4 blade prop?

[stylze76]

I currently have a 13 x 17p prop that is recommended for my 89 OMC Cobra 2.3L. The manual says ideal WOT rpm's should be 5200-5600. I can only get 4500 max not pulling anything and only 4 people in the boat. I was thinking of going with a higher pitch 4 blade prop which in theory should get me 400 rpms with the higher pitch but lose 100 because of the 4th blade. That would raise it hopefully enough to maybe see a difference. Does this seem crazy or is it worth a try?

 

[Texasmark]

You already have too much prop for your engine/boat. The 4 blade is lossier than a 3 so first of all you need to drop at least an inch for that. Second the type of 4 blade you choose as compared to the type of 3 you currently have can move the pitch either up or down; depends. Third, you are already 1000 rpms too low which IS a very big deal. DEcreasing the pitch brings the rpms up, not INcreasing.

How long have you had the boat? Used? Condition "all of a sudden"? If used, did the PO use it as is? Do you know that your engine is in good repair?

Mark

 

[Starcraft5834]

More more pitch = less rpms.. I would be more concerned that your engine is not healthy........typically if an engine is healthy and is using a prop with to much pitch it will take a very long time to reach plane, once it does the engine will get to it's recommended rpm range.. just takes way to long, the extra strain is not a good thing. hence the need for the correct prop.. I'd agree with Texasmark wondering if your engine is sound.. compression check? if that's ok, look at a 15p or less

 

[stylze76]

I guess I misspoke. I was thinking of going to a 13 x 15p 4 blade prop. Instead of a 13 x 17p 3 blade.

This has been a regular thing. Not all of a sudden. I am just finally seeing if I can do anything about it. It had a Stingray Hydrofoil classic on it when I bought it also and used it for the first 2 years but decided to try it without it. I was sort of ok pulling a 2 person tube last year with it and this year took it off and can hardly pull it. I have yet to put it back on and try pulling the 2 person this year yet. That's where I thought maybe the 4 blade 15p prop might help. I've had it 3 years and its actually in pretty good condition as far as engine and mechanics. The body has some wear and tear but for an 89 its pretty good. I bought it used from a friend. I assume he used it as is with the prop that is on it. He hadn't used the boat all but 3 times in 2 years. Before that I'm not sure. I have never had it into the shop for maintenance or tune up. I change the oil and winterize it myself. It's been running great for me besides the water pump I had to put on it.

 

[Starcraft5834]

15p is going in the right direction........ I use a 4 blade Solas 14.75x15p on my 20ft cuddy with 3.0 140hp... it's a deep V and heavy... the 15p does a real nice job for me, I punch it and Im up on plane in less than 5 seconds... Take a look at the Solas product....they are very good

 

[steelespike]

I suspect your motor may be a little tired.We can tell better what you need if you do a lightly loaded test run, just yourself, to get your rpm and gps speed.
What is the speed at 4500.Perhaps you can remember wot rpm and gps speed lightly loaded.

 

[stylze76]

The top speed that I've been able to get is 30mph but there were 3 people total in the boat.