View Full Version : 3 blade or 4 blade prop?
01-02-2007, 06:34 PM
I'm new a newbie to boating and recently picked up a 98 Moomba Outback. The boat came with both a three blade 13x13 OJ and a four blade 13x13 prop. I have them off the boat right now and will be getting some minor dings taken out of both of them, What is the difference in these? We will be wake boarding and skiing, so what would be better? The guy I bought the boat from said that he did not notice any difference. The guy who is machining them says that the minor dings would afect the motor preformace by 200-300RPMs but would'nt really say witch is better.
01-03-2007, 12:33 AM
The props (when new or recon.) are pretty close, the diff. you will feel in the 4 blade is; a better hole-shot, 2-300rpm increase with a 1/2- 1mph top end decrease, some say it is smoother, others feel the flutter in the floor or on thier butt. There is very little wake change on this prop. unweighted, however, it is designed to give the boat more lift aft (when weighted), to give it more hull displacement for a bigger wake. I would prefer the 4 blade for both skiing and riding, and use the 3 blade as a back up. I hope this helps, keep us posted. Brian Raymond
01-03-2007, 01:43 AM
I have a 98 Mobius and I've had a four blade SS Cutter prop since I got it and put the three blade nibral away as a backup. I like the hole shot for skiing which I do most.
01-03-2007, 06:47 AM
I just purchased '98 mobius, it has a 4 blade (bronze appears) on it, havent looked to see pitch etc. what should be my max rpm? Iran it up to like 5K other day and backed off quickly. it seemed to pull strong up to about 4-4500 rpm then just kinda went flat, more rev but no pull. I was thinking maybe of pulling prop and having it tweaked some to slow max rpm. any suggestions? what pitch and diameter are you running on your'98 Zab. and what is your top end speed and rpm? thanks, bob
01-03-2007, 10:24 AM
There is a good article in this months wakeboard mag that shows the difference between different props and what it does for performance.
Worth checking out
01-03-2007, 05:24 PM
I use the 13" X 13" My top speed is around 45mph and 4700-4800 rpm. I would recommend keeping your prop at the recommended pitch and talk to the propeller experts including SC as they have the experience with issues you may have. I don't think you would want to drop your RPMs lower than where it is now. I beleive the 350HO reline is about 4900-5100 RPMs (a little higher than the standard 350). Going to a larger pitch prop your RPMs will decrease at the high end but I doubt if you see much of a change in speed as your loading the engine as well. You will be slower out of the hole but should be more fuel efficient in the low to mid range RPMs. If you are looking at a higher top end speed, Mr. Raymond's info on the three bladed prop sounds like the way to go but again the increase is only 1 mph. I got more top end out of the boat by changing out the throttle linkage as someone who had my boat previosly had mofified the linkage and the carborator wasn't opening up all the way.
01-04-2007, 07:19 AM
Hey Zabooda, thanks for info, what or who is SC ? I'm not looking for really more top end etc. Just from my old hot rodding days the idea situation is to peak out rpm's & horsepower at the same time. Kinda like looking at the power band or horse power range when an engine is on a dyno , there will be peak H.P. at certain RPM. after that you may rev higher but power falls flatter. Just kinda like saying getting the best performance outta of what you got. I'm way over the need for speed :-) just looking to get it "geared right" ... I use to not mind winding them tight, but as I have become older it hurts worse when something tears up, I'm looking to drop rpm's a little more toward the safe side. I'll watch'em close myself but I have a son approaching 15 and if his buddy or another boat comes along side a rod out the side of block is probally last thing on his mind. I remember those days well... Heck when I was 15 my dad bought a 1970 El Camino SS with an LS6 454cid 450/HP I was murder on tires... when the cats away... any way enuff babble. I just noticed your from W.St. man yall have had it ruff ! friend of mine lives there said he's moving back to Fl. stay warm & safe... be blessed, bob
01-04-2007, 01:04 PM
SC = Skier's Choice = Parent company of Moomba and Supra tow boats.
01-05-2007, 03:05 AM
I think your RPMs are OK at 4600. When your son uses the boat just have him pay for the gas then he will know what effect the 4-barrel has on speed and the pocketbook. I used to live in Niceville and raced Hobie Cats in the late 70's early 80's and waterskied the bayous. Went to a few FSU games too. I miss that place. Always retirement time. Take care.
01-05-2007, 07:35 AM
ab. yea Niceville's not far, my son played in a baseball tourney their a couple yrs. back. as for the rpm's I'm with you as for 4600 would be good. what i was saying is it pulled strong up to 45-4600 then it continued to whined out to say 5100+ but not really pulling, so I backed of quickly, I was just saying with a 15 yr. old , kinda all they know is Wide open throttle, when feeling pressure :-) from the side. even though your top speed may have already been reached. Kinda like the old mistake outboarders make, they get on that trim button rpm,s keep going up but there comes the point where the MPH starts falling back and your just over revving. anyway I will play with it and see. I lean a little toward the babying side as I need to make this ride last. I really never thought we would be able to afford a boat of this calber but when I ran across this one at such an awesome price, I couldnt resist. I figured I bout dbld. my money> on paper anyway :wink: take care my friend and have a great wk.end. just heard weather, looks like we are gonna have 70's tommorrow, sure my boy will be looking to ride...
01-05-2007, 02:44 PM
Ah, now I get it. Yes, anything above 4800 RPM is rather high but it's odd that the 13X13 is allowing the RPMs to be that high. You may want to check out the tach first to make sure it is accurate as my tach often jumps around. Second, this is an afterthought but there could be some slippage allowing the higher RPMs which means transmission issues. Make sure you have the correct fluid level in the tranny or replace the fluid with the correct fluid and fluid level. The last fix would be to modify or replace the prop unless there are signs of damage or if the prop was modified as the 13X13 should be the correct size.
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