Prop Question

[Rochester]

I'm guessing this has been beat to death in the past, but I did a search on this site and found nothing conclusive. I bought my 2001 Sea Ray 180BR with the 135hp 3.0 Mercruiser 3 years ago. It only had 50 hours on it! What a deal! The boat had a J14.5x19P prop on it. There are a lot of areas I go into that are Slow/No Wake for extended distances, and it helps a lot if I get weight into the bow with respect to steering and getting the stern up because it is also very shallow. I hit a rock and dinged up the prop... not terrible, but I thought it should be fixed. I took it to a prop repair shop, and bought a new Mercury prop J14.25X21P, because that is what the Mercruiser recommendation is.

I have some friends who are pretty big, and it took forever to get on plane with the 21P prop. I dinged up the 21P prop very minor, and put the 19P prop back on after repair. I like the 19P a lot better. I'm thinking I should get the 21P prop fixed, but was also thinking about getting the pitch changed from 21P to 19P. (BTW, these are both aluminum props.) However, it seems like by the time I get it repaired and have the pitch changed, I could almost just buy a new 19P prop. I wish I knew who the mfr. of the 19p prop was... but I don't.

My question... I hardly ever run the boat WOT. If I do, it would be for a few minutes. I don't really care about the loss of top-end speed. What I really want is a prop that is going to give me the best hole-shot, and plane at the minimum speed. Also, even with the 19P prop, the boat porpoises if I trim it up much when on plane. It is fine if I trim it all the way down. I'd like a prop that is going to get the stern up as much as possible. I don't want stainless steel. I'm wondering if a 4-blade would be better than the 3-blade 19P, or would I not notice much difference? If I went with a 4-blade, would I want a 17P? Any brand recommendations? I'm hoping someone has a similar boat and messed around with some different props...

Thanks for any feedback you could provide...

 

[Leardriver]

A 4 blade with equivalent rpm performance to a 19 pitch 3 blade would be an 18 pitch 4 blade. However...there can be a variation of several hundred rpm from one style or brand to another.
A 4 blade works great to increase blade surface area when a bunch of horsepower hits the prop hard. Think of a blender beating the liquid to a froth. A lot of slippage. A 4 blade is similar to adding 4 wheel drive during start.
Your motor does not enjoy the luxury of horsepower, and is one of the few boats where a 4 blade might not give much reduced takeoff slippage, and would also lose 1-2 mph on the top end. The penalty for more blade surface area is increased drag.
Used props are cheap. $60 on ebay shipped. It wouldn't be too expensive to have 2-3 on hand to test, and sell them if you don't like them.
Having the right prop for your intended usage will increase your enjoyment of the boat.

 

[dutchman]

mine is an 2008 so can't be that much difference. We are at 3000ft for elevation. I still run the original merc 14-1/2 x 19 aluminum. With a light load I can hit 4800 rpm. This prop works great for all around boating, pulling cruising, etc. I did try a SS high five 19pitch (I think it was 13" or 13-1/2). Rpms and top speed were very close, but the bottom end was worse. The 4 cyl just doesn't have enough hp to take advantage of the H5.
What is you rpm at WOT with the 19P?

 

[Rochester]

Thanks for the feedback so far. Next time out I will check the RPMs and speed at WOT and post them.

 

[Rochester]

I finally got out and got some information. At WOT, with the J14.5x19P prop, I am running at 38 mph and 4500 rpm. As a reminder, what I really want is a prop that is going to give me the best hole-shot, and plane at the minimum speed. Also, even with the 19P prop, the boat porpoises if I trim it up much when on plane. It is fine if I trim it all the way down. I'd like a prop that is going to get the stern up as much as possible. I don't want stainless steel. I'm wondering if a 4-blade would be better than the 3-blade 19P, or would I not notice much difference? If I went with a 4-blade, would I want a 17P? an 18P? Any brand recommendations?


The Mercury prop selector showed two 4-blade props based on 38mph @ 4500 rpm, a Spitfire 14X19p or an Alpha 4, 14.5X18p. Is one of these better than the other? What is comparable from other manufacturers?

 

[dutchman]

From what you have posted, the 21P is definitely too much prop. The 19P is getting close. From my experience, I aim for the high end of my engine rpm, which in my case is 4800. If you hit that mark, it usually will make the entire rpm range work better, including the holeshot. If you went to a 17P, it will pickup the extra 300 rpm, and it will give you a better hole shot.
To make it more difficult, every manufacturer makes their prop a little different. A 19P in one kind may work better than another. Blade shape, cupped, etc. So it's hard to compare brands. It gets real expensive, if you don't have a shop that will let you try them out. Mine is a Merc 14.5 x 19.

As for the porpoise issue, I can't help you there. Don't know what causes that. My 175 doesn't do that at all. Using the trim, I can cruise along and watch the water spray pattern out the side as the trim lifts the bow. It is very noticeable, and can find that happy spot real easy. My buddy has same size boat, different brand, and the trim on his doesn't really affect the boat at all.