3 Blades Recommended for IO's

[Lastfin]

I've been looking at everything trying to come up with the right/better prop. I read the recommendations that iBoats made fro 3 vs 4 blades and see that 3 blades are recommended for IOs. My question is why? I've done an advanced search on this topic but don't see this answer.

Should I stick to a 3 blade? I've got a 2004 Larson 230 LXi running a VP 5.0/270 with an SX drive. Current prop is a 17 1/4 x 21 Alum. Trying to improve hole shot for skiing and tubing. I was thinking about a 4 blade 20 but not sure now based on your recommendations.

 

[Robbabob]

Re: 3 Blades Recommended for IO's

Hello Lastfin and welcome to iBoats! There is no single answer for every application; thus, you're not finding it.

Please review the top of the Prop topics section for the information necessary to assist with prop changes. There are several questions about your current setup, many of which you've identified, but still missing 1 or so.

In general, the 4-blade will give better hole-shot for the pulling of toys, and your top speed may go down. The in general applies as I think you're already aware. Provide more information and you'll get very good explanations.

Good luck!

 

[Snobike Mike]

Re: 3 Blades Recommended for IO's

3 blades recommended for I/O's?

Depends. What Iboats may be telling you is based on what info you provided 3 blade "could" be the best.

There are many 4 and 5 blade props out there and selecting the correct prop can be a little bit of a black art.

Good luck.

 

[cribber]

Re: 3 Blades Recommended for IO's

I run a 4 blade stainless steel prop on my 3.0l I/O. I gave up top end speed for holeshot to pull a tube. It all depends on what changes you're wanting to make. As long as you keep your WOT rpm near max recommended you'll be okay.

 

[Lastfin]

Re: 3 Blades Recommended for IO's

Thanks fro the answers so far. My question really relates to the "Prop Characteristics" section of the propeller help guide in the Marine store page. It says:

3 blades... or 4?
We recommend 3-blade propellers for recreational boats with 3, 4, and 6 cylinder outboards and I/0 engines.

These propellers provide good "hole shot" and top-speed performance.

We recommend 4-blade propellers for bass boats and boats with high performance hulls running high horsepower outboard engines.

Compared to 3 blades, they provide better "hole shot" performance with less steering torque and less vibration at high speeds.

When switching from 3 to 4-blades, generally a 1" pitch decrease is required. So, a 21" pitch 3-blade prop is replaced with a 20" pitch 4-blade prop. Pitch is increased when switching from 4 to 3-blades.

So the real question is why is a three blade prop recommended for IOs and 4 blades fro outboards? Is it a best compromise recommendation? This has been bugging me since I started investigating new props over the last year. I don't want to invest in a 4 blade prop if a 3 blade is preferred. I know I have almost unlimited choices, but like most, I don't have an unlimited budget.

 

[emilsr]

Re: 3 Blades Recommended for IO's

We recommend 4-blade propellers for bass boats and boats with high performance hulls running high horsepower outboard engines.


So the real question is why is a three blade prop recommended for IOs and 4 blades fro outboards? Is it a best compromise recommendation? This has been bugging me since I started investigating new props over the last year. I don't want to invest in a 4 blade prop if a 3 blade is preferred. I know I have almost unlimited choices, but like most, I don't have an unlimited budget.

Perhaps they're saying this because boats running a high drive height usually benefit from extra blades to cut down on prop slip. High performance boats generally will run the prop at or near the surface, while most boats will run the prop deeper in the water where the 3 blade has some advantages.

In your case, a 4 blade prop MIGHT help your holeshot, but a lower pitched 3 blade could also help it....I say "might" and "could" because the only way to know for sure is to test.

Some prop shops have a loaner program; that might be a good option for you.

 

[Dhadley]

Re: 3 Blades Recommended for IO's

There are props designed for I/Os in both 3 and 4 blade. Those props are designed to run deeper in the water than some other props made for outboards. You can run either prop on either unit, it has to do with what we refer to as the X dimension (how deep or how close to the surface the prop runs). It's rather difficult to change the X dimension on an IO, rather easy on an outboard.

Once you pick a brand you'll find that they generally describe their props pretty well. It's a fairly "prop specific" world anymore. Let me know if you have any questions, I'll be glad to help.

BTW - No big deal but I think you'll find your prop is 14 1/4" diameter, not 17 1/4". That'd be a pretty big prop for sure!

 

[Go Aweigh2452]

Re: 3 Blades Recommended for IO's

Hole shots are better with more blades.

The discussion may have been confused with aluminum verses stainless. Most people going for more blades end up with stainless vice aluminum. I think the other input would be that some I/O's are more subject to electrolysis with a big ole 4 blade stainless prop which may have wormed its way into this discussion? Having enough sacrificial anodes is the best solution for some I/O's?

 

[emilsr]

Re: 3 Blades Recommended for IO's

t has to do with what we refer to as the X dimension (how deep or how close to the surface the prop runs). It's rather difficult to change the X dimension on an IO, rather easy on an outboard.

Not exactly....

The "X" dimension (in simple terms) is the distance between the center line of the input shaft to the bottom of the boat. Prop depth is the distance between the center line of the prop shaft and the bottom of the boat. It's actually pretty easy (but not cheap) to adjust this by using a non-standard lower (shortie) on an I/O with spacers to fine tune the prop depth....but I'm not aware of a shortie drive for a Volvo so this is probably a moot point.

I would agree that most outboard props are designed to run shallower than stern drive props, but there are several exceptions to this rule. Also, there is some cross pollination....some stern drive props will work well on certain outboard applications and vice versa.

A 20p 4 blade of similar diameter and blade area is probably what the guy is looking for, I just hate to say "this will work and the other won't" until it's actually been tested. I've been burned on that before, and have the props to prove it.

 

[Lastfin]

Re: 3 Blades Recommended for IO's

Dhadley,

You're right it is 14 1/4 vice 17 1/4. I'm well versed in typing but can't seem to get those fingers trained properly!

I think I'm getting it now. The X dimension sounds right. On another thread I saw something about 4 blades being more susceptible to vibration, hence a 3 blade being a good compromise.

 

[Dhadley]

Re: 3 Blades Recommended for IO's

Generally speaking a 4 blade seems to be smoother in some aplications but it's really hard to tell unless any blade is damaged. When we talk about the X dimension on recreational boats we're refering to (basically) how deep the prop is running. When we think of recreational IOs we usually think of props running deep. It doesn't make sense to buy a prop with a lot of technology that should be running near the surface if the drive is rather deep. IE - we wouldn't normally consider running something like a Turbo TXP or a Merc Pro ET on a recreational IO. The TXP & ET is designed to run with the propshaft near, even or higher than the keel or pad. Most IO propshafts are well below the keel.

 

[Tail_Gunner]

Re: 3 Blades Recommended for IO's

If you select the right pitch and blade type a four blade will outperform a 3 blade in midrange applcations "almost" every time... however there are no absolutes in life. If you would or could post your current known speed at wide open throttle and the rpm's the boat runs at when at WOT you will get some suggestions. Is your current prop worn and ragged is it a factory prop.. info the will make for a better selection there are a lot of variables.

A few things to think about....In a boat of your type most people run somewhere between the 2500-3500 rpm range....Ask your self do you run at WOT all the time? If you do.. well a 3 blade will run 1-5 mph faster and if that appeals to you well run a 3 blade. But from the hole shot to 4000 rpm a 4 blade will feel smoother have more midrange punch and yes pull skiers tubers and wakeboards more effeicently than a 3 blade the prop has more blade area..Thats pushing errr pulling power.

 

[crewscontrol]

Re: 3 Blades Recommended for IO's

Seriously, way back in college we had this discussion in physics class. The professor (an avid boater) said the most EFFICIENT prop would be a one blade. I bet it would be hard to balance that sucker.

 

[Seadoomanls]

Re: 3 Blades Recommended for IO's

a 21 pitch seems kind of high in my opinion. I run a flats boat 19' with a 225 evinrude. For 2 man fishing (go faster) I run a 21p. But when I tow a 3 person tube or a wakeboarder I use a 17p. (I even have a 15p for when I load the boat with 8 people). Now my parents do own a propeller shop so I have access to all these, but I would definitely consider running a 17p. Keep your 21 for cruising and getting the best fuel economy for the highest speed, and get a 17p for towing a tuber. You can always call Turning Point Propellers and their experts can help you within minutes.

 

[Brewman61]

Re: 3 Blades Recommended for IO's

The best prop of any situation is the one that you're most happy with. On my 220hp I/O, I went from a 21P AL 3 blade to a 19 P Stainless 4 blade, and was extremely happy with the result. Goes up and maintains plane at lower speed. Don't care if it shaves a mph or two off the top end, since I seldom drive that fast anyway.
Use what fits both your boat, and your wallet, that you're happy with. Recommending a specific prop over another is mostly a matter of opinion vs hard fact. Important to stay within the correct operating range (WOT MAX, size, etc.....) other than that use what works best for you.

 

[swl]

Re: 3 Blades Recommended for IO's

on my 3L alpha, if I'm fishing or just cruising, I use a 14x21 aluminum 3 blade. It will max out around 37-39 mph at about 42-4300 rpm on a good day. When i got the kids and wife tubing I put on the 20P comprop. cant run WOT, it hits like 5000 rpm, but it is great for pulling tubes around. It was only like 100 bucks. when I try to pull the kids with the 3 blade it seems to lug the engine too much. That comprop works for me, plus its a lightweight spare

 

[Robbabob]

Re: 3 Blades Recommended for IO's

Hello Lastfin and welcome to iBoats! There is no single answer for every application; thus, you're not finding it.

Please review the top of the Prop topics section for the information necessary to assist with prop changes. There are several questions about your current setup, many of which you've identified, but still missing 1 or so.

In general, the 4-blade will give better hole-shot for the pulling of toys, and your top speed may go down. The in general applies as I think you're already aware. Provide more information and you'll get very good explanations.

Good luck!

The sticky I mentioned includes this text:
~~~~~~~~~~~~
ESSENTIAL DATA REQUIRED
When posting a question about propellers, you cannot get a reasonable answer unless you provide the following information in your post: Items 1-4 are essential for meaningful response to most questions.
1) Performance issue you are trying to correct.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch (required).
4) Wide open throttle RPM and speed with an average load (very helpful)
5) Engine/drive make, model, year, and HP
6) Boat make model, year, length and weight
~~~~~~~~~~~~~~

I think you've been given plenty of information regarding why the 3 or 4 blade is used in different applications, but I don't know that you've determined what direction to take for your situation/setup. As has been done, many directions (all good information) have been discussed, but without the "ESSENTIAL" information from you, you're still not going to get the best advice for your next prop.

Get back with us on your current WOT throttle rpm and if your 21P AL is in great condition. This matters A LOT.

 

[Seadoomanls]

Re: 3 Blades Recommended for IO's

Just reread the original post. I think we are misunderstanding the original question. It isn't what prop is best for his application (atleast no yet)...his question was why does Iboats list 3 blades as being a better prop for an I/O.
"I read the recommendations that iBoats made fro 3 vs 4 blades and see that 3 blades are recommended for IOs. My question is why?"

So lets answer that...then we can grill him and get the information we need to properly recommend the correct propeller. (which may be 2 different ones)

 

[wbc1957]

Re: 3 Blades Recommended for IO's

Why does any retail parts supplier make a recommendation as broad as that? Inventory is the key....

 

[HT32BSX115]

Re: 3 Blades Recommended for IO's

So lets answer that...then we can grill him and get the information we need to properly recommend the correct propeller. (which may be 2 different ones)

I donno......I think 6 blades are best.......