hubless prop or not

[speed5]

hello i have a evenrude 115 v4 motor on a 16 foot larson senza my question is can i put a high performance prop on this motor one without the center tube in the middle or do i have to stick with the original style

 

[DJ]

Re: hubless prop or not

Knowing the year of your engine would be a huge help.<br /><br />Yes you can put a "Non thru hub" prop on. But, those are quite limited in performance. They are, mostly, meant for racing.<br /><br />If you put a non thru hub on an engine designed for a thru hub, you'll get allot of "blow out" on acceleration. THe reason being the exhaust gases will go over the blades, affecting bite.

 

[speed5]

Re: hubless prop or not

the year is 1991 the motor is on a speed boat not really used for racing but i love to get more speed out of it

 

[Dhadley]

Re: hubless prop or not

Tell us more about your set up. Whats the hull like? A straight V or does it have a pad? A step? Is the motor on a jackplate? What prop are you running now? What X dimension? Is it high enough that it has a nosecone / low water pick up? If so, what brand? What (accurate) speed? Top rpm?

 

[speed5]

Re: hubless prop or not

its a shallow vee and the motor is mounted on the back of boat (no jack plate) im running a hustler prop that is 13 1/4 x 17 and tops out about 45 mph at 5300 rpm

 

[imported_Curmudgeon]

Re: hubless prop or not

I think what you'll most likely do is blow up your engine. Two strokes with thru hub depend on tuned back pressure for proper operation. Plug up that big hole and you're asking for trouble.

 

[walleyehed]

Re: hubless prop or not

Over-hub exhaust doesn't plug the hole...the "tuned" back pressure is in the mid section, and the back pressure itself is dependant on the height of the engine...Lower unit exhaust relief is above water on plane on most engines anyway, or at least part of it.

 

[Dhadley]

Re: hubless prop or not

Speed5, something is off a bit. Most likely the speedo if thats what we're going by. With a 17 at those rpm's your top theoritical speed with no slip is about 43. If we can confirm the speed we'll calculate things again.<br /><br />In the meantime, theres acouple of things to think about. I think we can get you going a bit better with what you have by playing with the set up. At 5300 the motor is being lugged and "that aint good". Lets try raising the motor a bit on the transom to see if we gain rpm and speed. Losing drag should increase efficiency. <br /><br />As for an over the hub prop, I dont remember seeing one in a 17 pitch that will fit your gearcase. Also those props like to surface so we'd need to get the motor quite a bit higher. A jackplate, low water pick up nosecone and those type props all kinda go together. OMC made an over hub, round ear prop (Silver Streak) for that gearcase but the smallest was a 23". Trust me, that aint gonna work for you at this point. <br /><br />Lets play with what you have before we spend any of your hard earned $$$.

 

[speed5]

Re: hubless prop or not

the top speed was found by gps and i dont think i can raise the motor out of the water because its mounted to the boat throught the hull the prop is large for its size but been running it for years if so what size prop should i use for this boat would a smaller prop spin faster and make speed that way or should i stick with what i got

 

[lark2004]

Re: hubless prop or not

you should listen to Dhadley. He has been racing boats for longer than some of us have been alive.<br /><br />You can raise the motor, It is only held on to the hull with bolts. You would be wise to get an engine hoist, and use that to take the weight of the motor, then undo the bolts that hold motor on, and raise the motor up one set of holes. then bolt it all up again, and take her for a run on the water. Then report back with what happened.