Propping DF70 on pontoon

[18pontoon]

Fixer upper motor came with a 13.25x16 stainless prop but only got 4k rpms and 8mph. Guy at west marine recommended a 13.75x15 we have now but were still only at 12 mph and 4k rpms. Should I go for a 13 pitch or lower? 18 foot pontoon.

[keakar]

you need to get it up around 5800 rpms to be right so based on that you should figure 200-300 rpms change for every change in pitch.

since you need to go up 1800 rpms, that's a really BIG gap so forget about the list of recommended props for your motor since the load (pontoon) makes those recommendations not apply so none of those props will work well. you will need to select the prop that fits the pontoon best and I don't think you will find it on any "recommended" chart.

you don't want a larger diameter prop for sure, what you need to do is reduce the diameter as well as the pitch to get those rpms up.

something like this might be just what you need: http://www.ebay.com/itm/Clean-Used-O...866047&vxp=mtr

it may have even come off of a pontoon boat.

the key will be to find someone else with a pontoon of similar size and hp then match the prop they use and that should get you the correct info on what to buy so you can get it in the correct 5600-5800 range. hopefully someone here on the forum has something like yours and can tell you what they use

[Moonlighter]

Expert advice is what you need now, i agree with previous post, you need to get the engine revving at WOT to around 5800rpm. What diameter would be best is beyond me because my experience with pontoon boats is zero!

I would suggest you give Ken at the Propgods.com a call, there is very little they don't know about props. Yours is more complicated than normal due to being on the pontoon boat, but they would no doubt be able to help you.

[18pontoon]

Thanks for the help. I'll see if I can get a 10 or 11 pitch at whatever diameter west marine has today... Too eager to try out the replacement motor. Will probably just get something that will work for today and continue tweaking after.

[18pontoon]

So the 14x11 at west marine did not fit on the DF70 foot... The diameter of the prop where it meets the foot was slightly larger than the other prop. Need to make a couple of calls during the week to find out what I need.

Is there any way to know for sure a prop will fit a certain motor? The mating diameter is not specified, just the manufacturer and HP. Is that all there is to go off of to check for fit? I want to try not to waste more time with props that wont even fit.

[keakar]

So the 14x11 at west marine did not fit on the DF70 foot... The diameter of the prop where it meets the foot was slightly larger than the other prop. Need to make a couple of calls during the week to find out what I need.

Is there any way to know for sure a prop will fit a certain motor? The mating diameter is not specified, just the manufacturer and HP. Is that all there is to go off of to check for fit? I want to try not to waste more time with props that wont even fit.

there are hub sizes that are mostly standard but there are a few different versions so you just need to get a prop for your hub diameter.

I couldn't tell you what hub diameters average for what size motors but measure your prop on the small end for inside and outside diameters of the ring (not sure which is used) and that is the hub you need to find a prop in.

call that pontoon guy listed above and he will be the best guy to guide you through this stuff since everything about your needs are special and not under the normal prop finding process

[18pontoon]

Ordered a 14x10 from boatersland.com. Can't find anything locally so I just wanted to get one on order.

Quicksilver QA3828X Black Diamond 14" X 10" 3 Blade RH Propeller - Quicksilver QA3828X - Evinrude/Johnson 40-75 HP Outboard Propellers - Evinrude/Johnson Outboard Propellers - Outboard Propellers - Propellers - Boatersland Marine

Specifically says its for a DF70 and 10 pitch could work... Price is nice.

[keakar]

Ordered a 14x10 from boatersland.com. Can't find anything locally so I just wanted to get one on order.

Quicksilver QA3828X Black Diamond 14" X 10" 3 Blade RH Propeller - Quicksilver QA3828X - Evinrude/Johnson 40-75 HP Outboard Propellers - Evinrude/Johnson Outboard Propellers - Outboard Propellers - Propellers - Boatersland Marine

Specifically says its for a DF70 and 10 pitch could work... Price is nice.

based on your rpms with the 13 x 16 (4k) you should gain about 1200 rpm with that prop dropping 6 pitches down to the 10 pitch but by going up in diameter size to a 14, this hurts you and will turn about 200 rpms slower because of that so you might only be able to get 800-1000 more rpm from it which is still too low but a world better then you have now.

you really should try this one:

Solas Amita 3 Aluminum Propeller 11.1 diameter x 14 pitch (for mid size motors) http://www.ebay.com/itm/191206381363...84.m1555.l2649

and if that's not enough then try:

Quicksilver QA2064X Black Diamond 11-1/4" X 10" 3 Blade RH Propeller http://www.boatersland.com/qspqa2064x.html

or one of the Apollo 10" diameter props listed here: http://www.boatersland.com/e-j-40-75...ard-props.html

thinking of it in terms of cars, the diameter change is like a gear change in the rear end and has the most impact on power, speed, torque, and rpms where the pitch size is more of a transmission gear selection and not as great an impact

aftermarket props will be your source and im sot sure but I think you need to go down in both diameter and pitch to get there

now the disclaimer: im not a pontoon guy so im basing my recommendations just on what I have learned about how pitch and diameter changes effect your rpms and "actual results may vary" as they always say so the math isn't always going to give you the expected result.

I strongly suggest you source a boat salvage dealer or yard so you can borrow props to try so you don't spend money buying unusual prop sizes you may not be able to sell to get your money back from.

[taney county dude]

I just went through this with a DT60 on a 18' pontoon. The motor came with a 11 1/8 X 16 pitch prop. 17 mph was the best I could get. I didn't know what the rpm was because I didn't have a tach hooked up at the time but I have one hooked up now. But, after consulting with a prop shop he recommended a 11 1/2 x 12 maybe a 11. I bought the 12. My manual on the motor specifies the rpm to be between 4800 t0 5500. That prop got me to 5200 rpm, 22 mph. If I can find a deal on a 11 pitch I will probably get it to see what it will do, in the mean time the one the prop shop sold me is working great. If you have a local prop shop you trust they should be able to fix you up.

[noelm007]

Way back in the "good old days" you used to be able to buy a big bladed, low pitch props for displacement boats, they provided very high thrust because of the blade area, but were able to get the RPM up to manufacturers specs, anyone know if such props are still available?

[18pontoon]

14x10 works like a champ. 18.5 mph at 5800 RPM with a very light load. Needed more weight in front in order for it to plane properly. Had it trimmed down all the way but it didn't quite level out at speed. Will see how it goes this weekend with more people and coolers