Prop Question

Harry Woods · Post by **Harry Woods** » Dec 1st, '14, 19:41

I am reducing the wheel pitch on my 4LH Yannies by one inch in order to pick up an additional one hundred RPM's. I have located a set that has a slight cup. Will the cup take RPM's away from the hundred I am trying to gain. Also, what is the recommended cruise RPM for the 4LH Yannies? Thanks.
Harry

Kevin · Post by **Kevin** » Dec 1st, '14, 21:41

Harry,
You can have your current props re-pitched unless they have already had 2 inches or more of pitch taken out. I forget the maximum amount recommended but any the prop shop should be able to tell you if you have room to spare.
Yes, adding cup will reduce your RPM but the amount varies depending on how much cup is added.
Lots of discussion on props and every boat is different. Taking out more pitch and adding cup helped my boat to the point is was measurable on the GPS. You can only go so far though.
If you decide to buy used props I recommend getting them checked out anyways. You will not be able to see subtle variances such as if they are out of rake just by looking at them unless there is obvious damage. It is worth it when you factor in boat haul out, prop swap labor and long term fuel consumption.
Do a google search on your particular engines. Get the cruise and wide open throttle rpm specs. Make sure you can hit your wide open throttle RPM per specification for engine longevity.

Harry Woods · Post by **Harry Woods** » Dec 2nd, '14, 16:54

Kevin,
The prop shop agrees with you in keeping the cup and reducing the pitch. They stated that the addition of a number 2 cup will reduce RPM's by 100 and that reducing the pitch by 1 inch will increase the RPM's by a like amount. Further, that performance will be enhanced. I am running the same boat as you are and value your performance comments. Do you remember the pitch reduction you used when adding the cup? Thanks again for your help.
Harry

mike ohlstein · Post by **mike ohlstein** » Dec 3rd, '14, 02:33

Cruise @ 3100 rpm forever, as long as you can wind them up to 3450 or so…..

Charlie J · Post by **Charlie J** » Dec 3rd, '14, 09:07

I run mine at 2400 - 2600
and open them up every now and then

Harry Woods · Post by **Harry Woods** » Dec 3rd, '14, 12:13

Mike & Charlie,
I have been running at 2750 for ten years. I am in the middle between you guys. Doing a little wheel work to boost the max RPM to 3400. I hope the cup works out. Thanks for your feedback.
Harry

Kevin · Post by **Kevin** » Dec 3rd, '14, 15:29

Harry,
I have been experimenting over the years with props. Original gassers had 17x17. Switched to diesel right away and I think I went to 17x16 no cup for a few years and cruised about 22kts. A year or two ago I had the prop man make them 17x15 with light cup. End result was higher cruise speed with same RPM.
Shortly there after I removed bottom paint and Mark (Buju) hooked me up with a nice n smoov bottom paint job using VC Performance epoxy. Got a some more speed out of it.
Some of the speed increases were from tweaking rudder surfaces to reduce (I think) drag. Weight and balance is VERY important in a 28. The more in the back the better. The more weight I moved from the front to the back helped as well.
Bottom line is every boat will be a little different depending on power plants and weight distribution. I'm low on the HP side but decent amount of torque. Nothing like a Cummins 6B though.
Now the boat seems to be pretty much at its best cruise around 25 knots. I don't think I can get it any higher with the power I have.

Eddy G · Post by **Eddy G** » Dec 5th, '14, 10:32

I have the 240 Yanmars in my B28 with 1.5 to 1 ZF63a's and run DJX 18 x 18 props with a #3 cup. Max rpm is 3425 and I choose to cruise 2750 at 25 mph (22 kts). Get consistently 2 stat miles per gallon. I've been running the DJX's since the repower in 2006 so can't compare them to other props, but I am told they add a little extra grip.

Eddy G.

Bill Fuller · Post by **Bill Fuller** » Dec 6th, '14, 12:19

Harry,
I run a similar set up to Eddy's with similar performance.
I like to run the motors at between 2500 and 2800 RPM. I have limited my continuous cruise RPM to 2900. It just seems like the motors start to really work hard above that RPM.
What 4LH motors do you have?
what is your gear ratio?
What props do you have now?
Bill

Harry Woods · Post by **Harry Woods** » Dec 6th, '14, 14:39

Eddy - The 2750 RPM seems to be a sweet spot for the engines. At that level they sip fuel.

Bill - I am running 1.5 gears and 17 X 17 no cup. I am looking to reduce Pitch and add a number 2 cup.
Thanks for the feedback.
Harry

Bill Fuller · Post by **Bill Fuller** » Dec 6th, '14, 19:41

Harry,

Still curious,
Which 4LH motors do you have?
4LH-DTE
4LH-STE
4LHA-DTE(P)
4LA-STE(P)

Bill

Harry Woods · Post by **Harry Woods** » Dec 7th, '14, 19:40

Bill,
DTE.
Harry

Eddy G · Post by **Eddy G** » Dec 8th, '14, 11:08

Well, I had the 170 DTE's prior to repowering with the 240's. Had Hurth 1.5 to 1 630a's and 18 x 16 Nibral "DynaJets" I believe with a slight cup. Maxed out at about 3400 rpm and cruised it at 2900. But that only got me 18 kts with the same fuel burn as the 240's doing 22 knots. I guess at 18 kts the boat is pushing water and not completely on top. Plus, I had to use some tab action to get that speed. Moving up to the 240's was an amazing upgrade to my boat.

Eddy G.

Charlie J · Post by **Charlie J** » Dec 8th, '14, 14:11

bill
I am running the 4LHA STE Bahia mar
mike o is running the same with a FB

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