Prop advice

[ripster]

I have a 1984 Sea Ray Seville, 18' bow rider, 3.0 mercruiser w/1.98 gears, and 15 X17 three blade aluminum prop. WOT is 4500 RPM and 30 mph with three adults and one child (around 600 lbs). The prop has some dings on it and I want to replace it. My hole shot is slow but I don't want to give up on the top end since it is pretty slow already. Are there newer prop designs that could give me better hole shot without losing top end?

 

[JimS123]

Re: Prop advice

I'm quite familiar with your boat....your numbers don't add up. You should be turning a higher rpm and getting more speed than you report.

Better check your tach and verify your speed with a GPS.

 

[ripster]

Re: Prop advice

Speed was checked with a GPS. Two runs in opposite directions. I don't have a handheld tach to verify RPM's.

 

[JimS123]

Re: Prop advice

All I can say is that my guess would be that you should be turning at least 4800 rpm @WOT with the trim all the way in, and achieveing a speed in the low 40's. Either your prop is more damaged than you imagine, or your engine needs an overhaul. A 17 on that boat should literally fly out of the water.

 

[ripster]

Re: Prop advice

I borrowed a hand held tach to verify engine speed, maybe I should be looking at a compression test. I would imagine that if it is the state of the engine it would have to be in really bad shape to cause this poor performance.
I've tried to attach a photo of the prop. I've just owned a boat for a year and I don't know how much this prop could affect performance.

 

[JimS123]

Re: Prop advice

I just can't say about the prop. I have had props with a lot less damage than that and had them fixed right away. The compression test isn't a bad idea. You can buy a tester for 20 bucks. Also, look at all of the spark plugs to verify that they are firing correctly and look the same. You can replace them for another 10 bucks, and that's not a bad idea anyway.

 

[ripster]

Re: Prop advice

So my test with the hand held tach didn't tell me much. I didn't get readings that I felt I could trust. So, should I replace with a 17 pitch or go with something different? Are all 17's the same or is there one that is better than the others?

 

[JimS123]

Re: Prop advice

Just repair the one you have and try it out again. If you need a different pitch, at least now you'll have a spare.

 

[nitrosteve]

Re: Prop advice

This could be a dumb question.

Are you trimming the boat for max speed? Just trim it up slowly till it starts to loose speed then bump it back down till the speed pics back up.

You should be able to spin that 17 up to 4800 or so easily even with the load you have. At 4800 you should be running 36-38 mph.

Is the boat full of wet wood and foam? This can add a couple hundred pounds.

Has it ever ran at higher speed or is this consistent with the way its been since you owned it?