cup a prop??

[buggiedad_67]

hey guys me again, may not be in the right place for this but here goes,i need more hole shot with my boat but dont want a new prop, i can pull my son who is 6 ft 5 and 285 lbs on a tube just fine, she will jump out of the hole and runs great, but if i put two tubes and 400 lbs it is real slow comeing getting out of the hole, some one told me i could recup my prop and do better than a new prop, if case you have forgot i have a merc 120 i/o alpa 1 , its in a 84 152 tempest glasstream, running 15x17 prop (cast)so if i what is recuping and how do i do it.

 

[JCF350]

Re: cup a prop??

Methinks you really need more engine. Your at about the power limit for that package with one person and past it with 2 peoples.

 

[bruceb58]

Re: cup a prop??

hey guys me again, may not be in the right place for this but here goes,i need more hole shot with my boat but dont want a new prop, i can pull my son who is 6 ft 5 and 285 lbs on a tube just fine, she will jump out of the hole and runs great, but if i put two tubes and 400 lbs it is real slow comeing getting out of the hole, some one told me i could recup my prop and do better than a new prop, if case you have forgot i have a merc 120 i/o alpa 1 , its in a 84 152 tempest glasstream, running 15x17 prop (cast)so if i what is recuping and how do i do it.

Cupping your prop is going to hurt more than help. It essentially is adding more pitch to the trailing edge of your prop. You probably need to drop pitch.

What is your WOT RPM?

 

[buggiedad_67]

Re: cup a prop??

Methinks you really need more engine. Your at about the power limit for that package with one person and past it with 2 peoples.

the boat is 15.5 feet and only carrying two people inside it pulls two fine once you get it to plane, once on plane 3200 rpm will give them a good ride, am only talking about a extra 50 ydrs so,

 

[buggiedad_67]

Re: cup a prop??

Cupping your prop is going to hurt more than help. It essentially is adding more pitch to the trailing edge of your prop. You probably need to drop pitch. i guess i should add that the engine is not stock, i know it has 30 over pistons, and i was told last night from the i guy i bought it from said the cam was from a 130 hp or 140 he wasnt sure, however the guy has lied to me before so i dont take much stock in what he says, i do knopw the pistons are 30 over because i had the head off

What is your WOT RPM?[/
rpm for engine is 4300 and it runs 4200 now,

 

[JustJason]

Re: cup a prop??

your asking to much of your boat/engine... If anything you need a seperate prop for heavy duty towing. Cupping is going to hurt not help. A 15x13 should get you where you want to be... for towing only. If you run it without towing the motor will over rev, you so would have to manually keep it in the range... Or change props for non tow days. It's easy enough to do.

 

[Don S]

Re: cup a prop??

Moving to Prop forum.

 

[rndn]

Re: cup a prop??

I would strongly suggest going to a four or even a five blade prop. It made a world of difference to my stern heavy Baja I used to have. When I had more than just the wife and I on the boat I used to have to ask people to stand up and come toward the front of the boat so I could get the thing to plane. The only change I made is I went to a four blade SS stiletto prop from a three blade aluminum prop and honestly the thing would launch out of the water afterwards. I never had to ask people to get off the back seat to get the boat on plane. I'm sure that smart tabs would have helped as well, but I just didn't need them afterwards.

 

[steelespike]

Re: cup a prop??

What is your max rpm and speed one aboard.Can't make any reccomendations without this info.The I/O in general has some difficulty with hole shot.15.5 ft doesn't seem too big for 120 hp.Trim tabs will help something like smart tabs are easy to install and reasonable.With your specs we can tell you if a prop change will help and the approximate results.It is possible the tabs alone will help.

 

[JCF350]

Re: cup a prop??

the boat is 15.5 feet and only carrying two people inside it pulls two fine once you get it to plane, once on plane 3200 rpm will give them a good ride, am only talking about a extra 50 ydrs so,

Get a prop with less pitch for the tubing. 0.030 over bored is not gonna give anything (might could tell on a dyno). If you had a 120 hp outboard you would be okay but the extra weight of the sterndrive package makes a big difference.

 

[buggiedad_67]

Re: cup a prop??

What is your max rpm and speed one aboard.Can't make any reccomendations without this info.The I/O in general has some difficulty with hole shot.15.5 ft doesn't seem too big for 120 hp.Trim tabs will help something like smart tabs are easy to install and reasonable.With your specs we can tell you if a prop change will help and the approximate results.It is possible the tabs alone will help.

the says 4300 its running 4200 with a 15x17 prop, if i changed to a four blade how would i tell which prop i need

 

[buggiedad_67]

Re: cup a prop??

What is your max rpm and speed one aboard.Can't make any reccomendations without this info.The I/O in general has some difficulty with hole shot.15.5 ft doesn't seem too big for 120 hp.Trim tabs will help something like smart tabs are easy to install and reasonable.With your specs we can tell you if a prop change will help and the approximate results.It is possible the tabs alone will help.

the book says 4300 it runs 4200 with 15x17

 

[JCF350]

Re: cup a prop??

Oops!!

 

[robjen1019]

Re: cup a prop??

Ive got an old mercruiser with a 110 hp i/o on a 16ft boat. I have a 15in x 17 pitch prop that is great for cruising and will pull one tube ok, but when I go skiing with adults I take out my 13 pitch cupped prop, and boy o boy can I jerk someone out of the water. Last year I pulled a 250 lb guy out of the water on a slolom ski. I have to watch the rpms on the topside, but the boat will jump out of the water and turn without losing rpm's.



I only use the prop for skiing and tubing. best 100 I have spent for that boat.