Prop for 16ft with Johnson 115-82

[He rik]

Hi.
(sorry for the spelling and grammar, not english-speaking, hope you understand anyway)

After figuring out most of the issues on the motor I belive its time to get a new prop.
Have reading a little and found out there is a lot to think about (come from roadracing and suspension seems to be a similar subject, lots of ways to get were you want to go) tougt it was more just to buy one like 19 in a material and go.

!6ft long and 420kg/926lb is the boat, now its fitted with a 19 alu, dont know the dia. but know that it was fitted mid -80 when the previous owner bought the motor and hade it mounted so maybe the original one.

Now WOT at 5300/44knot-50mph and the question is if I can benefit from at steel-prop./more blades or just should go for a new 3-blade alu with the same charateristics.

This one got some marks and have hit something in the water, manage to fix it so so but now when I know the rest is ok I want to fit it with a new one.

Have two comprops I bougt in the early 2000 but havent tested now, boat been sitting on land for 15 years, one 19/13 3-blade and a 17/12,8 4-blade, the 19 gave me more rpm (5500 as I remember) but lower speed (40knot) and a lot noisier, the 17 was bougt to been abel to load the boat to create a bigger wake for wakeboarding but only tried ones or so, low speed and a Lot of power as I remember.

Its sligtly overmotorised (if that is possible...) manufactor says it built for 20-70hp and marked 100hp max on typeplate so it goes easily to plane, Ill actually hold back on throttle until its on plane to be "nice" to her and save some more years before material fautigue happens, just lift her up instead of shooting.
Same as I pull skis or wakeboard, its easy to get up anyway


The boat gets a little unstable over 38knot/44mph so faster is unsafe when there are waves, calm water its fine.
But speed is fun, faster is always welcome, just be careful when to use the power.

So, question is, what type prop. do I order, same I know is working or 4-blade steel or something else?

Help me prop. gurus!
Attached some pics of hull, bad ones and can try to do better if necessary.

 

[WesNewell]

I ran my 1983 evinrude 115 on a Kingfisher 15V that weighed 750# dry with either a 21 or 23P ss 3 blade prop. too long ago to remember pitch for sure. Probably a 23P. Hull design similar from what I remember. But I didn't pull any skiers, wake boards or tubes. With your boat, if I were trying to get maximum speed out of it, I'd install a jack plate so I could raise the engine 2 more inches and go with a 3 blade 21P ss prop, max speed would probably be around 55 mph. Otherwise, you seem to be pretty good where you are now. Might try a 21p ss 3 blade for more speed, but you're probably not going to see more than a few mph more.

 

[Texasmark]

You know what you have with what you have. Replacing with like kind is your best/cheapest bet. If money is no issue then start experimenting. SS props are usually high performance and grab more HP/inch of pitch for their attributes. Running the same pitch in a 3 blade SS will lower your rpms and yours are fine where they are. They can perform better in higher speed applications where you do things like jack the engine up on the transom, or using a jack plate, high trim angles used at speeds above 35 or so MPH. Some come with ports (holes under the leading edge of the blade) which allows you to run several inches higher in pitch for dazzling WOT performance, yet push hard in the "hole shot" like your current pitch does.

 

[He rik]

As I tought, a lot to consider...

A fourbladed SS 18 of some sort then?
Or smaller dia but 19 to keep the wot-rpm?

The one I got now hade caviationburns (right word?) before I fixed (built up with PP) and painted it, anything to weight in?

And yes, money is an issue, have some but not enough to "buy and try" so therefore I ask before.

 

[Texasmark]

Would not put a 4 blade on that rig.....not needed and performance can suffer with the 4th blade getting in the water that the other 3 are trying to use for propulsion. 4 and 5 blade (vented) SS props are for getting heavy BBs out of the hole with a big mil to swing them. Diameter for a given series of props to fit a certain diameter gearbox varies as a function of the pitch. To get smaller diameter you might have to change mfgrs/types, or increase pitch in your current model.....here you go playing with the unknown. Besides just pitch, and not addressing the adjustments to the blades to cause that pitch change....progressive pitch, rake, has little meaning in the "thrust" equation....whatever that is.

If your current prop was cupped as are most SS props in doing your repair job, you could have upset the balance of the prop (introduced unwanted vibrations) and reduced the effectiveness of what you may have had in cup resulting in more ventilation at high trim angles....needed to run on your pad, and high transom mounting to reduce the LU drag. Also paper calculations put 1" of additional pitch on cupped props....so you may have lost an inch of pitch.

 

[He rik]

First, I need you to calculate my numbers, I dont think it could be a 19p but Im not sure, rather a 21 and that would explain my comprop experiance with higher rev-lower speed, numbers just dont add up but I cant find any markings on the prop...

I was careful when "fixing" the prop.sprayfiller and grained it down only to fill the holes but its dented in the leading edge, clearly visibel on one blade, and I built up with cemical metal were there was material missing (also leading edge) but trailing edge is mostly untouched and if its cupped it would be on that end, right?

Only "fixed" it to test everything after spent the last 15 years on land untouched before throwing big money on it, started to look for SS and 5-800 felt expensive just to throw away if the motor was scrap and a new alu would be throwing away that money too if SS was better.

Feel good now as I had order wrong prop with the (lack of) knowlegdes I got anyway.


If I had posted a question about this boat and motor but "newly wed", what would your prop.recommendation been?

And, are there any reason to get a SS prop or is it better to just use an alu? (cheaper and works)

SS I maybe need to back off an inch, find out what rake-pitch-cup-bladethickness-dia and recalculate those numbers according to what I now got and still "take a plunge" in the wallet and hope for the best, alu-buy and be happy.

So, if (big if) I "hit the sweet-spot" with SS, do I gain something compared to an alu exept the lower weight of my wallet?

I dropped the 4-blade tougths and come to mind my old merc. 65hp-64 who had a 2-blade prop, are there anyone manufacturing those now or is it 3-blade all over?
Would actually be fun to try.

 

[He rik]

I ran my 1983 evinrude 115 on a Kingfisher 15V that weighed 750# dry with either a 21 or 23P ss 3 blade prop. too long ago to remember pitch for sure. Probably a 23P. Hull design similar from what I remember. But I didn't pull any skiers, wake boards or tubes. With your boat, if I were trying to get maximum speed out of it, I'd install a jack plate so I could raise the engine 2 more inches and go with a 3 blade 21P ss prop, max speed would probably be around 55 mph. Otherwise, you seem to be pretty good where you are now. Might try a 21p ss 3 blade for more speed, but you're probably not going to see more than a few mph more.

Maybe its a 21p alu I got, not shure but I think so.

Your boat weights almoast 200 less so maybe a 20 SS or a 21 for more speed or just a new alu then?

 

[WesNewell]

Should be a number on it somewhere. Maybe back of hub. Aluminum or ss, your choice.

 

[Texasmark]

Turning point Hustler gives you the benefits of a SS in a 100 buck aluminum prop. You can go through 3-4 of those for fine tuning purposes before you hit the cost of a SS. At your speed you probably wouldn't notice the only difference....thinner blades. Weight of the prop is not a consideration in performance numbers....per big guns on here that play with some LARGE-FAST toys.

They sell them right here. If you buy the removable hub TP, you only need to buy the shell *after the first purchase) saving you 35 bucks per prop.....so tweaking is all that much cheaper.

 

[He rik]

Found the markings now on the hub, 13x19, same as my comprop, 13x19,

Seems like comprop 3-bladeprops flex a lot so maybe thats why its such a big difference between them.
And I do have to check up on my actually speed, the numbers dont add up!

Anyway, think I just buy a new alu this season, its almoast over here anyway, so what brands are good ones?

Michigan, solas/rubex seems to be the ones easy to find here, anyone better than the other and what model, or what brand should I look for? Acceleration and speed tops handling.


Will read up on props this winter, probably ask a lot of questions along the way.

 

[He rik]

Turning point Hustler gives you the benefits of a SS in a 100 buck aluminum prop. You can go through 3-4 of those for fine tuning purposes before you hit the cost of a SS. At your speed you probably wouldn't notice the only difference....thinner blades. Weight of the prop is not a consideration in performance numbers....per big guns on here that play with some LARGE-FAST toys.

They sell them right here. If you buy the removable hub TP, you only need to buy the shell *after the first purchase) saving you 35 bucks per prop.....so tweaking is all that much cheaper.

Sorry, posted before I updated so I missed your answer, will check this out, thanks!

I understand its not much to gain for me with my "gear", but its fun!...if the cost isnt to high...

I put a huge amount of time in learning roadracing-suspension but without the practical tests the knowlege is worthless, feel this could be a little of the same, you got to test the theorys!

Thank you!

 

[QBhoy]

Here is what I know and don’t know about this.

So I have a classic Glastron cvx16 Roger Clarke U.K. version. But having spoken to a few guys in the US who have the US version of rbis 16ft boat. Many of them have this very engine on them and swear by the raker prop on that set up.
I don’t know anything about that prop. Never even seen one. But I do know they love them on that v4 and cvx16. But I would add that none of them have as low as a 19” pitch on them. They are all certainly 21” and over even.

I can also tell you with some certainty that you defo don’t want a 4 blade on that boat. You’ll ruin it, if you are at all interested in it performing as it should.

Id watch the rpm you might actually be pulling with a v4 on a 16ft boat and only a 19” prop. I’d suspect you may actually be a little over the rpm you should be.

 

[He rik]

Ok, I try to check the rpm, looking for some meter or tach-gauge now.

But, if the tach-reading is off it would have been so since the mid -80s when the previous owner bought the motor used and had the shop where he bought it set it up.
He had it for about 10 years before us and said he didnt do anything but change gearoil and plugs, maybe been sitting on land some years before we bought it as he had bought a new battery and fixed it up a bit that spring we bought it.

One previous owner on the motor who crasched the LU and the shop who sold it in the first place took it in and sold him a new, changed the LU and then he bougt it and had it fitted, cant verify that story but I belive it, it was in a very good shape, both mecanical and visable, when we bought the boat.

But, if I understand everything right something is off, for starters Ill check the actual speed with gps, just have to find the time and hope for fairly good weather, been windy and rainy here the last days and now work...
The comprop I got behave like I read a 19p would but my alu dont, way to less slip for an 19p alu if the speed is correct (even if I take off 10% speed if the speedometer just is happy)

Didnt think about this before as I belive "if it aint broke, dont fix it" and everything just worked, now the prop is broken so I have to fix it...

 

[Texasmark]

I didn't read anything in your post about your water pump "impeller"...the rubber gear inside the water pump housing, attached to the drive shaft (from the power head to the prop shaft), that pumps water to your powerhead for cooling purposes. Sitting up and aging are bad on those rubber parts and failure could cost you an engine.

 

[He rik]

I didn't read anything in your post about your water pump "impeller"...the rubber gear inside the water pump housing, attached to the drive shaft (from the power head to the prop shaft), that pumps water to your powerhead for cooling purposes. Sitting up and aging are bad on those rubber parts and failure could cost you an engine.

Brand new, housing and all, changed it as soon I new it started (put some fuel in the tank, started it dry at home for a couple of sec. just to see if it started and run) before first time in water.

Changed every fule-line too, and plugs and plug-wires(probably the original ones, still got the lable wich plug to use on it)

And gearoil of course, looked brand new but a little "smelly", had maybe 3-4 hours on it 2005, then we moved and the boat been sitting, new propshaft seals 2004 due to some fishingline cutting the old ones otherwise just as I bought it, just works.

The rest still seems good.

 

[He rik]

Actual speed 47mph but it was a little waves so couldent get a fixed digit from speedo, the pitot lost preassure every wave past 37knot and jumped around so i dont know if the speedo is accurate, seemed fairly correct up to 37, should be around 50mph on calm water on a good day I guess.

This speed with a 19p prop and 10% slip would be 5700rpm at 47mph, right?
Or am I missunderstand anything?

My tach have always read out around 5200-5300 at that speed earlier, today almoast 5500 but it was not steady as it use to be.
Tach behaved erratic at lower rpm,, follow the voltage when getting in and out of gear(voltage 14,5-above 15 and tach raises and drops with it) havent done that earlier but have dissconnected the regulator now for charging reasons and this time I didnt have anything on to regulate, last time I got coolbox and stereo on to hold steady charging under 15V.

Is it the signal or the tach who is the problem with tach readings?
Should I connect the regulator again and see if the tach will act normal (wery low charging but just to test, 13,1V)?

And any suggestions of how to get an fairly accurate tach-reading to compare mine with (really not intrested in buying a fluke...) and a new tach is worthless if the signal is the problem, checked around but cant seem to find anything realistic to buy for at hobby user.

As I understand its step one before buying a new prop, get a accurate tach-reading so I know what pitch to choose...

 

[Texasmark]

I can only comment on Mercury so maybe you can correlate colors:

2 yellow wires are AC input to the rectifier/regulator from the stator under the flywheel for battery charging and tach output.
Full wave bridge rectifier rectifies the AC input producing half sine wave pulses which exit the module on the Grey wire for the tach input with Mercury engines of 1000 year models and some earlier.
Other wires are battery supply, regulated voltage output on the red wires, and black for ground(s) unless the aluminum case is ground and designer chose to not include a safety black wire to ground under a screw.

If you disconnect your rect/regl, you disconnected your tach input. If you tach is erratic, it may be caused by internal friction if analog.

 

[He rik]

Johnson -82 have a rectifier and a regulator, rectifier connected on y-y/w from stator and 12V from battery, regulator connected to y from stator and 12V from ignitionswitch, tach is connected direct to stator y/w.

Troubleshoot says to disconnect regulator if no or low charging, if it charge, replace, I would happily replace but the regulator is out of production so...

But, my tach seems to dislike the unregulated signal from stator or the unstable volt (dont know if tach use 12V for more than light, its a Faria) so here I am.

Have decided to buy an inductive rev/hour gauge and connect the regulator and if they both showe the same its probably correct, have looked at some laser meters too but it seems a little risky to hang over the flywheel to get a reading so I think I skip that....

 

[Texasmark]

ebay has little digital tachs selling for $30 price range. Comes with strips of reflective tape you just put a strip on your flywheel...of any rotating device and point the laser at the strip. Quick, easy, and cheap with digital accuracy.

 

[He rik]

Tested today with rebuilt carbs and a inductiv hour/rev-gauge and between 2700-4400 my tach and the inductive showed aboute the same numbers(hard to say exact), at wot I couldnt leave the wheel and check as I was alone so cant say if it shows the same there too.

WOT at 5500 now and hit 52mph briefly but not certain the rpm is correct.

How is this possible with a 19p alu on?

Even if I hit 6000 it would be to fast with a 19p alu, need to go somewhere close to 6500 to be somewhat normal.... or do I missunderstand something?