What pitch prop do I need?

[Art Bernard]

Engine- 150 HP evinrude-late 80's model
current prop- 15 x 15 stainless, no cup at all, manufacturer unknown
Boat- 1977, 19' Viking Deck boat
Current RPM @ WOT 4500rpm @ 32 mph as read on new speedometer and new Tach (tach is set to 6)

This engine and prop came off my last boat (the one in my avatar) and on that one she was good to go. The engine is in great shape, no problems at all with her. Carb butterflies open fully, etc... I know that this engine is supposed to be turning between 5500-5800 rpm at wot and I don't want to lug it and ruin it. The boat itself is not waterlogged. So, what would be the correct pitch for me? I'm not looking for top speed, just to get the engine operating where it's supposed to at wot. Any help is greatly appreciated and thank you.

Art

 

[Art Bernard]

Re: What pitch prop do I need?

Ok, did some more research and found that according to multiple sources, I'm wrong about the wot rpm. I thought it was 5500-5800 rpm @ wot, but according to research it's actually 4500-5500 rpm @ wot. So according to that info I'm currently at the bottom range for this motor and shouldn't be in danger of ruining it. However I would still like to get the rpm's up a bit for better fuel economy. This boat is a lake cruiser, light fishing, family boat that will pull tubers/wake boarders now and than. What would be a good pitch to accomplish that? Also, I have a 14 1/2 x 19 alum prop I've never run, what do you think the effect on performance would be with that prop? Thanks again.

Art

 

[Howard Sterndrive]

Re: What pitch prop do I need?

Also, I have a 14 1/2 x 19 alum prop I've never run, what do you think the effect on performance would be with that prop? Thanks again.

Art

that's going the wrong way, Art
If you want more rpm, you want to LOWER your prop pitch, not raise it.
I think I'd stay with 15P if I were you.
13P props are starting to get less efficient.
But jeez...I've never seen those 150's run anything that low....something weird about your setup
Maybe the engine needs to be raised a bit on the transom. I might try lifting it an inch... or get the whale tail off there.

 

[Art Bernard]

Re: What pitch prop do I need?

I just went out and measured it. The cavitation plate is 2 1/2" below the bottom of the hull. This is one of those areas where I admittedly don't have allot of experiance in so any help is greatly appreciated. Thx much.

Art

 

[Robbabob]

Re: What pitch prop do I need?

From what I read, that tail should be even or 1" above the hull bottom. That is a start to the correct set-up.

Do some runs with this change and get back to us with new performance spec's.

Enjoy!

 

[Art Bernard]

Re: What pitch prop do I need?

I went out and raised my motor. 1/2" below the bottom of the hull was the higest I could go without drilling and filling holes in the transom and I don't want to go there

Art

 

[steelespike]

Re: What pitch prop do I need?

Give it a try at that height. Depending on the weight and hull configuration I feel with a 15" prop you should be running about 5,500 and about 40 mph.
Look at it this way if your setup was right now you would have to drop 5" of pitch to gain 500 to 1,000 rpm.that would put you at 10" pitch A prop you would find on something hard to push like a pontoon.Does the boat respond to up trim?

 

[Art Bernard]

Re: What pitch prop do I need?

Yes, she responds to trim. Going to try to put her in the lake tomorrow and see what I got.

Art

 

[Art Bernard]

Re: What pitch prop do I need?

Ok, just got back from the lake and the results are good. By moving the engine up to 1/2" below the keel I picked up 3mph and 100 rpm, so top speed is now 35mph @ 4600rpm wot. She responded well to the helm and hole shot was decent. I'm happy with how she's running though I would still like to get the rpm's up to at least 5000. What pitch do you think would put me close to 5000rpm, 14 deg or 13 deg? and should I put some cup in the blades as there is 0 cup now. Thank you for the advice.

Art

 

[steelespike]

Re: What pitch prop do I need?

I still think you have issues other than the prop.I checked several deck boats with new 150s esentially the same gear ratio all ran 15 or 16 " props at roughly 5400 to 5700 rpm all over 40 mph.
A 13" should get you close to 5,000.You should stay with stainless for more predictable results.
A stainless will likely have some cup.