Prop selection help TP, Solas, Michigan Wheel

[Bikestdy]

Hi all, I just joined after reading many of your posts so I am looking forward to your advice.
I have a 1985 4Winns 170 Horizon 17ft with a Mercruiser 470 170hp with 1.84 gears. I have a 14 ¼ 17p Turning Point 3bl that I damaged this past summer, so I am looking to replace it. Max RPM is 3800-4200. With the damaged prop bent back as best possible I was at 35mph (boat speedometer not gps) and 5000 RPM at WOT. I ran that both with and without about 400lb of sandbags added to compensate for passenger weight (with 1 pass in boat, typically have 3-5 adult passengers in boat) without any noticeable change. I am not really looking to cure any issue (besides the over revving at WOT). The boat is used almost exclusively for skiing and tubing, so top speed is not a priority just a bonus.

I want to stay with an aluminum prop. I am looking at Turning Point, Solas Rubex and Michigan Wheel Vortex XHS but am open to other brands or composite if felt to be beneficial. A local shop (airmarineinc.com I have heard very good things from several people about their recommendations and they guarantee their recommendations) recommended a Solas 4bl 19p (they don’t deal with Turning Point). I also emailed Turning Point for their recommendation and they recommended a 4bl 21p.

I am a little concerned about loosing too much hole shot for skiing from going up on pitch, but understand the 4bl should help with that. Besides buying all 3 to try out, can you provide me a recommendation/what I could expect with each prop? From what I have read in other posts, I am thinking of staying with Turning Point, but the Solas sounds to be a good contender as well, of what I have seen, most don’t seem to favor Michigan Wheel.

Hopefully that is enough/all the info you need to help me.

 

[jimmbo]

What RPM were you getting prior to damaging the old prop?

 

[Bikestdy]

I don't know, I only checked it after. The boat is new to me, but was my parents prior. My dad did not know what it was either, he did not know it was over revving either.

 

[Sea Rider]

Do you go skiing while boating with 3-4 passengers at same time regularly ? Whichever prop you go after must be water tested on a wot run on calm flat water cond. No one will have a correct answer about your request if wot rpm of previois beaten prop is not known..

Is it possible to rebuild old prop instead than investing on 3 different props ? With a healthy engine and tach can go go from there playing with pitches.. Ideal is to have a starting prop and then going for a prop maximization to suit your boating needs and requirements.

Anyway is a bad idea to go skiing and boating at same time with other passengers, if you prop right that combo to plane fast at say max wot revs which skier needs, when lightly loaded engine will surely overrev bad.

Happy Boating

 

[Bikestdy]

I do not understand what you mean by "skiing while boating." Yes, there are normally 3 to 4 passengers in the boat and it is used almost only for water sports.

I did say "Max RPM is 3800-4200. With the damaged prop bent back as best possible I was at 35mph (boat speedometer not gps) and 5000 RPM at WOT." With it bent back there was very little vibration, so I feel it was a fairly accurate test.

I probably could get it serviced, but don't know where to go with it. I also do not know if it has been serviced prior and it is about 10yrs old. I do not intend on buying 3 props, those are just what I am looking at selecting from.

Can you please explain/clarify your comment "Anyway is a bad idea to go skiing and boating at same time with other passengers" I understand the second half, that based on load the "correct" prop changes. And I think I understand that you are saying that for skiing you want a prop that spools up faster, but will over rev if used for cruising/light load.

I had to read your reply several times as I didn't feel it was very clear, so please clarify if I misunderstood what you were saying/asking.

 

[Sea Rider]

Recapitulating, We're both lost somewhere, LOL!!

To know, posted : Max RPM is 3800-4200.. There's a min and max wot rpm range for all engines, or is it : min 3800 and max 4200 wot rpm ? please clarify that as it's very important to know, If not, post true wot rpm range for that engine. Will continue from there

Happy Boating

 

[Bikestdy]

Well I'm glad I wasn't the only one that was confused.
Yes, now your on track with me. The engine max WOT range is 3800-4200.

I know I out a lot of info in that first post, to try and avoid questions like this. I guess it made for information overload though.

 

[Sea Rider]

What doesn't up is that all engine specify a fixed wot rpm range as per factory specs and you have posted 2 different max wot rpm range. For an engine that revs way low compared to a typical OB, 400 wot rpm difference could be a day/night water performance difference. If not asking too much specify min-max wot rpm range for that engine as per factory specs.

Let's see if other boater that knows those wot rpm specs chimes in to clarify that.

Happy Boating

 

[porscheguy]

The merc 470 has a factory WOT range of 4200-4600.

When functioning properly, the 470 is known to be a strong engine that makes a lot of torque. They could be trouble prone engines so mercury eventually discontinued them when the GM 4.3 proved itself a reliable and much cheaper alternative. The 470 was usually packaged with a 1.84 outdrive.

Are you claiming that the factory WOT limit is 3800-4200RPM? Or are you saying 3800-4200RPM is the fastest you can go?

As I stated at the beginning of this post, the factory WOT limit is 4200-4600RPM for the merc 470.

My question for OP is, are you holding it back because you believe the redline is 4200? Or are you only capable of turning 4200RPM?

if you’re holding it back, you need to up your pitch.

If a 17’ boat with a merc 470, 1.84 gears, and a 17P prop is only able to turn 4200RPM, the you’ve got an issue with the engine. That thing ought to fly with a 470.

 

[Scott06]

I would think a 17" on that boat with 170 hp would over rev but be good for water sports in terms of hole shot . I had a 17 ft sea ray with a less powerful 3.0 and a 17" would give the slower top speed and over rev easily similar to your results

On that boat I used a 16" 4 bblade Michigan vortex for skiing (I'm 270 lbs) and an 18" 4 blade vortex for tubing and cruising. Vortex is pretty inexpensive on line, or the 19" 4 blade you were reccomended would probably be good. Will this shop you mention let you try it out? That's how I ended up with two I liked them both for different uses, the 16" was a huge difference over the 17" for skiing.

Also verify your tach with a shop tach as comments above are right on. Would think you can overrev easily with the 17"

 

[Bikestdy]

Attached are pictures of the sticker on the engine and from the manual stating that engine max WOT range is 3800-4200RPM. I am not pulling these numbers from my butt, they are right off the engine and out of the manual. The 4200rpm that I am quoting is the max specified.

I would like to know where you found 4200-4600 porscheguy?

My actual observed (for the third time) was: "With the damaged prop bent back as best possible I was at 35mph (boat speedometer not gps) and 5000 RPM at WOT." With it bent back there was very little vibration, so I feel it was a fairly accurate test." Yes, that was with the throttle pushed all the way forward as far as it would go, not holding anything back.
I know I need to go up in pitch to put it within the proper range, my question was more about the performance differences between TP, Solas, and MW.

The shop will let you try the props, however they are about an 1-1.5hrs away from me, so it makes it a bit difficult.

 

[Bikestdy]

One of the online dealers I was considering buying from confirmed in private message that I could try and return a prop as long as it was not damaged. I am considering trying several, but that does mean I would need to pay return shipping. I am wondering if there is a performance difference between those brands on my boat. That is more what I am curious to explore, as with anything they all claim to be the best or have the best features, but I want to know real world difference or if they are all really about the same.

 

[porscheguy]

The 3.7 @ 170hp has a max throttle range of 3800-4200rpm. The 3.7 @ 190hp is 4200-4600. It also has a 4 barrel carb.

the rotating assembly in both engines is the same and that’s why you didn’t destroy it when you spun it up to 5k.

If you can turn a 17P up to 5K, you can be safe bumping it up to 19P and running at 4400 or so. There’s not much difference in performance from one aluminum prop to the next, but whatever is cheap.

 

[Bikestdy]

Just curious if anyone else has an opinion as to which brand. Also to 3 vs 4 blade. From what I understand the 4 blades push harder with hole shot, so that makes it a better ski prop.

 

[porscheguy]

I’d go with the 3 blade Michigan wheel or a quicksilver. You’ve got a 17’ boat. Even with adults onboard, it’s not that heavy. Those props are over 14” in diameter which is pretty large and provides a lot of blade surface area to get skiers out of the water. If you had a 19’-22’ boat I’d suggest the 4 blade.

 

[Bikestdy]

I just wanted to update this post as to what I actually went with and how it worked.

I decided on a 19x4 Turning point prop. I was just able to get out and try it. At WOT I was at 4000rpm and 37mph trimed up (GPS verified)(before i got stopped for going to fast after dusk by the conservation officer, but he just gave me a verbal warning thankfully). I was unable to try it out skiing due to darkness, but I am thinking I will need to drop back to a 17p . While it did lower my rpms (as expected), it dropped more than I anticipated due to increased effiancy (if i understand the voodoo side of things a bit). The17x3 I had was at 19.97 prop slip (also this prop had a hit things a few times the last being a tree stump and bent back, and that is where my numbers came from, so it wasn't in top shape, but ran with a very small amount of vibration), where as the new 19x4 was 5.38 a difference of 14.59. So the previous 5000rpm x .1459 prop effiancy difference= 729.5 rpm from the increase in effiancy. So then 1000rpm difference of old WOT to new WOT - 729.5= 270.5 rpm change from the pitch change. At least that is how I make sense of the voodoo... Maybe someone will explain me wrong...

While it did put me in the correct rpm range, by feel i don't think it was pulling as hard as i want for skiing, so i am thinking i might need to drop back to a 17x4 to get where i want to be. I had thought the prop change would put me at about 4500rpm which is about where i had wanted to end up. But i may need to try to ski behind it and see how it is.

 

[Chris1956]

I think the TP is the highest performance of the three your specified, and therefore the best choice. I like 3 blades for performance hulls.