Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

[tblack111]

The 2007 25hp 4 stroke is on a Bass Tracker 170tx aluminum bass boat. It performs as well as expected with one fisherman and gear. But when you pull out with 2 fisherman, gear, and a livewell full of fish....everything boggs down. Especially later on in the day when it warms up. The boat will take longer to plane, and never reaches it's max rpms of 6000. The boat will usually catch up and plane out eventually after a long run, but rpms are still low. I nicked up the current prop Saturday and thought about replacing it with a new one with different diminsions to see if I could get a little better performance. It currently has a 9.75 dia. X 9.5 pitch alluminum prop. But Turning Point Props is recommending a 10.38 dia. X 11 pitch on there "prop selector program" Does anyone have any recommendations of what I should go with? What would those changes in dimentions do for the 25hp? I would like to move across the water a little better than I do when the boat is weighted down if possible. Any info other than "buy a bigger motor" would be appreciated,lol...Thanks.

 

[steelespike]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

We need the max rpm and speed lightly loaded.
And rpm and speed when planed loaded.While your not going to get much out of it
we should be able to improve the hole shot and maybe maintain plane easier.
Based on your description its hard to believe 11" pitch would get up at all.

 

[tblack111]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

Max rpm is 5800 lightly loaded running about 16 mph
Max rpm is around 5000 loaded running about 10 to 12 mph....but it takes a while to build up to that

rated max rpm - 6000

 

[Sea Rider]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

You need 2 props, standard one for actual light load that turns 5800 and a second same size smaller pitched to increase + 5500 rpm to significantly better hole shot, a 2" decrease in pitch results in achieving 300-400 more rpm. There are several smaller pitched props for your engine. If wanting more power, check if you could pass that 25 to 30 HP, see which parts will need to make the conversion and if not that expensive to do so. Same size less pitch works well with heavier loads on sib/ribs configurations don't know if applies same on alum heavier boats.

Happy Boating

 

[steelespike]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

You could give some thought to a Solas Saturn 9" 4 blade.It should get you up on the water quicker maintain plane easier.Should be smoother and resp[ond better around the dock.
Going down to a 9" will also help the hole shot and keep your rpm up.
While 2 props might be ideal I think that setup needs the 4 blade all the time.

 

[tblack111]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

Mercury recommends a 9.3 x 9.5 spitfire 4 blade...any thoughts? Plus Where would I get one? Cant find any online . And all I can find on a Solas Saturn is a three blade. Stainless or alluminum? Thanks

 

[boater1234]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

I had that engine for a week and sold it because of the same problem.It has no balls.They need to knock the gear ratio up on it to give it more punch like they did with the 15 and 20hp 4stroke.The 20hp 4stroke performs way better then the 25 i had.It has a ton of punch and is like 40lbs lighter.Now saying all that you def need a smaller pitch prop but you may loose some top end.It was a great running engine it just didn't have that extra punch you need with 2 people.Try a ss prop it has less give may get you on plane faster also.Could also try a dolphin.

 

[steelespike]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

Mercury recommends a 9.3 x 9.5 spitfire 4 blade...any thoughts? Plus Where would I get one? Cant find any online . And all I can find on a Solas Saturn is a three blade. Stainless or alluminum? Thanks

Here at iboats 5233-100-09Didn't realize it was ss but it should work well if its not too rich for your wallet. $187.The Merc spitfire is about the same price in aluminum.

 

[tblack111]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

Here at iboats 5233-100-09Didn't realize it was ss but it should work well if its not too rich for your wallet. $187.The Merc spitfire is about the same price in aluminum.

Thanks Steelespike, but would you recommend the above 4 blade prop over a 3 blade SS prop (solas) with an 8 pitch? Considering that supposedly dropping pitch and a 3 blade gives more top end. Keep in mind im running a 9.5 pitch now.....anymore help is greatly appreciated. just want to get the best one

 

[steelespike]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

A very difficult ? al to ss introduces all kinds of unpridictable results.
8" should put you way beyond your 6,000 max. Your setup has high slip numbers
which is normal when under powered.A ss prop should help the slip numbers
a 4 blade ss should help even more.
speaking very basically theoretical 9.5" speed is about 26 obviously not on your boat.
an 8" would be about 22. both at 5800 rpm. Though the 8" would run way over 6000.
Sometimes a ss prop in the same pitch will increase rpm others reduce depending on the design and the reaction of the boat and if the prop is the right pitch etc,etc.
I feel good about the 9" 4 blade ss prop because the 1/2 drop in pitch should more than make up for the additional blade and improved slip numbers.
None of this is carved in stone any prop change is a gamble.
Of course a 9" ss 3blade might produce the best top end but it just seems a 4 blade would have less slip.

 

[tblack111]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

Ok you sold me, I am ordering the 4 blade stainless...I'll let you all know how it does. Thanks again for all the help

 

[steelespike]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

Check the Solas Titan review just above our posts.Much more boat and motor but excellent results.

 

[tblack111]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

I received and installed the SS Solas Saturn 4 blade 10 X9 today. Took it for a quick run and this is what I found.
My max rpms was 5200...medium load. Definately handles better with more bite. I do get on plane quicker. May have lost a mph or two but no real problem with that. My speedometer just died on me last week. I am getting more vibration..when I place it in gear, around the low rpm range...say 1000 rpms or so...I do experience greater vibration. I dont know why that is. I guess I now have 2 questions.
1.)Is running at 5200 when rated at 6000 ok, will it hurt anything?

2.)What may I do to eliminate or reduce the low rpm vibration? Doesnt last long....when I get to about 1200rpms it smooths on out. Will this harm any bearings?

Thanks

 

[steelespike]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

If the vibration goes away its no problem.
I think you can see the problem when going to ss from al.You would think a 2" reduction in
pitch wiould make up for rpm lost to a 4 blade.
Looking back you may have had a lot of slip with the 11" prop or the tach wasn't accurate.
or the speedo was off.
The motor will perform better closer to that 6000.
If you could borrow a GPS for speed it would be easier to tell if everything adds up.
With an accurate speed its easier to tell if the rpm is accurate.
I hesitate to suggest a further reduction in pitch without an accurate speed.
Does the boat seem to be planed out about the same bow angle as the 11" prop.
Have you tried adjusting trim for the best speed?Up trim might add some speed.
The 4 blade may allow you to raise the motor on the transom which might add a little rpm and speed.

 

[tblack111]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

The vibration does go away, but my old alum. 3 blade prop was a 9.5 pitch. You probably seen where someone else has recommended an 11. I do have a GPS and I will check out my speed next time out and repost. Adjusting the trim up at wot does give a little more speed and rpm...100 - 200. (front end will raise some) The boat does plane out pretty close to what the 3 blade did. Maybe not quite as parallel to the water. Should I stick with it or try to return it? Which maybe impossible.

 

[steelespike]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

Your motor on a light reasonably fast boat with a 9" prop at 5200 rpm would do about 21 mph at 10% slip. Your under powered boat would likely have higher slip numbers and thus a slower speed.
Your old prop at 5800 would make about about 23 at 10% slip. again a light reasonably fast boat. yours is slower due to higher slip. I have to wonder now about your 16 mph figure perhaps the boat wasn't intirely on plane. Maybe your about to fail speedo was low.
Maybe see if the dealer will do an exchange if we can figure what to do.
A number of options; replace the prop,have a prop shop remove some pitch,or remove some cup. I'd like to see a carefully set up test with each prop. Maybe lightened some so we can see results closer to a typical setup.

 

[tblack111]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

Should I have replaced the thrust washer when installing the prop? It looked ok. Does anyone know how much torque that should be applied to the 25 hp Merc 4 stroke efi prop nut?

 

[steelespike]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

I believe it is something like 25ft lbs.You just need to be sure it is tight and lock it in
place.My 88 Evinrude has never had the thrust washer replaced or the prop nut torqued.
If the washer looks sound should be ok.
If your thinking it might help your vibration give it a try.

 

[tblack111]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

Got on the lake with a buddy this morning, 5200 RPms and 21-22 mph according to the GPS

Later in the day, after it warmed up a little 4900 Rpms and around 18-19 mph

Seemed to have gained hole shot and top end compared to the 3 blade, if my speedo was right. Still have some vibration but not as bad as it was. Maybe the nature of a 4 blade on a small engine. I guess the warmer air and engine may rob a few rpms later in the daY????

 

[steelespike]

Re: Is there a better prop available for 25hp Mercury 4stroke EFI ? Need advice

21-22 is right on at 5200 rpm and 10% slip.But the motor definately will be happier with an 8" prop.Assuming it could make 6,000 rpm it would actually be a smidge faster.
and be much better with a load.Also You could see if a prop shop thinks its a good idea to remove or alter the cup for more rpm.I have seen some excellent results here with a cup change.Sometimes a shop can remove a little pitch. If the dealer will let you exchange the prop for an 8" it might be the simplest way out.