Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

I did all all the researches for a month then bite the bullet on a typhoon 14x19 4 blade prop from my original 14.5x17 3 blade both are SS. I'm going to be out of town for a few weeks so I can't test this but I'm itching to find out what it's going to be like.

95 Seaswirl striper

5.7L with an OMC Cobra SX 1.66 gear ratio.
WOT = 5k RPM
top speed 45mph +-
cruise at 3500rpm (is that the right cruise RPM?) @ 26mph +-
The boat dry weight is 4600lbs fully loaded I'm thinking 5500 - 6k lbs

ATM I hate how my bow points to the sky when I take off even with my trim tabs.

My goal is to bring my WOT down to around 4600-4800 RPM which I believe is the manufacture recommendation. Going up to a 19p prop would most likely achieve this but the only difference is I'm going from a 3 blade to a 4 blade and a 14.5" to a 14" prop, what would these factor play on my performance?

I hope to maintain a cruise speed of at least 25mph while lowering my cruise RPM down to maybe 3200rpm hopefully this would yield some better fuel economy for me.

Re: Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

Can't be too specific but the 2" increase should drop "about" 300-400 rpm going to a 4 can drop
"about" 100 rpm.The 4blade may lower top end a little though some have seen same or slightly better speed.
But there are lots of pluses. It should improve hole shot,stay on plane with less throttle and
handle better at speed and at the dock.

Re: Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

Based on what you're saying, I'll be around 4500 to 4600 RPM would that be where I want to be at?

Re: Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

You really want to be near the max recommended WOT rpm and you'll likely be around 4500 with that setup. Take it out for a trial run and if you're lugging the motor you may need go possibly to a 14x18" prop. See if you can get a trial prop deal to dial in your setup.

Re: Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

My info only goes to 93 but should be accurate. the 5.7 is rated for a max of 4,600.
You should be in the ball park.

Re: Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

dannieboiz said:

ATM I hate how my bow points to the sky when I take off even with my trim tabs.

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This has me concerned no matter what you do . . . This condition could actually get worse with the selection you've made. Are you trimming all the way in? Full throttle? Trim Tabs full down?

Re: Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

QC said:

This has me concerned no matter what you do . . . This condition could actually get worse with the selection you've made. Are you trimming all the way in? Full throttle? Trim Tabs full down?

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I don't adjust my trim tabs until I start moving I usually ease the gas and take off slowly never taken off full throttle before. After I adjust my trim tab and get on the plan then I trim my outdrive until the engine purrs.

Re: Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

dannieboiz said:

I don't adjust my trim tabs until I start moving I usually ease the gas and take off slowly never taken off full throttle before. After I adjust my trim tab and get on the plan then I trim my outdrive until the engine purrs.

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Howdy,



Try starting with the drive all the way DOWN/IN or 1 or 2 "bumps" UP/OUT from all the way down.
Bow rise on hole-shot is VERY dependent on drive position.



Also, tachometers can be as much as 500 RPM OFF at the top end. Before you change props, you should verify the tach. (use GPS to verify the speedometer)

To get ball park numbers, you can use a prop-slip calculator for reference. Use 12-15% slip.

Re: Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

The tach I have is a brand new tach the engine is also newly rebuild from the bottom up. The speed I'm giving you is GPS speed. So don't start with the drive all the way in?

on my old boat with a 3.0l engine (different type of boat though) I had hydrofoil and it goes on plane almost right away regardless of where I have the drive. It's actually hard to get the bow to go up intentionally.

Re: Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

dannieboiz said:

The tach I have is a brand new tach

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All the more reason to check that it is accurate . . . Make sure it is set for 8 cyls. Check for an online manual for your tach if this isn't making sense.

dannieboiz said:

So don't start with the drive all the way in?

I had hydrofoil and it goes on plane almost right away regardless of where I have the drive. It's actually hard to get the bow to go up intentionally.

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As Rick said, all the way down or a click or two up. Biggest thing is put your tabs all the way down and try it. Bow should not rise. Don't even think about a hydrofoil if you have trim tabs, just forget it. Use all of your adjustments available to you including the throttle. Full throttle starts are fine, and will probably jump right up. At least try it. Good luck with everything, and let us know how it goes

Re: Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

dannieboiz said:

The tach I have is a brand new tach the engine is also newly rebuild from the bottom up. The speed I'm giving you is GPS speed. So don't start with the drive all the way in?

on my old boat with a 3.0l engine (different type of boat though) I had hydrofoil and it goes on plane almost right away regardless of where I have the drive. It's actually hard to get the bow to go up intentionally.

Click to expand...

I actually said:

Try starting with the drive all the way DOWN/IN OR 1 or 2 "bumps" UP/OUT from all the way down.

Click to expand...

Bow rise with a stern-drive is ALL drive position. You may have IN-limit blocks in your trim cyls preventing you from getting it all the way IN.

Put the boat on the trailer and run the drive all the way down and look from the side.

Your cav plate/prop center-line should be either parallel to the keel or slightly lower.

If it's not, you may have in-limit blocks preventing it from going all the way in.

If the boat sits too low in the trailer to check, park it close to a slope so you can run it all the way down/in.

The tach I have is a brand new tach

Click to expand...

New doesn't guarantee accurate. You should still check it against a known one.... Or another one. It's unlikely that both would off the same amount.....

If your "new" one is off by just 300-400 RPM, that can completely screw up your prop selection....

Re: Hope I made the right choice on this prop 14.5x17 3blade to 14x19 4 blade

I did make sure that the setting is on for a v8. I guess the only way to be 100% sure about the tach is to hook up another tach.

I've never see if I have an in limit block but when I store my boat I never leave my drive in the out position. My trailer has good height so I just trim it all the way down until I can hear the change of sound on my pump. It does appear to be all the way down cause I have to watch it when another person trim it down in case there's a change in ground level each time I park.

There's been a lot of good tips from you guys that I haven't tried. I'm going to try that next time I'm on the water.

On the same note, the 17p prop is the original prop that was on there when it had a Ford 302 motor which maybe 180hp. I never got to run the boat with the 302 since I went straight to a 350 which is supposed to be something like 260h but a heavier motor.