runnin 50mph in a flet isnt fun when hit a wave from the side) Thank you guys for the inputs it will get me in the right direction....

 

[flatboy]

Re: need help with prop selection!!!

Hey guys! Thanks to all who gave me some input , but i may have found the problem! I lost or should say burnt the #4 piston on my motor. Im having it rebuilt now.I will repost when its finished.Everything from top to bottom will be new!

 

[Dhadley]

Re: need help with prop selection!!!

Just a note about your fin - the water coming in the boat is a result of the motor being too low. That is somewhat of a typical result of putting a fin on and not adjusting the set up for it. I'm not a huge fan of that brand but the concept is sound. Remember, the fin is a tool that allows you to do other things to improve efficiency. As you noticed, by itself it can decrease efficiency.

 

[steelespike]

Re: need help with prop selection!!!

Hey guys! Thanks to all who gave me some input , but i may have found the problem! I lost or should say burnt the #4 piston on my motor. Im having it rebuilt now.I will repost when its finished.Everything from top to bottom will be new!

OUCH! a motor rebuild.
You may want to look into what might have caused the burnt piston.
possibly running lean. When you get back on the water as Dhadley
suggests check the motor height it appears it may be low.
The anti vent plate (just above the prop)even with the bottom of the boat
is considered a starting point to begin raising the motor.

 

[flatboy]

Re: need help with prop selection!!!

thanks !!several people told me the same thing but werent sure the fin height was supposed to be . I will check it out when i get my boat back. The burnt piston is due to a miss fire seems i had a bad coil and that carb was clogged.