Sea Ray 175 with Mercruiser 3.0 prop questions

[deepghosh]

Hey guys,

Just took my new to me 2006 sea ray 175 out last weekend with my wife and brother in law. It has the merc 3.0 135hp. It is currently fitted with a 14.5x19p aluminum prop, however at WOT it was doing about 40mph at 5000 rpm. I’m guessing moving to a 21p prop would get the boat back into its operating range (4400-4800) if it’s just me and one or two other people, right?

Additionally, I found an amazing deal on a 13.5x17p stainless high five prop and went ahead and bought it. I know the pitch is low but I’m wondering if the boat was fully loaded (6-7 people) and pulling a tube, would the 17p high five help out with getting on plane and towing? I wouldn’t be going WOT so I’m not concerned about top end speed/rpm. If the 17p is too small I was just going to sell it.

Thanks in advance for any feedback!

 

[Chris1956]

You clearly need to test the 17P prop, with the heavy load and see what the max RPM is.

With the 19P prop, you should throttle back a bit to keep the RPMs within range.

Expect about a 600RPM drop with the 21P prop, over the 19P prop. The right prop is the one that gets you into the max RPM range with the usual load.

 

[QBhoy]

The hi 5 will be a rocket ship to take off...but will need serious holding back on the throttle at top end. You might want to stick with the one you have at a 19” but if you want top end and maybe suffer a little with anymore than 2 on board...get a good 21”.

 

[Scott06]

Yes the 17" high five will help with loaded towing and lower planing speed. I had the same boat and engine just a bit older than yours I used a 16" 4 blade for skiing. I would verify your tach, I doubt the 3.0 would be able to hit 5 k with a 19", and I think the rev limiter would be kicking in at 5 k.

 

[deepghosh]

I ended up buying a 19" Solas Amita 4 blade and took it out last weekend. Was only hitting 4200 rpm at around 33-34 mph with me my buddy and his dog. Could still hit about 32mph with 5 people on board. I installed my stainless smart tabs last week too, which made a huge difference in planing and handling. I'm wondering if I should go back to the 19" 3 blade prop, or maybe the high five prop paired with the smart tabs would get me into the 4400-4800 operating range. I have verified my tach and I don't believe the 3.0 has a rev limiter. Any input is appreciated!

 

[Scott Danforth]

your smart tabs add drag.

go back to your 19p prop

Lugging your motor will lead to melted pistons

the only three rev limiters a 3.0 have is the load on it, your right arm controlling the throttle, and ultimately the RPM when the motor grenades and the pistons ventilate the block

 

[deepghosh]

your smart tabs add drag.

go back to your 19p prop

Lugging your motor will lead to melted pistons

the only three rev limiters a 3.0 have is the load on it, your right arm controlling the throttle, and ultimately the RPM when the motor grenades and the pistons ventilate the block

Thank you. So you think my original 19p 3-blade prop will get me back into the operating range now that the smart tabs are installed?

 

[QBhoy]

Hi
you will easily hit 5000 rpm with that searay 17ft hull, 19” and a 3.0 with the usual ratio on the alpha.
The go to prop would be a 21” and ideally a laser. I know literally at least a dozen or more boats like this and similar. Mainly 18ft maxums, Mariah and bayliner 175s. My marina is full of them. Without doubt the most popular set up that ever came across to the U.K. was this size of boat and the 3.0. All are now well propped with 21” 3 blades and the odd 21” hi 5 for water sports.
Smart tabs added into the equation may mean a 19” will suit you better, especially if you have a lot on board.
the 17” hi 5 will be off the scale with the rpm with the Queen Mary on tow even. Terrible on fuel too in comparison.

 

[Scott06]

the only three rev limiters a 3.0 have is the load on it, your right arm controlling the throttle, and ultimately the RPM when the motor grenades and the pistons ventilate the block

My old Sea ray 170 with 1990 3.0 LX with DDIS (yes lucky it worked as long as I owned it) had a rev limiter that kicked in just a hair over 5k - couldn't hit I think with a 19" black max but could with a 17" black max lightly loaded. Neither of the Michigan vortex 16 or 18" 4 blades could tap it. I gues the newer EST ones don't have a limited?

Fun boat did a lot of towing tubes and skiing... very cheap on gas and very durable with basic a maintenance

 

[QBhoy]

What’s ddis Scott ?

 

[Scott Danforth]

My old Sea ray 170 with 1990 3.0 LX with DDIS (yes lucky it worked as long as I owned it) had a rev limiter that kicked in just a hair over 5k - couldn't hit I think with a 19" black max but could with a 17" black max lightly loaded. Neither of the Michigan vortex 16 or 18" 4 blades could tap it. I gues the newer EST ones don't have a limited?

Fun boat did a lot of towing tubes and skiing... very cheap on gas and very durable with basic a maintenance

Are you sure it wasnt valve float at 5000 rpm?

 

[deepghosh]

Hi
you will easily hit 5000 rpm with that searay 17ft hull, 19” and a 3.0 with the usual ratio on the alpha.
The go to prop would be a 21” and ideally a laser. I know literally at least a dozen or more boats like this and similar. Mainly 18ft maxums, Mariah and bayliner 175s. My marina is full of them. Without doubt the most popular set up that ever came across to the U.K. was this size of boat and the 3.0. All are now well propped with 21” 3 blades and the odd 21” hi 5 for water sports.
Smart tabs added into the equation may mean a 19” will suit you better, especially if you have a lot on board.
the 17” hi 5 will be off the scale with the rpm with the Queen Mary on tow even. Terrible on fuel too in comparison.

I'm thinking I need to reduce the pressure of the smart tabs, they may be too high and that's what was causing the low rpm's with the 19p 4-blade solas. I'll start looking for a 19p laser ii, hopefully I can find a good deal on one

 

[Cortes100]

My last boat was a 2008 Searay 175 with the 3.0L.
It came stock with a BlackMax 3 blade 19P. Max WOT was 4800, at around 41-42 mph. Overall, it pulled great and always went back to this prop after anything I experimented with. On the rare occasion the boat was overloaded with people, it would loose a few hundred rpm's.
I also tried the SS H5 and found the little 3L didn't have enough bottom end power to take advantage of what the H5 is supposed to give you. Still could hit 4750 rpm, but the bottom end was no better than the blackmax 19P.

I would go back to your original 19P. Watch the throttle with a light load. Then when you have an extra person onboard, it will be right on the mark.

 

[QBhoy]

Strange results above compared to here in the U.K. much heavier boats than this with the same engine and drive ratio can easily turn a 21” laser 2 to 4800 rpm. Boats like Mariah, maxum 18 footers. I’m amazed the high five couldn’t be turned if it was a 19”. What was the pvs plugs you had in ? There are a couple of bayliner 175 turning 21” hi 5 props to the max and pull boarders out the water no bother. Mayne the difference in fuel here helps, but I doubt it.

 

[Scott Danforth]

Strange results above compared to here in the U.K. much heavier boats than this with the same engine and drive ratio can easily turn a 21” laser 2 to 4800 rpm. Boats like Mariah, maxum 18 footers. I’m amazed the high five couldn’t be turned if it was a 19”. What was the pvs plugs you had in ? There are a couple of bayliner 175 turning 21” hi 5 props to the max and pull boarders out the water no bother. Mayne the difference in fuel here helps, but I doubt it.

QBhoy, keep in mind, you folk in the UK eat beans for breakfast..... that expulsion of gas helps propel your boats along a bit more. :lol:

 

[QBhoy]

QBhoy, keep in mind, you folk in the UK eat beans for breakfast..... that expulsion of gas helps propel your boats along a bit more. :lol:

Haha.”more beans boss” blazing saddles style !!

 

[Cortes100]

If elevation has anything to do with it, I'm at 3000 ft. We did a couple long road trips to lakes that are in that 900-1000' range and there was a noticeable difference in how the engine ran. I'm guessing that's normal for a carbed model.

As for the beans, I've tried that and it don't help

 

[QBhoy]

If elevation has anything to do with it, I'm at 3000 ft. We did a couple long road trips to lakes that are in that 900-1000' range and there was a noticeable difference in how the engine ran. I'm guessing that's normal for a carbed model.

As for the beans, I've tried that and it don't help

That will explain a lot. Yeah.

 

[Scott06]

What’s ddis Scott ?

DDIS was a distributorless ignition system mercruiser used for a handful if years. Had a coil pack with individual coil for each cylinder. There was a trigger wheel and sensor on what looked like a sawed off distributor without a cap and rotor to trigger it. Very similar to what's used on cars these days except there would be a crank position sensor vs the distributor like position sensor on the 3.0. Must not have worked well as merc dropped it pretty quick

to scott danforths question. No wasnt valve float , manual mentioned rev limiter at that rpm

link to pic of system.

https://www.google.com/search?q=merc...gzeSMK5H3LIjM:

link to manual referencing limiter speeds

https://www.manualslib.com/manual/822660/Mercruiser-Gm4.html?page=183

 

[deepghosh]

Just an update for anyone else who has questions for the mercruiser 3.0 and a 17-18ft boat... I ended up getting a used 19p Laser II and reduced pressure on the smart tabs by one hole and wow the boat flies now. With just my buddy and me we were hitting over 44mph on GPS at about 4900rpm. Only thing is the boat didn't plane as quickly as with the 4-blade and higher pressure on the smart tabs but I guess that's the tradeoff