confusion & questions
 

I took my new to me 1997 180SE Shabah out for the first time this weekend and it was great. Saturday I was to excited about being on the lake to really pay attention to the numbers because we had friends with us and we were skiing and what not.. But Sunday when it was just me and my brother I paid a little closer attention to all the gauges.

I have a Volvo Penta 4.3L with the Cobra SX drive. At WOT I'm running 40mph at right under 3000rpm. The rpms seem low so maybe my tach is off? I want to replace the prop because the one that came on it is in pretty bad shape. It appears to be a 17 pitch judging from the 14x17 markings on it. I know nothing about props or pitch or the correct diameter. And when I look into them I find there are several options for my particular engine/drive setup. But then as I dig further I discover different rotations, 3 blade or 4, aluminum or SS and I have no idea what to get. I'm looking for something that will give me the best of both worlds as far as low end grunt and a good top speed. I figure with all the different prop options there has to be a middle ground somewhere. I was able to pull my buddy that slalom skis pretty easily once I moved his and my wife to the front of the boat. It took a few seconds to get him up and on plane but after that we were fine. My boat also has smart tabs if that means anything to anybody. How hard is it to change a prop? I am very mechanically inclined so if it doesn't have to be taken to a boat mechanic then I know I can do it. Will the new prop come with everything I need or will I need seperate parts also? I appreciate the help and apologize for the newbie questions.

Re: confusion & questions
 

If you are "very mechanically inclined" then i'm pretty sure you can handle removing a nut, sliding off the old prop, sliding on the new prop then reinstalling the nut. :)

Lets start with a basic primer on props. Note the following comments are general information only and there are always exceptions to the rules but for the most part this should guide you in choosing the correct prop.

Aluminum props are good all-round props that are reasonably cheap to buy and relatively easy to repair if damaged. I would recommend them if you are boating in waters that tend to have debris, rock shelves, tree stumps etc just for those reasons. SS props tend to perform better than aluminum props due to their stiffness but that performance improvement comes at a much higher initial purchase cost and if damaged, a higher repair cost. My personal opinion (& a couple of members here will disagree with me) is to avoid composite props like the plague. They are good as backups only.

As for diameter, most will be somewhere between 14" and 14.5" in this range. Usable pitch will range from 17" to 23" with probably 98% of these boats using a 19" - 21" pitch prop. The general rules are: when you reduce prop pitch your rpms increase at WOT, you get improved low end grunt but your top speed decreases. The opposites are true when you increase your prop pitch. Going too far in either direction causes performance issues and significant extra wear & tear on your engine/outdrive.

A 3 blade prop provides the lowest amount of drag & balance while in the water. It is the 'standard' when it comes to props. A 4 blade prop provides a little more "bite" which works well for wakeboarding/skiing etc & tends to run slightly smoother but due to the extra drag (more blade surface in the water) takes 1-2mph off your top end and generally runs at a slightly higher rpm than a similar sized 3 blade. There is a 5 blade (Hi-Five) prop out there that some members here use and are very happy with the performance but again at a significantly higher price. I wont try to get into prop dynamics & blade shaping/venting etc cuz it will only get confusing....

As for your tach i suspect it isn't reading correctly if it says you are running at 3000 rpm while doing 40mph with the 4.3. There should be a small dial on the back of the tachometer. If you can access it, give the dial a spin a few times then reset it to "6 cyl". Sometimes a bit of corrosion or wear causes them to misread.

All that said, your 4.3 is designed to run most efficiently between 4400 - 4800 rpms at WOT and your boat should hit the high 40's with the correct prop. Generally speaking the 14.25" x 19" pitch 3 blade aluminum prop will give you just what you are looking for. I've always liked the Quiksilver Black Diamond or the Michigan Wheel Vortex as good props for the price. Here's a link to iboats.com and their selection of 19" props for your particular boat/motor/outdrive.

Personally i have 3 props for my 180 with the 4.3LX: a 19" 3 blade Black Diamond, a 21" 3 blade Vortex and a 20" 4 blade SS Michigan Wheel 'Apollo'. I rarely use the 21" as on my boat, it sacrifices too much low end grunt just to gain 1-2mph at top end. I probably use my 20" most of the time as for me, its an excellent compromise and has me sitting right on 4800rpm at WOT with a top GPS speed of 47-48mph. MOST people dont run their boats at WOT for long. It causes too much wear & tear and uses far too much fuel. I've found that the compromise props (19" or 20") gives that low end grunt with decent mid range acceleration & a reasonable top speed.

Best of luck & let us know what you decide to do!

Re: confusion & questions
 

Wow thanks Mikey for the help. One more question. I noticed the props in that link you provided some are standard rotation and counter rotation, which one do I get?

Re: confusion & questions
 

Standard rotation.

Re: confusion & questions
 

One more thing LOL!!! Some of those listed come with hubs and some dont. Whats the difference, which one should I use?

Re: confusion & questions
 

Probably best to buy one with a new hub. That way u dont have to worry about it.

Re: confusion & questions
 

I ended up going with a 4 blade 14.25 x 19. We are going to be doing a lot of skiing and tubing so I figure it's a better option. Thanks for the help Mikey

Re: confusion & questions
 

Please let us know how it works out for you.

Re: confusion & questions
 

Should have a report this weekend

Re: confusion & questions
 

Ok took her out on Saturday with the new four blade prop and let me tell you its like a whole different boat. First thing I noticed was how smooth it was with the new prop. Before there was a vibration you could really feel and that is gone now. I set the tach on 6cyl and it worked fine. At WOT my rpms are right at the 4800rpm mark so I think I'm right on the sweet spot. I managed to get 40mph out of her with 6 adults and a 13yr old, 2 full coolers and everyones gear and what not. And I had the Bimini up so it was just acting like a parachute. I figure with me and just the wife and a small cooler I could get a lot more speed out of her.

I am super happy and I appreciate all the help guys thanks.

Re: confusion & questions
 

Glad to hear it worked out for you. Carrying that many adults/weight in the boat can certainly affect the speed but i'm still a little surprised you weren't slightly higher (42-44mph).