boat propeller recommendations for my little Larson

[Oldhillbilly]

Hi there. I recently got a little bowrider runabout. It is a 1996 Larson Flyer 166. Has a '96 Johnson 90hp J90TLEDA v4 2 stroke with 137 hours. The recommended rpm range on it is 5000-6000 rpm and I had heard it was usually best to be near the upper end of the rpm range for best overall performance. Boat, motor, gas, oil, and me is about 1650-1700 pounds and at heavy loads about 2300 pounds. It came with two propellers, both of which seem too big to me. One is an aluminum 14x17 3 blade that I haven't figured out the brand on. The other is a 3 blade stainless Ballistic 13.5x17.

The aluminum prop runs about 5050 rpm at about 38 mph lightly loaded with good acceleration. Heavy load drops it to about 4900 and 35 with lackluster acceleration

The stainless runs about 5000 rpm at 40 mph light with okay accel but not quite as good as the aluminum. Heavy sees about 38 mph at 4900 rpm with poor accel.

I will use the boat mostly on Table Rock lake in sw Missouri. It is a good sized lake where sometimes it is nice to cruise somewhere 50 miles from where you start so decent cruise efficiency and top speed would be nice. But most of the time the boat will have about 3-4 people on it and do lots of toy pulling within a few miles from the dock. I wouldn't be against having two props of the right sizes if there was enough advantage to be worth swapping props for different uses but I am hoping to come up with a prop that is good enough all around to not have to bother unbolting them.

So any recommendations for the best overall prop or the ideal props for my specific uses would be greatly appreciated. I would be happy to try and provide any further info needed.
Thank you.

 

[steelespike]

Is your speed by gps? It does appear that the 17s are a little too much prop.
It indicates that a 15" pitch would do well for you.Should add about 400 rpm.It should improve hole shot,
be less fussy at cruise speed,rpm should hold up better as you add weight.
When you decrease pitch you can lose top end;but your rpm was so low that your speed may hold up.
I do think your actual rpm is a little higher than what you see. Your slip on both props is about 6% ,possible but unusually low.
This can be an indication that speed is inflated or the tach is low.We can prove the speed with a gps.

 

[SkiDad]

i'd drop down to 15p if you are into water sports - 40 mph is about max for that boat and previous owner was probably trying for that - a 15p will put you more like 35-37 mph but will run a lot easier. Michigan match makes a nice alumimum prop that will be predictable - or find out what is stamped on your 17p AL and just duplicate that prop in the lower pitch. Sell one of the other props and you won't be out any money.

 

[Oldhillbilly]

Thanks for the quick response. Speeds are just indicated by speedo and I would not be at all surprised if they are off and indicating too high. Boat is in town now so cannot try gps. Tried using gps in phone while out in boat the other day but it just showed location and not speed. Have since found correct app that will show speed. Personally I have more faith in the tach than the speedo, but it is the one that I can check right now since I have a timing light with tach and a tub to run it so I will see if my timing light agrees with the tach and post back in a little while.

 

[steelespike]

You should't rev too much in neutral as this could trigger a runaway.
You should probably wait till you can compare through the full range on the water.
The difference is probably only about 300 if that much.

 

[Oldhillbilly]

Wow. Another response I hadn't even noticed before I went out to check the tach, thanks guys.

I had the boat already backed up to the tub since I just replaced the water pump impeller and wanted to see it run. When I set the rpm on the boat tach to 1000 my digital light was showing in the 1020 to 1025 range. Boat tach at 3000 and showing a little over 3040 on light. So it looks like the tach is pretty close but maybe a little slow. Also limited by my ability to accurately set analog boat tach. Guessing my speedo is a little optimistic but hoping the speed numbers I have are good enough in a comparative aspect if not in actual mph really accurate.

From what I had read so far, it looked like each inch of pitch was supposed to change rpm by around 200. If so it sounds like a 15p should still be turning less than 5500 rpm with just me and even less with passengers. What about a 13p? If I give up 25% of my pitch but gain close to 20% rpm will I lose so much top speed and efficiency that the prop will not seem good or might a 13 be even better for skiing and tubing? Might I be best off to just get one new prop in a smaller pitch and keep the current 17p stainless for when it is just my wife and I cruising the lake? Or would the right 15p stainless possibly even go faster since it would be better into the powerband?

 

[Oldhillbilly]

Well steelspike, I guess I got lucky. the old outboard went smoothly to 3000 for me but wasn't there for long. What is a runaway? Does the throttle become ineffective? Couldn't I just use kill switch?

 

[steelespike]

Something about hot carbon igniting the fuel in a snowball affect The ignition isn't involved.
I assume that this would be more likely if an individual was playing for some time.
I guess you could disconnect the fuel.
In prop selection if you go too low you will lose top end.
While the 17 was a little too much you were inside the rpm range with a light load just no room for loads.
I think you will be surprised with the 15 and you may save your top end.
Your tach probably isn't too far off.