Two Identical Props, one is 3blade, one is 4, which one is best?

ShawnQ · Nov 24, 2003

I know this question has been asked about a million times, and I DID search for an answer. However, it seems that these kind of questions are 'boat-specific', so I figured I'd ask. I have a 15' boat with a 90hp motor(Nissan NS90A 2 stroke, 1995,maxed out hp rating for the boat). I am more then happy with the top speed, actually a little worried with it (scary fast). I currently have a 3 blade prop on the boat, stamped 15. I am not sure on the diamater. When I bought the engine, the guy included a 4 blade prop, stamped 15 as well. Again, I am not sure of the diameter, but it is similar to the 3 blade. I am running right around 5200 rpm with the 3 blade prop. I can trim up, and get more RPM, but I like the way the boat handles with more engine in the water. Would I be better off running the 4 blade prop to achieve a better hole shot, and maybe lose a few mph (no prob). In general, I have read that the more blades you have the better the whole shot. Will more blades affect handling characteristics? Lastly, lets say I change out prop. What else can I maintainence while I have the prop off? All I really need to do is pull the pin, loosen the nut, pull the old prop off. Re-grease the shaft, and put the old prop on, right? Sorry, this will be my first prop change. I figured since the guy included the 4 blade, I may as well ask. Thanks! Shawn

LubeDude · Nov 24, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

Try it!!!!!!!!!!!!! LubeDude

JasonJ · Nov 24, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

I'm with Lubedude, slap 'er on and see! I had an older boat with an 85 horse Merc and had two props. One was a two blade, the other was a three blade. Same pitch, same diameter. In my case I lost a few MPH going to the three blade, but it did bite better. Typically, the less blades, the less drag, but it also doesn't bite and hold as well either. In the end, tryin' it out is the only way. Good luck...

backdraft · Nov 26, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

ShawnQ, I believe your hole shot will be better, the mid range will be about the same, and the top end speed will be slightly faster with a slightly lower rpm. There are so many variables , that I'm just theorizing but I thought I take a W A G. nevjb

kenneths · Nov 26, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

nevjb, bare with me on this, but I gotta' add my 2 pennys..... In my experience of testing props (not just a few) the 4-blade in the same pitch will do a couple of things. #1, your hole shot may be better. #2, your mid-range accelleration should increase. #3, your top-end will suffer slightly unless other measures are taken such as lifting engine on transom-NOT TRIM-engine hight above transom. #4, less steering torque. #5, smoother operation through-out the powerband. OK, my 2 cents.........

backdraft · Nov 27, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

kennys, I had forgot about the reduction in torque steer. I have found that ,at times , there is an increase in top speed, 2 to 4 mph primarily because the engine is drawn back into the better torque range of the engine , if it's set up right. Boy ,this should start the hot debate over again,{ not between us} on the running rpm of an engine and which is best. Running at the max rpm or the high end of the torque band, where I prefer. Have a peaceful happy holiday. nevjb

OBJ · Nov 27, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

Wait'l dhadley throws in his "Dimension X".

That'll get things rolling.

ShawnQ · Nov 27, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

Well guys, I plan to put the 4 blade on before the next time I head out. Anything I need to pay special attention to before I do it? Undo the cotterpin, undo the nut, pull the old one off. Grease the prop shaft, install the new one. That's it, right? Any kind of seals I can peak at? Thanks! Shawn

backdraft · Nov 27, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

ShawnQ , no and no. Let us know what the results are. nevjb

ShawnQ · Nov 28, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

WOW! WHAT A DIFFERENCE! I can honestly say that I am on a plane in under 3 seconds, easily! (of course, it's a 15ft boat with a 90hp motor that has a fin on it) The 4blade made a HUGE difference in the take-off, completely different boat. If I take off at a hair over half throttle with the 4 blade, it's the same as taking off at full throttle with the 3 blade. I also noticed that I can run more RPM with the 4 blade (I thought it would be the other way around). I can almost redline the engine with the 4 blade (5500), where I could barely get to 5000 with the 3 blade. I think the top end is about the same...if not, then it is just a HAIR slower, but not much. It's hard to tell, because it 'sounds' faster due to the higher RPM's. It seems like the boat and motor like the 4 blade a lot better though, and I definitely like the hole shot! One question: Is it better to run the boat at 4800 RPM (3blade) or 5300 RPM (4 blade)? It's a 90hp Nissan NS90A. The tach's redline (actually yellow) starts at 5500. Thanks! Shawn

backdraft · Nov 29, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

ShawnQ, run the four blade. Sounds like it has less pitch. nevjb

ShawnQ · Nov 29, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

Is it better to run it at a higher or a lower RPM? Some people seem to think the 2 strokes need to be run at a higher RPM...should I run it at 5000 or 5300?

backdraft · Nov 30, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

Shawn Q 5300 nevjb

LarryMP · Nov 30, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

You want your motor to be able to reach its' highest possible rpm not that your going to leave it there all the time. if you put to high of a pitched prop on your motor it will drop your rpm and put a strain on your motor. With a change of prop blades from 3 to 4 it's just a change of performance.

seadiva · Dec 2, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

hey other than putting greese on the shaft look for fishing string wrapped up there by the seal. just try to make that a habit when you change your prop. mabey ill see you here around calaveras if you go there? or port a area.

ShawnQ · Dec 2, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

seadiva, I fish calaveras about once a week. (Not quite as often in the winter). We've been catching a lot of 2-3lb channel cats everytime out, as well as a few undersized reds. Shoot me an email if you head out at S_Queeney@hotmail.com Tight lines shawn

BillP · Dec 3, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

Now you know one of the reasons why the flats boat guys prefer 4 blade props...

kalteri · Dec 10, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

hi i have same kinda problem as shawnq. have 90hp evinrude '93 outboard behind my openbow 15'4 Glassmaster. I use it for wakeboarding and 2-4 people + added weight( ballast cans water) 200lbs to produce more wake. I think I have 15 pitch 3-blade alu prop, WOT about 5500. (max. 35mph) boat weight 1500-2000lbs? It takes pretty long to get on plane and I preferably even add more weight. So what do you reckon? - 4-blade prop - lower pitch prop (13) - both of those above - hydro fin stabilizer ? do you think that stabilizer would help? It's hard to find 4 -blades in low pitch like 15 or under. Is it any good/reason to change pitch if change to 4 blade. Would 3-blade 13 pitch give a big effect compared to 15 pitch. I think I may overrev if I change lower pitch I think recommended WOT is 4500-5500 what is definition for hole-shot? good tips to improve low speed acceleration planing when wakeboarding thanks in advance

ShawnQ · Dec 11, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

Kalteri, I would say I have a 'hole shot' of less then 3 seconds (I consider this the time from when you are at a dead stop to the time you are on plane). That is a very quick hole shot as far as I'm concerned. I do have a fin on my boat, as well as the 4 blade prop. The 4 blade prop made a huge difference over the 3 blade for hole shot...so I would think that adding a 4 blade in your situation would help as well. But, I'm no expert. Unfortunately, I didn't get to try the boat without the fin on it, so I can't tell you the before and after of it. Last time I was out, I had 4 people on the boat, and the hole shot was considerably slower then when it is just myself and one other. Maybe the added weight is hurting you? Shawn

james082273 · Dec 11, 2003

Re: Two Identical Props, one is 3blade, one is 4, which one is best?

Kalteri, I think a 3 or 4 blade (if you can find one) 13 pitch will do the trick. You may have to throttle back to keep from over reving if you run wot a lot. If your adding weight to increase your wake size it would be counter productive to put a hydro foil stabilizer on. Yes it may shorten your planing time but it would lift the back of the boat and make your wake smaller also. My .02 Jon Boater

Two Identical Props, one is 3blade, one is 4, which one is best?

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