PROP BLADES

[fishingfool]

I have a 16ft Bayliner with an 85hp motor, theres a 3 blade prop on it now, but i was thinking of upgrading to a four blade for more speed.I need to replace the prop soon anyways.

 

[DJ]

Re: PROP BLADES

fishingfool,<br /><br />Four blades do not generally give you more speed. Four blades are used for greater "hole shot" and to reduce cavitation.<br /><br />To gain more speed you GENERALLY have to go up in pitch. ie; 19" as opposed to 17".<br /><br />However, guessing is not a good idea. You want your engine to run near the top of its RPM range with a lightly loaded boat. If you do not have a tachometer, you will be guessing.

 

[12Footer]

Re: PROP BLADES

Let me start by saying, props is rocket science to me <br /><br />There is so much you must punch-into the eqaution when choosing the proper prop. I would stick with the three blade prop,unless you have access to a wall full of test props.<br />Blade surface area is all the same ,regardless of the number of blades, up to a point of compressabiltity, or the point at which the water cannot be pushed anymore.<br />4,5,6-blade props come into play when the HP,shaft RPM and hull wieghts become non-factors, (as in some multi-engine offshore beasties). In these cases, the hull shape is dictated by the class and by the folks that design them for racing. The engine guys are afterthought,after they have been given hull space for thier engine(s). After that, the engine guys look at thier prop guru, and say, "your turn,mack". The prop he 'tries' is picked from a limitless rack of props. But he picks the ones he has figured will push the hull at it's max speed ,given the weather and water he predicts for the competition....That's all the rocket-science part, and even Mack has leeway with the wallet.<br /><br />On our boats, we are restricted to the ammount of RPM we can subject the motor to. The throttleman's job is to make this judgement underway, and his is a make/break job in the race.<br />My advice is to find the max RPM allowable for your motor, make sure it is tuned and tweeked to perfection, and chose a three blade which will do the same job cheaper.<br /><br />But all that to say it really is a science, one that I admit to knowing very little about.

 

[Hooty]

Re: PROP BLADES

You didn't say which 85hp engine you had so I gotta guess it's a Force. <br />Mercury makes a four bladed prop called a Trophy. I don't have any idea it would help your boat but if you can get your hands on one you can turn 57-5800rpms, give it a try. You may have to diddle around with the "X" dimension but it'll give ya something to do and maybe it'll work for ya.<br /><br />g'luck & c/6<br /><br />Hooty

 

[evin300]

Re: PROP BLADES

What do ya have on it now? SS or Alum? Who made it? What RPMS are you turning with what kind of load in the boat? Do you want to ski and make lots of sharp medium to low speed turns? or is speed your big concern.<br /><br />Hi Hooty

 

[Boatist]

Re: PROP BLADES

Fishing fool<br />I agree with Djohns. 4 blade for better hole shot but less top end. For more speed and fuel mileage get a 3 blade stainless with the higest pitch that will still keep engine in low side of WOT range.