props

[anotherhassel]

just read mccullicuddy's post and was wondering what a stern lifting prop is, why or how it works, and what situations to use them. thanks john

[McGillicuddy]

Greetings another hassel,

I have no idea. Just a buzzword I heard and thought it was cool. I first heard it from Fr. Frank who suggested my Seafari would perform best with a stern lifting prop. He's probably rigged more hi-performance boats than I'll ever see, so I believe him. I'm guessing he'll chime in after seeing my butchering of this very hydro-dynamic subject.

In simple terms some boats ride better when their bow is down a bit (deep-V)and some only want the aft in the water (bass boat or flats boat). Some boats are just bow heavy and some are stern heavy. Differences in propellers can make them achieve their maximum capabilities. A bow heavy boat will just plow water below cruising rpm if it can't rise to say 3-5 degrees off level. By getting the bow up a bit it will reduce drag and enable it to get on plane at lower rpms, thereby increasing efficiency. If a boat has too much weight aft, the rear of the boat is pushing water and needs a means to level it out to get on plane. This can be done with a hydrofoil, trim tabs or with a stern lifting prop.

In very general terms, a propeller that has more rounded blade tips and cupping at the front of blade will tend to have bow lifting characteristics, while those with a straighter back edge thus a sharper blade tip (semi-cleaver)and cupping on the back of the blade may have more stern lifting capabilities. AS to the why? part, well that's more hydrodynamic physics than I can wrap my meager mind around.

Do a search for "stern lifting propellers and you'll likely find a boston whaler site called continuouswave.com There is a pretty spirited semi-technical discussion there among engineers and boatsmen, certainly far more depth than I can offer.

Still others will say there is no such thing as a stern lifting prop. If not, there are some great marketeers out there...

[Fr. Frank]

Without getting into too much detail, the higher the percentage of generated thrust is produced closer to the center of propeller rotation, the greater the amount of stern-lift is produced.

This is why, generally speaking, 4 blade props and cleaver props produce more stern-lift. The inner 50% of thrusting surface on the propeller produces greater than 50% of the thrust produced.

A caveat: for some reason, unknown to me, every now and then a prop defies the expectations even of the design engineers. FOr instance, the Mirage, Mirage +, and PowerTech Offshore series 3-blades are all pretty-much diametrically balanced props, yet all produce good stern-lift.

Still, the best way to find just the right prop for your boat is to try 'em all, or at least as many as possible, making sure to take advantage of the experience of others who have used those propeller types.

Believe it or not, the major boat manufacturers still use the "Hey! Let's try that one" method of finding and selecting the prop to be included or suggested for their new boats. Sometimes even the experts are surprised by what ends up working well.

[anotherhassel]

thanks guysI actually have the style prop that mccullicuddy got out bid on. My boat not a seacraft runs pretty well with its 130 hp yammi. The boat is about the same size as a "21" tracker seacraft which is like 20'-5". Someday when I can figure out how to get the pic off of photobucket I ll post it. Thanks again for clearing that up.

[McGillicuddy]

Login to photobucket. Go to the picture you want. As you hover cursor over it, 4 boxes should pop up. Left click on bottom of 4 dialogue boxes that pop up (IMG Code) That copies the link. Then log on to this site and paste link to post box. that should do it.

[1bayouboy]

For example the Rev4 is a really good sternlifter whereas the Enertia seems to be a bow lifter at least in my boat which is a sterndrive and hence sternheavy. With the Rev4 it just smoothly runs up on plane with minimal tabs.....with the Enertia the bow really goes up and it takes tabs to get her down.

[anotherhassel]

Thanks Mcgillicuddy they were on myfishpix but ssame principle. Here she is they called it a 21, she has a 130 yammi. She isnt a seacraft but I love her anyway. She is fast to about 40 mph 5800 rpm.

[peterb]

I just got of a pair of lightly used the rev fours to do a little stern lifting on my 23'. Between twin 200 HP OX66's and a full flotation bracket I have to have around 1,200 pounds or so hanging off my transom.

I have not tried them out yet. May have to wait until spring.

[Fr. Frank]

I just got of a pair of lightly used the rev fours ...
I have not tried them out yet. May have to wait until spring.

emphasis mine

Sob, Sob. Peter, that may be the saddest thing I've heard today.

[lost2a6]

emphasis mine

Sob, Sob. Peter, that may be the saddest thing I've heard today.

Yea I agree, I think that I'll take the ole Seavette out tomorrow and put some time on the new ZZ502.