Size my prop

[clemsonfor]

Ok here is an easy one, hopefully. Since i do not know with out looking, and im not near the boat, i will not give the current size allthough its a 4 blade prop is all i can remember now.

I have a 1990 javeln 378 (i think are the #s) fish and ski, with a 1990 johnson GT 150. It has the windshield and 2 swivel chairs and a row of 3 seats behind them. Its rated for 5 people, we have 4 adults often in it. With just me it will only turn a touch of 5k so i know its not turning up all the way, due to being overpropped. The motor runs smooth and lickages and butterflies open all the way ans the timing advances all the way. In my opinion the motor is capable of producing the rpms if propped correctly. Im looking at ebay to buy a stainless raker 3 blade prop, thinking like 13.5 x 21 is this still too high

 

[steelespike]

Re: Size my prop

What is a Javelin 378? I wouldn't hazard a guess on the prop size.Especia;lly if your buying ss.If the old prop is aluminum that would be a further complication.
Going from a 4 to a 3 is another complication.Really need the rpm and speed to tell if the setup appears to be working.It does seem that a 21 would be a step down
depending on what the 378 is.But a step down friom what; we don't know if your present prop is allready a step down.

 

[clemsonfor]

Re: Size my prop

Oops Mind is fater than the hands, i though i wrote the size in here. It a 17 foot Fish and ski v-hull. The current SS prop with just me, motor turning 5200 according to tach, trimmed up right, will go between 50-55 mph. fast yes but its slow out of the hole with 4 people and dosent this motor need to be 5500-6000 WOT with a light load in it (ie. me)?

 

[steelespike]

Re: Size my prop

Yes it needs to be at least 5,500.Get your prop size and go from there.
If you have ss then stick with it for a little more predictable results.
Same brand if possible. 1" pitch change = "about" 200 rpm.and will improve hole shot.I can't tell you what props have bow lift but bow lift will delay hole shot
but help to get the boat out of the water for more speed.

 

[clemsonfor]

Re: Size my prop

OK sorry this took so long i forgot to post first of the week.

My prop is a 4 blade OMC "shooter" 13.5 x 23, 4 blade.

So from what your saying going to a 13.5 x 23, 3 blade would put me around 5500RPM and dropping to a 13.5 x 21 will get me around 5700 WOT. Putting me right in the range i want to be in.

 

[steelespike]

Re: Size my prop

The four blade will tend to have a lower top end rpm and speed compared to a 3 blade.But usually will improve hole shot.Yes going to a 3 blade should improve max rpm and speed but not likely to improve hole shot.A 21" should help your hole shot.
Can't really be too specific about rpm;but yes going from a 23 4bld. to a 21 3 blade could add 400 to 500 rpm.

 

[sethjon]

Re: Size my prop

Can't tell without knowing what you have now and until you do, don't even think about buying a new one.

 

[clemsonfor]

Re: Size my prop

read post #5, i tell what size prop i had on my boat.