I have all the numbers with new prop. Please help.

choppywaters

Petty Officer 2nd Class
Joined
Apr 27, 2012
Messages
127
After a couple posts ago I finally had the chance to get all my numbers with a new prop. Here goes.....We went from a 14 1/4 x 19p to a 14.5 x 17p prop. My 4.3lx mercruiser's max rpm's are 4400-4600 and yesterday I really watched the rpm's and we were running at 35mph at 4400 rpm's. When I went almost to wot, the rpm's went to almost 5000 and there was still some throttle left and I didn't want to chance scattering the engine. The 17p prop. seemed to help getting out of the water a bit but with 2 adults, 2 teen boys and my 6 year old daughter the boat still seemed to lug. I'm hoping the addition of my Smart Tabs will be more beneficial. But with those numbers am I good for the prop? Thank you.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: I have all the numbers with new prop. Please help.

You want to be at the upper part of the max RPM range, with a typical load in the boat. So what is the max RPM range for that motor? How close are you to it?


If the boat is stern heavy (most 18-21' I/Os are) tabs will help. The best are hydraulic trim tabs.
 

choppywaters

Petty Officer 2nd Class
Joined
Apr 27, 2012
Messages
127
Re: I have all the numbers with new prop. Please help.

Hi Chris, the max rpm's are 4600 but my wot will take me to 5000 + I believe. Im not looking for speed so its rarely close to wot, in fact we were cruising yesterday at 30mph at 3000 rpm's and it was where I wanted to be. We are either just cruising or pulling a tube so top speed is not important.
 

Philster

Captain
Joined
Sep 15, 2009
Messages
3,342
Re: I have all the numbers with new prop. Please help.

No, you are not good with that prop.

You need more pitch, but also like watersports. Sounds like an 18p, 4-blade prop would be right. If you can get one with vent holes, that will help the prop spin up faster from a holeshot, and this will remove the feeling of lugging.

So, the all-out solution would include:

SS, 4-blade, 18p prop with vent holes and toss on tabs. That's doing it right.
 

coastalrichard

Lieutenant
Joined
Apr 6, 2009
Messages
1,255
Re: I have all the numbers with new prop. Please help.

No, you are not good with that prop.

You need more pitch, but also like watersports. Sounds like an 18p, 4-blade prop would be right. If you can get one with vent holes, that will help the prop spin up faster from a holeshot, and this will remove the feeling of lugging.

So, the all-out solution would include:

SS, 4-blade, 18p prop with vent holes and toss on tabs. That's doing it right.

As usual, I have to agree with the Philster...seems like the 17p is a bit too slim. The 18p will likely give you a full stick in your range at wot. Good Luck
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: I have all the numbers with new prop. Please help.

The boats dry weight is about 1600 not bad for a 19 ft.I/O. it would seem a 4.3 would do better with hole shot.
Especially with a 17" that overevs at speed. Would be good to know the speed at 5000.Is the down trim going all the way down?
Do you move people forward for hole shot.
Perhaps the foam under the floor has absorbed water. Is the bottom clean and smooth.
Wouldn't hurt to know the numbers with the 19".
 

Philster

Captain
Joined
Sep 15, 2009
Messages
3,342
Re: I have all the numbers with new prop. Please help.

Five people in the boat...and if she is sitting heavy in the rear and the prop is vanilla and he is tabless, a less-than-thrilling hole shot would not be surprising at all, even for a boat that could run past its max RPM range.

Like to know more about the prop.
 

choppywaters

Petty Officer 2nd Class
Joined
Apr 27, 2012
Messages
127
Re: I have all the numbers with new prop. Please help.

Five people in the boat...and if she is sitting heavy in the rear and the prop is vanilla and he is tabless, a less-than-thrilling hole shot would not be surprising at all, even for a boat that could run past its max RPM range.

Like to know more about the prop.

The prop. is a 14.5 x 17p Michigan aluminum. The old prop is a aluminum 19p, unknown maker, there were no markings at all. The dealer said "oh one of those generic ones". The numbers from the old prop, if I remember right were around 4400ish rpm's we were doing 40ish mph but the hole shot was terrible. This new prop seems to plane a couple seconds quicker.
 

choppywaters

Petty Officer 2nd Class
Joined
Apr 27, 2012
Messages
127
Re: I have all the numbers with new prop. Please help.

The boats dry weight is about 1600 not bad for a 19 ft.I/O. it would seem a 4.3 would do better with hole shot.
Especially with a 17" that overevs at speed. Would be good to know the speed at 5000.Is the down trim going all the way down?
Do you move people forward for hole shot.
Perhaps the foam under the floor has absorbed water. Is the bottom clean and smooth.
Wouldn't hurt to know the numbers with the 19".

Yes the trim is all the way down but no one towards the front. The bottom is very clean and smooth, there are only a few spider cracks around the bottom and none that I can see on the actual bottom.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: I have all the numbers with new prop. Please help.

Counts 5 but probably weighs closer to 3 adults.
Wet foam under the floor comes from poor storage like sitting in a slip with water standing in it or winter storage
with snow and water standing in the boat. weight is right near the stern where it does the most damage for a quick hole shot.
 

choppywaters

Petty Officer 2nd Class
Joined
Apr 27, 2012
Messages
127
Re: I have all the numbers with new prop. Please help.

With this prop. and weight we had I counted to 7 and it was on plane. Maybe I should have asked if thats too long or not. I remember my parents boat (21ft Larson CC with 305 merc.) and when we had 4-6 grown adults it would take forever to get on plane.
 
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