Prop Question.

[CraigM]

I have a Stratos 219F with a 175 Evinrude. It has a ss Renegade 13.5 x 25 4 blade prop. If I take off fairly hard on the hole shot it cavitates bad. I assume this is caused by having the wrong prop. Any ideas on what would fix the problem. The boat will do over 70mph on the gps, so I don't care if it gets slowed down a little. Thanks.

[marine_man]

What are your turning for RPM at WOT?

marine_man

[CraigM]

It runs right at 5000 rpm @ wot.

[marine_man]

It sounds like you need to step down in prop pitch a bit... you should be running closer to 5500 - can you provide the year for your 175 evinrude and I'll double check to be sure, but you'll need to step down to a 21 pitch prop probably to get your holeshot back and reduce your cavitation.

marine_man

[trackerbrent]

Something is not right here. Running #'s you should only be running somewhere around 58 mph at 5000 RPM, assuming a 1.85 gear ratio and 10% prop slip. To get to 70 mph on GPS you would have to be spinning the motor at 6100 RPM, which is way too much for your motor. Your tach may be off and you are over revving your motor.

Anyways, this is happening to my boat also. I raised it up a hole to try to get some more RPM out of it. It worked I am getting 5300 RPM out of my 150 Johnson now, but blows out if I gun it out of the hole. Thinking of lowering it back down one notch. This is something else you could try. Check your #'s to make sure your tach is not off that much. Do not want to blow up a motor.

[CraigM]

The motor is a '95'. The speedo shows that it is running right around 58 to 60 but I have been told the gps don't lie. What is the best way to check the tach cause you're right, I don't want a grenade on my hands.

[trackerbrent]

I do not know how to check the tach without trying a different one. Hopefully someone will chime in on the procedure, because I would be interested also. I always thought GPS speed was dead on too.

Nice boat by the way. That is my dream boat. Seems no manufacturers make a fast walleye hull anymore. The 219f is a fast boat and yours has an old reliable v-6 OMC, which I also like. I still like old school things, 2 stroke carb is the way to go for me. Always get you back to the dock!

[marine_man]

The motor is a '95'. The speedo shows that it is running right around 58 to 60 but I have been told the gps don't lie.

A couple of things:

1) For a 1995 175 hp Evinrude top RPM is 5500.

2) Are you sure you don't have your speeds switched around? Usually the speedometer over-estimates the speed and the GPS is lower, which is the opposite case this time. The other thing that makes me wonder this is that you're pretty close to Brent's speed estimate (thanks by the way) if your speeds are switched around.

3) I'd be surprised if your tach was off by that much. There are a couple of ways to double check your tach - get a hold of another one and plug it into the harness to see what that one says or get a hold of a meter that shows RPM based on timing. When tach's are off they're usually way off or off by 100 rpm at the most.

marine_man

[CraigM]

I know that I don't have the gps speed and speedo reversed. I also thought that was odd because boat speedo's are usually so generous. If it makes any diff., the boat does have a different speed pick up mounted on the hull than what came stock. maybe it's not calibrated properly. Next time out I'll check speed with my hand held gps to see if it matches and I'll see if I can pick up another tach to hook up.

[CraigM]

Thanks for the compliment. I actually just bought the boat. I was leary of buying a 13y.o. boat but it is in almost showroom condition and with the economy the way it is I couldn't justify spending 30 or 40 grand on a comperable newer boat. Just have a couple of small issues to fix up and will then have a like new boat for 1/4 the cost.