Need Prop advice

[Powderpro]

I was hoping Larry might see this thread... I'm only at 80% load wide open and am wondering how much pitch to add to get into the 92-94% load range. Current top speed is 23.5 knots burning only 19.8 gph. Properly loaded the engine should be burning about 24.8 gph according to John Deere. New build 38 Wesmac, weight 17,000 lbs, JD 9 liter 500hp at 2,400 rpms (electronically limited to 2,450 rpms), 2:1 reduction, current prop is DQX 28x28. I'm thinking of adding at least 2" of pitch. Any pros out there who could give me some advice? Thanks.

 

[plowin]

Very interested in the answer for this one, I too have a boat running at 81% at rated rpm of 2600 with a 26"x28" 4 blade. I know I need more wheel just not sure how much. These electronic engines make it more difficult to get the wheel just right. When it was all based on rpms it was much easier. For what its worth I have been told by numerous Cummins technicians to wheel it to rated rpm and not WOT. They tell me it will still over spin the wheel at 99-100% engine load. Supposedly the electronic engines love to have a load on them.

 

[Powderpro]

On my new builds, I've always had to reduce pitch by an inch or two, this is the first time I've had to add pitch. From experience of reducing pitch, 1" of reduced pitch usually equaled to around 4% load reduction. So using that theory, I would have to add 3" of pitch to get an additional 12% load. I'm not real confident that my past experience will translate accurately when it comes to adding pitch, although it should. I want to get it right because pulling boats and tweaking props gets real expensive. I want to re-pitch once and be done with it.

 

[lobstercatcher]

You should really limit your change in wheel pitch to 2" max. If you can't return the wheel and swap it for the right one or at least another trials wheel , I'd add 2". Also , Since you are a work boat. Do you really want to be over square.. if anything, for weight carrying maybe bump up to a 30 x 28 or 30 x 26

 

[Powderpro]

You should really limit your change in wheel pitch to 2" max. If you can't return the wheel and swap it for the right one or at least another trials wheel , I'd add 2". Also , Since you are a work boat. Do you really want to be over square.. if anything, for weight carrying maybe bump up to a 30 x 28 or 30 x 26

I'll be calling my prop shop and talking more with the Deere mechanic on Monday. I may even call Larry and see what he thinks. Adding 2" to my current prop may be my only option as there isn't much time until the fishing season starts.

 

[lobstercatcher]

I'll be calling my prop shop and talking more with the Deere mechanic on Monday. I may even call Larry and see what he thinks. Adding 2" to my current prop may be my only option as there isn't much time until the fishing season starts.

How big of a wheel can you swing? The 30 x26 I mentioned probably will use less engine than what you use with the 28 x 28 so disreguard that one as a actual wheel for thought. Maybe 32 x 26. is what I should have said for a example of under square. Being under square opposed to over square on a work boat that carries weight is what I was getting at. both those are probably to small. Knowing how big of a wheel she'll swing is a good place to start.

 

[steveinak]

Brian i'd load that boat up like you have all your gear on it you know heavy fishing weight then see what you get for load & rpm's, i think most guys underestimate how much extra weight they have on the boat(i know i do), no matter what happens your still going to have the best rig around !!

 

[Powderpro]

Brian i'd load that boat up like you have all your gear on it you know heavy fishing weight then see what you get for load & rpm's, i think most guys underestimate how much extra weight they have on the boat(i know i do), no matter what happens your still going to have the best rig around !!

It currently is loaded up except for the 500lbs of net, so I'm real close to fishing weight. When we only had 45 gallons of fuel on board, it went 23.7 knots, load was 80%, and burn was 19.8 gph at WOT. We put on an additional 200 gallons of fuel (1,500lbs) and it topped out at 23.5 knots, load was still 80%, and fuel burn was still 19.8 gph at WOT. So that indicates to me that the boat will not slow down but maybe .1 knots when I get my net on board. I would like to get to at least 90% load, my preference would be 92-93%.

 

[lobstercatcher]

It currently is loaded up except for the 500lbs of net, so I'm real close to fishing weight. When we only had 45 gallons of fuel on board, it went 23.7 knots, load was 80%, and burn was 19.8 gph at WOT. We put on an additional 200 gallons of fuel (1,500lbs) and it topped out at 23.5 knots, load was still 80%, and fuel burn was still 19.8 gph at WOT. So that indicates to me that the boat will not slow down but maybe .1 knots when I get my net on board. I would like to get to at least 90% load, my preference would be 92-93%.

How slow did it go at a idle? With 2 to 1 you should get a really good range of speeds.

 

[BillD]

Maybe my thinking is way off, but IF a little extra speed is NOT a requirement to making $money$ fishing with the boat why not leave the load "as is" @ 80%.

It never hurts an engine leaving a little hp "on the table" and burn a little less fuel.

FWIW, Bill D

 

[Powderpro]

Maybe my thinking is way off, but IF a little extra speed is NOT a requirement to making $money$ fishing with the boat why not leave the load "as is" @ 80%.

It never hurts an engine leaving a little hp "on the table" and burn a little less fuel.

FWIW, Bill D

I paid for 500hp, and I want to be getting my money's worth. If I wanted 420hp I would have sprung for the 6.7 Iveco and saved $15,000 . I think my current speed is close to what the 6.7 Iveco 420hp would have pushed the boat propped at 99-100% load, which is a very respectable speed. 23.5 knots isn't anything to be ashamed of, but I think even with a re-pitch of 2 additional inches, we should be hitting 25 knots and still be around 90% load. The boatdiesel calculator, for what it's worth, suggests 33" of pitch. That's too much, but it also estimates top speed of 26.5 knots.

 

[captainlarry84]

Just saw this post. I would move slow on the wheel. She is a new build so she will gain some weight. I would add 1" of pitch and maybe a # 4 cup. You can always add a little more. The last thing you want to do is add too much and then bend it back. 1" increase in pitch will drop you 75 RPMs. You did not stat what your WOT RPMs are. If they are 2450 RPMs pinned against the governor, then 1" & a little cup will bring you to 90+ load.

 

[steveinak]

It currently is loaded up except for the 500lbs of net, so I'm real close to fishing weight. When we only had 45 gallons of fuel on board, it went 23.7 knots, load was 80%, and burn was 19.8 gph at WOT. We put on an additional 200 gallons of fuel (1,500lbs) and it topped out at 23.5 knots, load was still 80%, and fuel burn was still 19.8 gph at WOT. So that indicates to me that the boat will not slow down but maybe .1 knots when I get my net on board. I would like to get to at least 90% load, my preference would be 92-93%.

How about ice & slush load ?? food, tools, brailers, anchor & chain the list goes on, they are always heavier than you think. You'll get your 90% load when the fishholds are plugged !! I'd rather have is spin a little easier and not lug a new engine, let the next owner tweak it and burn it up !!

 

[BillD]

i paid for 500hp, and i want to be getting my money's worth. If i wanted 420hp i would have sprung for the 6.7 iveco and saved $15,000 . I think my current speed is close to what the 6.7 iveco 420hp would have pushed the boat propped at 99-100% load, which is a very respectable speed. 23.5 knots isn't anything to be ashamed of, but i think even with a re-pitch of 2 additional inches, we should be hitting 25 knots and still be around 90% load. The boatdiesel calculator, for what it's worth, suggests 33" of pitch. That's too much, but it also estimates top speed of 26.5 knots.

got it !!!!

 

[backman]

remving pitch below square

NB 36, I'm maxing out at 2300-2310 fully loaded and need 2350-60; ie need 50 more RPM's.

26 X 26 wheel with #2 cup. I removed 1 cup this winter and added 20-30 RPM but have some cavitation I never noticed before.

Rather than pulling out more cup - can I drop one inch of pitch ( 26 X 25) and then if needed add in more cup later?

 

[Powderpro]

OK- I had 2" of pitch added to the prop, so the prop is now 28x30 (no cup), and I gained 6% load and 1 knot at WOT. At full fishing weight top speed is now 24.5 knots, 88% load, 21.2 gph. I'm extremely happy with this boat's performance, it's every bit as good as I could have hoped for. And I still could have added another inch or two of pitch and been fine.

 

[lobstercatcher]

OK- I had 2" of pitch added to the prop, so the prop is now 28x30 (no cup), and I gained 6% load and 1 knot at WOT. At full fishing weight top speed is now 24.5 knots, 88% load, 21.2 gph. I'm extremely happy with this boat's performance, it's every bit as good as I could have hoped for. And I still could have added another inch or two of pitch and been fine.

I think they frown against repitching more than 2". Maybe they will forget they already did 2" and you can get another inch pitch next time

 

[Powderpro]

I think they frown against repitching more than 2". Maybe they will forget they already did 2" and you can get another inch pitch next time

I agree, I don't want to tweak the original prop more than 2".

 

[Bill]

Looking for little advice . No idea with this prop stuff right now I'm running a 22x22 3 blade.. 2/1 gear .. 240 Yanmar (max 3300 rpm) getting the following for different speeds max I'm getting is 3050 rpm
2000 15
220" 16.5
2600 20.5
3050 26 kts

Boat is 27 Terry Jason . Don't know the weight. Thanks a lot

 

[steveinak]

Looking for little advice . No idea with this prop stuff right now I'm running a 22x22 3 blade.. 2/1 gear .. 240 Yanmar (max 3300 rpm) getting the following for different speeds max I'm getting is 3050 rpm
2000 15
220" 16.5
2600 20.5
3050 26 kts

Boat is 27 Terry Jason . Don't know the weight. Thanks a lot

i think your over propped, if those yanmars are anything like volvos you don't want to be lugging them with props that are to big.