3 Or 4 Blade Stainless Prop

[TCROfreak]

I have a 2004 Glastron with a 3.0L Volvo Penta, it has has a 3 blade alumninum prop. I would like a to get a stainless prop but am not sure if a 3 or 4 blade is better and if I do get a 4 blade would I use the same pitch as the 3 blade that is on the boat.

 

[tommays]

Re: 3 Or 4 Blade Stainless Prop

It really depends on were you AT NOW and what you want to achieve

Current WOT and speed

On my 3.0 i have a 17",19",21" and a 4 blade 20" i have come to favor the 4 blade 20" prop for long trips at speeds of around 25 MPH


If i want to take out 6 big folks than i really need to use the 17" and be carefully not to exceed the rated WOT of my motor

 

[TCROfreak]

Re: 3 Or 4 Blade Stainless Prop

I have a large family my wife, myself and 5 children, we plan on taking small trips on the river and lots of tubing I am sure, when the children get older I am sure wakeboarding will be added. Top speed is 45mph at 5k rpms. I would like a little more top speed and some more torque on the bottom end.

 

[Silvertip]

Re: 3 Or 4 Blade Stainless Prop

More top speed and better low end? You do realize those are contradictory terms. Get in your car and try to get top speed with the transmission locked in LOW. You have one gear in a boat so the prop needs to be selected that allows the engine to rev in the manufacturers recommended wide open throttle rpm band with an average load. You are already 200 RPM over that so the prop you have is almost spot on. Increasing pitch will help top speed but will hurt hole shot. Keep what you have. Since you are normally loaded heavy and do water sports, you might consider a four blade stainless of the same pitch you currently have. That will help hole shot but you might have to sacrifice a tad on top end. To increase speed you need to increase revs, pitch, or both. You are alredy over reving so that's not an option. Increasing pitch hurts hole shot and may actually hurt top end as well as you might begin lugging the engine to the point where it can't reach the top end of the rpm band with the loads you carry and water sports.

 

[TCROfreak]

Re: 3 Or 4 Blade Stainless Prop

I do realize that more top end and better torque don't go together. I am new to this boat thing am trying to learn. Having to choose I would say it would be more important to have lower end. My oldest child just turned 11 so I am not too likely to tow her down the river over 45mph. I bought the boat used and was told max rpm was 5k. I also noticed the boat cavitates when I take tight turn and have to trim down allot, will a 4 blade fix the cavitation?

 

[wca_tim]

Re: 3 Or 4 Blade Stainless Prop

More top speed and better low end? You do realize those are contradictory terms.

not intending to be contrary, but that's not entirely been my experience...

vented props can make a huge difference in coming out of the hole which can offset the loss you would normally get by going up a little in pitch to increase top end. Ironically, I have a custom drilled 26" turbo that is a good bit faster out of the hole than my 23" Laser 11. The Turbo is also my fastest top end prop. it's not my favorite because it cavitates out more easily in turns, but it makes the point about vented props.

You could go with a vented stainless prop that has the plastic inserts (please excuse myu not knowing specifically what is available for your set-up)

At lower speeds, vented props dump exhaust gas along the surface of the blade, creating something akin to cavitation (increasing slip) and getting engine rpms up for more power out of the hole. Not altogether unlike putting a stall converter in your street rod, wlthough not so dramatic.

I have one solas prop I got from iboats (12" hr titan). It's not vented, but it is one of the smoothest runing props I have. I got a 21" for pulling skiers, etc... and because the lasr 11 23" is just about right for an all around on my boat as it sits today. I probaby would have been just as well off to get a 23" in the solas, since it resulted in about 300 rpm incerase, and is so strong out of the hole that if I take off without putting the trim back in it will literally stand the boat up at well over a 45 degree angle.

All that being said? In your shoes, I would look for a vented 3 bladed prop, ideally one with inserts like the merc props so you can just change the cheap plastic inserts to change the size of the vent holes to tune how much extra slip you create out of the hole. 4 bladed set-ups are nice, and a lot smoother in my experience, but generally offer no advantage on tope end and somtimes even a slight decrease in top end. They can bite better out of the hole, but if you're trying to increase both top end and holeshot you don't want it to hook up so good out of the hole.

Hope this is helpful...

Hope this is helpful.

 

[wca_tim]

Re: 3 Or 4 Blade Stainless Prop

I also noticed the boat cavitates when I take tight turn and have to trim down allot, will a 4 blade fix the cavitation?

probably, but in my experience some props just hold better in turns on a particular hull than others, and trial and error is the best way to figure it out.

Not sure how the dealers are in your area or what your relatinship is with them, but a couple of the shops I buy things from keep a large stock of used props. I can usually borrow 3 or 4 at a time and see what works best when setting something up... it would be worth asking around... or checking with frisnds to see what they have. For example, I've got 6-8 stainless props around the house at this point and once i a while will loan a couple to a buddy to see how they work.

If you're not so worried about the top end increase (and aren't going up in pitch), I really do like the hr titan 4-blade I got from iboats for a little over $300 new it was a bargain.

 

[TCROfreak]

Re: 3 Or 4 Blade Stainless Prop

I took the boat out for the first time this season and really watched what the boat did with the entire family in the boat. The current prop is a 14.5" X 19 at WOT the rpm was 5200. I reseached in my volvo book and found wot should be 4200-4600. If I use and 3 or 4 blade prop and want to bring my rpm back down into range what should I use for a pitch and or blade count. I would also like to keep an all around good performance for family outings I am willing to give and take on both the top end and bottom end. Any help would be great.
I changed the oil and inspected the filter after the over rpm trip.

 

[wca_tim]

Re: 3 Or 4 Blade Stainless Prop

I would try an all-around 22" or 23" 3-bladed stainless steel prop, preferably with vents. If not vents and winds up being a choice between 21 and 23, I think I'd go with a 21. Note that I'm really pleased with a 21" 4-bladed solas titan that I got off here (not vented). They're a good prop for the money. Don't know off the top what is available for your outdrive.

 

[TCROfreak]

Re: 3 Or 4 Blade Stainless Prop

21 or 23 prop with 3 blades, would it be better to use a 21 or 23 prop with 4 blades vented or not vented.