Enough pitch?

[opposedtwin]

Is 10 enough pitch to move a 14 foot aluminum boat with just me in it? It’s an alumacraft FD. The motor is a 30 hp mark 30.

The reason I ask is because I’ve spent (too much) money on props with a lot of pitch to go faster only to find they’re crap. Specifically, I tried "speed" props on big twins and my FD-11. The additional pitch seems to be a waste of good money. People screamed how "awesome" the AJC417 twin blade brass prop works on the FD. I got one and found it does almost nothing more than the standard cheap painted aluminum 3 blade prop that came with it from Johnson back in 1957. The brass "looks" awesome, but looks (it turns out) don’t make the boat go faster. 😯

Thoughts?

[dave-bernard]

if you carry a load it is fine . use a tach and see where the RPM’s are should be 5600 – 5800 full throttle. go from there . for each in pitch you will changes 200-250 RPM’s

[fisherman6]

Scott,
I’m certainly not an expert with regard to the pitch question, but from my experience it seems like 10" pitch is a little shallow for 1 person (lightly loaded) in an Alumacraft FD with a 30hp motor. When I run my Merc 25XD on my 14 foot Sea Nymph I get about 25mph. I’m running an 11" pitch on that motor and it could use more pitch for more speed. I believe it would benefit from a 13 pitch prop. I haven’t measured the rpm with a tach but it winds up. I likely won’t mess with it since I rarely run that motor with no one else in the boat. (I like a Fastwin on this boat with just myself in it) It will push a full load along at a nice clip. That boat is a bit of a handful in rough water running flat out with the Merc 25 on the back. It is pretty comfortable cruising at 20mph at a little over half throttle though. I have a video on my YouTube channel of me running the 25XD on the Sea Nymph. I hit 25mph flat out in that video. She’s screaming along at WOT. Here is the link if you want to see it.

https://youtu.be/muHFxQJ0Hi8

It makes some difference if you are tiller steering or forward steering too. Sorry for the lengthy post. I hope this helps some.
-Ben

OldJohnnyRude on YouTube

[RICHARD A. WHITE]

Wanting to chuckle as I know this will catch grief, BUT…..
Why in the world do you want to use an OMC and try to go fast?? Plant a Merc back there and let it ripo..
My 1947 Merc KE7, off a fresh rebuild, stock prop, does upwards of 22 mph, from a 10 hp, on my 14 foot 1963 StarCraft Seafarer. I weigh in at a healthy 260+ lbs and can’t get to the middle seat so I know with a smaller person that setup should be near 25-30 mph depending on who is driving, find a speed prop and good night. I love my OMC’s for cruising. I have a Wizard Super 10 that is actually faster than the KE7 and that is with carrying the extra 6 gallon tank of fuel, and they have the same prop, both bone stock…. I was running near neck and neck with a 25hp OMC on a 16 foot StarCraft couple of years ago, only 2 mph slower with my Wizard Super 10 on my 14 StarCraft.
Shoehorn a Mk28 power head under a Super 10 cover and watch the OMC guys cry for they won’t catch you…

Come to the dark side if you want speed from a smaller 10 hp motor, stick with OMC for everyday cruising, wanna play with the big boys….
buy a Big Four…LOL

Enjoy brother, it is all fun

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[PM T2]

"using an OMC" and "going fast" in the same sentence… u funny…….

all kidding aside, I also prefer the Mercs, for the simple reason that I find a better power-to-weight ratio always works in my favour.

My 22.5 HP 1955 electric-start Elto weighed in around 130 pounds fully dressed. My 1957 manual-start 40 HP Mark 55 weighs 110 pounds. 18 more HP from 20 less pounds of motor. Math works. I also get better fuel mileage out of the Mercs. The Merc four-cylinder could get me 3.5 hours of WOT out of a tank of gas. Same tank of gas lasts almost an hour less running the OMC twin of comparable displacement (35.7 cu in OMC versus 40 cu in Merc)

Whose afraid of a little grief? Not I, lol.

I’d rather lug a Mark 75 on my back across the desert… or be forced to turn a cactus inside out and use it for a canoe….. than run any classic OMC on any of my boats………hehehe

Enjoy.

Best,
PM T2

He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...

[fisherman6]

I’m certainly not afraid of a little grief. You guys sure are dishing it out to a couple of guys that were both talking about running Mercs to begin with. 😉 Scott was talking about a 10 pitch prop on a Mark 30 and I was comparing it to running my Merc 25XD with an 11 pitch (even though I am more of an OMC guy and prepared to take any grief that might get me). Scott said he found no real advantage to the AJC417 and I said I prefer a Fastwin on my 14′ Sea Nymph. 🙂 I won’t argue that a Merc will typically give a better power to weight ratio. There are other reasons I like my OMCs. It’s no fun if we can’t trade a little ribbing though, right! 😆 😛
-Ben

OldJohnnyRude on YouTube

[RICHARD A. WHITE]

Well, heck, missed that, saw the FD-11 and was instantly transfixed with the 1957 Johnson FD-11…LOL
But he does specifically mention Big Twins, and his FD-11, is the FD referring to the boat? 😀

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[fisherman6]

The boat is an Alumacraft model FD. Lots of people say how great the AJC417 prop performs on an FD / Big Twin. I believe that was the message. Scott, correct me if I’m wrong.

The best part is how easy it is to stir up the Merc guys by mentioning speed and OMC together. 😆 No argument here. I’m an OMC fan but am always impressed with the speed a small Merc can deliver. I also enjoy some friendly ribbing. 😛 It’s all fun!

Anyway, back to Scott’s question. I still think the Mark 30 will benefit the from more pitch with a lightly loaded 14′ Alumacraft FD when going for top speed with a light load. What do you guys think?
-Ben

OldJohnnyRude on YouTube

[auldscott]

Propeller pitch is only one factor in propeller selection. Diameter, number of blades, blade shape, LU gear ratio, blade edge condition, cupped/not cupped etc. all play a major part.

opposedtwin’s experience with the "speed" prop probably is not a predictor of what would happen with the Mark 30/FD rig with a change of pitch but using the same basic propeller design.

If your motor is operating at the upper end of its rated RPM on your boat, and the boat is loaded as you intend to use it, you have the correct pitch propeller. If it is winding too high, the propeller should have a higher pitch, but all else should remain the same (within reasonable limits).

Cupping has the effect of increasing pitch, but the specific effect of cupping is beyond my expertise.

You can get most propellers re-pitched for a reasonable cost, which might be an alternative to trying to find another propeller with higher pitch but the same basic design.

[chinewalker]

Going for a "speed prop" when the rig isn’t set up for it is akin to putting racing slicks on a Winnebago. Most of the AJC props are pretty tall (high in pitch). Putting a tall prop (AJC-417 is 12-inch pitch) on a 18hp FD-11 and expecting it to push a heavy 14-foot tinny at a high rate of speed is asking a lot. Works better with a light load.

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