SS prop confusion!!!

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Permalink Reply by jon sarakas on September 6, 2009 at 12:45pm

Hey crash I had the same problem... I had a 19 pitch i replaced it with a 21 and my Engine was working to hard so i went to a prop specialist and i told him what i did he told me i went backwards i bought a 15 pitch and WOW what a difference when you run full throttle you should tact at 4800/ 5200 no less no more....

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Permalink Reply by Crash Coleman on September 6, 2009 at 10:39pm

Thanks for the info. I thought I would have to go down in pitch from what I have read but I was getting conflicting info from various shops and people. Was the prop specialist local? At top end the engine currently runs 5800/6200 rpm. and it is hard to get on plane and keep it on plane in the 25/35 mph range. I thought it was a fuel/filter/pressure problem and had that checked. They said it was all good but that 1 bank off plugs had fowled out. Never heard of one side fowling, but then again I'm new to this and learning. Took it out and still runs the same. The plaining thing is driving me crazy. The mechanic said the new SS prop should help with that but don't know.

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Permalink Reply by Henry on September 6, 2009 at 2:16pm

There are many variables that must be considered. Knowing what performance you have with your
current prop is a good way to start. Stainless will have less drag and flex, but the basic performance
will still be relative to the spec's of the prop. If 19" pitch is working well now, that is a good area
to start. If you are finding that you are limited in throttle, and you are sure it's not the motor, fuel, etc,
then less pitch is in order, wheras easily reaching WOT means more pitch is in order. All of this is
based on what your boat is doing now. Do a benchmark test, and record the figures, such as max RPM
at WOT, time to max RPM, Time to plane. Make sure the boats loading is known (amount of fuel, number
of people, etc,). Ideally you want to do the test with the boat loaded as you would normally use it. Making
a prop change now allows you to compare the difference to a known standard, and see what kind of
difference it really made. 3 blade vs 4 blade also makes a difference in top end vs bottom end performance.
You can go to the Yamaha website and get some test with various boats and engine combinations and see
the performance with the prop they used, and compare it to yours (they go back as far as 2000 motors).

Henry
Wile E Coyote

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Permalink Reply by Crash Coleman on September 6, 2009 at 11:16pm

Thanks for the help and info Henry. Some of it is a little technical (still learning this stuff, trying to be a sponge) but I had done some of the things you suggested prior to posting my question. I filled the boat to about 3/4 of a tank, loaded fishing gear, coolers w/ ice and in fish boxes, and had 2 of my friends come out with me. The 1st few times we could not get the boat on plane. I had to try numerous ways of throttling up and finally got it on plane. Ran good at top end at 5800/6300 rpms at 44/46 mph. But once I would slow down to 35/37 mph it would loose plane. I thought I had a fuel/filter/pressure problem. I got the boat in May and had only been run about 1 or 2 times a month by the previous owner. I thought the E10 had got me. The original owner said he used Stabil to help prevent this. Anyway, then it just wouldn't get on plane. Loaded the boat up and took it to have it checked and repaired if neccesary. They checked the fuel in the tank,lines, and pumps. All good. Pressure and filters were good. Did get some good news. The motor is a 03 and only had 74 hrs on it. What he did find was one bank of plugs was fouled out, but doesn't know why. Any ideas? Replaced all plugs and tried again. Gets on plane better but doesn't like mid range. Would prop help this? thanks for any help.

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Permalink Reply by Henry on September 7, 2009 at 10:22am

Pitch is the theorecical thrust or forward movement of the prop through the water, not counting
slipage. A greater pitch will provide more forward movement at a given RPM than a lesser pitch
prop would, similar to a car running in 4th gear vs 3rd, at the same RPM. This does however
require the power behind the prop to match the pitch vs load so as to allow the performance
goals to be met. A lesser pitch prop is like pulling it into a lower gear. You will have more power
throught the range, but could max out on RPM before your intended top speed. Also by going
too low on pitch and being forced to run at higher RPM's economy, and engine durability would
be compromised. You can figure up to a couple hundred RPM's gained per inch of decreased.
Your situation is a little strange in that you seem to be "plowing" until you are up on a plane,
then you can get good RPM's. Are you running trim tabs? Have you tried different engine tilt
angles to sustain a low speed plane? is the motor "bogging down" when it starts dropping out
of plane, or maintaining RPM's? Also is your current prop 3 balde or 4? A SS prop with a given
pitch and diameter will have similar performance as the stainless. The stainless has a little less
flex under heavy load than aluminum, a little less drag, and more durability. If any flex is occuring
it would not be very notivable, but would actually help your situation. Is this the motor that was
origonally on the boat? There are multiple bolt holes on the mounting plate for the motor, and if the cavitation plate of the motor is above the keel, performance could be lost also. If the boat is plowing
in the water at your mid RPM range, it may be more of a trim tab, or motor trim issue.

Henry
Wile E. Coyote

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Permalink Reply by Larry Mac & Ernie on September 11, 2009 at 5:20am

Before tweaking the prop pitch/diameter, address the issue of getting-up and staying on-plane. I have used the Sting Ray XP hydrofoils on numerous boats and THEY WORK! Use the XP Jr. on small craft (I have 'em on a 13' Whaler and 14' RIB) or the larger models on medium-sized craft. Sting Ray XP hydrofoils are available everywhere: West Marine, Wal Mart etc.

I believe this is THE best upgrade you can do for any outboard or I/O boat.
Details are here:

http://www.marine-dynamics.com/2009_MD_Brochure.pdf

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Permalink Reply by Tim, Jane, Michael and Patrick on September 16, 2009 at 9:18pm

Im no expert, but I think Henry is right on point, If you are running trim tabs, it sounds like you may the bow down too far as you come back into your mid-range speed. I experienced this when some tabs stuck in the down position during a sea trial. I suspect that your boat would also be difficult to control as it comes off plane. Frankly, I have the opposite problem, my Merc 225 has a 15 on it, great out of the hole, but the top end suffers and it is easy to over rev the engine. Sounds like we need to swap props! Given your HP, I would advise against going all the way down to 15, but I would not mess with the Diameter.
good luck.

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Permalink Reply by John Fowler on September 18, 2009 at 11:21am

Crash, just went through this process several months ago. I have 21 foot Grady white walkaround with a 200hp merc. I was running a 19 inch pitch aluminum max rpm 5200 - 5500 running about 35 to 38mph. I checked with the mercury marine website as they have a pretty good prop selector feature on their site. Mercury recommended based on boat weight, load etc. a 19 inch pitch (the same as the aluminum prop) so that's what I put on. I haven't had any problems with planning, performance or fuel economy. Also, just to note I haven't noticed any appreciable increase in perfromance or economy, pretty much the same as the aluminum. The dealer where I bought my outboard said that the SS prop really won't make any dramatic change in performance it's just that the SS prop is much more durable and may make the boat plane faster (less flex under load). he also said that if you run in shallow water a lot you might want to rethink using a SS prop as when you hit an obstruction the SS prop might cause more damage to your lower unit (cracked housing, bent shaft etc.) as it will not give or break like an aluminum. That tack i'm taking now is that fall thru spring when i run offshore a lot I use the SS. During the summer months when running in the river i use the aluminum.

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Permalink Reply by Steve Austin on September 21, 2009 at 3:14pm

Actually John an Aluminum prop will plane quicker due to the flex. The flex lets the prop spin to a higher RPM faster giving better push on the lower end. Cruising and top end a SS prop will win due to the lack of flex and the ability to cup the tips. Go to someone like Ken at Prop Gods. He will come to you and let you try pops before you buy one. I have not used him but have heard he is first rate. He also carrys knowledge that a novice boater does not have.

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Permalink Reply by jack sonntag on September 23, 2009 at 8:11am

It is IMPERATIVE that your engine be able to achieve the recommended WOT rating. The closer to the top end of that range the better. I cannot over-emphasize the importance of this. I used to be a Yamaha factory rep, and no repair would be undertaken until the propping was correct. More pitch == lower WOT, and vice versa.

Stainless v. aluminum has various pros and cons, but is not overly key to having the proper pitch.

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Permalink Reply by Jeff & Rhonda on November 4, 2009 at 9:02am

for all on this post,,,, the thing I see here is a efficientcy problem. A 19 pitch propeller on any v-6 outboard should lend a top end speed of nearly 50 mph. A couple of you here are not recieving this. For Crash this can cause the fouling of his spark plugs and IS causing his poor performance. Like Henry stated there are many variables to these issues thus there are many different design propellers and just refering to a propellers pitch is not apples to apples. Over 30yrs in the propeller business I see that boat dealers many times give bad advise to their customers on props, and also manys times sell a boat with the wrong propeller on it. Boat manufatures tests are under "perfect" conditions and can only be used as a reference. The prop calculators will give theoredical results from pitch to pitch but cannot account for the increased weights that newer motors are becoming and different designs of boats. Anyone having these issues feel free to contact me on my page or post you problem and I will gladly discuss a solution for you

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