prop pitch question

[skully_68]

ok i have a 55 hp evinrude triumph it has a 13x19 prop im guessing it's a 19 pitch prop, can some one tell me if the 19 pitch is a better top end performer, my question is what pitch is better for top end speed and would a stainless prop help with with speed.thanks for any help

 

[jay_merrill]

Re: prop pitch question

Yes, I believe your prop is 19" in pitch. Correct prop pitch for a boat is determined by WOT (wide open throttle) rpm. You must find out what the acceptable WOT range is for your motor. For example, that range for my 1972 65hp Johnson is 4500 to 5500 rpm. You should also check this in your boat with a load that is typical of the way you operate it. If you run light most of the time, check it light, and if you operate the boat heavily loaded most of the time, check it in the same condition.

If the motor exceeds the allowable range at WOT, you are underpitched and need to increase pitch. If the observed rpm is under the bottom of the range, you need to decrease pitch. In each of these cases, you may damage your engine by either over-revving it or lugging it. Generally speaking, each inch of pitch change will give you a 200 rpm change. Usually, however, the rpm range will fall somewhere between the two limits and you just have decide whether or not you want to change props.

I suggest that you surf the web for info on the various types of props and their advantages/disadvantges. There is a lot of information available and you will be able to decide the best course of action for you.

Enjoy your boating!

 

[Lakester]

Re: prop pitch question

ok i have a 55 hp evinrude triumph it has a 13x19 prop im guessing it's a 19 pitch prop, can some one tell me if the 19 pitch is a better top end performer, my question is what pitch is better for top end speed and would a stainless prop help with with speed.thanks for any help

hello,

if you source the oe service manual, it will tell u what prop is standard for your engine and what are the suggested optional props; with size and pitch.

for example, u r running a 13x19 on 55HP. i am running 85HP and my engine uses a 13 1/4" x 17. that is what my engine came with and it is the std prop size for my yr, model and HP.

is your prop the original prop? sounds like it may have been changed. sounds like a lot of prop for 55HP. imo, more of a top end prop if u can pull the rpms. but if it was mine, i would bring in the power gently so as to let the engine breathe well as it spools up. also, if it were mine, i would not put a ss prop on it. the alum is lighter and will enhance throttle response, and be easier on the rotating assemblies, all things considered...

if ur prop has any ruff edges, burrs, etc. i would dress these off. a good fine file will do the job. u want to just kiss off the burrs, and perhaps enhace the balde's edge with gental rounding; perhaps use emory paper 300 grit or so for to sand the rounded edge. not much is needed. minimal metal removal. wont hurt its balance. should run smoother, too.

regards
lakester

 

[Texasmark]

Re: prop pitch question

Ask moderator JB.

Mark

 

[walleyehed]

Re: prop pitch question

Well, first of all, there is no "std" prop listed by the engine manufacturer...the prop was installed by whoever set the boat up.
On that engine, you want to be at the Top of the RPM range because thats where you will see the best over-all performance.
I would never prop it for anything that allows under about 5200-5300RPM, and over-reving won't hurt while it's in gear. The best explanation I can give for that reason, is a quote from one of our race-techs and profesional prop guru's here, Dhadley..."It's nothing but an air-pump....the reeds will begin to flutter before it would ever get to the point of damaging anything if it's in decent shape to start with".
I've tested this theory, many many times..it works, the engine stays cleaner inside and the ones I pull down of customers, I can tell if they were not only under-propped, but if it was run in the upper or middle of the RPM range....The WOT mid-range RPM engines have sticky rings and cyl walls...the engines run at or slightly above max are much cleaner and have much less issues..
And!! As far as Prop Guru's, you have 2 of the best in the industry right here on this site, and many others that have a very good understanding of prop technology.
Iboats also handles great product lines in both aluminum and SS....many choices available right here.

 

[Frank Acampora]

Re: prop pitch question

Unless your engine is grossly incorrectly propped, don't expect too much from a prop change. It is, after all, only a 55. You didn't specify, but if it is on a say 15 foot fiberglass runabout, for example, you might squeak out a couple of mph more, and by playing with engine height a couple more, but that's about it.

Generally, a stainless prop in the same brand, diameter, and pitch will give a couple of hundred RPM more and maybe 2 MPH more than the aluminum, BUT--Is it worth the extra money to you to get that small increase in top speed?

 

[Texasmark]

Re: prop pitch question

I'll agree (too much prop) from what I said earlier about boats of that era. Only one person I knew ran a 19P OMC SS on a 3 cyl OMC engine of from 55 to 65 hp and that was a guy (160#) who fished alone and had a 15' Kingfisher bass boat and didn't water ski, nor carry buddies. The boat was light, had a good flat bottom for hole shot, and he didn't load it up with stuff. Also it ran the boat at around 37-38 mph. I know his speed because I was running a 125 John on a 17' trihull, setup for family and skiing, and I did 39 and I could barely leave him.

I don't know what you have in front of your 55 but it sounds like you are hauling a lot of prop for that engine. Course if your 15' boat is light and fast, no biggie.

My 2c.

Mark