Prop Selection - Bayliner 175

[jlh3rd]

For my application, what kind of pitch spread would y'all generally expect going with a 2-prop approach? (One prop for fully loaded slower speeds, and one prop for unloaded higher speeds). I get that it's hard to say exactly without testing, but just in general. Are we talking 2" pitch difference between the "fast" and "slow" prop? Or something more dramatic like 4" or 6"?

A Merc. 3 blade 16x13 pushed my pontoon to it's best performane #'s lightly loaded. 25+ mph but maxed rpms were 5800. 6000 is ideal. But it was a dog when loaded down.
A Merc 3 blade 16x12 gave only 22+ mph @6000...I could go over the 6000 however.
But when loaded down (pulling teens on tubes) my rpms stayed up around 5600+.
So just 1" pitch made a difference.

 

[jlh3rd]

these are my #'s with different props. 3 give the same #'s, 1 is my load prop.
There isn't a magical prop, at least not for me. Not for trying. And a pontoon isn't a planing hull, but props aren't magical. The #'s are just not that far apart.

 

[gsbarry]

15p in a 4 blade is the highest I would consider.


adding a blade is like adding 2" of pitch. adding blades and adding pitch both add load to the motor requiring more torque at a given speed.


I had 3 props in my 3.0 powered boat (see post #11). and pulling skiers, I still had to have most of the people toward the front to get a good hole shot.

Thanks Scott. Looks like your pitch range was 19P on the large end and 15P on the small end. Were these both 3 blades or 4 blades?

 

[gsbarry]

This thread is about prop selection, but earlier my compression test numbers and method came up. I re-verified my old numbers using the old method (all other plugs in, throttle closed) and got the same results. I hooked my gauge up to my air compressor and compared it to another gauge i have at 150 psi and it was within 2-3 lbs so the gauge is fairly accurate. Lastly, I re-ran the compression test with all plugs out at once, and WOT, and all cylinders read ~10 lbs higher in the same pattern as the initial test, so in the 180 to 190 range. 1st pic is cylinder 1 under new method, 2nd pic is cylinder 1 under old method, 3rd pic is of the plugs, which are nearly new, only about 1 hour on them. Notice the discoloration of the side electrode on cylinder 2. What do y'all make of that? Seems like light ash fouling to me. Valve seal? The brown stuff on the threads is just anti-seize that i put on there. Cylinders 2 and 3 read at the high end of the range, cylinders 1 and 4 at the low end. 180, 190, 190, 181 in that order with the new method.

 

[cyclops222]

I and others have found Ken at prop gods to get the correct props for any boat.

 

[alldodge]

There has to be some liquid in the cylinders
Plugs look steam cleaned, any signs of water?

 

[gsbarry]

No signs of water in the motor when I changed the oil. Other than cylinder 2, the plugs look normal to me. What are you observing that makes them look steam cleaned? Remember these plugs are nearly new, only one hour on them.

 

[Scott Danforth]

Thanks Scott. Looks like your pitch range was 19P on the large end and 15P on the small end. Were these both 3 blades or 4 blades?

All 3 blades.

Tried a 17p 4 blade, couldn't get out of the hole as fast as the 3 blade. Lugged the motor too much. Tried selling it for a while. Tossed it into the fire about 15 years ago

 

[Scott Danforth]

Agree with AD. You are either steam cleaning your plugs from a water ingest issue, or you are painfully lean

 

[Scott06]

Thanks Scott. Looks like your pitch range was 19P on the large end and 15P on the small end. Were these both 3 blades or 4 blades?

I’ll play the other side of the fence… do not mean to imply that other advice given is bad, just some of my experince in a similar boat is different.

Thanks for the feedback on the 3 blade. I respect y'alls opinions but I'm left a little confused on the recommendation. This may be because I didn't really talk about my typical boating conditions and performance desires. Typically, the lakes/time of day that I plan to boat on are fairly choppy from either weather or boat traffic, or both. Also, I personally put more emphasis on low end torque and hole shot rather than top end. From my reading a 4 blade provides better handling at low speeds, and improved hole shot, sacrificing top end, which in my mind is similar to going down in pitch. So I'm confused when you say a 19P 4 blade is equal to a 21P 3 blade, I would have thought it was the opposite, that a 21P 4 blade would be equal to a 19P 3 blade. What is it about my application that makes 4 blades a poor choice? Just trying to learn and understand.
View attachment 405452

Like you my last two boats are primarily used for loaded down watersports. Previous boat was a 1991 sea ray 170 3.0lx 135 hp, current boat is 2004 sea ray 200 sport with. 5.0 with 4 bbl carb ( repowered from a 4.3).

on my old boat best overall use I got was with 4 blade props. I used michigan vortex 18” for cruising and tubing, 16” when we were skiing. Previously had used a 17” and 19” black max for same. Michigan drops and inch of pitch for their 4 blade Aluminum props. i trialed these props and bought both what I saw was better holeshot, more stern lift, and was able to hold a plane at a lower speed. Bottom line worth trying if watersports are your thing. The 18” I could hit 4700 maybe 4800 rpm , the 16” could tap the rev limiter at 5 k just like the 17” 3 bLade.

as mentioned some 4 blades have enough bite that it inhibits the engine spinning up into power band fast on holeshot. I didn’t see that with vortex 4 blades or the spitfire / nemisis on my old boat or current boat. on my current boat I run a Revolution 4 that absolutely has enough bite to limit holeshot somewhat Vs the Vensura 4 blade I have that has less cup and smaller blades.

bottom line try a few different ones til u find what you like for how u use your boat. Of course get any engine issues fixed before going down this road

 

[gsbarry]

Agree with AD. You are either steam cleaning your plugs from a water ingest issue, or you are painfully lean

Can you pls explain why you think this? Would you expect more carbon buildup after only one hour of runtime?

 

[Scott Danforth]

They should be coffee colored after an hour of run time

 

[cyclops222]

Excessively hotter heat range plugs run super clean. Been there on boats doing trolling al day.

 

[gsbarry]

These are the plugs the manual calls for: BPR6EFS 3623 which is heat range 6 (medium heat). Perhaps a leak down test is in my future. No signs of water in the old oil, when I pulled the exhaust/intake manifold it was in good condition.​

 

[Pmt133]

The #4 plug almost looks like it has signs of detonation on it.

 

[gsbarry]

The #4 plug almost looks like it has signs of detonation on it.

Can you describe what it is you are seeing that indicates detonation on #4? I can see one blurry black spec if i zoom in really close, but doesn't look like "peppering" to me.

 

[cyclops222]

I just looked at those sparkplug pictures. Plugs look terrible. What is that hazzy look on all the surfaces ? And the 1 plug ground bar has a yellowish build up on it. Why did you put anti seizing gook on the plug threads ? That stuff could be causing the plugs to look so bad in 1 hour. Some anti seize stuff has fine metal bits in it. I am not sure there are any antiseize mixtures to be used in a combustion chamber.

 

[cyclops222]

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[cyclops222]

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[gsbarry]

I just looked at those sparkplug pictures. Plugs look terrible. What is that hazzy look on all the surfaces ? And the 1 plug ground bar has a yellowish build up on it. Why did you put anti seizing gook on the plug threads ? That stuff could be causing the plugs to look so bad in 1 hour. Some anti seize stuff has fine metal bits in it. I am not sure there are any antiseize mixtures to be used in a combustion chamber.

The yellowish buildup on #2 was what caught my eye as well. Since it's only on one cylinder I'm thinking perhaps there's a valve seal issue on that cylinder. I'm not sure what you mean by hazy look on all surfaces... I'm not seeing that. Could you be more specific? I make it a habit of putting anti seize on all plugs that I install. The reason being, as one would suspect, to prevent plugs from rusting in place in the block (which would be really bad). The anti seize is only on the threads, and therefore is not exposed to the combustion chamber.