Props

[JimCt]

Is it fair to say that an I/O would use the same prop as an outboard given the same HP, boat weight & waterline length?  It makes sense to me that the props would be the same but is there some difference I'm missing?

I'm trying to establish what diameter/pitch prop I should use for my 240.  I've tried using the prop finder Mercury Marine has on their site but after I plug in the length, weight, hp and so forth the selector bombs out.  The numbers for the rig are: weight approx. 4300#, waterline length about 21.5', HP 230, max WOT revs @4600, Alpha Drive ratio of 1.62, and the mission is good "all-around" performance.

Lastly, are S.S. props all that superior to aluminum props?

Any guidance as to what would be a good prop choice is appreciated.

[John Jones]

Jim, I'm not expert but there is one that hangs out in Florida Sportsman Boating section.  http://outdoorsbest.zeroforum.com/zeroforum?id=16

Make a post there with all the details.  "Dunk" is a marine surveyor from south Jersey and is great with props as well as other stuff and has helped a lot of folks.  He will answer your post within a day or two.

[JimCt]

Will give it a shot.  Just signed up.

 Tx JJ!

[pete]

A ss prop is definately the way to go,much stiffer than alum so there is less flex,your pitch stays truer,also much sturdier and easy to have repaired,I have had ss props on my last 3 boats and wouldn't go any other way.one prop will last as long as you own the boat,if it gets nicked up or bent just take to a prop shop and get it refurbished.

[Bluesbrother]

Its true that the SS props can be repaired, but remember if you hit something it will not giveway as easy as an alloy prop. The shock is essentially absorbed by the lower unit and shaft. If you damage those it is much more expensive. Also the SS prop is much heavier.  I really wonder if you will notice the difference between the two on these type of boats. ( they are not race boats)

[GoneFission]

Stainless steel props are more efficent due to having thinner blades and more cup.  Also, an aluminum blade will break off when you hit something, and a SS prop will usually spin on the rubber hub and not break when you hit something hard.  Stainless is the way to go...

The prop shaft is the same for Merc outboards over 135HP and the Alpha outdrive, so the propellers are interchangable, but the gear ratio is different.  Outboards have a 1.87 gear ratio, and your Alpha drive has a 1.62.  Therefore the props will not be exactly the same.  I would gues a 17 pitch and 14 inch diameter wheel would work, but that may be off by a bit.  However, as the ad says, your mileage may differ.  You may want to try a couple different props before you settle on one.  See if you can find a parts dealer with several pitches that you can try out - then pick the one that works best.  

Good luck!

[ddd222]

jim, w/out a doubt ss props are better and provide optimium performance, but depending where you boat aluminum may leave more options if u hit anything. For example, everyone on N shore of LI uses aluminum because of the rocks, better to lose a prop than gearcase. Sshore dudes run ss because its 95%mud and sand.
    As far as perfect size i would get the guy who sold u the power to be a non commital as possible. When i repowered my 222' the tech's guessed at prop size and came close but were off by a half inch, and they wouldn't swap out $700 yamaha s/s prop. The problem w/ mine and what you should be concerned w/ is optimum specs of maufacturer. Mine at WOT maxed out at 5100 rpm. Everyone concerned said it was a bit low, but not where it would damage the motor. No swapping out prop so i learned to live w/ it, but after talking more i realized that WOT should have been 5600-6000. So regardless of prop cast, i would lock down the size to cruise and WOT for best performance and effieciency. Ideally they should have test props handy before u commit, inboard, i/o, or outboard.

[Bluesbrother]

GoneFission:
Also, an aluminum blade will break off when you hit something, and a SS prop will usually spin on the rubber hub.

That is if you are lucky, I have seen several people bend shafts and damage gears because of the SS prop....

[JimCt]

OK, thanks for the info.

Will investigate what shops around here will let me experiment with props.  Still have a long way to go before propping but the "off season" is a good time to do the homework.

[Anonymous]

As for the prop design there are props made specifically for sterndrives but most outboard props will work well. As a (very) general rule of thumb, the 14 1/4" 3 blade props for a Merc outboard will work on your drive. There are some much larger diameter props, like the Turbo Lightning or TXP, that are made for outboards running a high X dimension and certian kinds of hulls. There's no need (generally) to buy one of those for a sterndrive. You'd be buying a lot of technology that you couldn't take advantage of easily.

What prop(s) have you run? If we can get an idea of what you've tried we can guide you thru the process. If you're looking at 3 blade props don't overlook the Stiletto line. I have Stiletto's and Turbo's so we may be able to hook you up if we have an idea of what you're running now.