Props, Props, and More Props!!!

Far2hip

Seaman
Joined
Aug 8, 2015
Messages
57
I wanna ask a few questions on props and pitch, but first an explanation of that ridicules avatar I have above my name, lol. The iPad won't let me drag that little white box to choose that part of the picture to show so I have to get to my laptop to fix it later. So for the time being, yes, you are corresponding with a piece of vinyl siding, LMAO!!! Just don't let anyone see your screen and they won't call in for the white jacket just yet. Yet again, you do restore old boats so maybe you're already at that point of legally insane!! This is my first and I am already getting there!!

Back to the topic at hand, props.

I am sure that this topic has been beaten to death many times but I just need to hear it as directed at my specific situation. The boat is a 1964 14' Arkansas Traveler (very cool little old boat) fitted with a 45hp Mercury Classic 50 2 stroke 4cylinder outboard that revs at an optimal WOT range of between 5000 and 5500rpm as per the Merc guidelines. VERY strong motor. This motor originally came off of a 21' pontoon boat and was fitted with an 11" prop with a 9" pitch. On the maiden, maiden voyage (the first maiden doesn't count because the dingaling that I am had the wiring harness positioned through the motor such that it was holding the choke open and I couldn't seem to figure it out until I got it back on the trailer. Moron, lol) the boat JUMPED out of the water and planed off instantly and when to an over rev right away with both me at 225lbs and my brother at about 190lbs. I did some research and arrived at a 10 3/8" x 13" pitch which planed of very quickly as well and gave me 27mph up from 22mph but was also go to an over rev at WOT with a full tank of fuel (6 gals), a full cooler, and just me in the boat. It was sucking fuel like crazy. So, I purchased yet another prop sized at 10" x 16" pitch and with the same load, that prop came up out of the water nicely and planed off relatively quick, used quite a bit less fuel and the GPS speed was primarily around 29 and hitting 30 periodically. There would be moments of sputter at the top end of the revs but nothing that held and it went back to feeling as if it was pushing a load. It's important to mention, I do not have a tach in this boat and the rpms at this point is by feel and what I have heard from the sound and pitch of those vids I have been able to hear of these motors running optimally. I have a pretty good sense of the sensitivities of pushing a motor and can tell when a motor is being pushed. But to be sure I will be getting a tach installed very soon. I just like the naked look of the dash.

So here are the questions:

Do you think it would make sense to go and get another prop going up to say, a 17" pitch and verify that it can take it without dogging the motor at this point? With the 16" pitch it does still plane off quickly enough to not be dogged down in any way so will one more inch make that much difference? The fuel consumption has gone way down but it is still drinking a bit more fuel than what I was told to expect out of this motor on average. Would one more inch of pitch possibly make it hit a sweet spot in that department and increase efficiency of MPG/GPH?? Secondly, does anyone have any experience with a somewhat relative boat size motor set up and feel that that peak of 30mph is what should be expected of this set up with a nominal load on moderate to smooth water conditions on a freshwater river??

Thanks in advance for your help!!!
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
Without a tach you will never know if it's correct. You cannot tell the RPM's by ear or feel, you need a tach and GPS for best results.
 

Far2hip

Seaman
Joined
Aug 8, 2015
Messages
57
I pretty much figured that ondarvr at this point, you are correct. With this much smaller boat than I am used to, I have learned A LOT about how the seemingly smallest detail can make such a huge difference. Do you have any experience with the spark plug wire attached versions of a tach to get the RPMs?? If so, is there a particular brand that is known to be the better of the versions available? Before I go and spend any more money on props, it is surely a better idea to get a tach on this thing somehow. I just don't want to booger up the dash. As I said, I like that naked look it has with that faux wood. Maybe hang one under the dash near my right knee under my switches and DC outlet. But it is now an obvious must.
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
You can use a clamp on timing light/tach combo, or there are $10.00 small Chinese units on ebay, they work OK, they just wrap around the plug wire and can be used only while you're testing.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
I have the kissing cousin of your motor a 1965 Merc 500 50 hp.Without a tach.It is on a 18ft bare bones Crestliner utility all up weight of 1000 lbs.
I know the history of the motor. Allways on this boat It has always run with 11 or 12" pitch apparently preferring the 11.While I have no idea of the actual rpm
I'm sure it doesn't over rev.The boat is noticeably slower than my present bare Crestliner with a 88 50 evinrude.I'm pretty sure our motors have the same gear ratio. 1.64
The bare Crestliner is 330 lbs. dry weight with the all up 1000 lbs I mentioned.
If you tell us the dry weight and aluminum or fiberglass or the model I think we can come up with a weight.
I wouldn't be jumping to a 16 or 17" until you get an accurate rpm.
If we run your numbers through the prop calculator 1.64 ratio,13" prop,guess 12% slip,27 mph we get about 4100 rpm.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,468
Ayuh,.... Google up yerself a Tiny Tach,....
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Or a Hardline Hour/Tach which holds on screen achieved Max Wot Revs, can check revs later by pressing a small pressbutton. Install the tach at front cowl if with available space.

Happy Boating
 

Far2hip

Seaman
Joined
Aug 8, 2015
Messages
57
Thanks everyone!! All the advice is greatly appreciated!!

I am going to give a try to a 4 blade Mercury Spitfire 10.1" x 15". I was able to get my friends timing tach and he calibrated it for what my motor would be doing (pretty elaborate thing but very cool). It showed that at WOT I was right at about 5200 which is dead nuts in the middle of the recommended RPM range with this 16" pitch prop. This motor is SO strong it impresses me each time I go out with it so I think it's worth the extra few bucks to try and see if I can squeak out a little more performance. I have heard many great reviews regarding the Spitfire 4 blade and to match it up with where I am now it would mean dropping pitch by 1". Any opinions on this particular prop??
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Was 5200 middle wot rpm achieved with you alone and bare bone boat ?

Happy Boating
 

Far2hip

Seaman
Joined
Aug 8, 2015
Messages
57
Sea Rider, it was me, my 24lbs dog Maxwell, full 6 gallons of fuel with an extra 5 gallon tank on board, a full cooler, and various small items not collectively exceeding about 30lbs. With the current 16" pitch the boat comes up pretty quickly and at WOT I am right at that 5200. They said to test it with basically what you may have on an average outing. The only thing not on board was the girlfriend at about 130lbs and it seems as though that won't be much of an issue. This motor really pulls strong.
 

Far2hip

Seaman
Joined
Aug 8, 2015
Messages
57
This is why I am thinking that I can find a bit more with that 4 blade 15" pitch Spitfire.
 

Sea Rider

Supreme Mariner
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Sep 20, 2008
Messages
12,345
Post your wot rpm results running a 4 blade 15 pitch to see if equals same 5200 rpm achieved with 3 blade 16 pitch. Maintain same load on deck as on last test to be fair.

Or try againt the 16 pitch prop on a wot spin with you alone and bare bone boat with just 2-3 gallons of fuel, check wot rpm. Try the new 4 blade15 pitch and perform same wot test. If formula is precise should achieve same wot rpm with both props.

Probably 16 & 15 pitch will over rev the engine while being that light ?

Happy Boating
 
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Far2hip

Seaman
Joined
Aug 8, 2015
Messages
57
Sea Rider, today I ordered that Spitfire 4 blade and I will definitely test it in a few different identical scenarios to get some absolutes on performance and efficiency. I am also installing a hard mounted tach so I can keep an eye on the RPM's out past this test with my friends test tach. I did get some numbers with the light load scenario you had suggested and it increased the RPM's about 200 so not out of the recommended range which is very good to see. I am in the right neighborhood. I really cannot wait to give this thing a whirl and see what comes of this. It's a pretty expensive prop for an aluminum, but if it gives all that the reviews and Mercury say, I should get not only great hole shots but also better bite trimmed up and not get any blowouts that I get when it gets a bit rough and I am making a harder turn. That would be VERY sweet!! I will absolutely post my findings in here along with posting another topic so others can see what I found with this Spitfire prop.

I gotta add that, as I said, this motor pulls VERY strong. Even though I was at the middle portion of the recommended RPM's, it just felt like it wanted more prop. Don't know how to explain it but I am sure you know what I mean. Surges that I could feel being snuffed out when the nose stuffed a bit of rough water. It would just bear down and push really hard. Kind felt like there was more than 45hp there, lol. I only have great things to say about the Classic 50 motor.. So my thinking is that if the 4 blades can lift me up a bit in the water on plane, I may get a bit more efficiency out of the motor in the fuel consumption department as well as a few more MPH on the GPS. That would be very nice. :)
 
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Far2hip

Seaman
Joined
Aug 8, 2015
Messages
57
Well that was a bit of a revelation Sea Rider. Loaded exactly the same with the new Spitfire 10.1 x 15" pitch the boat took slightly longer to get up on plane and at one point did get me up to just a hair under 28mph trimmed up for speed which is about 1mph off of what the 3 blade 16" that it was replacing. On top of that, it was lugging the motor and RPM's went down about 400 RPMs. Way too much prop even though it was only one inch below the Vortex 16" that I was replacing. It is going to get swapped out for a 13" pitch version to get me back the RPMs lost and see how much that changes things. On the plus side of things, boy does this prop have some bite! You basically have to trim this sucker out of the water completely for it to blow out!! A few really hard turns showed that this thing REALLY grabs A LOT of water!! And even though the motor was lugging, it still burned a fraction of the fuel the other two Vortex 3 blade props I have tried. Quite perplexing but on with the quest. At some point I will find the right dang prop for this old boat!!
 

littlerayray

Lieutenant
Joined
Feb 17, 2013
Messages
1,456
Good luck hopefully dropping in pitch with the spitfire gets you the results your looking for because I got more then I expected with the spitfire
 

Sea Rider

Supreme Mariner
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Sep 20, 2008
Messages
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Will be interesting just for the record to traduce in rpm your last test.

Wot range for that engine is 5000-5500 rpm, right ?

-You alone with bare bone boat, with 3 blade 16 pitch, rpm was..... ?
-You alone " " " " " 4 blade 15 " " " .......?

Experienced a 400 rpm reduction from which rpm ? now imagine boating as usually loaded...

If understood your post correctly, your blade/pitch experiment didn't match at all, right ? if so, that formula is not spot on for all watercrafts and engines as near rule of thumb stated.

Can you post a pic shot sideways of engine to check upper water deflector plate and lower AV plate configuration ?

Happy Boating
 

Far2hip

Seaman
Joined
Aug 8, 2015
Messages
57
Well Sea Rider, after doing a bit more experimenting and having my brother drive the boat while I was eyeballing where the ventilation plate was positioned while moving at WOT with the 12" pitch Spitfire 4 blade on there, it became absolutely obvious where a major source of the issues where coming from. That whale tail vent plate was under water!!! At 5500rpm (and still going north) that Mercury Classic 50 (45hp) was dragging that damn plate through the water and still getting the top speed up to 26mph on the GPS!!! It came up out of the hole with zero hesitation and was up on plane super quick. That was a pretty good show of what sort of push that 4 cylinder 2-stroker is capable of. This 14' 1964 boat had myself and my brother, both over 220lbs, 2 full 6 gallon fuel tanks, and a full cooler (and some gear to simulate a full load) was pulling like a monster that 12" pitch 4 blade Spitfire. So I wanted to try something being is that I now had the 15" pitch Spifire 4 blade.

I went back to the shop and we raised the motor 2 holes up, left the 12" pitch Spitfire on there, made the same load arrangement, and went back to the river. The results were WOT with some over revving the 5500rpm ceiling at 27mph but a TOTALLY different boat on the water and a dramatic decrease in fuel consumption!! The bite of that Spitfire 4 blade is friggin legendary! Boat turns nicely with no blowout trimmed and steady speed with wake bumps and rougher waters. But for some reason the speed numbers with the 1.83 gear ratio simply don't add up and I am tossing that up to possibly prop slip being it is a pretty heavy little boat. Now was time to try the 15" pitch Spitfire.........

I put on the 15" pitch Spitfire and went back out. HOLY SMOKES!!! That prop grabs A LOT of water!!! With that 15p the boat still came up out of the water very nicely. Not as instantly as the 12p but surprisingly quick with the load in the boat. At WOT it was at 5100rpms trimmed for speed and we were quickly at 27mph on plane and up to 31mph after trimming up. The only issue was periodic blow out and I could see looking over the transom that we were higher in the water and with a bit too much trim the tail was a touch too high and that 4 blade was sucking down water so hard it was pulling air in from the surface. Back to the shop, dropped the motor one hole, and now that thing gets me WOT of 32mph on the GPS at 5200rpm, doesn't blow out even in a hard turn, and rides terrific across the water as well as handles great for a cable steer rig!

This all goes to show that propping a boat is SO extremely particular to your specific set up. But if you do enough refining you CAN find the right combination to suit your needs. You just may end up with a few extra props in your workshop, lol. :)
 
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